Association between algal productivity and phycosphere composition in an outdoorChlorella sorokinianareactor based on multiple longitudinal analyses

Abstract

Microalgae as a biofuel source are of great interest. Bacterial phycosphere inhabitants of algal cultures are hypothesized to contribute to productivity. In this study, the bacterial composition of theChlorella sorokinianaphycosphere was determined over several production cycles in different growing seasons by 16S rRNA gene sequencing and identification. The diversity of the phycosphere increased with time during each individual reactor run, based on Faith's phylogenetic diversity metricversusdays post-inoculation (R = 0.66,P < 0.001). During summer months,Vampirovibrio chlorellavorus, an obligate predatory bacterium, was prevalent. Bacterial sequences assigned to the Rhizobiales, Betaproteobacteriales and Chitinophagales were positively associated with algal biomass productivity. Applications of the general biocide, benzalkonium chloride, to a subset of experiments intended to abateV. chlorellavorusappeared to temporarily suppress phycosphere bacterial growth, however, there was no relationship between those bacterial taxa suppressed by benzalkonium chloride and their association with algal productivity, based on multinomial model correlations. Algal health was approximated using a model-based metric, or the 'Health Index' that indicated a robust, positive relationship betweenC. sorokinianafitness and presence of members belonging to the Burholderiaceae and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium clade. Bacterial community composition was linked to the efficiency of microalgal biomass production and algal health.