**Krishna Gopal Ghosh**

Chapter 1

Introductory Chapter: Current

Frontiers, Issues and Challenges

1. Current research direction/inclination in Fluvial Geomorphology

geomorphology has experienced awesome progress in understanding of the trends and patterns of riverine landscape dynamics [3, 4]. However, it is necessary to understand the current research interests of the fluvial geomorphologists amid the global challenges. In this direction, all regular research articles allied to fluvial geomorphology in one of the leading geomorphological journals, Geomorphology (ISSN: 0169-555X), are scrutinized for 2018. Among all the 329 regular articles published in 24 volumes (300–323) during 2018, 112 (34%) are within the discipline of fluvial geomorphology. Afterward, the subject matters of the selected articles are grouped into 10 broad themes (Table 1 and Figure 1). As this review work considers one single globally recognized journal and takes a single year as sample therefore, the result may not necessarily highlight all the current research progresses but obviously

Over the last one and half century, the prime interest area of fluvial geomorphology has meandered from global system and local process [1]. Returning to the disci-

While going through the title and abstracts of the 112 sampled research papers, we have grouped them quite readily into 10 broad themes (Figure 1) which are addressed further in turn by the focal words (Table 1). The theme 'Fluvial sediment environment' had the greatest number of papers counting 25 (22%); 20 (18%) fall within 'Holocene Fluvial Chronology (Historical Channel change, Stratigraphy, Paleo Hydrology)', 18 (16%) in 'Modelling fluvial environment and application of advanced techniques', and 11 (10%) in 'Anthropogenic Controls'. 'Fluvial morphology (Processes and forms)' and 'fluvial hydraulics' include 7 (6%) articles each, while 6 (5%) fall under '(Neo)tectonics', and 'Gully and hill slope erosion'. Apart from these, 5 articles (4%) addressed Riverine ecology and 7 (6%) fall within 'crosscutting fields' (i.e. fluvial geomorphology in association with other branches of geomorphology). It is interesting to note that there is no article pertaining to 'river management and restoration' which is one of the focal themes in present research

In consideration of the popular remark 'Geomorphology is largely an intellectual child of the Twentieth Century' [6], the review results show that fluvial geomorphology is continuously refocusing on process and forms and thereby making interface with other disciplines like sedimentology. Moreover, much of the research articles we have revisited for the present assessment are basically geomorphological

Geomorphology: Research

Krishna Gopal Ghosh and Sutapa Mukhopadhyay

pline's critical role in regional-to-local scale problem solving [2], fluvial

could detect the directions in which the subject is developing/inclining.

frontiers of fluvial geomorphology [5].

1

Practice in Fluvial

Faculty of Natural and Mathematical Sciences, Department of Geography, Presidency University, West Bengal, India


**2.3 Enzyme renaturation and proteolysis**

After electrophoresis, the enzymes are renaturated by replacement of the anionic detergent SDS by the non-ionic detergent Triton X-100, through gel washing. Then, gels are incubated under conditions ideal for detection of the desired peptidase. For instance, metallopeptidases are known to require neutral to basic pH for activity, while cysteine peptidases require an acidic pH and a reducing agent, usually DTT (Branquinha et al. 1996). However, it is common to screen biological samples, where there is no previous clue on what peptidase class shall be present, nor the best conditions for proteolysis. Therefore, it is necessary to assess several parameters, such as incubation time, pH, temperature, influence

Fig. 1. Extracellular and cell-associated proteolytic enzymes of *Crithidia deanei* cells, an insect trypanosomatid. Parasites were cultured in a complex medium (brain heart infusion) for 48 h at 28◦C. Then, cells were harvested by centrifugation, the culture supernatant was filtered in Millipore membrane 0.22 µm and concentrated 50-fold by dialysis (cut-off 9000 Da) against polyethylene glycol 4000 overnight at 4oC. The cells were lysed by: the addition of SDS, generating whole cellular extract, or by Triton X-114 to obtain the hydrophilic (cytoplasmatic and intravesicular fraction) and hydrophobic (membrane fraction) phases. The extracellular and cellular extracts were applied on gelatin-SDS-PAGE to evidence the proteolytic enzymes. The gels were incubated in 50 mM sodium phosphate buffer pH 5.5 supplemented with DTT 2 mM at 37oC for 24 h. MP, metallopeptidase and CP, cysteine

After electrophoresis, the enzymes are renaturated by replacement of the anionic detergent SDS by the non-ionic detergent Triton X-100, through gel washing. Then, gels are incubated under conditions ideal for detection of the desired peptidase. For instance, metallopeptidases are known to require neutral to basic pH for activity, while cysteine peptidases require an acidic pH and a reducing agent, usually DTT (Branquinha et al. 1996). However, it is common to screen biological samples, where there is no previous clue on what peptidase class shall be present, nor the best conditions for proteolysis. Therefore, it is necessary to assess several parameters, such as incubation time, pH, temperature, influence

peptidase. For experimental details see d'Avila-Levy et al. 2001, 2003.

**2.3 Enzyme renaturation and proteolysis**

of ions or reducing agents and finally assess the inhibition profile. A general flowchart for establishing such conditions is shown in Figure 3, and a general view of Gelatin-SDS-PAGE screening in an uncharacterized organism can be seen in Figure 4.

Fig. 2. Degradation of different proteinaceous substrates co-polymerized to SDS-PAGE by a surface metallopeptidase from *Herpetomonas samuelpessoai*, an insect trypanosomatid. The following substrates were individually incorporated into SDS-PAGE to evidence the proteolytic activity: gelatin, bovine serum albumin, human serum albumin, casein, immunoglobulin G (IgG), hemoglobin, mucin and gut extract from *Aedes aegypti*. The gels were incubated for 20 h at 37oC in 50 mM sodium phosphate buffer pH 6.0 supplemented with DTT 2 mM (A). The degradation halos, which correlate with degradation capability, were densitometric measured and expressed as arbitrary units of proteolytic activity (B). For experimental details see Pereira et al. 2010b. Reprinted with permission of *Protist*.


Acknowledgements

This work has been supported by grants from the Ministry for Science, Research and Culture, MWFK, Brandenburg, via BTU Cottbus-Senftenberg (project no. c90110631) and via Health Campus Brandenburg, Cluster "Consequences of age-associated cell and organ function" (project no. 92106360).