Genome-wide exploration of Escherichia coli genes to promote Chlorella vulgaris growth

Abstract

Microalgal interactions with bacteria are ubiquitous, and are crucial for algal survival. Nevertheless, the detailed mechanisms underpinning the bacterial interactions and their beneficial consequences are unclear. In the current study, we studied the interactions of the model microalga Chlorella vulgaris with a model prokaryote Escherichia coli. We employed a complete set of E. coli K-12 ORF archive (ASKA) library overexpressing a complete set of E. coli K-12 open reading frames to identify the target bacterial genes whose products enhance C. vulgaris growth. During three successive screening rounds, 32 genes were selected whose overexpression resulted in >1.4-fold increase in algal chlorophyll a content. Four genes ribA, ribD, ribE and ssuE that exerted a growth-promoting effect on C. vulgaris were finally identified. These genes were involved in the bacterial riboflavin biosynthesis pathway, which was validated by determining the riboflavin content in the four selected E. coli clones and confirmed by the analysis of the growth-promoting effect of synthetic riboflavin on C. vulgaris. Collectively, these observations revealed a new bacterial determinant involved in microalgae growth promotion. The genome-wide high-throughput screening system provided insight into the long-term adaptation of C. vulgaris to bacterial interactions.