Bacterial abundance and diversity in Microchloropsis salina (formerly Nannochloropsis salina) cultures in response to the presence of ammonium, nitrate and glycerol

Ammonium and nitrate were compared as nitrogen sources for mixotrophic growth of Microchloropsis salina (formerly Nannochloropsis salina) on glycerol. The effects of nitrogen source and glycerol on the abundance, composition and profile of bacterial communities were examined by 16S rRNA sequencing. The effect of bacteria on culture performance was assessed by comparing ampicillin-containing and ampicillin-free cultures. The productivity of M. salina was higher with ammonium than with nitrate, and lower with bacteria present. Glycerol utilization by M. salina was minimal in the absence of a nitrogen source and the addition of glycerol increased the abundance of bacteria. Bacterial profiles were influenced by nitrogen source, with Pseudomonadaceae proliferating with ammonium, Alteromonadaceae with nitrate and Beijerinckiaceae prevalent with either. The presence of nitrate and glycerol led to aerobic-denitrifying bacteria capable of diverting both resources away from algal metabolism. These findings demonstrate significant advantages of providing ammonium during mixotrophic cultivation of M. salina on glycerol.