Contributions of the microbial community to algal biomass and biofuel productivity in a wastewater treatment lagoon system

The vast majority of research on algal biofuel production has been conducted on single species as monocultures in small, closed systems. Growth of algae in wastewater has potential to help overcome shortages of water, nitrogen, and phosphorus availability; however, cultivation in open wastewater systems presents several unique challenges that include colonization by a variety of bacteria, archaea, viruses, and other eukaryotic species. Here, we monitored the microbial community, water chemistry, and fatty acid methyl ester (FAME) content of 5 connected wastewater treatment lagoons over the course of a year. DNA was sequenced from all three Domains in addition to viral DNA specific to eukaryotic algae. Each lagoon demonstrated a unique community profile even when taxa were classified at the coarsest level. Significant correlations were observed between community members, chemical variables, and FAME concentrations. In contrast to previous findings that correlated elevated FAME with nutrient deprivation, we observed high levels of FAME (up to 48% w/w) in some nutrient replete lagoons. High FAME concentrations (%w/w) were significantly correlated to ammonia, nitrite, total Kjeldahl nitrogen (TKN), pH, phosphate, and total phosphorus (R2 = 0.74). FAME quantified by volume (g L−1) correlated with higher biomass concentrations (R2 = 0.78) whereas high FAME as %w/w coincided with lower algal cell densities. Under these uncontrolled conditions, high biomass concentrations provided for a higher overall biofuel content (g L−1), rather than high lipid content with low biomass concentration. High FAME (>19% w/w) also correlated to the abundance of particular bacteria and the major capsid protein (MCP) specific to dsDNA viruses that can infect eukaryotic algae (Phycodnaviridae). Our findings inform the potential of algal biofuel production using wastewater lagoons and estimates of interactions within the diverse microbial community. The resulting data can provide significant insight into biomass and/or lipid accumulation in a large open system.