Metagenome Survey of a Multispecies and Alga-Associated Biofilm Revealed Key Elements of Bacterial-Algal Interactions in Photobioreactors

Abstract

e Photobioreactors (PBRs) are very attractive for sunlight-driven production of biofuels and capturing of anthropogenic CO 2 . One major problem associated with PBRs however, is that the bacteria usually associated with microalgae in nonaxenic cultures can lead to biofouling and thereby affect algal productivity. Here, we report on a phylogenetic, metagenome, and functional analysis of a mixed-species bacterial biofilm associated with the microalgae Chlorella vulgaris and Scenedesmus obliquus in a PBR. The biofilm diversity and population dynamics were examined through 16S rRNA phylogeny. Overall, the diversity was rather limited, with approximately 30 bacterial species associated with the algae. The majority of the observed microorganisms were affiliated with Alphaproteobacteria, Betaproteobacteria, and Bacteroidetes. A combined approach of sequencing via GS FLX Titanium from Roche and HiSeq 2000 from Illumina resulted in the overall production of 350 Mbp of sequenced DNA, 165 Mbp of which was assembled in larger contigs with a maximum size of 0.2 Mbp. A KEGG pathway analysis suggested high metabolic diversity with respect to the use of polymers and aromatic and nonaromatic compounds. Genes associated with the biosynthesis of essential B vitamins were highly redundant and functional. Moreover, a relatively high number of predicted and functional lipase and esterase genes indicated that the alga-associated bacteria are possibly a major sink for lipids and fatty acids produced by the microalgae. This is the first metagenome study of microalga-and PBR-associated biofilm bacteria, and it gives new clues for improved biofuel production in PBRs.

Exploring the potential of algae/bacteria interactions

“…In addition to these nutrients, interactions via particular vitamins have been elucidated; for instance, eukaryotic algae are auxotrophic for vitamin B 12 (cobalamin) that can only be synthesized by prokaryotes, and studies have revealed mutualistic relationships between vitamin B 12 -dependent algae and heterotrophic bacteria [16 ,17]. On the other hand, a metagenomic survey of alga-associated biofilms has revealed that genes involved in the biosynthesis of B vitamins and those for lipases and esterases are abundant and functional, suggesting their key roles in algae-associated bacteria [18 ]. We suggest that this approach is useful to find interactions via compounds that are difficult to be detected by chemical methods.…”

Effect of lake water on algal biomass and microbial community structure in municipal wastewater-based lab-scale photobioreactors

“…Recent studies have focused on characterising communities in multi-species photobioreactors with molecular methods and have provided valuable insights (Krohn-Molt et al 2013 andCarney et al 2014). In addition, the development of these methods for use in photobioreactors should lead to the development of specific molecular probes for rapid monitoring of the communities present in the reactors (Carney et al 2014).…”

Effects of bacterial communities on biofuel-producing microalgae: stimulation, inhibition and harvesting

“…In the first extensive metagenomic study of the bacteria present in biofilms in a PBR in which the microalgae Chlorella vulgaris and Scenedesmus obliquus were grown, Krohn-Molt et al (2013) found that the bacterial community comprised ca. 30 species.…”