The Characteristics Of Sulfate Reduction Transformation Mediated By Microorganisms In A Subtropical Mangrove Wetland Of Beibu Gulf

Mangrove ecosystems are located in the intertidal zones of land and ocean,have high ecological value and protect the coast from erosion.Mangrove sediments are characterized by hypoxia,high sulfur,high salt,and nutrient-rich.Microbes are one of the important components in mangrove sediments and are sensitive indicators of environmental changes,which play an essential role in biogeochemical cycles.The mangrove ecosystem is suffering from domestic pollution,shrimp breeding,agriculture,and species invasion.Thus,studying the correlation between the sulfur cycle and environmental factors in mangrove sediments has gained increased interest.There are some limitations in analyzing the sulfur cycle using existing public databases.The effects of mangrove plants,invasive species,different depths,and seasons on sulfur metabolism have not been well elucidated.The mechanism of the synergistic biotransformation of phosphorus and sulfur in mangrove ecosystems is unclear.In this study,the high-throughput sequencing technology and q PCR strategy were used to analyze the effects on sulfur metabolism of mangrove plants,invasive species and different depths,and constructed the model of sulfide biotransformation and the coupling of sulfur and phosphorus of mangrove ecosystem.An online professional sulfur gene database was manually constructed based on the limited of the current functional database.This study aims to reveal the sulfur cycle mechanism in the marine mangrove wetland system of subtropical Beibu Gulf,and provide a theoretical basis for the protecting of microbial resources in mangrove ecosystems.This work mainly includes the following contents:1.The KEGG,Meta Cyc database and references were referenced to retrieve gene involved in the sulfur cycle to develop a manually curated sulfur metabolism gene integration database(SMDB),which was used to analyze the sulfur cycle genes and taxonomic groups for shotgun metagenomes.The online database of the sulfur gene with high coverage,fast retrieval,and low false positives was constructed.The SMDB contained 175 gene families and covered 11 sulfur metabolism processes with 395,737 representative sequences affiliated with 110 phyla and 2340 genera of bacteria/archaea.SMDB was applied to characterize the sulfur cycle from mangrove sediments,upland forest,deep-sea sediments,marine waters,and river sediments.Gene families involved in assimilatory sulfate reduction were abundant in upland forest,whereas those of dissimilatory sulfate reduction were abundant in deep-sea sediments and mangrove sediments.Marine sediments and mangrove sediments have a higher abundance of sulfate reduction genes than others habitats.Further analysis showed that the structure and composition of sulfur-metabolizing microorganism communities were significantly different among the five habitats.A strong positive correlation was found in sulfur-metabolizing microorganisms and sulfur genes.2.The effects of mangrove plants on the sulfur cycle and the characteristics of sulfide biotransformation in subtropical mangrove ecosystems were accurately evaluated using metagenomic sequencing and quantitative polymerase chain reaction analysis.The most abundant genes were related to the organic sulfur transformation.Furthermore,an ecological model of sulfide conversion was constructed.Total phosphorus was the dominant environmental factor that drove the sulfur cycle and microbial communities.We compared mangrove and non-mangrove sediments and found that the former enhanced metabolism that was related to sulfate reduction when compared to the latter.Total organic carbon,total organic nitrogen,iron,and available sulfur were significantly higher in mangrove sediments than in non-mangrove sediments,which is the key environmental factor that effectively influenced the dissimilatory sulfate reduction.The taxonomic assignment of dissimilatory sulfate-reducing genes revealed that Desulfobacterales and Chromatiales were mainly responsible for sulfate reduction.Chromatiales were most sensitive to environmental factors.The high abundance of cys E and cys K could contribute to the coping of the microbial community with the toxic sulfide produced by Desulfobacterales.3.The effects of invasive species and depths on the sulfur cycle,and the characteristics of the coupling biotransformation of sulfur and phosphorus were accurately evaluated.Phylogenetic analysis profiling,a distinctive microbiome with high frequencies of Gammaproteobacteria and Deltaproteobacteria,appears to be an adaptive characteristic of microbial structures in subtropical mangrove ecosystems.Functional analysis reveals that the levels of sulfate reduction,sulfur oxidation,and poly-phosphate(Poly-P)aggregation decrease with increasing depth.However,at depths of 25–50 cm in the mangrove ecosystems with S.alterniflora invasion,the abundance of sulfate reduction genes,sulfur oxidation genes,and polyphosphate kinase(ppk)significantly increased.A strong positive correlation was found among ppk,sulfate reduction,sulfur oxidation,and sulfur metabolizing microorganisms.The sulfide content was significantly and positively correlated with the abundance of ppk.Further microbial identification suggested that Desulfobacterales,Anaerolineales,and Chromatiales potentially drove the coupling biotransformation of phosphorus and sulfur cycling.In particular,Desulfobacterales exhibited dominance in the microbial community structure.4.The effect of season on the sulfur cycle in mangrove sediments was analyzed.Identifying sulfur-metabolizing microorganisms suggested that Proteobacteria was the dominant bacterial phylum,while Euryarchaeota is the dominant archaea.Seasonal succession did not affect the dominant microorganisms of Proteobacteria and Desulfobacterales.It was found that season was significantly differed on sulfur genes structure and sulfur-metabolizing microbial communities.Sulfate reduction genes(i.e.,aprA,and dsr B)were more frequent in the wet season than those in the dry season.TOC and Fe contents in the wet season were significantly higher than those in the dry season,while TP content in the wet season was significantly lower than those in the dry season.Sulfide content was the key environmental factor that effectively influenced the sulfur-metabolizing microorganisms.In contrast,TOC content was the key environmental factor that effectively influenced the sulfur gene structure in mangrove sediments.In conclusion,the mechanism of the sulfur cycle in the marine mangrove wetland system of subtropical Beibu Gulf was systematically analyzed by metagenomic sequencing and q PCR strategies,revealed the influence of S.alterniflora invasion and different depths on sulfur cycle and phosphorus metabolism,completed the biotransformation mechanism of sulfide in mangrove sedments,and revealed the correlation of environmental factors and sulfur cycle.This study provides a theoretical basis for studying the sulfur cycle mechanism in subtropical mangrove ecosystems,and provides the co-biotransformation of phosphorus and sulfur in mangrove ecosystems.