Microbial origin of bioflocculation components within a promising natural bioflocculant resource of Ruditapes philippinarum conglutination mud from an aquaculture farm in Zhoushan, China

Ruditapes philippinarum conglutination mud (RPM) is a byproduct from the aquiculture of an important commercially bivalve mollusk R. philippinarum and has been recently reported as a promising natural bioflocculant resource. However the origin of bioflocculation components within RPM is still a pending doubt and impedes its effective exploitation. This study investigated the probability that RPM bioflocculation components originate from its associated microbes. RPM samples from an aquaculture farm in Zhoushan of China were applied to characterize its microbial community structure, screen associated bioflocculant-producing strains, and explore the homology between extracellular polysaccharides (EPS) from bioflocculant-producing isolates and RPM flocculation components. Results showed that RPM exhibited high bacterial biodiversity, with Proteobacteria, Bacteroidetes and Actinobacteria as the most abundant phyla; hgcI_clade, CL500_29_marine_group, Fusibacter, MWH_UniP1_aquatic_group and Arcobacter as the dominant genera. Fourteen highly efficient bioflocculant-producing strains were screened and phylogenetically identified as Pseudoalteromonas sp. (5), Psychrobacter sp. (3), Halomonas sp. (2), Albirhodobacter sp. (1), Celeribacter sp. (1), Kocuria sp. (1) and Bacillus sp. (1), all of which except Bacillus sp. were reported for the first time for their excellent flocculation capability. Furthermore, EPS from the bioflocculant-producing strains exhibited highly similar monosaccharide composition to the reported flocculation-effective RPM polysaccharides. On the other hand, the existence of fungi in RPM was rare and showed no flocculation functionality. Findings from Zhoushan RPM strongly supported that RPM flocculation components were of bacterial origin and make RPM reproduction possible by fermentation approach.

Ruditapes philippinarum 粘结泥（RPM）是重要商业双壳贝类 R. philippinarum 水产养殖的副产品，近期已被报道为一种具有潜力的天然生物絮凝剂资源。然而，RPM 中生物絮凝成分的来源仍是一个悬而未决的疑问，阻碍了其有效利用。本研究探讨了 RPM 生物絮凝成分可能源自其相关微生物的可能性。来自中国舟山一家水产养殖场的 RPM 样本被用于表征其微生物群落结构，筛选相关的生物絮凝剂产生菌株，并探索生物絮凝剂产生菌株的胞外多糖（EPS）与 RPM 絮凝成分之间的同源性。结果显示，RPM 表现出高水平的细菌多样性，其中变形菌门、拟杆菌门和放线菌门是最丰富的门类；hgcI_clade、CL500_29_marine_group、Fusibacter、MWH_UniP1_aquatic_group 和 Arcobacter 是优势属。筛选出 14 种高效的生物絮凝剂产生菌株，并系统发育学上鉴定为假交替单胞菌属（5 种）、嗜冷杆菌属（3 种）、盐杆菌属（2 种）、白黄杆菌属（1 种）、快速杆菌属（1 种）、库斯氏菌属（1 种）和芽孢杆菌属（1 种），其中除芽孢杆菌属外，其他菌株均首次报道具有优异的絮凝能力。此外，生物絮凝剂产生菌株的 EPS 表现出与已报道的絮凝有效 RPM 多糖高度相似的单糖组成。另一方面，RPM 中真菌的存在极为罕见，且未表现出絮凝功能。来自舟山的 RPM 研究结果表明，RPM 絮凝成分源于细菌，并通过发酵方法使其繁殖成为可能。