海洋细菌在藻类多糖的降解和循环中起着重要作用。然而,海带腐烂过程中附生细菌群落的动态及其在藻类多糖降解中的作用尚不清楚。这里,我们进行了宏基因组分析,以研究海带在海带腐烂早期和晚期阶段的附生细菌群落的身份和预测的代谢能力。在海带腐烂期间,优势的附生细菌群落从γ变形杆菌转移到Verrucomicrobia和拟杆菌。在粳稻的早期腐烂阶段,附生细菌主要针对海带衍生的不稳定藻酸盐进行降解,其中γ变形杆菌弧菌科(特别是弧菌)和嗜冷科(特别是嗜冷菌),属于多糖裂解酶(PL)家族PL6,PL7和PL17的藻酸盐裂解酶是关键的藻酸盐降解剂。较复杂的岩藻依聚糖优选被附生细菌在日本血吸虫腐烂后期降解,主要来自Verrucomicrobia(特别是Lentimonas),Planctomycetes的Pirelulaceae(特别是Rhodopirelula),Kiritimatielota的Pontiellaceae,和拟杆菌的黄杆菌科,这取决于使用来自GH29,GH95和GH141家族的糖苷水解酶(GHs)和来自S1_15,S1_16,S1_17和S1_25家族的硫酸酯酶来解聚岩藻依聚糖。基于宏基因组组装的基因组分析,重建了优势附生细菌群中藻多糖降解的途径。本研究揭示了不同附生菌在褐藻多糖降解中的作用。重要海带是沿海海洋生态系统中重要的初级生产者。多糖,作为褐藻生物质的主要成分,构成了海洋中很大一部分有机碳。然而,有关海带腐烂过程中褐藻多糖降解过程中附生细菌的身份和途径的知识仍然难以捉摸。这里,基于宏基因组分析,在日本糖精的早期和晚期衰变阶段研究了附生细菌群落的演替及其代谢潜力。我们的研究揭示了海带腐烂过程中藻类多糖降解细菌的转变,从降解藻酸盐的γ变形菌转变为降解岩藻依聚糖的Verrucomicrobia,Planctomycetes,Kiritimatiellota,和拟杆菌。藻细胞壁多糖动态降解的模型,复杂的有机碳,提出了海带腐烂过程中的附生微生物群。这项研究加深了我们对附生细菌在海洋藻类碳循环中的作用以及藻类培养中病原体控制的理解。
Marine bacteria play important roles in the degradation and cycling of algal polysaccharides. However, the dynamics of epiphytic bacterial communities and their roles in algal polysaccharide degradation during kelp decay are still unclear. Here, we performed metagenomic analyses to investigate the identities and predicted metabolic abilities of epiphytic bacterial communities during the early and late decay stages of the kelp Saccharina japonica. During kelp decay, the dominant epiphytic bacterial communities shifted from Gammaproteobacteria to Verrucomicrobia and Bacteroidetes. In the early decay stage of S. japonica, epiphytic bacteria primarily targeted kelp-derived labile alginate for degradation, among which the gammaproteobacterial Vibrionaceae (particularly Vibrio) and Psychromonadaceae (particularly Psychromonas), abundant in alginate lyases belonging to the polysaccharide lyase (PL) families PL6, PL7, and PL17, were key alginate degraders. More complex fucoidan was preferred to be degraded in the late decay stage of S. japonica by epiphytic bacteria, predominantly from Verrucomicrobia (particularly Lentimonas), Pirellulaceae of Planctomycetes (particularly Rhodopirellula), Pontiellaceae of Kiritimatiellota, and Flavobacteriaceae of Bacteroidetes, which depended on using glycoside hydrolases (GHs) from the GH29, GH95, and GH141 families and sulfatases from the S1_15, S1_16, S1_17, and S1_25 families to depolymerize fucoidan. The pathways for algal polysaccharide degradation in dominant epiphytic bacterial groups were reconstructed based on analyses of metagenome-assembled genomes. This study sheds light on the roles of different epiphytic bacteria in the degradation of brown algal polysaccharides.IMPORTANCEKelps are important primary producers in coastal marine ecosystems. Polysaccharides, as major components of brown algal biomass, constitute a large fraction of organic carbon in the ocean. However, knowledge of the identities and pathways of epiphytic bacteria involved in the degradation process of brown algal polysaccharides during kelp decay is still elusive. Here, based on metagenomic analyses, the succession of epiphytic bacterial communities and their metabolic potential were investigated during the early and late decay stages of Saccharina japonica. Our study revealed a transition in algal polysaccharide-degrading bacteria during kelp decay, shifting from alginate-degrading Gammaproteobacteria to fucoidan-degrading Verrucomicrobia, Planctomycetes, Kiritimatiellota, and Bacteroidetes. A model for the dynamic degradation of algal cell wall polysaccharides, a complex organic carbon, by epiphytic microbiota during kelp decay was proposed. This study deepens our understanding of the role of epiphytic bacteria in marine algal carbon cycling as well as pathogen control in algal culture.