Abstract
Microalgae, a diverse group of single-celled organisms exhibiting versatile traits, find broad applications in industry. However, high production costs require further efforts to optimize their production and to enhance biomass yields. In the present study, co-occurrence of algae and methylobacteria was observed when naturally occurring microalgae biofilms were subjected to 16S rRNA gene fragment amplicon sequencing. This bacterial group is so far less explored than other microalgae-associated bacteria in terms of mutualistic relationships that might be exploitable for biotechnological applications. In order to assess the potential of four plant growth-promoting strains from the genus Methylobacterium for increased algae biomass production, co-cultivation experiments were conducted with three industrially relevant microalgae (Chlorella vulgaris, Scenedesmus vacuolatus, and Haematococcus lacustris). For S. vacuolatus and H. lacustris, a significant increase in algal biomass formation of 1.3-fold to up to 14-fold was observed after 7 days of co-incubation. 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 the algae’s surface forming a biofilm-like assemblage. Genome analyses revealed that features attributable to enhanced algal growth include genes involved in the synthesis of vitamins, siderophores and plant hormones. Our results provide evidence for the constructability of novel symbiotic algae-bacteria relationships with inter-kingdom supportive capacities, underlining the potential of microbial consortia as promising tool for sustainable biotechnology and agriculture.
Highlights
In the recent past, the potential of microalgae for industrial purposes increasingly gained importance at a global scale
Our study revealed a co-occurrence of microalgae and methylobacteria in a natural biofilm when the whole bacterial community was assessed with high-throughput sequencing
The identified bacterial features assigned to the genus Methylobacteria occurred in rather low abundances, when compared to other bacterial constituents, we hypothesized that a synergistic relationship might occur between microalgae and distinct members of this genus
Summary
The potential of microalgae for industrial purposes increasingly gained importance at a global scale. Algae Growth-Promoting Methylobacteria cultivated either in open pond systems for bulk material production or in closed photobioreactors for the production of high-value compounds Both cultivation methods often fail to reach economic competitiveness in terms of biomass yields, contamination prevention and the involved costs (Benemann and Oswald, 1996; Wang et al, 2013). One means of increasing microalgae populations and enhancing yields might be the co-inoculation with beneficial microorganisms as already successfully applied in agriculture for increasing yields of vascular land plants (Berg, 2009; Lugtenberg and Kamilova, 2009; Berg et al, 2013) This strategy is primarily applicable for large-scale production where cultivation conditions are not optimal and contaminations with other microorganism are unavoidable. While binary algaebacteria interactions were explored in the past, little is known about the algae-associated microbiota as well as potentially beneficial algae-microbe interactions with distinct members of the plant microbiota
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