Bacteria of the phylum Bacteroidota are important representatives of the gut microbiome, where they break down dietary fibers and contribute to a healthy gut [1]. Because they naturally produce organic acids which may be used as commodity chemicals, our objective was to study Bacteroidota as platform organisms for bioconversions. Furthermore, Bacteroidota have also been described to form biofilms, but studies that do not focus on pathogenic strains are scarce [2]. For us, this would be of interest, since we may utilize them in bioreactors as catalytic biofilms.

Initially, we screened twelve anaerobic Bacteroidota strains for their ability to form biofilm in vitro. For that purpose, strains were incubated in 24-well plates in PYG medium for 24 – 72 h. Biofilm formation was observed after crystal violet staining by measuring absorption at 540 nm (A540) and protein content and conversion of glucose to organic acids were quantified as well. Of all tested strains, Segatella copri (former Prevotella) showed the best biofilm formation.

We studied the time course of its biofilm development: After 4 h the protein content started to increase in the biofilm, reaching a maximum after 12 h. Within this time, glucose was completely consumed, and succinate and acetate were produced in amounts similar to batch culture. Interestingly, the A540 still increased between 12 and 16 h, although biomass formation already stagnated, raising the question if the higher A540 results from changes in biomass composition. Additionally, we performed a live-dead staining and monitored CFUs: Here, the first sample showing a biofilm was at 8 h. Up to 36 h the biofilm mainly consisted of living cells, while at later time points the proportion of dead cells increased, and the CFU decreased.

Our results indicate that the most important phase during biofilm development is within the first 12 to 16 h. Currently, we study the influence of different culture conditions on biofilm formation and organic acid production, and also focus on the matrix composition in more detail.

[1] Wexler 2007, Clin Microbiol Rev

[2] Béchon and Ghigo 2022, FEMS Microbiol Rev