Enterobacter sp. AI1 produced a thermo-acidic-tolerant laccase with a high potential for textile dyes degradation

Abstract

Biocatalytic decolourisation of synthetic dyes is hindered by the characteristic properties contained in the textile effluents. Cow dung was sampled from the University of Fort Hare farm, Eastern Cape Province, South Africa. The sample was subjected to selective enrichment, and the organism isolated was texted on various phenolic plates and quantitatively examined for laccase activities. The isolate was molecularly identified using 16S rRNA and subjected to extracellular laccase production. Agrowaste and time course were the factored optimised process conditions applied for laccase production. The laccase produced was purified and applied to degrade various synthetic dyes. The primary screening results showed various colour halo zone oxidation on the phenolic plate. The quantitative study gave a laccase activity of 54.71 and 38.21 (U/mL) on ABTS and PFC substrate molecularly identified as Enterobacter sp. AI1. Corn Stover (CS), Banana Peel (BP), and Wheat Bran (WB) optimally gave a laccase yield of 18.47, 18.87, 20.19 (U/mL) with a 12-day laccase yield of 38.25 U/mL. The purified laccase showed a specific activity of 187.88 U/mg of protein and a molecular weight of 75 kDa with a strong affinity for ABTS at 52.27 U/mL laccase activity. Laccase kinetic showed a Km and Vmax value of 0.23 and 51.28 and was optimum at pH4 and at 60 °C. The purified laccase maximally displayed decolourised effect of 78, 85.7, 77, 81, and 73 (%) on Malachite Green (MG), Congo Red (CR), Methyl Orange (MO), Remazol Brilliant Blue R (RBBR), and Reactive Blue 4 (RB4), respectively. The molecular identification Enterobacter sp. AI1 showed it belongs to the class of gammaproteobacterial. Their nucleotide sequence has been deposited in NCBI with the accession number MN686605. Conclusively, cow dung served as a rich source for isolating ligninolytic bacteria with active bioactive compounds applicable to bioprocess control.