Chromium(VI) reduction in Streptomyces sp. M7 mediated by a novel Old Yellow Enzyme

Genomic and proteomic analyses reveal the reduction mechanism of hexavalent chromium by the culturing supernatant of strain Pediococcus acidilactici 13-7

This study used lactic acid bacteria with high antioxidative properties to screen for strains capable of reducing hexavalent chromium [Cr (VI)] in their culturing supernatants. The strain Pediococcus acidilactici 13-7 exhibited potent Cr (VI)-reducing capability and remarkable resistance to Cr (VI) even at concentration as high as 24 mM. Comparative genomics analysis revealed a unique gene, ChrR, associated with Cr (VI) reduction in this strain, distinguishing it from four reference strains of P. acidilactici. The proteomic investigation identified proteins linked to the ChrR gene, such as nqo1, frdA, and gshR, indicating significant enrichment in redox-related functions and oxidative phosphorylation pathways. These findings suggest that P. acidilactici 13-7 possesses superior electron transfer capacity compared to other strains, making it more adaptable under highly oxidative conditions by modulating the external environment to mitigate oxidative stress. Collectively, the results demonstrated the potential application of this lactic acid bacterial strain for bioremediation of heavy metals by its ability to reduce Cr (VI), and shed light on the molecular mechanisms underlying Cr (VI) reduction of the strain P. acidilactici 13-7.

PGPR-Enabled bioremediation of pesticide and heavy metal-contaminated soil: A review of recent advances and emerging challenges

The excessive usage of agrochemicals, including pesticides, along with various reckless human actions, has ensued discriminating prevalence of pesticides and heavy metals (HMs) in crop plants and the environment. The enhanced exposure to these chemicals is a menace to living organisms. The pesticides may get bioaccumulated in the food chain, thereby leading to several deteriorative changes in the ecosystem health and a rise in the cases of some serious human ailments including cancer. Further, both HMs and pesticides cause some major metabolic disturbances in plants, which include oxidative burst, osmotic alterations and reduced levels of photosynthesis, leading to a decline in plant productivity. Moreover, the synergistic interaction between pesticides and HMs has a more serious impact on human and ecosystem health. Various attempts have been made to explore eco-friendly and environmentally sustainable methods of improving plant health under HMs and/or pesticide stress. Among these methods, the employment of PGPR can be a suitable and effective strategy for managing these contaminants and providing a long-term remedy. Although, the application of PGPR alone can alleviate HM-induced phytotoxicities; however, several recent reports advocate using PGPR with other micro- and macro-organisms, biochar, chelating agents, organic acids, plant growth regulators, etc., to further improve their stress ameliorative potential. Further, some PGPR are also capable of assisting in the degradation of pesticides or their sequestration, reducing their harmful effects on plants and the environment. This present review attempts to present the current status of our understanding of PGPR's potential in the remediation of pesticides and HMs-contaminated soil for the researchers working in the area.

A sustainable solution for alleviating hexavalent chromium from water streams using Lactococcus lactis AM99 as a novel Cr(VI)-reducing bacterium

Chromium, extensively used in various industries, poses significant challenges due to its environmental impact. The threat of Cr(VI) causes critical concerns in aquatic ecosystems as a consequence of the fluidity of water. The conventional approach for the treatment of effluents containing Cr(VI) is reducing Cr(VI) to low-noxious Cr(III). This research is related to a Gram positive bacterium newly isolated from tannery effluent under aerobic conditions. To characterize functional groups on the isolate, Fourier transform infrared spectroscopy was utilized. The effect of different factors on Cr(VI) bioreduction was investigated, including temperature, initial Cr(VI) concentration, acetate concentration, and Tween 80 surfactant. Under optimal conditions (37 °C and 0.90 g/L sodium acetate), the bioreduction rate of the isolate, identified as Lactococcus lactis AM99, achieved 88.0 % at 300 mg/L Cr(VI) during 72 h (p < 0.05). It was observed that Cr(VI) bioreduction was enhanced by the acetate in both the quantity and intensity, while Tween 80 had no impact on the reaction. The strain AM99 exhibited remarkable characteristics, notably a marginal decrease in growth at elevated concentrations of hexavalent chromium and an exceptional potential to reduce Cr(VI) even at very low biomass levels, surpassing any prior findings in the associated research. Furthermore, The isolate could tolerate 1400 mg/L Cr(VI) in a solid medium. These distinctive features make the isolate a promising and well-suited candidate for remediating Cr(VI)-polluted environments. Additionally, the impact of biogenic extracellular polymer produced by the strain AM99 on reduction was examined at different temperatures.

Elucidating Multiple Electron-Transfer Pathways for Metavanadate Bioreduction by Actinomycetic Streptomyces microflavus

While microbial reduction has gained widespread recognition for efficiently remediating environments polluted by toxic metavanadate [V(V)], the pool of identified V(V)-reducing strains remains rather limited, with the vast majority belonging to bacteria and fungi. This study is among the first to confirm the V(V) reduction capability of Streptomyces microflavus, a representative member of ubiquitous actinomycetes in environment. A V(V) removal efficiency of 91.0 ± 4.35% was achieved during 12 days of operation, with a maximum specific growth rate of 0.073 d-1. V(V) was bioreduced to insoluble V(IV) precipitates. V(V) reduction took place both intracellularly and extracellularly. Electron transfer was enhanced during V(V) bioreduction with increased electron transporters. The electron-transfer pathways were revealed through transcriptomic, proteomic, and metabolomic analyses. Electrons might flow either through the respiratory chain to reduce intracellular V(V) or to cytochrome c on the outer membrane for extracellular V(V) reduction. Soluble riboflavin and quinone also possibly mediated extracellular V(V) reduction. Glutathione might deliver electrons for intracellular V(V) reduction. Bioaugmentation of the aquifer sediment with S. microflavus accelerated V(V) reduction. The strain could successfully colonize the sediment and foster positive correlations with indigenous microorganisms. This study offers new microbial resources for V(V) bioremediation and improve the understanding of the involved molecular mechanisms.

Streptomyces: connecting red-nano and grey biotechnology fields

Anthropogenic activities are often related to the occurrence of simultaneous contaminations with heavy metals and toxic organic compounds. In addition, the increasing demand for food, clothing, and technology has increased the worldwide contamination level. Although it is not fully demonstrated, the high level of contamination in association with the indiscriminate use of antibiotics, led to the appearance of multi-resistant pathogenic microorganisms. Grey and red biotechnologies try to counteract the negative effects of pollution and antimicrobial resistance respectively. Streptomyces is well known in the field of biotechnology. In this review, we discussed the potential of these bacteria to deal with organic and inorganic pollutants and produce nanostructures with antimicrobial activity. To our knowledge, this is the first work in which a biotechnological bacterial genus such as Streptomyces is revised in two different fields of global concern, contamination, and multi-drugs resistant microorganisms.

Genomic analysis and proteomic response of the chromium-resistant and phenanthrene-degrading strain Streptomyces sp. MC1

AIM

Chemically disparate toxic organic and/or inorganic molecules produced by anthropogenic activities often hinder the bioremediation process. This research was conducted to understand the capacity of Streptomyces sp. MC1 to remove chemically disparate toxics such as Cr(VI) or phenanthrene.

METHODS AND RESULTS

Genomic, metabolic modeling and proteomic approaches were used in this study. Our results demonstrated that Streptomyces sp. MC1 has the genetic determinants to remove Cr(VI) or degrade phenanthrene. Proteomics showed that these genetic determinants were expressed. Metabolic versatility of the strain was confirmed by two metabolic models in complex and minimal media. Interestingly, our results also suggested a connection between the degradation of phenanthrene and synthesis of specialized metabolites.

CONCLUSIONS

Streptomyces sp. MC1 has the genetic and physiological potential to remove Cr(VI) or degrade phenanthrene SIGNIFICANCE AND IMPACT OF STUDY: The probability of a microorganism to survive in the presence of different contaminants depends on its genetic potential and the ability to express it. The genetic and proteomic profiles obtained for Streptomyces sp. MC1 can be recommended as model and predict if other Streptomyces strains can be used in bioremediation processes. Our work also hypothesized that intermediates of the phenanthrene degradation serve as precursors for the specialized metabolism.

Systems and synthetic biology to elucidate secondary metabolite biosynthetic gene clusters encoded in Streptomyces genomes

Covering: 2010 to 2020 Over the last few decades, Streptomyces have been extensively investigated for their ability to produce diverse bioactive secondary metabolites. Recent advances in Streptomyces research have been largely supported by improvements in high-throughput technology 'omics'. From genomics, numerous secondary metabolite biosynthetic gene clusters were predicted, increasing their genomic potential for novel bioactive compound discovery. Additional omics, including transcriptomics, translatomics, interactomics, proteomics and metabolomics, have been applied to obtain a system-level understanding spanning entire bioprocesses of Streptomyces, revealing highly interconnected and multi-layered regulatory networks for secondary metabolism. The comprehensive understanding derived from this systematic information accelerates the rational engineering of Streptomyces to enhance secondary metabolite production, integrated with the exploitation of the highly efficient 'Design-Build-Test-Learn' cycle in synthetic biology. In this review, we describe the current status of omics applications in Streptomyces research to better understand the organism and exploit its genetic potential for higher production of valuable secondary metabolites and novel secondary metabolite discovery.