Journal of Bioremediation & Biodegradation

Abstrait

Safe Biodegradation of Textile Azo Dyes by Newly Isolated Lactic Acid Bacteria and Detection of Plasmids Associated With Degradation

Khaled Elbanna, Gamal Hassan, Manal Khider and Raafat Mandour

Since azo dyes are recalcitrant to complete biodegradation due to their complex structure, lactic acid bacteria under an anaerobic/aerobic sequential system was used in an attempt to achieve complete mineralization of textile azo dyes for safe degradation products. A total of 120 lactic acid bacteria (LAB) were screened for decolorization of the textile azo dyes; Reactive Lanasol Black B (RLB), Eriochrome Red B (RN) and 1, 2 metal complexes I. Yellow (SGL). The screening results showed that a total of 80 out of 120 LAB isolates were able to decolorize the dyes, in 4 h ranging from 75 to 100%. Based on API 50 CHL and 16S rDNA sequences, Lactobacillus casei and L.paracasei were the nearest phylogenetic neighbour for both strains Lab11 and Lab13, with an identity of 99 %, while L.rhamnosus was the nearest phylogenetic neighbour for isolate Lab2 with an identity of 99 %. The biodegradation products of RLB (as a model of textile azo dyes) by Lab2 formed during anaerobic and sequential anarobic/aerobic treatments were analyzed by HPLC. Peaks at different retention times were observed in the anaerobic stage, and these peaks completely disappeared at the end of anarobic/aerobic incubation. This result clearly indicates that the dye had been catabolized and utilized by Lab2 isolate. Among the different plasmid curing treatments, SDS at 42°C was found to be an effective treatment for curing of these isolates. Plasmid profiles of wild-type strains and their cured derivatives indicates that the loss of the ability to decolorize azo dyes correlated to loss of a 3 kb plasmid, suggesting that the genes required for textile azo dye degradation were located on this plasmid. Azo dye degradation products were less toxic to growing Sorghum bicolor than the original azo dyes.