Table_2_Adaptations of Alteromonas sp. 76-1 to Polysaccharide Degradation: A CAZyme Plasmid for Ulvan Degradation and Two Alginolytic Systems.XLSX

Studying the physiology and genomics of cultured hydrolytic bacteria is a valuable approach to decipher the biogeochemical cycling of marine polysaccharides, major nutrients derived from phytoplankton and macroalgae. We herein describe the profound potential of Alteromonas sp. 76-1, isolated from alginate-enriched seawater at the Patagonian continental shelf, to degrade the algal polysaccharides alginate and ulvan. Phylogenetic analyses indicated that strain 76-1 might represent a novel species, distinguished from its closest relative (Alteromonas naphthalenivorans) by adaptations to their contrasting habitats (productive open ocean vs. coastal sediments). Ecological distinction of 76-1 was particularly manifested in the abundance of carbohydrate-active enzymes (CAZymes), consistent with its isolation from alginate-enriched seawater and elevated abundance of a related OTU in the original microcosm. Strain 76-1 encodes multiple alginate lyases from families PL6, PL7, PL17, and PL18 largely contained in two polysaccharide utilization loci (PUL), which may facilitate the utilization of different alginate structures in nature. Notably, ulvan degradation relates to a 126 Kb plasmid dedicated to polysaccharide utilization, encoding several PL24 and PL25 ulvan lyases and monomer-processing genes. This extensive and versatile CAZyme repertoire allowed substantial growth on polysaccharides, showing comparable doubling times with alginate (2 h) and ulvan (3 h) in relation to glucose (3 h). The finding of homologous ulvanolytic systems in distantly related Alteromonas spp. suggests CAZyme plasmids as effective vehicles for PUL transfer that mediate niche gain. Overall, the demonstrated CAZyme repertoire substantiates the role of Alteromonas in marine polysaccharide degradation and how PUL exchange influences the ecophysiology of this ubiquitous marine taxon.

研究可培养水解细菌的生理学与基因组学，是解析源自浮游植物（phytoplankton）和大型藻类（macroalgae）的海洋多糖——一类关键营养物质——的生物地球化学循环的有效途径。本研究描述了从巴塔哥尼亚大陆架富褐藻胶（alginate）海水中分离得到的交替单胞菌属菌株76-1（Alteromonas sp. 76-1）降解藻类多糖褐藻胶和藻聚糖（ulvan）的巨大潜力。系统发育分析显示，菌株76-1可能代表一个新物种：其与近缘菌株萘降解交替单胞菌（Alteromonas naphthalenivorans）的差异在于对截然不同生境的适应性——前者为高生产力开阔海洋，后者为海岸沉积物。菌株76-1的生态分化特征尤其体现在其丰富的碳水化合物活性酶（carbohydrate-active enzymes, CAZymes）组，这与其分离自富褐藻胶海水以及原始微型生态系统中相关操作分类单元（operational taxonomic unit, OTU）丰度升高的结果一致。菌株76-1编码多个隶属于PL6、PL7、PL17和PL18家族的褐藻胶裂解酶，这些酶主要位于两个多糖利用基因座（polysaccharide utilization loci, PUL）中，可帮助其在自然环境中利用不同结构的褐藻胶。值得注意的是，其藻聚糖降解功能与一个长度为126 kb的专用于多糖利用的质粒相关，该质粒编码多个PL24和PL25家族的藻聚糖裂解酶以及单糖代谢相关基因。该菌株拥有广泛且多样的碳水化合物活性酶组，使其能够在多种多糖上良好生长：在褐藻胶上的倍增时间为2小时，藻聚糖上为3小时，与葡萄糖上的3小时相当。在亲缘关系较远的交替单胞菌属物种中发现同源藻聚糖降解系统，这表明携带碳水化合物活性酶的质粒是介导多糖利用基因座转移、从而获得生态位优势的有效载体。综上，本研究证实的碳水化合物活性酶组明确了交替单胞菌属在海洋多糖降解中的作用，以及多糖利用基因座的水平转移如何影响这一广泛分布的海洋类群的生态生理学特征。