Phylogenetic diversity and predictive functional profile of bacteria associated with marine microalgae, <em>Isochrysis galbana</em> using next generation sequencing

Abstract

In aquaculture, microalgal-bacterial interaction has ecological significance, and thus demands better understanding for improvement of sustainability and productivity of large scale microalgal cultivation. Here, we assessed the bacterial diversity, including the uncultivable bacterial assemblage associated with the marine microalgae Isochrysis galbana using next generation sequencing approach. Isochrysis has been considered as one of the most favoured types of live feed in aquaculture and hence, chose Isochrysis galbana MBTDCMFRI S002. Total genomic DNA was extracted from I. galbana culture and 16S rDNA V3 region was sequenced with an Illumina MiSeq platform. A total of 30 different known bacterial genera were detected from 1190 identified operational taxonomic units. These bacterial phylotypes were affiliated to Alphaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Actinobacteria, Acidimicrobiia, Bacteroidia, Flavobacteriia and Bacilli classes. These 30 bacterial genera comprise only 4.62% of the total OTUs obtained and remaining 95.38% of the sequences do not exhibit any similarity against known bacterial genera in the taxonomic database. The functional profile of bacterial communities was predicted using PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) analysis. The results indicated that these associated bacterial communities are mainly involved in environmental as well as genetic information processing, membrane transport and nutrient metabolism. These functions may mediate their interaction with the phytoplankton host, and thus improve bacterial survival in microalgal habitat. Overall, the present study enhances the understanding of microalgal-bacterial interaction in terms of diversity and functional role of associated microbial community.