Reactive species produced in the cell during normal cellular metabolism can chemically react with cellular biomolecules such as nucleic acids, proteins, and lipids, thereby causing their oxidative modifications leading to alterations in their compositions and potential damage to their cellular activities. Fortunately, cells have evolved several antioxidant defense mechanisms (as metabolites, vitamins, and enzymes) to neutralize or mitigate the harmful effect of reactive species and/or their byproducts. Any perturbation in the balance in the level of antioxidants and the reactive species results in a physiological condition called “oxidative stress.” A catalase is one of the crucial antioxidant enzymes that mitigates oxidative stress to a considerable extent by destroying cellular hydrogen peroxide to produce water and oxygen. Deficiency or malfunction of catalase is postulated to be related to the pathogenesis of many age-associated degenerative diseases like diabetes mellitus, hypertension, anemia, vitiligo, Alzheimer's disease, Parkinson's disease, bipolar disorder, cancer, and schizophrenia. Therefore, efforts are being undertaken in many laboratories to explore its use as a potential drug for the treatment of such diseases. This paper describes the direct and indirect involvement of deficiency and/or modification of catalase in the pathogenesis of some important diseases such as diabetes mellitus, Alzheimer's disease, Parkinson's disease, vitiligo, and acatalasemia. Details on the efforts exploring the potential treatment of these diseases using a catalase as a protein therapeutic agent have also been described.

Diseases in aquatic organisms, including fish, are a major concern in aquaculture production. In this present investigation, we have evaluated the beneficial effects of dietary Bacillus amyloliquefaciens CCF7 (GenBank Acc. No. KP256501) supplementation in rohu (Labeo rohita) challenged by a pathogenic strain of Aeromonas hydrophila MTCC 1739. Four experimental diets were formulated: control diet (no probiotics) and three experimental diets (different concentrations of probiotic candidate B. amyloliquefaciens CCF7 at 10 (T1), 10 (T2), 10 (T3) CFU/g). Further, we have divided the feeding trial into pre-challenge (70 days) and post-challenge (28 days) periods and various immune parameters (serum protein, globulin, albumin, lysozyme, and IgM), and stress parameters (malondialdehyde, catalase, and superoxide dismutase) were examined during both the periods. Throughout the entire experiment, control group was fed with probiotic free basal diet, while the treatment groups received probiotic supplemented diets (PSD). After challenge test, serum aspartate transaminase (AST), serum alanine transaminase (ALT) activity, and liver malondialdehyde level have increased significantly in control groups; however, level of these parameters were considerably lower in fish fed with PSD. In contrast, liver catalase and superoxide dismutase activities and serum globulin concentration was significantly higher in the group fed with T3 diet followed by T2. Furthermore, an elevated level of serum IgM and higher activity of serum lysozyme was also recorded in PSD fed groups, especially for T3 group which confirmed the probiotic efficiency of the bacterium B. amyloliquefaciens CCF7. We strongly believe that B. amyloliquefaciens CCF7 will be a good probiotic candidate in aquaculture industries.

In the present investigation, probiotic potential (antagonistic activity, enzyme production, hemolytic activity, biosafety, antibiotic sensitivity and bile tolerance level) of Bacillus subtilis LR1 was evaluated. Bacteriocin produced by the bacterial strain B. subtilis LR1 isolated from the gastrointestinal tract of Labeo rohita was purified and characterized. The molecular weight of the purified bacteriocin was ~50 kDa in 12 % Native PAGE and showed inhibitory activity against four fish pathogens such as Bacillus mycoides, Aeromonas salmonicida, Pseudomonas fluorescens and Aeromonas hydrophila. The purified bacteriocin was maximally active at temperature 40 °C and pH 7.0, while none of the tested surfactants affect the bacteriocin activity. Extracellular enzyme activity of the selected bacterial strain was also evaluated. Amylase activity was estimated to be highest (38.23 ± 1.15 µg of maltose liberated mg protein ml of culture filtrate) followed by cellulase and protease activity. The selected bacterium was sensitive to most of the antibiotics used in this experiment, can tolerate 0.25 % bile salt and non-hemolytic in nature. Finally, the efficiency of the proposed probiotic candidate was evaluated in in vivo condition. It was detected that the bacterial strain can effectively reduce bacterial pathogenicity in Indian major carps.

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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.