Microalgae host varied microbial consortium harboring cross-kingdom interactions with fundamental ecological significance in aquatic ecosystems. Revealing the complex biofunctions of the cultivable bacteria of phycosphere microbiota is one vital basis for deeply understanding the mechanisms governing these dynamic associations. In this study, a new light-yellow pigmented bacterial strain LZ-28 was isolated from the highly-toxic and harmful algal bloom-forming dinoflagellate Alexandrium catenella LZT09. Collective phenotypic and genotypic profiles were obtained to confidently identify this strain as a new Mameliellaalba member. Comparative genomic analysis showed that strain LZ-28 shared highly similar functional features with other four marine algae-derived M. alba strains in spite of their distinctive isolation sources. Based on the bioactivity assaying, the mutual growth-promoting effects between bacterial strain LZ-28 and algal strain LZT09 were observed. After the culture conditions were optimized, strain LZ-28 demonstrated an extraordinary production ability for its bioflocculanting exopolysaccharides (EPS). Moreover, the portions of two monosaccharides glucose and fucose of the EPS were found to positively contribute to the bioflocculanting capacity. Therefore, the present study sheds light on the similar genomic features among the selected M. alba strains, and it also reveals the potential pharmaceutical, environmental and biotechnological implications of active EPS produced by this new Mameliella alba strain LZ-28 recovered from toxic bloom-forming marine dinoflagellate.

This study investigated the monthly variations of bacterial communities in the surface seawater of the Wenzhou coastal area and their influencing factors, while exploring the ecological functions of microbial communities. The results indicated that the surface seawater bacterial communities in this region exhibited high diversity, with significantly higher diversity observed in the winter half-year compared to the summer half-year. The bacterial community structures showed distinct monthly variations, with high similarity between adjacent months, particularly from June to September. The dominant bacterial taxa primarily included Proteobacteria represented by the SAR86 clade, OM43 clade, and Rhodobacteraceae; Bacteroidota represented by Flavobacteriaceae; and Cyanobacteria mainly composed of Cyanobium PCC-6307 and Synechococcus CC9902. Temperature and nitrate ions were identified as the environmental factors most strongly correlated with monthly bacterial community variations, while dissolved oxygen, nitrite ions, and total organic carbon also showed significant correlations with relative abundances of certain taxa. Predictions of the bacterial community’s ecological functions revealed that chemoheterotrophic functions were most abundant throughout the year, whereas photoautotrophic functions were primarily enriched in summer. Denitrification and other nitrogen cycling-related functions also displayed obvious monthly variations. Collectively, this study provides valuable insights into the temporal changes in coastal microbial communities and their interactions with different environments.