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Environmental health is a critical concern, continuously contaminated by physical and biological components (viz., anthropogenic activity), which adversely affect on biodiversity, ecosystems and human health. Nonetheless, environmental pollution has great impact on microbial communities, especially bacteria, which try to evolve in changing environment. For instance, during the course of adaptation, bacteria easily become resistance to antibiotics and heavy metals. Antibiotic resistance genes are now one of the most vital pollutants, provided as a source of frequent horizontal gene transfer. In this review, the environmental cause of multidrug resistance (MDR) that was supposed to be driven by either heavy metals or combination of environmental factors was essentially reviewed, especially focussed on the correlation between accumulation of heavy metals and development of MDR by bacteria. This kind of correlation was seemed to be non-significant, i.e. paradoxical. Gram-positive bacteria accumulating much of toxic heavy metal (i.e. highly stress tolerance) were unlikely to become MDR, whereas Gram-negative bacteria that often avoid accumulation of toxic heavy metal by efflux pump systems were come out to be more prone to MDR. So far, other than antibiotic contaminant, no such available data strongly support the direct influence of heavy metals in bacterial evolution of MDR; combinations of factors may drive the evolution of antibiotic resistance. Therefore, Gram-positive bacteria are most likely to be an efficient member in treatment of industrial waste water, especially in the removal of heavy metals, perhaps inducing the less chance of antibiotic resistance pollution in the environment., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Nowadays when control of environmental toxicity is a matter of concern, the focus of the researchers is to find an eco-friendly process. Considering the hazards associated with chemical synthesis of nanoparticles, green synthesis approaches have gained considerable attention for their sustainable nature in nanomedicine and nanobiotechnology. Here, exopolysaccharide (EPS) synthesized by a geothermal spring origin B. anthracis PFAB2 is used for green synthesis of silver nanoparticles (AgNPs). Elemental analysis of EPS-coated AgNPs exhibited solid peaks of silver (39.66%) along with oxygen and carbon. TEM analysis confirmed the hexagonal shape of the AgNPs. Polydispersity index (PDI) reinforced the moderately monodisperse nature of the nanoparticles. High negative zeta potential indicated longer shelf life, good colloidal nature and high dispersive nature of the AgNPs. The B. anthracis PFAB2 EPS-coated AgNPs demonstrated prospective biocidal characters for both gram positive and gram negative bacteria along with some potentially hazardous fungi compared with the conventional antimicrobials. The results can be much expedient in the future for treatment of microorganisms that are otherwise resistant to traditional antibiotics or antifungal drugs. [ABSTRACT FROM AUTHOR]

Thermal ecosystems like hot springs are exclusive habitat of thermotolerant microorganisms that produce exopolysaccharides (EPS). In this study, EPS produced by a hot spring origin Pseudomonas species is structurally elucidated.The EPS is highly thermostable (Td 289.98 °C), has low molecular weight (1510 Da) and is rhamnoglucose type consisting α-(1 → 3) linked to L-Rhap and α-(1 → 6) linked to d-Glc substituted with O-acetyl groups. Irregular EPS sheets with smooth surface were observed that signify the compact structure of the biopolymer; a characteristic plasticized film-like feature. Intra- and inter-molecular aggregation of EPS units are observed in atomic force microscopy. The EPS showed good rheological property at neutral pH. EPS-mediated green synthesis of silver nanoparticles (AgNP) was performed using co-precipitation method. Size of individual AgNPs had a Z-average of 93.6 nm and 0.437 polydispersity index. The EPS-coated AgNPs were moderately monodisperse. These AgNPs also exhibited biocidal property preferentially against gram negative bacteria and some fungi. Incorporating EPS to the metal nanoparticles confers them biocompatibility. Green synthesis of silver nanoparticles has gained considerable attention for its eco-friendliness in nano-medicine and nano-biotechnology. Keeping in context, the results of our study will support a new polysaccharide-mediated green synthesis approach of metal nanoparticles that shows profound antimicrobial property. [ABSTRACT FROM AUTHOR]

The treatment of bacterial infections is becoming increasingly ineffective due to rapid mutation which leads to antibiotic resistant and resistant bacteria become more prevalent. As a result the existing antibiotics are gradually obsolete and again new drugs are needed to be designed for the same threat. However, the prediction of evolutionary processes/antibiotic resistance is uncertain. Still, the understanding of mode of evolution of resistance in bacteria is a determining step in the preclinical development of new antibiotics, because drug developers assess the risk of resistance arising against a drug during preclinical development. Multidrug efflux pump systems play an important role for making multidrug resistance to a range of clinically important antibiotics in gram-negative bacteria like Pseudomonas aeruginosa, which lower the intracellular drug concentration by exporting incoming antibiotics across the membranes. We tried to show that the wild type susceptible bacteria P. aeruginosa modified its genetic makeup at mutational hotspots under stress. This strain may either become multidrug resistant or remain susceptible depending on position of amino acid changes in regulatory proteins of efflux pump. Multidrug resistant strain made significant changes at the amino acid positions, 103rd (G → A) and 126th (E → V) through the mutation on the nucleotide position of 308th (G → C); both 377th (A → T) and 378th (G → T), respectively in mexR, a repressor of mexAB-oprM efflux pump. This mutant protein showed low affinity with their operator. But the alteration at 103th position (G → A) in mexR may provide almost similar structural and functional stability as wild type. It was found that mutation was seemed to be well regulated within the limit and position specific under stress which might be back to its original form by supplying counter stress unless addition or deletion takes place. [ABSTRACT FROM AUTHOR]