# Molecular characterization of chromium tolerant and gelatin hydrolyzing bacterial isolates from tannery wastes: Perspective on chrome-tanned leather waste biodegradation in Bangladesh

## TL;DR

Researchers identified bacteria from tannery waste in Bangladesh that can tolerate chromium and degrade leather waste, offering a potential solution to environmental pollution.

## Contribution

The study identifies specific chromium-tolerant bacteria with high gelatin hydrolysis and leather waste biodegradation capabilities.

## Key findings

- Three bacterial isolates (Enterococcus faecium, Bacillus cereus, Bacillus wiedmannii) achieved over 98% biodegradation of chrome-tanned leather waste.
- The isolates showed high chromium tolerance, with MTCs up to 1500 ppm for Cr(III) and 600 ppm for Cr(VI).
- Molecular characterization confirmed the isolates' identities and their gelatin hydrolysis potential.

## Abstract

•CTLW is responsible for environmental pollution.•Bacteria isolated from tannery wastes are resistant to Cr.•Cr-tolerance determination helps find bacteria potential for waste management.•Bacteria with gelatin hydrolyzing ability can be applied for CTLW degradation

CTLW is responsible for environmental pollution.

Bacteria isolated from tannery wastes are resistant to Cr.

Cr-tolerance determination helps find bacteria potential for waste management.

Bacteria with gelatin hydrolyzing ability can be applied for CTLW degradation

Improper management of chrome-tanned leather waste (CTLW) might potentially cause adverse environmental consequences. To mitigate that harmful impact, this study aims to find and conduct molecular characterization of bacteria from tannery wastes that can tolerate chromium (Cr) and hydrolyze gelatin. Bacteria from tannery wastes are naturally adapted to Cr; eight Cr(III) tolerant bacteria, namely bacterial isolate (BI) 1 to 8, were isolated from the collected waste samples. The isolated bacteria showed the maximum tolerance concentration (MTC) range of 700 to 1500 ppm for Cr(III) and 200 to 600 ppm for Cr(VI). Physiological and biochemical analysis, including the gelatin hydrolysis activity, identified those isolates up to the genus level. Among the isolates, BI 4, 5, and 7 were able to hydrolyze gelatin. Therefore, 16S rRNA molecular characterization was conducted for those isolates, which confirmed BI 4, 5, and 7 as Bacillus wiedmannii (Accession No: OR564007), Enterococcus faecium (Accession No: OR564008), and Bacillus cereus (Accession No: OR564009), respectively. Bacteria with gelatin hydrolyzing activity can be the potential for degrading hydrothermally treated CTLW. Thereby, those three isolates were applied to explore their biodegradation ability in real world scenario. The biodegradation experiments showed that Enterococcus faecium, Bacillus cereus, and Bacillus wiedmannii were able to biodegrade hydrothermally treated CTLW at 98.67 %, 98.33 % and 98.00 %, respectively. The present study demonstrates Enterococcus faecium, Bacillus cereus, and Bacillus wiedmannii having biodegradation of CTLW applications might mitigate environmental pollution caused by this waste in the perspective of Bangladesh.