# Selection of Soil- and Wastewater-Derived Indigenous Anaerobic Bacterial Isolates for Enhanced Lignocellulosic Substrate Degradation and Methane Production

## TL;DR

This study identifies native anaerobic bacteria that can break down lignin, improving methane production from plant waste.

## Contribution

Isolation and characterization of native anaerobic bacteria with ligninolytic activity for biogas enhancement.

## Key findings

- Twelve bacterial strains were isolated, capable of degrading lignin-derived compounds under anaerobic conditions.
- Bioaugmentation with the best-performing culture increased methane production by 174% compared to control.
- Lignin peroxidase and laccase enzyme activities were detected under low-oxygen conditions.

## Abstract

Lignocellulosic biomass is an abundant renewable resource, yet its effective utilization remains limited due to its structural recalcitrance, primarily attributed to lignin. While aerobic lignin-degrading microorganisms, particularly fungi, have been extensively studied, much less is known about bacteria capable of lignin depolymerization under low-oxygen conditions. This study focused on the isolation and evaluation of native anaerobic bacterial cultures capable of degrading lignin-derived compounds to enhance biogas production. Soil samples from decaying vegetation and olive mill wastewater were used as microbial sources. Enriched cultures were developed anaerobically using kraft lignin and p-coumaric acid as sole carbon sources. Twelve pure bacterial strains were isolated and screened for their ligninolytic activity. All strains were able to degrade p-coumaric, with the highest biomass concentration reaching 387 mg L−1 and maximum substrate consumption rate at 438 mg L−1 d−1. When kraft lignin was used as sole carbon source, 9 out of 12 strains showed growth, with a maximum of 55 mg L−1 over 11 days. Enzyme activity assays confirmed the production of lignin peroxidase and laccase, with highest values at 2.10 and 0.15 U mL−1, respectively, even under conditions of limited oxygen. The enriched cultures were applied in biomethane potential (BMP) batch tests, resulting in increased methane production. The best performing culture resulted in a bioaugmentation percentage of 174% compared with control. These findings suggest that native ligninolytic bacteria can serve as promising bioaugmentation agents in anaerobic digestion of lignocellulosic waste.