Anaerobic oxidation of methane (AOM) is one of the major processes of oxidizing methane in marine sediments. Up to now, extensive studies about AOM coupled to sulfate reduction have been conducted because SO₄²⁻ is the most abundant electron acceptor in seawater and shallow marine sediments. However, other terminal electron acceptors of AOM, such as NO₃⁻, NO₂⁻, Mn(IV), Fe(III), are more energetically favorable than SO₄²⁻. Iron oxides, part of the major components in deep marine sediments, might play a significant role as an electron acceptor in the AOM process, mainly below the sulfate–methane interface, mediated by physiologically related microorganisms. Iron-coupled AOM is possibly the dominant non-sulfate-dependent AOM process to consume methane in marine ecosystems. In this review, the conditions for iron-coupled AOM are summarized, and the forms of iron oxides as electron acceptors and the microbial mechanisms are discussed.

Biogenic and thermogenic gas are two major contributors to gas hydrate formation. Methane hydrates from both origins may have critical impacts on the ecological properties of marine sediments. However, research on microbial diversity in thermogenic hydrate-containing sediments is limited. This study examined the prokaryotic diversity and distributions along a sediment core with a vertical distribution of thermogenic gas hydrates with different occurrences obtained from the Qiongdongnan Basin by Illumina sequencing of 16S rRNA genes as well as molecular and geochemical techniques. Here, we show that gas hydrate occurrence has substantial impacts on both microbial diversity and community composition. Compared to the hydrate-free zone, distinct microbiomes with significantly higher abundance and lower diversity were observed within the gas hydrate-containing layers. Gammaproteobacteria and Actinobacterota dominated the bacterial taxa in all collected samples, while archaeal communities shifted sharply along the vertical profile of sediment layers. A notable stratified distribution of anaerobic methanotrophs shaped by both geophysical and geochemical parameters was also determined. In addition, the hydrate-free zone hosted a large number of rare taxa that might perform a fermentative breakdown of proteins in the deep biosphere and probably respond to the hydrate formation.

Megacity coastal areas, under human activity pressure, are recognized as reservoirs of human pathogens and antibiotic resistance genes (ARGs). However, the dynamics and potential health risks under different anthropogenic stressors remain unclear. In this study, surface seawaters were sampled from Shenzhen’s western (SZW) and eastern (SZE) coasts, considering the influences of intensive population and industrial activities, as well as tourism and recreational activities. This study revealed distinct microbiomes and selective enrichments of heavy metals and ARGs in SZW and SZE areas, with correlations between most ARGs with intl1. The microbiome-ARG co-occurrence network of SZE was more complex, containing diverse human pathogens and ARGs, highlighting health risks even in low-population density recreational areas. Hub pathogens and ARGs may contribute to shaping these networks, and have the potential to serve as new indicators for different coastal human disturbances. These findings aid in developing strategies for urban coastal sustainability and mitigating antimicrobial resistance.

Salt mines feature both autochthonous and allochthonous microbial communities introduced by industrialization. It is important to generate the information on the diversity of the microbial communities present in the salt mines and how they are shaped by the environment representing ecological diversification. Brine from Mahai potash mine (Qianghai, China), an extreme hypersaline environment, is used to produce potash salts for hundreds of millions of people. However, halophiles preserved in this niche during deposition are still unknown. In this study, using high-throughput 16S rRNA gene amplicon sequencing and estimation of physicochemical variables, we examined brine samples collected from locations with the gradient of industrial activity intensity and discrete hydrochemical compositions in the Mahai potash mine. Our findings revealed a highly diverse bacterial community, mainly composed of Pseudomonadota in the hypersaline brines from the industrial area, whereas in the natural brine collected from the upstream Mahai salt lake, most of the 16S rRNA gene reads were assigned to Bacteroidota. Halobacteria and halophilic methanogens dominated archaeal populations. Furthermore, we discovered that in the Mahai potash mining area, bacterial communities tended to respond to anthropogenic influences. In contrast, archaeal diversity and compositions were primarily shaped by the chemical properties of the hypersaline brines. Conspicuously, distinct methanogenic communities were discovered in sets of samples with varying ionic compositions, indicating their strong sensitivity to the brine hydrochemical alterations. Our findings provide the first taxonomic snapshot of microbial communities from the Mahai potash mine and reveal the different responses of bacteria and archaea to environmental variations in this high-altitude aquatic ecosystem.