DataSheet_1_Microbial communities associated with epilithic algal matrix with different morphological characters in Luhuitou fringing reef.docx

The microbiota is an important component of the epilithic algal matrix (EAM) and plays a central role in the biogeochemical cycling of important nutrients in coral reef ecosystems. Insufficient studies on EAM microbiota diversity have led to a limited understanding of the ecological functions of EAMs in different states. To explore the microbial community of EAMs in the Luhuitou fringing reef in Sanya, China, which has undergone the incessant expansion and domination of algae over the past several decades, investigations were conducted in the reef’s intertidal zone. Five types of substrate habitats (dead branching coral, dead massive coral, dead flat coral, granite block, and concrete block) were selected, and their microbial communities were analyzed by high-throughput sequencing of EAM holobionts using the 16S rDNA V4 region. Proteobacteria was the most abundant group, accounting for more than 70% of reads of the microbial composition across all sites, followed by Cyanobacteria (15.89%) and Bacteroidetes (5.93%), respectively. Cluster analysis divided all microbial communities into three groups, namely short, medium, and long EAMs. Algal length was the most important morphological factor impacting the differences in the composition of the EAM microbiota. The three EAM groups had 52 common OTUs and 78.52% common sequences, among which the most abundant were Vibrio spp. and Photobacterium spp. The three types of EAM also had unique OTUs. The short EAMs had 238 unique OTUs and 48.61% unique sequences, mainly in the genera Shewanella and Cyanobacterium. The medium EAMs contained 130 unique OTUs and 4.36% unique sequences, mainly in the genera Pseudomonas and Bacillus. The long EAMs only had 27 unique OTUs and 4.13% unique sequences, mainly in the genus Marinobacter. Compared with short EAM, medium and long EAM had a lower proportion of autotrophic bacteria and higher proportion of potential pathogenic bacteria. It is suggested that EAMs with different phenotypes have different microbial compositions, and the ecological function of the EAM microbiota changes from autotrophic to pathogenic with an increase in algal length. As EAMs have expanded on coastal coral reefs worldwide, it is essential to comprehensively explore the community structure and ecological role of their microbial communities.

微生物群是石附藻类基质（epilithic algal matrix, EAM）的重要组成部分，在珊瑚礁生态系统关键营养元素的生物地球化学循环中发挥核心作用。针对EAM微生物群多样性的研究不足，导致人们对不同状态下EAM的生态功能认知有限。为探究中国三亚鹿回头岸礁的EAM微生物群落——该区域在过去数十年间经历了藻类的持续扩张与优势化——研究人员在该礁的潮间带开展了调查。研究选取了5种底质生境：死亡分枝状珊瑚、死亡块状珊瑚、死亡扁平状珊瑚、花岗岩块以及混凝土块，并通过对EAM共生体进行16S rDNA V4区高通量测序，分析了其微生物群落组成。变形菌门（Proteobacteria）是所有采样点中丰度最高的类群，占微生物群落序列读数的70%以上，其次分别为蓝细菌门（Cyanobacteria，15.89%）和拟杆菌门（Bacteroidetes，5.93%）。聚类分析将所有微生物群落划分为3组，即短型、中型和长型EAM。藻类长度是影响EAM微生物群组成差异的最关键形态学因子。这3组EAM共拥有52个共有操作分类单元（Operational Taxonomic Unit, OTU）以及78.52%的共有序列，其中丰度最高的为弧菌属（Vibrio spp.）和发光杆菌属（Photobacterium spp.）。三类EAM同时拥有各自独特的OTU：短型EAM拥有238个独特OTU和48.61%的独特序列，其类群主要集中在希瓦氏菌属（Shewanella）和蓝细菌属（Cyanobacterium）；中型EAM拥有130个独特OTU和4.36%的独特序列，类群主要隶属于假单胞菌属（Pseudomonas）和芽孢杆菌属（Bacillus）；长型EAM仅拥有27个独特OTU和4.13%的独特序列，类群主要集中在海杆菌属（Marinobacter）。与短型EAM相比，中型和长型EAM的自养细菌占比更低，而潜在致病菌占比更高。研究表明，不同表型的EAM拥有不同的微生物组成，且随着藻类长度的增加，EAM微生物群的生态功能从自养型向致病型转变。鉴于EAM在全球近岸珊瑚礁中持续扩张，全面探究其微生物群落的结构组成与生态功能至关重要。