Abstract
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.
Highlights
Microbial bioflocculants (MBF) mainly refer to extracellular polymer substances secreted by microorganisms during their special growth period and characteristic of harmlessness and biodegradability
This study investigated the probability that Ruditapes philippinarum conglutination mud (RPM) bioflocculation components originate from its associated microbes
MBF are superior to traditional chemical flocculants due to their nontoxicity and environmental friendliness, high production costs and complicated fermentation/recovery processes have become the bottlenecks restraining their widespread commercial application, since most strains yield non-precipitating macromolecule polymers like extracellular polysaccharides (EPS) into the fermentation broth, and high-speed centrifugation and a large quantity of organic solvents are required for reclamation [6,7,8]
Summary
Microbial bioflocculants (MBF) mainly refer to extracellular polymer substances secreted by microorganisms during their special growth period and characteristic of harmlessness and biodegradability. MBF are superior to traditional chemical flocculants due to their nontoxicity and environmental friendliness, high production costs and complicated fermentation/recovery processes have become the bottlenecks restraining their widespread commercial application, since most strains yield non-precipitating macromolecule polymers like extracellular polysaccharides (EPS) into the fermentation broth, and high-speed centrifugation and a large quantity of organic solvents are required for reclamation [6,7,8]. Till date, the microbial community profile in RPM is still not known and flocculant-producing microbial strains have been rarely screened and identified systematically[10, 11]. It is a necessity to characterize the microbial community structure of RPM and identify its associated bioflocculantproducing microbes. Since the flocculation-active polysaccharides of RPM have been recently reported for their composition[9], comparing the chemical composition of EPS of flocculant-producing microbial strains with RPM polysaccharides will give sound proof for judging the origin of RPM bioflocculation components
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