918 / 2024-09-19 20:04:28

Transformation and utilisation of Chrysotila dentata-derived DOM by phycosphere bacteria CA6 and CF2 under the action of exogenous factor VB12

Chrysotila dentata, phycosphere bacteria, DOM, VB12

Chrysotila dentata is a major group of calcified protists that are covered with dense calcite coccoliths. Chrysotila dentata has a complex and close relationship with phycosphere bacteria, which play an important role in the carbon cycle.

In this study, purified C. dentata was used as the experimental object, and culturable phycosphere bacteria were isolated and identified. The isolated phycosphere bacteria, Marinobacter hydrocarbonocoticus (CA6) and Bacillus firmus (CF2), were co-cultured with Chrysotila dentata by adding exogenous factors-VB12. To investigate the growth of algal-bacteria and the changes in dissolved organic matter (DOM) in the solution.

Fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (EM-PARAFAC) was used in this study to analyze the changes of DOM, and fluorescence indexes were utilized to explore the DOM. Culturable bacteria were separated using a gradient dilution method, and 16S rRNA gene sequencing was applied for comparing, analyzing, and identifying the sequences of bacteria related to GenBank. Subsequently, a neighbor-joining tree (N-J tree) was constructed. The physical, physiological, and biochemical characteristics of the isolated colonies were also determined. A total of 7 free-living bacteria (CF1, CF2, CF3, CF5, CF6, CF7) and 5 attached bacteria (CA1, CA2, CA3, CA4, CA5) were isolated and identified in this study. The main culturable bacteria of Chrysotila dentata are α-Proteobacteria and γ-Proteobacteria; a small portion belong to CFB (Cytophaga-Flexibacter-Bacteroides) and Firmicutes.

It was found that CA6 and CF2 can increase the cell number and photosynthetic capacity of Chrysotila dentata, and also affect the Chrysotila dentata-derived DOM concentration. The protein-like components were effectively utilized, and the humic-like component increased with the prolongation of culture time. The ability of CA6 to consume protein-like substances and transform humic-like substances was stronger than that of CF2. However, the average concentration of protein-like proteins in incubated filtrate was the highest. Additionally, we also found that CF2 had a better consumption capacity for bacterial-derived DOM than CA6.When 100μg/L of VB12 was added, it was found that there was no significant change in the cell number of microalgae. The abundance of CA6 cells continuously decreased, as did the protein-like substances. The humic-like component was not affected.