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Elevated nitrate in the environment inhibits sulfate reduction by important microorganisms of sulfate-reducing bacteria (SRB). Several SRB may respire nitrate to survive under elevated nitrate, but how SRB that lack nitrate reductase survive to elevated nitrate remains elusive. To understand nitrate adaptation mechanisms, we evolved 12 populations of a model SRB (i.e., Desulfovibrio vulgaris Hildenborough, DvH) under elevated NaNO3 for 1000 generations, analyzed growth and acquired mutations, and linked their genotypes with phenotypes. Nitrate-evolved (EN) populations significantly (p

Mangrove sediments host a diverse array of microbial populations and are characterized by high heterogeneity along their vertical depths. However, the genetic diversity within these populations is largely unknown, hindering our understanding of their adaptive evolution across the sediment depths. To elucidate their genetic diversity, we utilized metagenome sequencing to identify 16 high‐frequency microbial populations comprised of two archaea and 14 bacteria from mangrove sediment cores (0–100 cm, with 10 depths) in Qi'ao Island, China. Our analysis of the genome‐wide genetic variation revealed extensive nucleotide diversity in the microbial populations. The genes involved in the transport and the energy metabolism displayed a high nucleotide diversity (HND; 0.0045–0.0195; an indicator of shared minor alleles with the microbial populations). By tracking the processes of homologous recombination, we found that each microbial population was subjected to different purification selection levels at different depths (44.12% genes). This selection resulted in significant differences in synonymous/non‐synonymous mutation ratio between 0–20 and 20–100 cm layers, indicating the adaptive evolutionary process of microbial populations. Furthermore, our assessment of differentiation in the allele frequencies between these two layers showed that the functional genes involved in the metabolic processes of amino acids or cofactors were highly differential in more than half of them. Together, we showed that the nucleotide diversity of microbial populations was shaped by homologous recombination and gene‐specific selection, finally resulting in the stratified differentiation occurring between 0–20 and 20–100 cm. These results enhance our cognition of the microbial adaptation mechanisms to vertical environmental changes during the sedimentation process of coastal blue carbon ecosystems. [ABSTRACT FROM AUTHOR]

Coastal blue carbon (C) ecosystems are recognized as efficient natural C sinks and play key roles in mitigating global climate change. Microbially driven C, nitrogen (N) and sulphur (S) cycles are crucial for ecosystem functioning, but how microorganisms drive C sink formation and C sequestration in coastal sediments remains unclear.In this study, we conducted a comprehensive analysis of amino sugars, C, N and S cycling genes/pathways and their associated taxa in coastal sediments of native (Cyperus malaccensis and Kandelia obovata) and alien (Spartina alterniflora and Sonneratia apetala) vegetation.Compared to the alien‐vegetated coastal sediment, the native‐vegetated coastal sediment had significantly (p < 0.05) higher microbial necromass C and higher functional potentials of chemoautotrophic C fixation, C degradation, methane cycling, N2 fixation, S oxidation and sulphate reduction. Also, our analysis of coastal sediment microbiomes showed that S oxidation could be coupled with C fixation and/or nitrate/nitrite reduction. S oxidation, C degradation and C fixation were found to be key functional pathways for predicting sediment microbial necromass C. Additionally, the sulphur‐oxidizing Burkholderiales metagenome‐assembled genomes (MAGs) were a key functional group that dominated chemoautotrophic C fixation in coastal sediments.These results suggested that chemoautotrophic S oxidizers, in particular Burkholderiales with a novel lineage, might be the key microbial group that dominates microbial necromass C formation in coastal sediments through microbial anabolism (C fixation);the coupling of microbially driven C, N and S cycling processes; and the deposition of microbially derived C. This study provides novel insights into the importance of chemoautotrophic S oxidizers for microbial necromass formation and shed new light on the microbial mechanism of C sink formation in coastal ecosystems, which also has important implications for enhancing C sequestration in coastal wetlands. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]