Co-culturing bacteria with monospecific microalgal biofilms for improved biomass and lipid production

Integrating microbiome engineering into microalgal biofilms could offer an environmentally sustainable and economically viable strategy to enhance biomass and lipid yields while leveraging the inherent advantages of biofilm-based systems. Building on this hypothesis, our objective was to improve biomass and lipid production in the naturally biofilm-forming marine benthic diatom, Amphora sp. (NCC169) by co-culturing it with two of its native biofilm associated bacteria, Nitratireductor sp. and Sulfitobacter sp., in a vertical porous substrate biofilm photobioreactor (PSBR) operated in batch mode. Axenic, non-axenic, and co-cultures were maintained in triplicate for 15 days in F/2 enriched artificial seawater at 18 ± 1 °C under continuous light (100 μmol photons.m⁻².s⁻¹). Biomass and lipid content were quantified gravimetrically, followed by fatty acid profiling via gas chromatography-mass spectrometry (GC-MS) at three harvesting days (3, 6, and 15). Results showed that the Amphora-Nitratireductor co-culture achieved the highest surface biomass (2.54 ± 0.39 g.m⁻²) and productivity (0.99 ± 0.26 g.m⁻².day⁻¹) on day 3, further peaking on day 6 (7.27 ± 1.31 g.m⁻²; 1.24 ± 0.16 g.m⁻².day⁻¹) and were significantly different from the non-axenic control. The Amphora-Sulfitobacter co-culture recorded a significantly higher lipid yield on day 3 (1.51 ± 0.31 g.m⁻²), surpassing axenic cultures by 3-fold, non-axenic by 6-fold, and Amphora-Nitratireductor by 5-fold, with a lipid content of 67.03 ± 17.80% of Amphora dry biomass weight. The fatty acid profile of Amphora sp. remained largely consistent across culture conditions and harvest days, dominated by palmitic acid (16:0) and palmitoleic acid (16:1), with low polyunsaturated fatty acid levels, highlighting its potential for pharmaceutical, nutraceutical, cosmetic, and bioenergy applications.