MerF is a novel regulator of deep-sea Pseudomonas stutzeri flagellum biogenesis and motility

Earthworm gut bacteria facilitate cadmium immobilization through the formation of CdS nanoparticles

Gut bacteria of earthworm Amynthas hupeiensis exhibit significant potential for the in-situ remediation of cadmium (Cd)-contaminated soil. However, the mechanisms by which these gut bacteria immobilize and tolerate Cd remain elusive. The composition of the gut bacterial community was characterized by high-throughput sequencing. Cd-tolerant bacteria were isolated from the gut, and their roles in Cd immobilization, as well as their tolerance mechanisms, were explored through chemical characterization and transcriptome analysis. The predominant taxa in the gut bacterial community included unclassified Enterobacteriaceae, Citrobacter, and Bacillus, which were distinctly different from those in the surrounding soil. Notably, the most Cd-tolerant gut bacterium, Citrobacter freundii DS strain, immobilized 63.61% of Cd2+ within 96 h through extracellular biosorption and intracellular bioaccumulation of biosynthetic CdS nanoparticles, and modulation of solution pH and NH4+ concentration. Moreover, the characteristic signals of CdS were also observed in the gut content of A. hupeiensis when the sterilized Cd-contaminated soil was inoculated with C. freundii. The primary pathways involved in the response of C. freundii to Cd stress included the regulation of ABC transporters, bacterial chemotaxis, cell motility, oxidative phosphorylation, and two-component system. In conclusion, C. freundii facilitates Cd immobilization both in vitro and in vivo, thereby enhancing the host earthworm's adaptation to Cd-contaminated soil.

Physiological and metabolic insights into the first cultured anaerobic representative of deep-sea Planctomycetes bacteria

Planctomycetes bacteria are ubiquitously distributed across various biospheres and play key roles in global element cycles. However, few deep-sea Planctomycetes members have been cultivated, limiting our understanding of Planctomycetes in the deep biosphere. Here, we have successfully cultured a novel strain of Planctomycetes (strain ZRK32) from a deep-sea cold seep sediment. Our genomic, physiological, and phylogenetic analyses indicate that strain ZRK32 is a novel species, which we propose be named: Poriferisphaera heterotrophicis. We show that strain ZRK32 replicates using a budding mode of division. Based on the combined results from growth assays and transcriptomic analyses, we found that rich nutrients, or supplementation with NO3- or NH4+ promoted the growth of strain ZRK32 by facilitating energy production through the tricarboxylic acid cycle and the Embden-Meyerhof-Parnas glycolysis pathway. Moreover, supplementation with NO3- or NH4+ induced strain ZRK32 to release a bacteriophage in a chronic manner, without host cell lysis. This bacteriophage then enabled strain ZRK32, and another marine bacterium that we studied, to metabolize nitrogen through the function of auxiliary metabolic genes. Overall, these findings expand our understanding of deep-sea Planctomycetes bacteria, while highlighting their ability to metabolize nitrogen when reprogrammed by chronic viruses.

The potential of microorganisms as biomonitoring and bioremediation tools for mercury-contaminated soils

Mercury (Hg) pollution is a global issue due to the high toxicity and wide dispersion of Hg around the world. Whether due to anthropogenic activities or natural processes, Hg emissions are steadily increasing, with very high levels in some regions, directly threatening human and ecosystem health. However, bacteria and fungi have evolved and adapted in response to Hg-induced stress and have developed tolerance mechanisms, notably based on the mer operon system that is involved in Hg uptake and biovolatilization via Hg reduction reactions. Other processes, such as bioaccumulation or extracellular sequestration, are involved in Hg resistance, and the study of contaminated soils has allowed the isolation of a number of microorganisms capable of these mechanisms, with strong potential for the implementation of bioremediation approaches. In addition to playing an important role in determining the fate of Hg in the biogeochemical cycle, these microorganisms can indeed be applied to reduce Hg concentrations or at least stabilize Hg for the remediation of polluted soils. Moreover, thanks to the development of biotechnological tools, bioremediation based on Hg-tolerant microorganisms can be optimized. Finally, these microorganisms are relevant candidates for biomonitoring, for example, through the engineering of biosensors, because the detection of Hg is a major issue in preserving the health of living beings.

Draft genome sequence of Pseudomonas sp. A46 isolated from mercury-contaminated wastewater

Pseudomonas sp. A46 was first isolated from mercury-contaminated groundwater in Taiwan. This study is the first to report the draft whole-genome sequence of Pseudomonas sp. A46. Its genome consists of 126 contigs, with a total length of 6,782,516 bp and a GC content of 64.7%. Phylogenetic analysis based on 16 S rRNA gene sequences revealed that Pseudomonas sp. A46 is closely related to Pseudomonas citronellolis. Assessment of the draft genome sequence revealed that Pseudomonas sp. A46 harbors sets of genes conferring resistance to heavy metals, such as mercury, zinc, lead, copper, cadmium, chromate, and arsenate. These identified genes enable this bacterium to tolerate heavy metal stress.

Pseudodesulfovibrio cashew sp. Nov., a Novel Deep-Sea Sulfate-Reducing Bacterium, Linking Heavy Metal Resistance and Sulfur Cycle

Sulfur cycling is primarily driven by sulfate reduction mediated by sulfate-reducing bacteria (SRB) in marine sediments. The dissimilatory sulfate reduction drives the production of enormous quantities of reduced sulfide and thereby the formation of highly insoluble metal sulfides in marine sediments. Here, a novel sulfate-reducing bacterium designated Pseudodesulfovibrio cashew SRB007 was isolated and purified from the deep-sea cold seep and proposed to represent a novel species in the genus of Pseudodesulfovibrio. A detailed description of the phenotypic traits, phylogenetic status and central metabolisms of strain SRB007 allowed the reconstruction of the metabolic potential and lifestyle of a novel member of deep-sea SRB. Notably, P. cashew SRB007 showed a strong ability to resist and remove different heavy metal ions including Co2+, Ni2+, Cd2+ and Hg2+. The dissimilatory sulfate reduction was demonstrated to contribute to the prominent removal capability of P. cashew SRB007 against different heavy metals via the formation of insoluble metal sulfides.