Distributional characteristics of chemolithoautotrophic bacteria and their potential drivers of carbon sequestration processes in mangrove sediments of Quanzhou Bay, Fujian

To explore the carbon fixation process mediated by chemolithoautotrophic bacteria in mangrove sediment, we studied the community structure and metabolic characteristics of chemolithoautotrophic bacteria in Quanzhou Bay, Fujian. Based on results of high-throughput sequencing of 16S rRNA genes it revealed that Campylobacteria and Gammaproteobacteria were the most abundant phyla in the mangrove sediments, and the most dominant genus were Sulfurovum and Woeseia. Notably, there were differences in the bacterial community composition among different sites and layers. The abundance and diversity of bacteria in sediments near the estuary were significantly higher than those of the nearshore. The genus Thiomicrorhabdus and Thermodesulfovibrio, which mediate aerobic sulfur oxidation and carbon sequestration in the surface layer, distribute in the upper sediment layer (0−<6 cm); Those of Desulfobulbus, Mariprofundus, Halomonas, and Hydrogenovibrio distribute in the middle layer of sediments (6−<12 cm), obtaining energy to fix CO₂ through sulfur disproportionation/sulfate reduction, iron oxidation, or hydrogen oxidation. Sulfurovum distributed in deep sediments (12−18 cm) oxidizes hydrogen or sulfide in the bottom sediments to obtain energy, coupled with nitrate or elemental sulfur for chemautotrophic carbon fixation. Thirteen chemoautotroph strains were isolated by culturable method, among which four strains CM-A-1, CM-B-1, CM-C-1 and CM-D-1 may be potential new species. Physiological and biochemical characteristics indicate that CM-A-1, CM-B-1 and CM-C-1 can use reducing substances such as thiosulfate and S⁰ as electron donors, and O₂ and NO₃⁻ as electron receptors to obtain energy for CO₂ fixation. Results provide experimental materials and theoretical references for exploring the carbon sequestration process involving microorganisms in mangrove sediments.