Isolation and Tolerance Screening of Potential Trihalomethane-Resistant Bacteria from Activated Sludge

Abstract

Trihalomethanes (THMs) are carcinogenic disinfection by-products that pose severe environmental and health risks, yet effective microbial candidates’ resistance to THMs remains underexplored. In this study, twelve distinct bacterial strains wereisolated from activated sludge at a pharmaceutical wastewater treatment plant to identify potential THM-resistant bacteria. The isolates were characterized, evaluated for growth rates, and screened for tolerance in mineral salt agar medium exposed to 30 and 50 mg/L of mixed THMs over 72 h. Screening results revealed that four strains, i.e., BFMZ, EFMZ, FFMZ, and IFMZ, exhibited superior resilience, maintaining cell growth scores between +2 and +5 at elevated THM concentrations (50 mg/L), while other strains suffered in terms of growth. Molecular identification via 16S rDNA sequencing and phylogenetic analysis confirmed these tolerant strains as genus Tsukamurella sp. isolate BFMZ (score +5), Klebsiella sp. isolate EFMZ (score +3), Bacillus sp. isolate FFMZ (score +2), and Bacillus sp. isolate IFMZ (score +4). Notably, isolate BFMZ demonstrated the highest physiological resilience under high THM stress despite a moderate growth rate. These findings highlight the potential of THM-resistant bacteria and provide promising candidates for removing recalcitrant disinfection by-products.