**1. Introduction**

Researchers have studied crude oil for many years because it is of major interest as a significant but limited resource. In addition, the crude oil index plays an important role among economists, policymakers, and investors, because fluctuations in either its price or its production have a remarkable impact on the world economy and stock markets. On the contrary, as a relatively environmentally friendly resource and a key fuel for the electrical power and industry sectors, natural gas has attracted increasing attention. Evidence for this increasing attraction comes from the fact that the consumption of natural gas has risen to a share of 23% of total energy resources, and is the fastest-growing fossil fuel among energy resources [1]. Another fact is that the demand for natural gas increased by 4.6% in 2018, accounting for almost half of all energy resource demand growth [2]. Thus, it is not difficult to conclude that fluctuations in the prices of crude oil and natural gas greatly influence economic activity and daily life.

Researches had shown that there is a correlation between US economic growth and exogenous oil shocks. For instance, Hamilton [3,4] and Hooker [5] proposed that after oil price increases, there were recessions in the US economy. However, as proposed by Kilian [6], depending on the underlying causes, such as supply shocks, aggregate demand, or precautionary demand, price fluctuations have varying dynamic effects on real prices, and hence on the economy. Other studies have agreed; for instance, Kling [7] reported that the association is obvious between crude oil price increases and declines in the stock market. However, Kilian and Park [8] reported that US real stock returns reacted differently to oil price shocks, depending on the origins driving the oil price shocks. Other research has also

analyzed the macroeconomic e ffects of oil market fluctuations. Oladosu et al. [9] adopted a quantitative meta-regression model to simulate the oil price elasticity of GDP in US and their results revealed that the estimated US GDP elasticity was negative, and particularly smaller than about 10 years ago. Jan van de Ven and Fouquet [10] identified the impact of energy shocks on economic activity using data from the United Kingdom for 310 years and their study indicated that the influences of supply shocks declined due to the partial shift from coal to crude oil, and that it is possible to reduce vulnerability and increase resilience by substituting renewable energy sources for traditional energy sources. Ju et al. [11] used data from 1980 to 2014 to investigate the macroeconomic performance of oil price shocks by adopting three methods, namely, empirical covariance, robust covariance, and support vector machine methods, and the results implied that the outlier performances of GDP, CPI, and the unemployment rate are consistent with the oil price shock process. Correspondingly, some literature investigated the relationship between natural gas price shocks and macroeconomic aggregates. Nick and Thoenes [12] extended the structural vector autoregression (SVAR) model and analyzed the e ffects of di fferent fundamental influences on the price of natural gas in the German market. Their results revealed that in the short-term, the price of natural gas tends to be a ffected by some factors, such as temperature, inventory, and supply insu fficiencies, and, by contrast, in the long-term the price tends to be influenced by the overall economic climate and the substitutional relationship between crude oil and coal. Zhang et al. [13] used a computable general equilibrium model to investigate the macroeconomic e ffects of natural gas prices in China and their results showed that when natural gas prices increase, the CPI would increase and GDP would decrease. In addition, research has also emphasized the transmission effect of oil demand and supply shocks on the natural gas market. For example, Jadidzadeh and Serletis [14] analyzed the e ffects of supply-demand shocks stemming from the global oil market on the real price of natural gas and found that oil supply-demand shocks accounted for approximately 45% of the fluctuation in the price of natural gas.

This study's first objective is to decompose shocks to the real price of crude oil and natural gas into three components: (1) oil/gas supply shocks, (2) global aggregate demand shocks, and (3) specific or precautionary demand shocks. Its second objective is to evaluate important di fferences in how US macroeconomic aggregates, such as CPI and real GDP growth, react to various oil shocks underlying the real price of crude oil and natural gas. The third objective of this study is to compare its results with Kilian's results regarding crude oil in 2009, in order to determine whether conditions have changed since 2007. Our data cover the period from 1973:1 to 2019:6, whereas Kilian [6] only had data up to 2007:12. Its fourth objective is to compare the impacts on crude oil and natural gas of di fferent types of shocks to US macroeconomic aggregates. We expect this study to have implications for market operators and investors.

Because one of the objectives of our study is to compare our results with Kilian's work, and because we used the same approach as Kilian [6], there is a necessity to demonstrate the similarities and discrepancies between the two works. We used the same methodology and variables as in Kilian's work. However, because the importance and the potentiality of natural gas has gradually increased, we added natural gas to our study to check the e ffects of each structural shock on the real price of oil and gas and compare their e ffects on the US macroeconomic aggregates; in contrast, Kilian's work focused on the crude oil market. Another di fference is that our sample period of crude oil is longer than Kilian's to verify if there are any changes after 2007.

Our findings in this study are threefold. First, by constructing an SVAR model to quantify the responses to one-standard-deviation structural shocks, we found that there were di fferences between the e ffects on crude oil and natural gas in the response patterns of real economic activity due to precautionary demand shocks. Second, by decomposing historic real prices to check the cumulative contribution from each demand and supply shock to the real price, we found that the cumulative e ffect of precautionary demand shocks was varying in degree between crude oil and natural gas; specifically, the cumulative contribution of an oil-specific demand shock to the real oil prices is larger than the cumulative contribution of a gas-specific demand shock to the real gas prices. Third, by utilizing the

regression model to investigate how oil and gas demand and supply shocks that underlie the real price of oil and gas influence US macroeconomic aggregates, we found that precautionary demand shocks on crude oil and natural gas have di fferent e ffects on CPI inflation and had similar e ffects on real GDP growth. Both oil- and gas-specific demand shocks led to a small, but statistically insignificant, reduction of the US GDP level.  This result implied policymakers should react di fferently to gas-specific demand shocks and oil-specific demand shocks.

The remainder of this paper is organized as follows. Section 2 provides a detailed description of the data and introduces the econometric model, a two-stage method based on the SVAR model proposed by Kilian [6]. Section 3 identifies the structural shocks that drive the real price of crude oil and natural gas. We quantify the historical evolution of these shocks and the response to these shocks from production, real activity, and the real price of crude oil and natural gas. We decompose the real price of crude oil and natural gas over time to assess the respective cumulative contribution of each shock to real prices. Finally, we analyze the e ffects of those shocks on US macroeconomic aggregates. Section 4 concludes the study.

#### **2. Materials and Methods**

## *2.1. Data*

Table 1 describes the datasets we utilized and their sources. These datasets included crude oil production, gas production, a real economic activity index (the Kilian index available on his website), crude oil prices, natural gas prices, and US real GDP, deflated using US CPI (Kilian [6]).

**Table 1.** Data descriptions and sources.

1 Real price means price which is deflated by US CPI. 2 Data from the International Energy Agency.

We collected data from Bloomberg, Thomson Reuters, and OECD Stat. These datasets include the crude oil spot price (West Texas Intermediate, WTI) and the natural gas spot price (Henry Hub). *l*\_*rpot* defers to the real price of crude oil expressed in log terms. *l*\_*rpgt* defers to the real price of natural gas expressed in log terms. Regarding the dataset of the Kilian index, we collected the data from the Lutz Kilian website. From Kilian (2009), the Kilian index is a detrended real freight rate index constructed as a measure of monthly global real economic activity, which could imply the variation of worldwide real economic activity and capture the shifts in the demand for industrial commodities throughout international markets [6,15] (see Appendix A for details). In this study, *l*\_*reat* defers to the Kilian index; because the minimum of the Kilian index is −161.643, we added 196 to every data point and expressed the series in log terms. We collected production data for oil and gas from the International Energy Agency (IEA), and calculated the change rate of oil/gas production in percentage terms to reflect the percentage change of worldwide oil/gas production. Δ*oprodt* refers to the percentage change in global crude oil production, and Δ*gprodt* refers to the percentage change in global natural gas production. US

real GDP growth and US CPI data was collected from the Organization for Economic Co-operation and Development (OECD); because data for the US real GDP growth rate is unavailable at a monthly frequency, we adopted the quarterly frequency when we downloaded the US real GDP growth rate and US CPI datasets. The sample period for crude oil data was from January 1973 to June 2019, but the natural gas sample was limited by the available data period of January 1994 to June 2019.

The descriptive statistics and stationarity tests for the variables are shown in Table 2. This table indicates the mean, maximum, minimum, and standard deviation of each variable. (Although the log of the real price of natural gas may have a unit root, we checked the stability condition of the SVAR system and found that the system is stationary; more details are provided in Appendix B.)

**Table 2.** The results of unit root tests for the variables.


**1. Introduction**

Stabilin-1 (Stab1), belongs to a family of scavenger receptors, is a type 2 macrophage marker and is expressed in tissue macrophages and different endothelial cell subtypes [1–3]. Stabilin-2 (Stab2) belongs to the same family of scavenger receptors and shares 55% identity with Stab1 at the protein level [1,2,4,5]. Both Stab1 and Stab2 are expressed in macrophages and endothelial cells of various organs, including the liver and spleen [6,7]. Stab1 acts as a scavenger receptor for clearing debris and apoptotic cells through macrophage phagocytosis and is involved in the transcytosis of several components, including placental lactogen (PL) [1,3,8,9]. Stab1 modulates angiogenesis, supports leukocyte adhesion and transmigration, and regulates immune responses [1,3,9]. Stab2 is involved in clearing noxious blood factors and degrading apoptotic cells [10]. Stab2 also regulates extracellular matrix turnover and hyaluronan resorption to maintain body fluids, and participates in the defense against bacterial infections and recruitment of lymphocytes [6,7].

During pregnancy, the placenta undergoes structural changes to transfer maternal nutrients, oxygen, metabolites, and hormones to the fetus at different stages of development. These alterations are essential for the development and growth of the fetus [9,11,12]. One such change that occurs in early pregnancy is that the diameter of maternal blood vessels increases to supply a massive amount of maternal blood through the placenta at a low blood pressure. This phenomenon is called spiral artery remodeling, which is an essential change in the development of the placenta. During spiral artery remodeling, fetal origin trophoblasts invade maternal spiral arteries and replace endothelial cells undergoing apoptosis [12,13]. Apoptotic cells and debris are eliminated by placental macrophages and uterine natural killer (uNK) cells [12,13]. Rapid removal of apoptotic cells and debris is important for spiral artery remodeling. Inhibition of such removal hinders spiral blood vessel formation [12,13].

Stab1 and Stab2 proteins are expressed in endothelial cells and macrophages, which play a predominant role in artery remodeling in the placenta during pregnancy [12]. These proteins are closely related to factors mediating cell signaling pathways that regulate angiogenesis [4,9,14]. Functional studies of Stab1 and Stab2 in tissue macrophages have demonstrated their importance in the phagocytosis of apoptotic cells, suggesting that Stab1 and Stab2 contribute to placental reconstruction during pregnancy [1–3,10]. Interestingly, several studies have reported that Stab1 is expressed in placental endothelial cells and macrophages during pregnancy, and that it might be involved in cell adhesion and molecular scavenging in placental macrophages [1,3,9]. Previous studies have also suggested that Stab1 regulates differences in the concentration of mouse PL in maternal and fetal blood circulation [1,9]. However, the role of Stab1 in the placenta remains poorly understood and, to the best of our knowledge, the role of Stab2 in the placenta has not been reported yet.

In this study, we analyzed the mRNA expression levels of Stab1 and Stab2 in the placenta and compared them with those in the liver. In addition, we generated a double-knockout mouse strain lacking both Stab1 and Stab2 (Stab1/2 dKO mice) and observed defective reproduction in pregnant Stab1/2 dKO female mice. Furthermore, to determine the causes underlying these reproductive defects, we conducted a descriptive study to phenotypically characterize reproduction and placentation in pregnant Stab1/2 dKO female mice. This study provides the first description of Stab1/2 dKO affecting reproductive capacity and placental development, suggesting that Stab1 and Stab2 play an important role in placental reconstruction and remodeling during pregnancy.


**Author details**

Andrea Berruti1 , Roberto Borriello1 , Alberto Orgiazzi2 , Antonio C. Barbera3 , Erica Lumini1 and Valeria Bianciotto1

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1 National Research Council, Plant Protection Institute – Turin UOS, Torino, Italy

2 European Commission, Joint Research Centre, Institute for Environment and Sustainability, Ispra (VA), Italy

3 DISPA, University of Catania, Catania, Italy


**1. Introduction**

Lithography is one of the key technological processes in the production of semiconductor integrated circuits, storage devices, and precision devices for optics and micromechanics. Laser lithography, near-field, and probe technologies, and radiation exposure methods are widely used to create nanoscale structures [1, 2]. Among the methods of obtaining nanoscale structures, it is necessary to note laser lithography, which allows to carry out mask less image formation in the photoresist layer on the surface of the substrate with a laser beam. Research in the development and manufacture of nanostructures for various purposes is largely determined by the level of development of technologies that allow atomic accuracy to obtain nanostructures of

the required configuration and dimension, as well as a comprehensive diagnosis of the properties of nanostructures. Modern methods of nanoscale optical recording are based on the use of various methods, including photoinitiation with high beam intensity. A significant limitation on the size of the elements is due to the ability to focus optical radiation to sizes smaller than the diffraction limit. Many technical solutions are proposed and developed to realize the possibilities of optical nanolithography [1–3]. Special photosensitive materials can be used to form nanosized structures with focused laser radiation. Direct optical lithography can be created without the use of organic photoresists of functional inorganic nanomaterials. The ability to directly pattern completely inorganic layers using a radiation dose comparable to that of organic photoresists provides an alternative method for producing thin-film devices [4, 5]. Among these materials should be noted inorganic resist based on films of chalcogenide glassy semiconductors (CVS). Inorganic resists based on CVS films can be effectively used in the creation of micro- and nanoelements of optoelectronic devices, micro- and nanoelectromechanical systems (MEMS/NEMS), and diffractive optical elements. The use of these materials is based mainly on their sensitivity to different types of radiation, which cause phase and structural changes in CVS films, and transparency in the infrared range [4, 6–9]. Numerous studies have been conducted aimed at studying the processes of formation of nanostructures on CVS films [7, 9–12]. A number of photoinduced changes are observed in CVS, which are associated with structural transformations, phase transitions, defect formation, and atomic diffusion [6–8]. It is important to determine technologies for the formation of micro- and nanoscale structures on CVS films, which can be used in the creation of diffractive optical elements for optoelectronic devices.

Photoinduced transformations in CVS have been widely used in the optical recording of information to create optical media of various types. This is largely because the properties of thin chalcogenide films allow recording at high speed and do not impose restrictions on the minimum size of the recorded elements and, consequently, on the density of information recording [7, 12]. Numerous theoretical and experimental studies of the interaction of electromagnetic radiation and particle fluxes with CVS have shown the possibility of achieving ultra-high resolution when exposed to optical radiation or electron beam [10, 11, 13, 14]. It is shown that the resolution of an inorganic resist based on CVS is determined by the size of the structural units that form the matrix of films and is 1–2 nm [10, 13, 14]. In this regard, CVS are promising materials for the formation of nanoscale structures on their surface and the creation of ultra-dense information recording devices [1]. Numerous experiments on the exposure of thin films of CVS and their subsequent selective chemical etching have shown that when using immersion optical systems, it is possible to record microrelief structures with submicron dimensions (120–150 nm). With electron beam exposure of chalcogenide films, it is possible to form structures with sizes of 50–70 nm [1, 7]. Particular attention was paid to the choice of CVS that do not contain highly toxic elements, modes of their heat treatment and selective chemical etching [15].


**Acknowledgements**

The author would like to thank the CSIRO's Division of Mineral Engineering and Advanced Fluid Dynamic Laboratory, for support in this work, to Dr. Lachlan Graham, in particular, for his imaging of many of these flows, and assistance in developing a deeper understanding their behavior and to Dr. Arno Talmon for his insights into the bed structure when using non-Newtonian carriers.


*Article* **Evaluation for Appropriate Tillage of Sandy Land in Arid Sandy Area Based on Limitation Factor Exclusion Method**

**Yan Xu 1,2,\*, Zhaoyang Cai 1, Kaige Wang 1, Yuwei Zhang 1 and Fengrong Zhang 1,2**

**Abstract:** Investigating and evaluating the quantity and spatial distribution of arable sandy land in arid and semiarid sandy areas is of great significance for the sustainable development and utilization of sandy land resources and the maintenance of the stability of the structure and function of regional ecosystems. Based on the characteristics of sandy soil, being without structure and susceptible to wind erosion, this study used the limiting factor exclusion method to investigate and evaluate arable sandy land in arid and semiarid areas. All sandy soils were taken as the evaluation objects of arable sandy land (including visible sandy land and invisible sandy land). On the basis of following the principle of ecological protection, the evaluation indicators and limiting factor exclusion evaluation methods of arable sandy land were determined. The results of Hangjin Banner are as follows: the total area of the visible sandy land and the recessive sandy land was 1.2 × 106 hm2; the visible sandy land accounted for 42.6%, and the invisible sandy land accounted for 57.5%. However, only 7.7% of the sandy land was suitable for farming, which is the current cultivated land of bare sand and sandy soil, extremely-low-coverage grassland, inland tidal flats, and other saline-alkali land. Even if these arable sandy lands are to be used sustainably after reclamation, reasonable ecological protection, irrigation engineering measures, and field protective farming measures must be taken. It is hoped that this study can provide a valuable reference for the sustainable development and utilization of arable sandy land and desertification control in arid and semiarid areas.


Preface

Wearable technologies are networked devices equipped with microchips and sensors, capable of tracking and wirelessly communicating information in real time. The rapid adoption of such devices in the past decade has made them the most attractive innovation in the word of technology. From fitness activity trackers to Google Glass, miniaturized wearable devices have shown great potential to be embedded in various domains including healthcare, robotic systems, prosthetics, visual realities, professional sports, and entertainment and arts. Since their first innovation in the 1960s, a wide variety of wearable devices have been developed. These include single functional sensors such as temperature, pressure, and strain detectors, to multifunctional wearable systems capable of monitoring two or more factors simultaneously.

The wearable technologies market is expected to grow 80% from now until 2021, with revenue increasing from \$220 million to approximately \$12 billion. This is attributed to the wide variety of services these products can offer potential customers. For instance, wireless headset technologies, such as Elinka, OldShark, and Goodaa Sunglasses, can provide users the ability to enjoy music as well as answer phone calls while keeping their hands free during walking, biking, or driving. Fitbit fitness watches can continuously monitor heart rate, track activity, and even provide on-screen workouts with no need to be manually configurated on a daily basis. With innovations on the horizon, the future of wearable devices will go beyond answering calls or counting our steps to providing us with sophisticated wearable gadgets capable of addressing fundamental and technological challenges.

This book investigates the development of wearable technologies across a range of applications from educational assessment to health, biomedical sensing, and energy harvesting. Furthermore, it discusses some key innovations in micro/nano fabrication of these technologies, their basic working mechanisms, and the challenges facing their progress.

## **Dr Noushin Nasiri**

Head of NanoTech Laboratory, School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney NSW, Australia

**1**

Section 1

Health

Section 1 Health

**3**

**2. Tear analysis**

**Chapter 1**

Monitoring

lion world market by 2021 [5].

sensing through noninvasive detection techniques.

*Noushin Nasiri*

**1. Introduction**

Introductory Chapter: Wearable

Wearable technologies are becoming increasingly popular as personal health system, enabling continuous real-time monitoring of human health on a daily basis and outside clinical environments [1–3]. The wearable device market is currently having a worldwide profit of around \$34 billion and is expected to reach above \$50 billion by 2022 owing to wearables' ease of use, flexibility, and convenience [4]. Real-time monitoring, operational efficiency, and fitness tracking are reported as main factors supporting the market growth of health wearable devices such as smart watches, smart glasses, and other wellness gadgets, with expected \$12.1 bil-

In the past decade, the recent progress in developing wearable devices was more focused on monitoring physical parameters, such as motion, respiration rate, etc. [3, 6, 7]. Today, there is a great interest in evolving wearable sensors capable of detecting chemical markers relevant to the status of health. Different approaches have been applied by researchers to design and fabricate wearable biosensors for remote monitoring of metabolites and electrolytes in body fluids including tear, sweat, and saliva [3, 8–10]. A great example would be the development of small and reliable sensors that would allow continuous glucose monitoring in diabetic patients [11, 12]. Diabetes is a chronic disease that can significantly impact on quality of life and reduce life expectancy. However, diabetics can stay one step ahead of the disease by monitoring their blood glucose level to minimize the complication of the disease by proper administration of insulin. Currently, blood analysis is the gold standard method for measuring the level of glucose in patient's blood. However, this technique cannot be applied without penetrating the skin, which can be painful and inconvenient, and requires user obedience. Therefore, current research focuses on the development of portable and wearable devices capable of continuous glucose

A majority of the recent studies in this field have targeted the area of personalized medicine, endeavoring to develop miniaturized wearable devices featuring real-time glucose monitoring in diabetic patients [12–15]. One great example is contact lens which is an ideal wearable device that can be worn for hours without any pain or discomfort [16]. Integration of glucose biosensors into contact lenses

Technologies for Healthcare


**1. Introduction**

The coloration of textile materials has been performed since ancient times [1,2]. The textile dyeing industry has long been environmentally challenging in several respects. First, there is very high water consumption during all stages of dyeing, which consequently generates a significant amount of contaminated water waste. Second, the use of very harsh chemicals is also a significant threat to the environment, especially given that residue from these chemicals can come into contact with consumers during their use of textile products. Third, the energy consumption during dyeing through the heating and drying stages is also very high. Finally, the dyes that are currently used are mostly of synthetic origin. One of the ways to reduce these issues is to use natural dyes. Natural dyes were in use before synthetic ones [1,3]; however, their extraction and use are technologically time-consuming and very expensive. In the past decade, research has focused on emerging, novel and exciting sources of natural dyes: bacteria [3–5]. Bacterial, or, as they are sometimes called, microbial dyes are byproducts of bacteria that represent a relatively novel and scarcely investigated source of natural dyes, with tremendous potential for dyeing various textile materials in very intense, durable and esthetically beautiful colors, which are nontoxic and safe for human skin, thus producing environmentally sustainable textile products.

Research into the possibility of using bacterial pigments as natural sources of dyes for the textile industry has grown. For this study, the Scopus and ScienceDirect databases were used with several research keywords, including "bacterial pigments dyes microbial textile fibers fabrics dyeing." After refining the search results by excluding all articles related to processes involving the decolorization of textile dyes from wastewater using bacteria or

**Citation:** Kramar, A.; Kostic, M.M. Bacterial Secondary Metabolites as Biopigments for Textile Dyeing. *Textiles* **2022**, *2*, 252–264. https:// doi.org/10.3390/textiles2020013

Academic Editor: Laurent Dufossé

Received: 1 March 2022 Accepted: 15 April 2022 Published: 19 April 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

the dyeing of textiles using plant extracts, there was only a small number of publications in the field relevant to the dyeing of textiles with bacterial pigments, and a slight increase in publication numbers occurring with time (Figure 1).

**Figure 1.** Number of publications per year (for years between 2008 and 2021) regarding textile dyeing using bacterial pigments, according to Scopus database.

In the search for representative articles, the term "microbial pigments" was used, even though microbial pigments cover pigments and dyes derived from both bacteria and fungi [5]. Fungal pigments are also important sources of natural dyes and have potential for the dyeing of textiles [6], but the use of fungal pigments as dye sources is beyond the scope of this study.

One of the first suggestions in the literature, which is not presented in Figure 1, is the possibility of using color pigment, published in 2000 by Shirata et al. [7]. This publication was followed by a study by Alihosseini et al. [8] in 2008; therefore, there was a gap of several years before the interest in bacterial pigments as textile dyes was revived. Together, the authors of these two studies can be considered pioneers in this field, since they produced the first results about the possibility of using a naturally occurring pigment derived from bacteria to dye various fabrics. The following years marked the growth of research groups studying this field, while in 2017, there was even a first mention of the use of biopigment for ink formulation in printing [9].

Their high production yield, non-toxicity and good safety profile make bacterial pigments or dyes novel, sustainable and promising alternatives to synthetic dyes. In this article, important studies regarding the utilization of bacterial pigments on different textile materials and fibers are presented, with a focus on the necessary step of the preparation of pigment solutions, the use of mordants, and other pre- or post-textile treatments to improve dye fixation on specific fibers and increase the exhaustion of the dyebath, as well as the possibility of imparting additional properties to colored materials, in order to obtain high-added-value textile products.

#### **2. Bacterial Dyes**

Bacterial metabolites/secondary metabolites are by-products of bacterial growth [5]. Usually, these byproducts are bacterial responses to external stimuli [10]. Besides color, these metabolites can possess important additional properties, such as potent antimicrobial activity against different pathogens, anticancer activity, antioxidative activity, UV properties, etc. [3,11–13]. These properties suggest that these pigments could be used as functional dyes for different textile materials, since they offer a range of potential applications in addition to their esthetic, qualities (Figure 2). Bacterial pigments, or biopigments, are terms that are used to describe these types of colorant or dyestuff, but from a textile-science point of view, these bacterial metabolites behave more as dyes than as pigments. Even though

they are not soluble in water, they can be considered dyes rather than pigments because it has been shown that they are chemically bound to textile materials, forming bonds with functional groups on fibers and, therefore, behaving as dyes. However, in current research, the term pigment is frequently used, since these bacterial products are usually insoluble in water, they are in powder form after isolation and drying and, in some cases, they are used as suspensions and not solutions.

**Figure 2.** Some of the properties of bacterial pigments that have potential to be transferred to textile materials during dyeing.

If dyes can offer additional properties to textile materials, by binding to textiles in a way that it does not disturb their antimicrobial or anticancer function, for example, then certain functions can be transferred to textile materials after dyeing. The vast range of special properties of bacterial pigments presented in Figure 2 opens up the possibility that dyed textiles possess the same properties. This is one of the most important aspects that should be explored in the future, i.e., whether certain properties of bacterial pigments are retained on textile materials after dyeing.

Several bacterial strains are able to produce pigments or dyes capable of imparting color to textile materials [11]. These bacteria are isolated from various sources, such as soil, water, plants, insects, etc. [11,12]. Among many, the most important are *Serratia, Streptomyces* and *Pseudomonas* [4,13]. The range of colors that these bacteria produce is wide, including pink, red-orange, yellow, blue, green, etc. [14,15]. However, it is important to note that the color of the extracted pigment does not always match the resulting color of the dyed fiber/fabric. As discussed later in this article, the resulting color depends on the nature of the substrate, meaning that various shades can be obtained by the same pigment on different fabrics; the shade also depends on the dyeing conditions (the temperature, pH, and use of mordants).

Pigment production using certain bacteria can be altered by using different conditions during growth. For example, Alihoseini et al. investigated the possibility of mutating *Vibrio gazogenes* to selectively develop the best pigment-producing strain capable of imparting, in addition to color, durable antimicrobial activity against *E. coli* and *S. aureus* to textile materials [16]. On the other hand, Kanelli et al. optimized the culture conditions of *Janthinobacterium lividum* for pigment (violacein) production and the simultaneous dyeing of fabrics, which resulted in dyed fabrics with significant antifungal activity against several *Candida* pathogens, *C. albicans*, *C. parapsilosis* and *C. krusei*, as well as antibacterial properties against *Escherichia coli*, *Staphylococcus aureus* and the methicillin-resistant *S. aureus*, MRSA [17].