大亚湾表层沉积物碳水化合物活性酶基因分布特征

Distribution of the microbial Carbohydrate-Active enzymes genes in the surface sediment of the Daya Bay,China

微生物的碳水化合物活性酶(carbohydrate active enzymes,CAZymes)是海洋沉积物有机碳降解过程中的关键。文章基于大亚湾2020年春季表层沉积物的宏基因组数据,分析鉴定编码CAZymes序列种类及其在微生物中的分布,并预测了微生物群落对不同结构聚糖的利用。结果表明,表层沉积物微生物群落对不同结构聚糖的利用能力不同。δ-变形菌纲是编码降解肽聚糖和几丁质相关酶类序列的最大贡献者;γ-变形菌纲、拟杆菌门和浮霉菌门具有最高的CAZymes家族的α-生态多样性(香浓指数),是编码降解结构复杂多糖(岩藻聚糖、昆布多糖、纤维素等)的CAZymes基因优势种群;酸杆菌是编码裂解寡聚半乳糖醛酸多糖酶序列的优势菌群。古菌对大部分CAZymes贡献低于1%,但对编码降解纤维素和半纤维素的碳水化合物酯酶(carbohydrate esterase,CE)序列、结合模块(carbohydrate binding module,CBM)基因序列贡献较突出(贡献介于2.18%~11.1%)。CAZymes的底物主要源自于湾内自生的有机碎屑,降解藻源有机碎屑的CAZymes序列的相对丰度于湾口高于湾东北部。与木质素降解相关的辅助活性家族(auxiliary activity families,AAs)序列相对丰度在湾东北部最高,主导的AAs可能有助于增加木质纤维素的溶解度,进而提高糖苷酶对木质纤维素的生物利用度。大亚湾表层沉积物中微生物及其CAZymes序列组成主要与上层水体有机颗粒沉降以及水深相关。

The microbial carbohydrate active enzymes(CAZymes)are important in the process of carbohydrate mineralization in marine sediment.In this study,metagenomic analysis is used to identify microbial CAZymes genes and predict glycan utilization in the surface sediments from the Daya Bay in spring.The microbial communities showed specific utilization for the different structure glycans.Delta-proteobacteria were dominant for encoding CAZymes genes for the degradation of peptidoglycan and chitin.Gammaproteobacteria,Bacteroides and Planctomycetes were the dominant groups encoding CAZymes genes for the degradation of complex polysaccharides(fucoidan,laminarin,cellulose and hemicellulose),which was associated with their highest Shannon diversity of CAZymes families.Acidobacter was the primary contributors of CAZymes genes for cleaving oligo-galacturonic acid.The contributions of Archaea to most CAZymes genes were less than 1%,while their contributions of genes encoding carbohydrate esterase,binding module relating cellulose and hemicellulose degradation ranged from 2.18%to11.1%.According to the functional of glycoside hydrolases,the substrate of CAZymes were mostly derived from autochthonous debris,i.e.,bacterial sugars(peptidoglycans andα-glucan),algal cell wall(fucoidan and laminarin)and chitin.The relative abundances of CAZymes genes in the mouth for the algal derived organic debris with complex chemical structure were higher than those in the east-northern of the bay.The relative abundances of Auxiliary Activity families(AAs)genes related to lignin degradation were the highest in the east-northern of the bay,and their dominant AAs may help to increase lignocellulose solubility and subsequently enhance the bioavailability of GHs to lignocellulose.The compositions of CAZymes genes were mainly related to the particulate organic matter deposition from water columns and the depth of water body.