Abstract
Coccolithophores are involved in oceanic carbon and nitrogen cycles, and they also have an impact on global climate change. Chrysotila dentata have a complex and close relationship with phycosphere bacteria. In this study, culturable phycosphere bacteria (free-living bacteria and attached bacteria) are isolated from C. dentata by a gradient dilution method and identified based on the 16S rRNA gene sequencing analysis. The phylogenetic tree (neighbor-joining tree, N-J tree) was constructed using the bacterial sequences and closest related sequences from GenBank. Colony characteristics, Gram nature, and physiological and biochemical characteristics were obtained based on a series of tests, such as the sugar utilization (glucose, arabinose, xylose, maltose, and mannitol) test, Voges–Proskauer reaction, urease tests, gelatin liquefaction, Gram test, starch hydrolysis, among others. In this study, seven strains (CF1, CF2, CF3, CF5, CF6, and CF7) of free-living bacteria (CF) and five strains (CA1, CA2, CA3, CA4, and CA5) of attached bacteria (CA) are isolated and identified. We found that the culturable phycosphere bacteria of C. dentata were mainly α-proteobacteria and γ-proteobacteria, with a small part of the CFB (Cytophaga-Flexibacter-Bacteroides) group bacteria and firmicutes. In this study, most α-proteobacteria can utilize malonate and positive in the urease test, meanwhile they can grow in a 7% NaCl medium. Differently to α-proteobacteria, γ-proteobacteria are more reactive, and can utilize maltose, glucose, arabinose, malonate, aesculin, and starch hydrolysis. Meanwhile, γ-proteobacteria can growth in a 7% NaCl and pH 5.7 medium, and some bacteria of this strain were positive in nitrate reduction. Firmicutes are similar to γ-proteobacteria: they are similar in reactivity, as they can utilize maltose, glucose, arabinose, malonate, aesculin, and starch hydrolysis, and can growth in a 7% NaCl and pH 5.7 medium. The difference is that some of firmicutes were positive in gelatin liquefaction and can utilize mannitol. The CFB group of bacteria were only positive in malonate, aesculin, and starch hydrolysis. The above results provide basic experimental data for further studies on the relationship between the coccolithophores and culturable phycosphere bacteria.
Highlights
IntroductionC. dentata are marine microalgae with a biomineralizing effect in the ocean [3]
Several culturable phycosphere bacteria were isolated from the samples of C. dentata, and we analyzed the 16S rRNA gene sequence of each culturable bacterial sample
Cho et al [28] identified 14 strains culturable bacteria isolated from Chlorella sp., and the results showed that actinobacteria, α-proteobacteria, β-proteobacteria, and the CFB group are the main bacterial taxa, with α-proteobacteria and CFB accounting for the majority of bacterial taxa
Summary
C. dentata are marine microalgae with a biomineralizing effect in the ocean [3]. The surface of C. dentata consists of calcium carbonate produced by the core of coccolithophores. C. dentata make impact of the light permeability of the ocean and global heat fluxes because its surface is covered with coccolith [5]. Coccolithophores are involved in the biological and carbonate pumps when they photosynthesize and calcify. They have a profound impact on the carbon cycle and carbonate system of marine ecosystems [1]. Dimethyl sulfur participates in the regulation of global climate by altering cloud condensation nodules through the sea–air exchange, as well as in the oceanic sulfur cycle. Dimethyl sulfur has a significant impact on the marine environment
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