Co-culturing with bacteria modulates fatty acid composition in benthic diatom biofilms for lipid-based biotechnologies: A case study of Amphora sp.

Despite being recognized as promising oleaginous microalgal resources, benthic diatom biofilms remain overlooked in microalgal biotechnology. To enhance their industrial potential, bacterial interactions can exploit to boost biomass, increase lipid yields and tailor lipid profiles. Given the complexity of natural biofilms, our study adopted a reductionist approach to investigate the impact of bacteria on the metabolism of a marine benthic diatom, Amphora sp., through binary co-cultures. Bacteria were isolated from non-axenic Amphora sp. biofilm cultures during the exponential phase in a lab-scale porous substrate biofilm photobioreactor. A bacterial biofilm assay was conducted to select biofilm-forming strains, followed by co-culturing them with Amphora sp. in bottle culture flasks, assuming these strains would persist and interact within the Amphora biofilm. All cultures were maintained for 6 days in F/2-enriched artificial seawater at 16 °C, under a 12:12 light:dark cycle (100 μmol photons.m −2 .s −1 ). Biomass and lipid contents were quantified using the gravimetric method, while fatty acid profiles were analysed using GC–MS. Results showed that some bacterial strains reduced Amphora sp. biomass, while Nitratireductor sp. and Sulfitobacter sp. had no noticeable effect. However, significant shifts in fatty acid profile of Amphora sp. were observed in most co-cultures while none of the individual bacterial strains substantially affected lipid production compared to its axenic and non-axenic counterparts. Co-cultures with Nitratireductor sp. and Sulfitobacter sp. yielded 50–55 % saturated, 40–50 % monounsaturated, and 1–6 % polyunsaturated fatty acids, indicating favourable biodiesel properties. Thus, modifying the microbiome of microalgal biofilms could be an innovative strategy for tailoring fatty acid composition for lipid-based applications. • Amphora sp. was studied as a case study of microalgal biofilms. • Amphora sp. in axenic, non-axenic, and ten co-cultures with bacteria were compared. • Amphora sp. in co-cultures showed significant variations in its major fatty acids.