Study on the ability of activated sludge bacteria to form biofilms in vitro

   The study aims to comparatively characterize in vitro biofilm formation in bacterial cultures isolated from activated sludge, as well as archival cultures capable of xenobiotics biodegradation: Alcaligenes faecalis 2, Acinetobacter guillouiae 11h, Rhodococcus erythropolis ILBIO, and Achromobacter pulmonis PNOS. An analysis of the 16S rRNA nucleotide sequence identified strains isolated from activated sludge: Paenibacillus odorifer, Bacillus subtilis, Micrococcus yunnanensis, and Bacillus proteolyticus.   The formation of biofilms by microorganisms was studied on LB medium and synthetic culture medium (with sodium acetate as a carbon source). With cell growth on LB medium, an increase in biofilm biomass was observed in Paenibacillus odorifer, Bacillus subtilis, Alcaligenes faecalis 2, and Achromobacter pulmonis PNOS. The cultivation stage duration (72 and 144 h), as well as the additional dosing of substrates, had an effect on the biofilm formation process: by 144 h of cultivation, the biomass values amounted to 0.6–1.3 optical units. An average 63–77% increase in biofilm biomass was noted for Bacillus subtilis and Paenibacillus odorifer cells as compared to the 72-hour process. At the final stage of cultivation (144 h), the values of exopolysaccharides in the matrix amounted to over 0.02 optical units for Bacillus subtilis and Paenibacillus odorifer. The metabolic activity of activated sludge bacteria forming the biofilm reached 628–3609 Fl./OD540. Thus, activated sludge microorganisms forming the biofilm were shown to retain viability and metabolic activity during growth under in vitro conditions.