bacterial cellulose bacterial cellulose bacterial cellulose is an organic compound with the formula (c6h10o5)n produced by certain types of bacteria. while cellulose is a basic structural material of most plants, it is also produced by bacteria, principally of the genera acetobacter, sarcina ventriculi and agrobacterium. bacterial, or microbial, cellulose has different properties from plant cellulose and is characterized by high purity, strength, moldability and increased water holding ability. in natural habitats, the majority of bacteria synthesize extracellular polysaccharides, such as cellulose, which form protective envelopes around the cells. while bacterial cellulose is produced in nature, many methods are currently being investigated to enhance cellulose growth from cultures in laboratories as a large-scale process. by controlling synthesis methods, the resulting microbial cellulose can be tailored to have specific desirable properties. for example, attention has been given to the bacteria komagataeibacter xylinum due to its cellulose's unique mechanical properties and applications to biotechnology, microbiology, and materials science. historically, bacterial cellulose has been limited to the manufacture of nata de coco, a south-east asian food product. with advances in the ability to synthesize and characterize bacterial cellulose, the material is being used for a wide variety of commercial applications including textiles, cosmetics, and food products, as well as medical applications. many patents have been issued in microbial cellulose applications and several active areas of research are attempting to better characterize microbial cellulose and utilize it in new areas. a wet microbial cellulose pellicle being removed from a culture. history as a material, cellulose was first discovered in 1838 by anselme payen. payen was able to isolate the cellulose from the other plant matter and chemically characterize it. in one of its first and most common industrial applications, cellulose from wood pulp was used to manufacture paper. it is ideal for displaying information in print form due to its high reflectivity, high contrast, low cost and flexibility. the discovery of cellulose produced by bacteria, specifically from the acetobacter xylinum, was accredited to a.j. brown in 1886 with the synthesis of an extracellular gelatinous mat. however, it was not until the 20th century that more intensive studies on bacterial cellulose were conducted. several decades after the initial discovery of microbial cellulose, c.a. browne studied the cellulose material obtained by fermentation of louisiana sugar cane juice and affirmed the results by a.j. brown. other researchers reported the formation of cellulose by other various organisms such as the acetobacter pasteurianum, acetobacter rancens, sarcina ventriculi, and bacterium xylinoides. in 1931, tarr and hibbert published the first detailed study of the formation of bacterial cellulose by conducting a series of experiments to grow a. xylinum on culture mediums. in the mid-1900s, hestrin et al. proved the necessity of glucose and oxygen in the synthesis of bacterial cellulose. soon after, colvin detected cellulose synthesis in samples containing cell-free extract of a. xylinum, glucose and atp. in 1949, the microfibrillar structure of bacterial cellulose was characterized by muhlethaler. further bacterial cellulose studies have led to new uses and applications for the material. biosynthesis chemical structure of cellulose bacterial sources bacteria that produce cellulose include gram-negative bacteria species such as acetobacter, azotobacter, rhizobium, pseudomonas, salmonella, alcaligenes, and gram-positive bacteria species such as sarcina ventriculi. the most effective producers of cellulose are a. xylinum, a. hansenii, and a. pasteurianus. of these, a. xylinum is the model microorganism for basic and applied studies on cellulose due to its ability to produce relatively high levels of polymer from a wide range of carbon and nitrogen sources. general process biochemical pathway for cellulose synthesis the synthesis of bacterial cellulose is a multistep process that involve two main mechanisms: the synthesis of uridine diphosphoglucose (udpgic), followed by the polymerization of glucose into long and unbranched chains (the β-1→4 glucan chain) by cellulose synthase. specifics on the cellulose synthesis has been extensively documented. the former mechanism is well known while the latter still needs exploring. the production of udpgic starts with carbon compounds (such as hexoses, glycerol, dihydroxyacetone, pyruvate, and dicarboxylic acids) entering the krebs cycle, gluconeogenesis, or the pentose phosphate cycle depending on what carbon source is available. it then goes through phosphorylation along with catalysis, followed by isomerization of the intermediate, and a process known as udpgic pyrophosphorylase to convert the compounds into udpgic, a precursor to the production of cellulose. the polymerization of glucose into the β-1→4 glucan chain has been hypothesized to either involve a lipid intermediate or not to involve a lipid intermediate, though structural enzymology studies and in vitro experiments indicate that polymerization can occur by direct enzymatic transfer of a glucosyl moiety from a nucleotide sugar to the growing polysaccharide. a. xylinum usually converts carbon compounds into cellulose with around 50% efficiency. fermentation production bacterial strains that produce cellulose micro­organism carbon source supple­ment culture time (h) yield (g/l) a. xylinum brcs glucose ethanol, oxygen 50 15.30 g. hansenii pjk (kctc 10505 bp) glucose oxygen 48 1.72 glucose ethanol 72 2.50 aceto­bacter sp. v6 glucose ethanol 192 4.16 aceto­bacter sp. a9 glucose ethanol 192 15.20 a. xylinum ssp. sucro­fermentans bpr2001 molasses none 72 7.82 fructose agar oxygen 72 14.10 fructose agar 56 12.00 fructose oxygen 52 10.40 fructose agar oxygen 44 8.70 a. xylinum e25 glucose no 168 3.50 g. xylinus k3 mannitol green tea 168 3.34 g. xylinus ifo 13773 glucose lignosulphonate 168 10.10 a. xylinum nust4.1 glucose sodium alginate 120 6.00 g. xylinus ifo 13773 sugar cane molasses no 168 5.76 g. xylinus sp. rky5 glycerol no 144 5.63 glucon­aceto­bacter sp. st-60-12 and lacto­bacillus mali jcm1116 (co-culture) sucrose no 72 4.20 cellulose production depends heavily on several factors such as the growth medium, environmental conditions, and the formation of byproducts. the fermentation medium contains carbon, nitrogen, and other macro and micro nutrients required for bacteria growth. bacteria are most efficient when supplied with an abundant carbon source and minimal nitrogen source. glucose and sucrose are the most commonly used carbon sources for cellulose production, while fructose, maltose, xylose, starch, and glycerol have been tried. sometimes, ethanol may be used to increase cellulose production. the problem with using glucose is that gluconic acid is formed as a byproduct which decreases the ph of the culture and in turn, decreases the production of cellulose. studies have shown that gluconic acid production can be decreased in the presence of lignosulfonate. addition of organic acids, specifically acetic acid, also helped in a higher yield of cellulose. studies of using molasses medium in a jar fermentor as well as added components of sugarcane molasses on certain strains of bacteria have been studied with results showing increases in cellulose production. addition of extra nitrogen generally decreases cellulose production while addition of precursor molecules such as amino acids and methionine improved yield. pyridoxine, nicotinic acid, p-aminobenzoic acid and biotin are vitamins important for cellulose production whereas pantothenate and riboflavin have opposing effects. in reactors where the process is more complex, water-soluble polysaccharides such as agar, acetan, and sodium alginate are added to prevent clumping or coagulation of bacterial cellulose. the other main environmental factors affecting cellulose production are ph, temperature, and dissolved oxygen. according to experimental studies, the optimal temperature for maximum production was between 28 and 30 °c. for most species, the optimal ph was between 4.0 and 6.0. controlling ph is especially important in static cultures as the accumulation of gluconic, acetic, or lactic acid decreases the ph far lower than the optimal range. dissolved oxygen content can be varied with stirrer speed as it is needed for static cultures where substrates need to be transported by diffusion. reactor based production static and agitated cultures are conventional ways to produce bacterial cellulose. both static and agitated cultures are not feasible for large-scale production as static cultures have a long culture period as well as intensive manpower and agitated cultures produce cellulose-negative mutants alongside its reactions due to rapid growth. thus, reactors are designed to lessen culture time and inhibit the conversion of bacterial cellulose-producing strains into cellulose-negative mutants. common reactors used are the rotating disk reactor, the rotary biofilm contactor (rbc), a bioreactor equipped with a spin filter, and a reactor with a silicone membrane. structure and properties types of cellulose genus cellulose type biological role acetobacter extracellular pellicle,ribbons maintain aerobicenvironment achromobacter ribbons flocculation aerobacter fibrils flocculation agrobacterium short fibrils attachment to plants alcaligenes fibrils flocculation pseudomonas non-distinct flocculation rhozobium short fibrils attachment to plants sarcina amorphous unknown differences between plant and bacterial cellulose as the earth's most common organic material, cellulose can be classified into plant cellulose and bacterial cellulose, both of which are naturally occurring. plant cellulose, which makes up the cell walls of most plants, is a tough, mesh-like bulkwork in which cellulose fibrils are the primary architectural elements. while bacterial cellulose has the same molecular formula as plant cellulose, it has significantly different macromolecular properties and characteristics. in general, microbial cellulose is more chemically pure, containing no hemicellulose or lignin, has a higher water holding capacity and hydrophilicity, greater tensile strength resulting from a larger amount of polymerization, ultrafine network architecture. furthermore, bacterial cellulose can be produced on a variety of substrates and can be grown to virtually any shape due to the high moldability during formation. additionally, bacterial cellulose has a more crystalline structure compared to plant cellulose and forms characteristic ribbon-like microfibrils. a hallmark of microbial cellulose, these thin microfibrils are significantly smaller than those in plant cellulose, making bacterial cellulose much more porous. three way branching point mechanism macro structure cellulose is composed of carbon, oxygen, and hydrogen, and is classified as a polysaccharide, indicating it is a carbohydrate that exhibits polymeric characteristics. cellulose is composed of straight chain polymers, whose base units of glucose are held together by beta-linkages. the structural role of cellulose in cell walls has been likened to that of the glass strands of fiberglass or to the supporting rods within reinforced concrete. cellulose fibrils are highly insoluble and inelastic and, because of their molecular configuration, have a tensile strength comparable to that of steel. consequently, cellulose imparts a unique combination of chemical resilience and mechanical support and flexibility to the tissues in which it resides. bacterial cellulose, produced by acetobacter species, displays unique properties, including high mechanical strength, high water absorption capacity, high crystallinity, and an ultra-fine and highly pure fiber network structure. one of the most important features of bacterial cellulose is its chemical purity. in addition to this, bacterial cellulose is stable towards chemicals and at high temperatures. bacterial cellulose has been suggested to have a construction like a ‘cage' which protects the cell from foreign material and heavy-metal ions, while still allowing nutrients to be supplied easily by diffusion. bacterial cellulose was described by louis pasteur as "a sort of moist skin, swollen, gelatinous and slippery." although the solid portion in the gel is less than one percent, it is almost pure cellulose containing no lignin and other foreign substances. although bacterial cellulose is obtained in the form of a highly swollen gel, the texture is quite unique and different from typical gels. cellulose has a high swollen fiber network resulting from the presence of pore structures and tunnels within the wet pellicle. plant cellulose water retention values 60%, while bacterial cellulose has a water retention value of 1000%. the formation of the cellulose pellicle occurs on the upper surface of the supernatant film. a large surface area is important for a good productivity. the cellulose formation occurs at the air/cellulose pellicle interface and not at the medium/cellulose interface. thus oxygen is an important factor for cellulose production. after an inducing and a rapid growth period, the thickness increases steadily. fibrils appear to be not necessarily linear but contain some "three-way branching points" along their length. this type of branching is considered to be related to the unique characteristics of this material and occurs from branching points produced by binary fission. sizes of synthetic and naturally occurring fibers properties and characterization sheet-shaped material prepared from bacterial cellulose has remarkable mechanical properties. according to brown, the pellicle of bacterial cellulose was "very tough, especially if an attempt was made to tear it across its plane of growth". the young's modulus for bacterial cellulose has been reported to be as high as 15 gpa across the plane of the sheet, whereas the highest values attained in the past by polymeric