Goutam Banerjee

The advancement of probiotics research and its application in fish farming industries

Fish are always susceptible to a variety of lethal diseases caused by different types of bacterial, fungal, viral and parasitic agents. The unscientific management practises such as, over feeding, high stock densities and destructive fishing techniques increase the probability of disease symptoms in aquaculture industries. According to Food and Agriculture Association (FAO), each and every year several countries such as China, India, Norway, Indonesia, etc. face a huge loss in aquaculture production due to mainly bacterial and viral diseases. The use of antibiotics is a common practise in fish farming sectors to control the disease outbreak. However, the antibiotics are not long term friend because it creates selective pressure for emergence of drug resistant bacteria. Probiotics are live microorganisms that confer several beneficial effects to host (enhances immunity, helps in digestion, protects from pathogens, improves water quality, promotes growth and reproduction) and can be used as an alternative of antibiotics. In recent year, a wide range of bacteria have reported as potential probiotics candidates in fish farming sectors, however, Lactobacillus sp. and Bacillus sp. gain special attention due to their high antagonistic activities, extracellular enzyme production and availability. In this present review, we have summarized the recent advancement in aquaculture probiotics research and its impact on fish health, nutrition, immunity, reproduction and water quality.

Characterisation and identification of enzyme-producing autochthonous bacteria from the gastrointestinal tract of two Indian air-breathing fish

Characterisation and identification of autochthonous enzyme-producing bacteria isolated from the proximal intestine and distal intestine of two species of Indian air-breathing fish, murrel (Channa punctatus) and stinging catfish (Heteropneustes fossilis), were investigated using conventional culture technique. Population levels of proteolytic strains were highest in the digestive tract of stinging catfish. In both species, the viable counts of amylase-producing bacteria were somewhat higher than cellulase-producing bacteria. Among the gut bacteria isolated, 8 strains (4 from murrel and 4 from stinging catfish) were selected as potent enzyme-producers on the basis of quantitative enzyme assays. All these strains were Gram-positive rods, but only four isolates (CPF4, CPH6, CPH7 and HFH4) were capable of forming endospores. The tested bacteria grew in wide range of temperatures and pH. The strains were further identified by 16S rRNA gene sequence analysis. Two strains, CPF3 (isolated from murrel) and HFH4 (isolated from stinging catfish) showed high similarity to Bacillus sp., strain HFH7 (isolated from the stinging catfish) was most closely related to Bacillus subtilis, while five strains belonged to Bacillus licheniformis. Based on the results of the present study, we suggest that incorporation of autochthonous enzyme-producing bacteria in aquafeeds merits further investigations.

Bacterial symbiosis in the fish gut and its role in health and metabolism

The bacterial community in the fish gut is very dense compared to surrounding water, which suggests that gastrointestinal tract (GIT) provides a favorable ecological niche for survival. GIT bacteria can be broadly divided into two groups; autochthonous (able to colonize on the mucosal surface) and allochthonous (free living). From the host’s point of view, autochthonous bacteria are considered to be more important than allochthonous, as they provide both nutritional as well as disease prevention support to the host. Among their several functions, the autochthonous bacteria are believed to produce several types of extracellular enzymes, block the attachment site for pathogens and secrete a wide range of bacteriocins. Most of the bacterial species in the gut are non-culturable and thus several types of sophisticated techniques such as Denaturing Gradient Gel Electrophoresis (DGGE), Temperature Gradient Gel Electrophoresis (TGGE) and Next Generation Sequencing (NGS) have been introduced to explore the microbial communities in gut. In this present review, we have summarized the impact of gut bacteria in fish with special emphasis on extracellular enzyme production by gut microbiota, bacterial composition, mechanism of attachment in epithelial surface and their role in disease prevention.

The talking language in some major Gram-negative bacteria

Cell–cell interaction or quorum sensing (QS) is a vital biochemical/physiological process in bacteria that is required for various physiological functions, including nutrient uptake, competence development, biofilm formation, sporulation, as well as for toxin secretion. In natural environment, bacteria live in close association with other bacteria and interaction among them is crucial for survival. The QS-regulated gene expression in bacteria is a cell density-dependent process and the initiation process depends on the threshold level of the signaling molecule, N-acyl-homoserine lactone (AHL). The present review summarizes the QS signal and its respective circuit in Gram-negative bacteria. Most of the human pathogens belong to Gram-negative group, and only a few of them cause disease through QS system. Thus, inhibition of pathogenic bacteria is important. Use of antibiotics creates a selective pressure (antibiotics act as natural selection factor to promote one group of bacteria over another group) for emerging multidrug-resistant bacteria and will not be suitable for long-term use. The alternative process of inhibition of QS in bacteria using different natural and synthetic molecules is called quorum quenching. However, in the long run, QS inhibitors or blockers may also develop resistance, but obviously it will solve some sort of problems. In this review, we also have stated the mode of action of quorum-quenching molecule. The understanding of QS network in pathogenic Gram-negative bacteria will help us to solve many health-related problems in future.

Probiotic Potential of Autochthonous Bacteria Isolated from the Gastrointestinal Tract of Four Freshwater Teleosts.

In this study, a total of 121 bacterial strains were isolated from the gastrointestinal tract of four teleostean species, namely striped snakehead (Channa striatus), striped dwarf catfish (Mystus vittatus), orangefin labeo (Labeo calbasu) and mrigal carp (Cirrhinus mrigala), among which 8 isolates showed promising antibacterial activity against four potential fish pathogens, Aeromonas hydrophila, Aeromonas salmonicida, Aeromonas sobria and Pseudomonas fluorescens and were non-hemolytic. The isolates were further screened in response to fish bile tolerance and extracellular digestive enzyme activity. Two bacterial strains MVF1 and MVH7 showed highest tolerance and extracellular enzymes activities, and selected for further studies. Antagonistic activity of these two isolates was further confirmed by in vitro growth inhibition assay against four selected fish pathogens in liquid medium. Finally, these two bacterial strains MVF1 and MVH7 were selected as potential probiotic candidates and thus identification by partial 16S rRNA gene sequence analysis. The bacterial isolates MVF1 and MVH7 were identified as two strains of Bacillus sp.

Impact of microbial proteases on biotechnological industries

Abstract The demand of enzymes in industrial sectors is increasing rapidly due to their economical and ecological advantages. Micro-organisms produce different types of extracellular enzymes for maintaining their own metabolism, defense, and normal physiological condition. Among several enzymes, proteases have gained special attention in industrial sectors. Several sources of extracellular enzymes are reported by various researchers, but enzymes obtain from microbial sources have high demand in industries due to lower cost, high production rate, availability, stability, and diversity. Among micro-organism, bacteria and fungi are reported to be good sources of different types of proteases such as alkaline protease, cysteine protease, aspartate protease, and metallo protease. In this review, we have summarized the available information about the sources of bacterial and fungal proteases, their purification strategies and their temperature and pH optima. Due to huge competition, companies are trying to reduce their manufacturing cost and that’s why microbial sources of enzymes are important. However, genetically engineered strains or engineered proteases have much more importance over natural isolates/protease in industries due to higher production rate and other advantages. Here we have also summarized the important applications of protease in different industries such as, paper mill, starch degrading sector, food processing factories, and detergent making companies.

Recent trends of modern bacterial insecticides for pest control practice in integrated crop management system

Food security and safety are the major concern in ever expanding human population on the planet earth. Each and every year insect pests cause a serious damage in agricultural field that cost billions of dollars annually to farmers. The loss in term of productivity and high cost of chemical pesticides enhance the production cost. Irrespective use of chemical pesticides (such as Benzene hexachloride, Endosulfan, Aldicarb, and Fenobucarb) in agricultural field raised several types of environmental issues. Furthermore, continuous use of chemical pesticides creates a selective pressure which helps in emerging of resistance pest. These excess chemical pesticide residues also contaminate the environment including the soil and water. Therefore, the biological control of insect pest in the agricultural field gains more importance due to food safety and environment friendly nature. In this regard, bacterial insecticides offer better alternative to chemical pesticides. It not only helps to establish food security through fighting against insect pests but also ensure the food safety. In this review, we have categorized insect pests and the corresponding bacterial insecticides, and critically analyzed the importance and mode of action of bacterial pesticides. We also have summarized the use of biopesticides in integrated pest management system. We have tried to focus the future research area in this field for the upcoming scientists.

Bacterial Diversity in the Digestive Tracts of Four Indian Air-Breathing Fish Species Investigated by PCR Based Denaturing Gradient Gel Electrophoresis

ABSTRACT An investigation was conducted to identify the allochthonous microbiota (entire intestine) and the autochthonous microbiota in proximal intestine (PI) and distal intestine (DI) of four species of Indian air-breathing fish (climbing perch; Anabas testudineus, murrel; Channa punctatus, walking catfish; Clarias batrachus and stinging catfish; Heteropneustes fossilis) by PCR based denaturing gradient gel electrophoresis (DGGE). High similarities of the allochthonous microbiota were observed between climbing perch and murrel, walking catfish and stinging catfish, indicating similar food behavior. The autochthonous microbiota of PI and DI from climbing perch and murrel revealed more similarity, than the result obtained from walking catfish and stinging catfish. The autochthonous microbiota of climbing perch and murrel were similar with regard to the allochthonous microbiota, but no such similarity was observed in case of walking catfish and stinging catfish. The fish genotype and intestinal bacteria are well matched and show co-evolutionary relationship. Three fish species has its unique bacteria; autochthonous Enterobacter cloacae, Edwardsiella tarda and Sphingobium sp. in DI of climbing perch, Pseudomonas sp.; allochthonous and autochthonous in PI of walking catfish and uncultured bacterium (EU697160.1), uncultured bacterium (JF018065.1) and uncultured bacterium (EU697160.1) for stinging catfish. In murrel, no unique bacteria were detected.

Autochthonous Gut Bacteria in Two Indian Air-breathing Fish, Climbing Perch (Anabas testudineus) and Walking Catfish (Clarias batrachus): Mode of Association, Identification and Enzyme Producing Ability.

Scanning electron microscopy (SEM) was used to define the location of epithelium-associated bacteria in the gastrointestinal (GI) tract of two Indian air-breathing fish, the climbing perch (Anabas testudineus) and walking catfish (Clarias batrachus). The SEM examination revealed substantial numbers of rod shaped bacterial cells associated with the microvillus brush borders of enterocytes in proximal (PI) and distal regions (DI) of the GI tract of both the fish species. Ten (two each from the PI and DI of climbing perch and three each from the PI and DI of walking catfish) isolated bacterial strains were evaluated for extracellular protease, amylase and cellulase production quantitatively. All the bacterial strains exhibited high cellulolytic activity compared to amylolytic and proteolytic activites. Only two strains, CBH6 and CBH7, isolated from the DI of walking catfish exhibited high proteolytic activity. Maximum cellulase activity was exhibited by the strain, CBF2, isolated from the PI of climbing perch. Six most promising enzyme-producing adherent bacterial strains were identified by 16S rDNA gene sequence analysis. The strain ATH1 (isolated from climbing perch) showed high similarity fo Bacillus amyloliquefaciens whereas, the remaining five strains (isolated from walking catfish) were most closely related to Bacillus licheniformis.

The effect of seasonal temperature on endogenous gut enzyme activity in four air-breathing fish species

Abstract The digestion process in fish is a complex phenomenon and is accomplished with the help of both endogenous and exogenous enzymes. A wide range of enzymes have been reported in fish and their secretion and concentrations highly depend on feeding habits, gut structure and environmental conditions. In this present investigation, we have demonstrated the activity of two endogenous enzymes (protease and amylase) in four economically important air-breathing fish species (Clarias batrachus, Channa punctatus, Anabas testudineus and Heteropneustes fossilis) at different seasonal temperatures. Our results demonstrated that protease activity was higher in all fish during the month of May, followed by September and December. It was also detected that enzyme activity was higher in the hindgut region (HG) compared to the foregut (FG), which suggests that HG is more active in digestion compared to FG. The optimization of feeding efficiency in aquaculture industries is very important, as the cost of feed is high and its availability is also limited. The information presented may be of importance when developing optimized diets and feeding regimes for the species considered.