Ecological Functions Of Novel Methanogens In Mangrove Wetlands

Methanogens are one kind of archaea that can utilize simple compounds to generate methane in anaerobic environments.Methanogens from the phylum Euryarchaeota are currently classified into seven orders,including one novel methanogen class,Methanofastidiosa(WSA2).Genomic analysis has found that this novel methanogen has unique methane metabolism pathways and extensive ecological distribution.Scientists speculate that it may play an important role in global carbon cycle and ecological regulation.The mangrove wetland ecosystem is highly concerned by the scientific community for its high productivity,high biodiversity and the main source of CH₄.Besides,it was found that Methanofastidiosa exists in the sediment of Shenzhen Futian mangrove nature reserve in previous study.In this study,we investigated the ecological distribution of Methanofastidiosa(WSA2)and its relative abundance correlation with environmental factors(total nitrogen,total carbon,p H,ammonium,nitrate,nitrite)in sediments at different locations and different depths in the Futian mangrove wetland.We also constructed genomes of Methanofastidiosa in the Futian mangrove wetland,and analyzed the phylogenetic status,methanogenesis pathways with their expression activities.Finally,combining the metabolic pathways analysis,different methyl compounds were used to enrich Methanofastidiosa.We also studied a new lineage of archaea named Theionarchaea which is very close to Methanofastidiosa according to the phylogenetic analysis and suspected to be a methanogen.Thus,the ecological distribution of Theionarchaea was investigated.Genomes of Theionarchaea were also reconstructed in Futian mangrove wetland,and their phylogenetic status and key metabolic pathways(carbon,nitrogen,sulfur)were investigated.Finally,combining with the transcriptome data,the ecological role of Theionarchaea played in the mangrove ecosystem was discussed.The main results of this study are as follows:1.Methanofastidiosa has a wide ecological distribution,12 categories of 219independent studies with environment information were obtained,of which 68were in activated sludge/reactors,27 were in marine sediments,25 were in the oil/gas storage tanks.2.Among the 6 sampling locations of Futian mangrove wetland ecosystem,the highest content of Methanofastidiosa occurs in the surface sediment of MF1,accounting for 59.34%of the total archaea.Pearson correlation analysis with environmental parameters showed that relative abundance of Methanofastidiosa was extremely significantly positively correlated with nitrite concentration(R=0.507,P<0.01),and significantly negatively correlated with total nitrogen(R=-0.335,P<0.05).3.Genomic analysis indicated that Methanofastidiosa uses the methyl-reducing methanogenesis pathway in the mangrove wetland ecosystem.At the same time,the Methanofastidiosa genome contains genes encoding substrate-specific methyltransferases for a variety of methyl compounds(including Mts,Mta,Mtb,and Mtt),suggesting that it can use H₂ to reduce various methyl compounds to produce methane.4.The enrichment culture experiment showed that the relative abundance of Methanofastidiosa in the experimental groups adding methylthiols and methanol were extremely significantly higher than that of the control group.The relative abundance of Methanofastidiosa in the methylthiols addition experimental group was significantly higher than that of the methanol addition experimental group.The genomic metabolic pathway analysis results are consistent,that is,Methanofastidiosa can use methylthiols or methanol to produce methane,further confirming that Methanofastidiosa may have diverse methanogenic capabilities in the natural environment.5.Theionarchaea is a new class of archaea that close to the Methanofastidiosa propose to be methanogen.Ecological distribution shows that it mainly distributed in the sediment environment.Phylogenetic analysis shows that Theionarchaea can be divided into three subgroups,of which subgroup 1 was mainly distributed in freshwater sediments,subgroup 2 was mainly distributed in the brackish-fresh water environment,and subgroup 3 was mainly distributed in higher salinity environment.6.Metabolic pathway analysis shows that Theionarchaea has the ability to degrade a variety of organics(such as proteins,sugars,and lipids),and can produce a variety of small molecular organics(acetic acid,ethanol,formate)that support other heterotrophic microorganisms in the environment.The diversified carbon,nitrogen,sulfur and hydrogen metabolism potentials of Theionarchaea enable them to survive and reproduce in different environments.We proposed that Theionarchaea play the ecological roles of"middleman"in the environment.