Structural and functional changes in biofilm during adaptation towards amaranth biodegradation

Abstract

In the field of the microbial ecology of biofilms and activated sludges, it is widely accepted that the microstructure of the communities depends on the environmental factors. Nevertheless, due to their complexity, the exact mechanisms are still unknown. In this study, we applied a stepwise increase of an azo-dye concentration as a selective factor for adaptation towards biodegradation. The degrading biofilm was developed in a lab-scale sand biofilter. It functioned in a semi-continuous regime for 623 h. The concentration of the azo-dye amaranth was increased from 10 to 55 mg L⁻¹. The effectiveness was 90% and the rate of amaranth elimination was 1.136 mg h⁻¹. The fluorescence in-situ hybridisation (FISH) revealed zones with high activity of Pseudomonas sp. Also increasing importance of the unculturable Pseudomonas sp. and the relationships in the biofilm were found. At the final stage of the experiment, a decrease of the azoreductase activity and an increase of the catechol-1,2-dioxygenase activity were established in the depth of the biofilter. The obtained results were linked with different Pseudomonas microstructures (shown by FISH). The obtained data showed that the changes in the biofilm structure occurred accordingly to the biodegradation of the toxic compound and it included the development of cooperative microbial relationships in the key genus Pseudomonas.

Keywords:

• Azo-dye
• biofilm
• digital image analysis
• fluorescence in-situ hybridisation
• Pseudomonas

Conclusions

In this study, microstructural changes were found among the bacteria from genus Pseudomonas in an azo-dye degrading biofilm. Microhabitats with high activity had been formed. They were related to the increasing biodegradation capacity of the sand biofilter driven by the increasing amaranth concentration. The activities of the key enzymes were linked with the structure of the microbial community and the elimination of the xenobiotic.

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This investigation has been supported financially by Operational Program ‘Science and education for smart growth’, co-financed by the European Union through the European structural and investment funds, project BG05M2OP001-1.002-0019: ‘Clean Technologies for Sustainable Environment - Waters, Waste, Energy for a Circular Economy’ and by Sofiyska voda AD, Veolia group, grant number 3190.