Screening and characterization of soil bacteria for lignin and textile dye effluent bioremediation and optimization using response surface methodology

In this study, 177 bacterial isolates were recovered from 55 agricultural soil samples collected from various locations in Egypt. Following purification, the isolates were evaluated in solid and liquid phase assays for their capacity to decolorize several types of dyes such as Azure B (AB), methylene blue (MB), and Congo red (CR). The 16S rRNA sequence analysis was used to identify isolates with the highest decolorizing capacity. The two bacterial isolates coded 304 and 434 which exhibited potential ligninolytic activity were identified as Streptomyces griseorubens and Streptomyces intermedius, respectively. Streptomyces intermedius test isolate was selected for optimization experiments using the one-factor-at-a-time approach (OFAT) followed by a statistical method of optimization using response surface methodology (RSM). The optimization experiments resulted in a 2.6-fold increase in dye decolorization capacity after 4 h of incubation with bacterium growth compared to basal conditions and thus indicated a significant reduction in dye decolorization time, accelerating the dye decolorization process and demonstrating enhanced efficiency in ligninolytic enzyme production. In addition, the whole genome sequencing (WGS) process was performed on S. intermedius isolate to detect the relevant genes related to lignin degradation and dye decolorizing activities. After annotation and analysis of the genomic sequence, various genes encoding enzymes related to lignin degradation and dye decolorization activities were identified confirming the genetic potential of this strain for efficient ligninolytic activity. The obtained WGS data was deposited in the NCBI database under the accession code SRR25321249. Taken together, the WGS data are in alignment with phenotypic dye decolorization activity of the selected isolate. Accordingly, the test isolate S. intermedius 434 was considered a potential candidate for lignin biodegradation and textile dye effluent bioremediation.