Algae growth-promoting methylobacteria. Algae growth-promoting methylobacteria

Microalgae, a diverse group of single-celled organisms exhibiting versatile traits, find broad applications in industry e.g. as feedstock for biofuel production, as animal feed and pharmaceuticals, or as sustainable alternative to synthetic fertilizers. However, high production costs require further efforts to optimize fermentation and to enhance biomass yields. In naturally occurring microalgae biofilms, which were studied by complementary 16S rRNA gene fragment amplicon sequencing, algae showed a mutual co-occurrence network with methylobacteria. Therefore, four strains of the genus Methylobacterium, well-known for their plant growth-promoting traits, were studied in co-cultivation experiments to assess the effect on growth of three industrially relevant microalgae (Chlorella vulgaris, Scenedesmus vacuolatus and Haematococcus lacustris). After seven days of co-incubation, for S. vacuolatus and H. lacustris, a significant increase in algal biomass formation of 1.3-fold to up to 14-fold could be observed. Visualization of mixed cultures using confocal laser scanning microscopy revealed a high abundance of methylobacteria in the phycosphere of H. lacustris and S. vacuolatus, visually attached to algae’s surface forming a biofilm-like “protection shield”. Genome analyses revealed that features attributable to enhanced algal growth include genes involved in the synthesis of vitamins, siderophores and plant hormones. Our results support the hypothesis of symbiotic relationships of algae and bacteria with inter-kingdom supportive capacities, underlining the potential of microbial consortia as promising tool for sustainable biotechnology and agriculture.