Co-cultivation of siderophore-producing bacteria Idiomarina loihiensis RS14 with Chlorella variabilis ATCC 12198, evaluation of micro-algal growth, lipid, and protein content under iron starvation

Co-cultivation systems offer the potential to commercialize microalgae biomass. The key purpose of the study was to understand the relationship between siderophore-producing bacterium Idiomarina loihiensis RS14 and Chlorella variabilis ATCC 12198 strain for Chlorella growth enhancement. After observing growth enhancement in C. variabilis by adding metal chelator deferroxamine mesylate (siderophore standard) and purified siderophore from I. loihiensis (1mgmL(-1)), a co-cultivation system was designed where axenic microalgae and co-cultured (microalgae + bacteria) aliquots were grown in (1:9, 9:1, 1:1) volumetric inoculum ratio (mL) under iron-sufficient and iron-deficient conditions. The co-culture volumetric ratio 1:1 (microalgae/bacteria) showed bleaching of microalgae and 1:9 showed less biomass (310 mgL(-1)) comparatively with 9:1 that increased 35% of biomass, i.e., 650 mgL(-1) (axenic) to 1000 mgL(-1) (co-cultured) in iron-deficient media. The inoculum ratios were optimized in 100 mL shake flask and 9:1 ratio was further scaled up with the similar conditions, and the co-culture showed 20% increase in biomass, i.e., 285.6 mgL(-1) (axenic) to 356mgL(-1) (co-cultured). The co-cultured biomass contains 19.70% lipid content compared with axenic algae, i.e., 18.41% which shows 7% of increase in co-culture. Protein content increased to 30% in co-culture microalgae compared with axenic microalgae. Scanning electron microscope images show crumpled surface of Chlorella cells in co-cultured compared with its axenic cells. This finding is of interest for biofuel production from microalgae, often attained through nutrient-starvation processes leading to oil accumulation.