Influence of oxygen supply on bacterial degradation of various azo dyes by Rhodoccocus opacus 1CP

Azo dyes are a primary group of synthetic dyes widely used for textiles, food technology, and paper printing. These compounds contain one or more azo bonds linking aromatic rings. Some dyes and their aromatic biotransformation products are toxic or carcinogenic, which makes them significant environmental pollutants. Azo dyes can be degraded by microorganisms under anaerobic, facultative aerobic, or aerobic conditions, depending on the type of organism used. Anaerobic degradation involves nonspecific enzymatic processes, whereby resulting amine compounds cannot be further broken down under these conditions and may be toxic. Under aerobic conditions, these amine compounds can be further degraded. It has also been shown that oxygen can inhibit dye decolorization, as evidenced by comparing static and shaking culture conditions. Additionally, the primary organic carbon source present can influence the degradation process under both anaerobic and aerobic conditions.

However, the effects of varying oxygen supply levels remain not fully understood, particularly for the organism Rhodococcus opacus 1CP. The study will focus on investigating the influence of oxygen supply on biodegradation efficiency. Oxygen transfer rate (OTR) measurements in 96-well plates allow for varying oxygen availability for bacterial cultures depending on the filling volume of each well. This high-throughput screening method enables simultaneous investigation of numerous different settings, combining azo dye decolorization measurements with mass spectrometric analysis of degradation products to examine the impact of dissolved oxygen on the complete biomineralization of various azo dyes.

Experiments confirmed the theory that rapid decolorization of the azo dyes methyl red and brilliant black occurs at lower OTRs due to reduced oxygen availability by the organism R. opacus 1CP. Additionally, a significant difference in the OTR profile during the cultivation of the organism was observed.

The data provided deeper insight into these processes, enabling targeted adaptations for cultivation settings that could lead to more efficient azo dye decolorization and by-product degradation through optimized oxygen supply.