Antimicrobial resistance is one of the leading challenges in the human healthcare segment. Advances in antimicrobial resistance studies have revealed various intrinsic, adaptive or acquired factors to be involved for pathogenicity. Antimicrobial agents are either bactericidal or bacteriostatic in action and prescribed according to the mode of action. Various factors are confined for the antimicrobial activity of these agents via biochemical, mechanical, physiological and molecular mechanisms. Microbial cell expresses a number of alternates responsible for the evolution of resistance against these agent activities involving cell surface modifications, enzyme inhibitions, modifications in efflux system, protein carriers and mutations in nucleic acids. Apart from this, the successful adaptations of such microbes have also been observed with the transfer of responsible genes through miscellaneous operations such as vertical evolution, horizontal gene transfer, co-selection, compensatory and random mutation. In addition, alterations or modifications in biochemical and physiological mechanisms at cellular levels are also responsible for antibiotic resistance. This article briefly shows the present scenario of antimicrobial resistance and the alternatives to overcome this global issue in future.
D-amino acids, the important components of the bacterial cell walls, are valuable molecular and genetic markers of bacterial-derived organic material in the environment. D-serine, a racemization product of L-serine is one such amino acid present in various prokaryotes and eukaryotes. It is a well-recognized regulator of various activities in the human nervous system. In plants, it has a role in the nitrogen cycle regulation and pollen tube growth. Serine enantiomers are present in different concentrations and few bacterial strains are reported to contribute to D-serine in the environment. During the present study, soil samples from different places in North India were collected and processed to isolate and screen the bacteria on M9 minimal media (Himedia) for D-serine synthesis. Thin-layer chromatography (TLC Silica gel 60 F 254 (20 × 20 cm, Merck, Darmstadt, Germany) and Mass spectroscopic analysis (Bruker MICROTOF II spectrometer) studies, etc were performed. D-serine-producing isolates were characterized as per standard procedures. Bacterial isolate A1C1 with maximum D-serine (0.919 ± 0.02 nM) synthesis under optimal growth conditions (37°C ± 0.5, 150 ± 0.5 RPM, and 7 ± 0.5 pH) was identified as Bacillus tequilensis based on 16sRNA sequencing. The isolate could be a valuable serine racemization tool for various industrial and environmental applications.
The bacteria isolated from the pomace dumping soil site (bacteria id A1C1) showed maximum growth (O.D600 = 1.97±0.4 X 109 cells/ml) within 48h in the minimal salt media supplemented with L-serine. The isolated strain was identified as ‘Bacillus tequilensis’ through 16sRNA sequencing. The strain was quantified for D-serine content by using RP-HPLC. The D-serine concentration was calculated as 0.919±0.02 nM in the bacterial cellular fraction by using a standard curve plot and linear curve equation. Further, recovery % was also calculated for the spiked samples which vary from 85-90%. The study’s peculiarity reflects the fact that the isolated strain was explored for the first time to detect the presence of serine enantiomers. The biochemical features also showed 70% similarity to the standard strain Bacillus tequilensis 10bT. The optimum growth parameters were recorded as 37℃±0.5, 150±0.5 RPM, and 7±0.5pH. The strain was Gram-positive and synthesized endospores. Morphological results showed its rod shape, large, irregular, and off-white-coloured colonies. A1C1 was also tested for the production of secondary metabolites and enzymes. A1C1 showed positive results for indole production, lactose fermentation, protease, and gelatinase whereas, negative results for catalase, MR-VP, citrate utilization, cellulase, amylase, and pectinase. Further, the strain was assayed for PGPR attributes and showed a negative phosphate solubilization index and IAA production. The antibacterial assay showed 5% and 2% efficacy of the extracellular fraction against MTCC 40 and MTCC 11949 respectively. These results demonstrate that Bacillus tequilensis A1C1 has antibacterial activity, the potential to secrete extracellular enzymes, and D-serine content in the intracellular fraction of the cultivated cells.
The bacteria isolated from the pomace dumping soil site (bacteria id A1C1) showed maximum growth (O.D600 = 1.97±0.4 X 109 cells/ml) within 48h in the minimal salt media supplemented with L-serine. The isolated strain was identified as ‘Bacillus tequilensis’ through 16sRNA sequencing. The strain was quantified for D-serine content by using RP-HPLC. The D-serine concentration was calculated as 0.919±0.02 nM in the bacterial cellular fraction by using a standard curve plot and linear curve equation. Further, recovery % was also calculated for the spiked samples which vary from 85-90%. The study’s peculiarity reflects the fact that the isolated strain was explored for the first time to detect the presence of serine enantiomers. The biochemical features also showed 70% similarity to the standard strain Bacillus tequilensis 10bT. The optimum growth parameters were recorded as 37℃±0.5, 150±0.5 RPM, and 7±0.5pH. The strain was Gram-positive and synthesized endospores. Morphological results showed its rod shape, large, irregular, and off-white-coloured colonies. A1C1 was also tested for the production of secondary metabolites and enzymes. A1C1 showed positive results for indole production, lactose fermentation, protease, and gelatinase whereas, negative results for catalase, MR-VP, citrate utilization, cellulase, amylase, and pectinase. Further, the strain was assayed for PGPR attributes and showed a negative phosphate solubilization index and IAA production. The antibacterial assay showed 5% and 2% efficacy of the extracellular fraction against MTCC 40 and MTCC 11949 respectively. These results demonstrate that Bacillus tequilensis A1C1 has antibacterial activity, the potential to secrete extracellular enzymes, and D-serine content in the intracellular fraction of the cultivated cells.
The current work was carried out to investigate serine enantiomers in bacterial cells. The bacteria isolated from the pomace dumping soil site (bacteria id A1C1) showed maximum growth (O.D600 = 1.97±0.4 X 109cells/ml) within 48h in the minimal salt media supplemented with L-serine. The isolated strain was identified as ‘Bacillus tequilensis’ through 16sRNA sequencing. The study’s peculiarity reflects the fact that the isolated strain was explored for the first time to detect the presence of serine enantiomers. The strain was quantified for D-serine content by using RP-HPLC. The D-serine concentration was calculated as 0.919±0.02 nM in the bacterial cellular fraction by using a standard curve plot and linear curve equation. Further, recovery % was also calculated for the spiked samples which vary from 85-90%. The optimum growth parameters were recorded as 37℃±0.5, 150±0.5 RPM, and 7±0.5pH. The strain was Gram-positive, rod shape, large, irregular, off-white-coloured, and synthesized endospores. A1C1 showed positive results (within 14±2h of incubation) for indole production, lactose fermentation, and protease (0.9 mm, clear zone). The antibacterial assay showed 5% and 2% efficacy of the extracellular fraction against MTCC 40 and MTCC 11949 respectively within 12h of incubation. These results demonstrate that Bacillus tequilensis A1C1 has antibacterial activity, the potential to secrete extracellular enzymes, and D-serine content in the intracellular fraction of the cultivated cells. Given results demonstrate the industrial significance and implication of the isolated strain for the synthesis of commercially valuable products.
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