Mechanistic insights into enhanced congo red biodegradation by a 3D scaffold-assisted biofilm formation by Bacillus tequilensis BS007.

Biofilm-based degradation of toxic Congo red dye has gained importance recently. This study investigated the performance of Nonwoven nylon pads (NWN pads) as a three-dimensional (3D) scaffold for Bacillus tequilensis BS007 biofilm development. The matrix for effective biofilm formation is crucial for successful biodegradation. Biofilm growth was characterized by scanning electron microscopy (SEM) and quantified using the crystal violet staining assay. The kinetic profile indicates that biofilm began to dissociate after 25 days and was completely disrupted by 40 days. This profile was also confirmed by confocal laser scanning microscopy (CLSM). Biofilm grown on NWN pads was used to decolourize Congo red dye, and parameters were optimized to achieve maximum degradation. At 27 ℃ and pH 7, more than 97% of 100 PPM Congo red was degraded after 16 h. The biofilm's dye-degradation efficiency significantly decreased after heat and chemical inactivation, indicating the requirement of active bacteria inside the biofilm. Degradation of Congo red into smaller derivatives was confirmed by UV-Visible spectrophotometry, and a Fourier-transform infrared spectroscopy (FTIR) study shows the absence of 1590 cm- 1. Gas chromatography-mass spectrometry (GC-MS) profiles of various intermediates were used to elucidate a possible dye-degradation pathway, representing initial cleavage of azo bonds by azoreductase, followed by the formation of aromatic amines, and ultimately leading to mineralization into simpler inorganic compounds. Partial detoxification confirmed by phytotoxicity test, which provides insight into the environmental safety. The present study indicates that the NWN pad is an efficient, low-cost 3D scaffold for promoting effective biofilm formation and subsequent Congo red degradation.