To investigate the diversity of culturable heterotrophic bacteria in deep-sea sediments from the Mariana Trench, this study focused on a sediment core collected from the Challenger Deep at a depth of 10 816 meters on July, 2020. Samples from the surface and various depths within the sediment core were selected, and multiple enrichment and isolation techniques were employed to enhance the culturability of marine bacteria from extreme environments. Cultivation was performed at three temperatures (4, 16, and 28 ℃) using two solid media (MA and R2A) for direct plating, and three enrichment media (IMB, IMB-DMSP, and IMB-Rpf) for selective cultivation. A total of 517 strains of heterotrophic bacteria were obtained, and preliminary identification of potentially novel bacterial taxa was conducted based on 16S rRNA gene sequence comparisons. The results revealed that the isolated 517 strains belonged to 4 phyla (Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes), 8 classes, 30 orders, 42 families, 74 genera, and 144 species. Different enrichment strategies yielded distinct bacterial isolates, with the IMB-Rpf medium enabling the recovery of a broader diversity of microbial species. The addition of revival factors such as DMSP and supernatants from Mcrococcus luteus had selective enrichment effects on various culturable microbial populations in the sediments. Additionally, compositional differences in the cultured bacterial species were observed among different sediments depths. 51 strains from the 4 phyla represented potential new taxonomic units, including 3 potential new genera and 41 potential new species. Notably, 2 strains of them belonged to the class Sphingobacteriia, which have not previously been isolated from Mariana Trench sediments. The research results will provide a substantial resource of deep-sea bacterial strains for future scientific studies and offer new insights into the isolation and cultivation of microorganisms from extreme deep-sea environments.

Dimethylsulfoniopropionate (DMSP) is an important sulfur-containing compound widely distributed in the ocean, playing a key role in the global carbon and sulfur cycles. It is also the primary precursor of the climate-active gas Dimethyl sulfide (DMS). Microbial chemotaxis towards DMSP significantly influences its utilization and the release of DMS. This review summarizes the major DMSP-chemotactic microbial groups and the ecological functions of DMSP in algae-bacteria symbiosis and coral reef ecosystems from three perspectives: microbial groups, molecular mechanisms, and technological advancements. It elucidates the molecular signal transduction pathways underlying chemotaxis and the potential coupling mechanisms between chemotaxis and DMSP cleavage. Additionally, the advantages and limitations of chemotaxis detection techniques, including capillary assays and microfluidic chips, are analyzed. Although the roles of microbial DMSP chemotaxis in various marine ecosystems are gradually being uncovered, the diversity of DMSP-chemotactic groups, the differences in chemotactic abilities, and the underlying mechanisms in marine environments require further investigation. Future research should combine high-throughput omics technologies, in situ observations, and predictive modeling to comprehensively explore the mechanisms of marine microbial DMSP chemotaxis, aiming to reveal their roles in biogeochemical cycling and the release of climate-active gases.

Methylmercury (MeHg) is a potent neurotoxin and bioaccumulates in food webs. Microbial transformation of inorganic mercury (Hg) produces most of the MeHg in the marine environment. The gene pair hgcAB encodes for Hg methylation, a process predominantly attributed to anaerobic bacteria. However, recent studies indicate the formation of methylmercury in low-oxygen zones within marine water columns, although the mechanisms remain poorly understood. "Blue holes" are marine sinkholes containing redox gradients stratified with depth and high microbial diversity across a range of biogeochemical cycles. Here, we present the first metagenomic analysis focused on the potential for Hg methylation in a blue hole ecosystem. Yongle Blue Hole (YBH), currently the world's deepest known blue hole, was selected as a representative site to investigate the genetic potential for Hg methylation and to explore the functional capabilities of putative Hg-methylators within this unique environment. Metagenomic analysis showed that the anoxic sulfidic deep water was likely to be a hotspot for Hg methylation, driven by abundant and diverse Deltaproteobacteria. In the suboxic intermediate layer, Nitrospina and Myxococcota dominated the Hg-methylating community. Furthermore, Hg methylators were found to have different lifestyles (free-living or particle-associated) and to occupy distinct ecological niches within the YBH. In addition, the contribution of sinking particles to Hg methylation, especially in the deep anoxic water column, was highlighted. Our study unveils the biodiversity and survival strategies of Hg methylators across distinct environments. The findings suggest that blue holes could serve as model stratified ecosystems for studying Hg methylation processes across different habitats.

Microbial degradation of methylphosphonate (MPn) is an important pathway contributing to the 'methane paradox' in the oxic ocean. Vibrio spp. are suggested to participate in this process. However, little is known about the molecular basis, phylogenetic breadth and catabolic efficiency of methane production in Vibrio species. Here, 18 Vibrionales strains known to be effective in MPn demethylation were obtained. The most effective strains, i.e., Vibrio gallaecicus HW2-07 and HW2-08, can convert 70%–80% of amended MPn into methane in 5 days. Estimations based on quantitative PCR determination indicated that Vibrio spp. were influential contributors to marine methane production. Genes flanking the common phn genes suggested a divergent gene arrangement and grouped the phn operons into nine types. This was consistent with the phylogeny of phnJ and phnL. The phn operons of cluster Ⅰ and Ⅱ were identified frequently in Vibrio isolates and were common in coastal seas and the open ocean. Addition of MPn increased expression of the phn genes, as well as an unexpected gene that encodes an acyltransferase (act), which frequently occurred in cluster Ⅰ–Ⅳ operons. This study provided experimental evidence and theoretical support for a further understanding that Vibrio spp. may play important roles in aerobic marine methane production.

Antibiotic resistance in gram-negative pathogens has become one of the most serious global public health threats. The role of the N-acyl homoserine lactone (AHL)-mediated signaling pathway, which is widespread in gram-negative bacteria, in the bacterial resistance process should be studied in depth. Here, we report a degrading enzyme of AHLs, MomL, that inhibits the antibiotic resistance of Pseudomonas aeruginosa through a novel mechanism. The MomL-mediated reactivation of kanamycin is highly associated with the relA-mediated starvation stringent response. The degradation of AHLs by MomL results in the inability of LasR to activate relA, which, in turn, stops the activation of downstream rpoS. Further results show that rpoS directly regulates the type Ⅵ secretion system H2-T6SS. Under MomL treatment, inactivated RpoS fails to regulate H2-T6SS; therefore, the expression of effector phospholipase A is reduced, and the adaptability of bacteria to antibiotics is weakened. MomL in combination with kanamycin is effective against a wide range of gram-negative pathogenic bacteria. Therefore, this study reports a MomL-antibiotic treatment strategy on antibiotic-resistant bacteria and reveals its mechanism of action.