The source of inoculum drives bacterial community structure in Synechocystis sp. PCC6803-based photobioreactors

Cyanobacteria, which grow using solar energy and carbon dioxide, provide an attractive avenue for sustainable production of biomass and biofuel feedstock. Heterotrophic bacteria can colonize photobioreactor (PBR) cultures of cyanobacteria and may affect the productivity of the system. However, little is known about the types of heterotrophic bacteria associated with PBR cultures of cyanobacteria. The objective of this work was to evaluate the heterotrophic communities in PBR cultures of the cyanobacterium Synechocystis sp. PCC6803 using terminal-restriction fragment length polymorphism (T-RFLP) and high-throughput sequencing. To improve the resolution of the heterotrophic bacterial genomic signatures in the PBR communities, we utilized a targeted T-RFLP strategy to remove the T-RFLP signal of Synechocystis sp. PCC6803 from the analysis. For all experiments, the results of high-throughput sequencing were consistent with T-RFLP results. In particular, the inocula contained heterotrophic bacteria despite appearing to be pure cultures by light microscopy or non-targeted T-RFLP. Furthermore, the heterotrophic communities in the PBRs were strongly influenced by the microbial community in the inoculum used to start the PBR.