Cadmium - and zinc-resistant Bacillus tropicus, Pseudomonas laurentiana, and Exiguobacterium indicum from the Mula-Mutha River, Pune, India.

Authors

Radhika Shevale, Shrikant Nalkar, Snehal Shirke, Sanjay Kharat

Published in

Environmental monitoring and assessment. Volume 198. Issue 8. Jul 13, 2026. Epub Jul 13, 2026.

Abstract

Pune's urban rivers face growing threats from untreated sewage and industrial waste, leading to toxic heavy metal buildup in sediments and posing ecological and health risks through bioaccumulation and trophic transfer. While contamination by cadmium (Cd) and zinc (Zn) has been documented, the presence of native metal-tolerant bacteria and their resistance genes in the Mula-Mutha River remains largely unstudied. This research measured Cd and Zn levels in sediments from five polluted stretches of the river and tested the heavy metal tolerance of local bacterial isolates. Metal content was determined via atomic absorption spectroscopy (AAS), and bacteria were enriched under increasing Cd and Zn concentrations (300-1000 ppm). Selected isolates underwent microbiological and molecular characterisation. Biosorption efficiency was assessed over 72 h, and Fourier-transform infrared spectroscopy (FTIR) identified functional groups involved in metal binding. The presence of the czc A resistance gene was confirmed using PCR. Results revealed significant contamination, with Cd (4.2-72.8 mg/kg) and Zn (145-428 mg/kg) levels exceeding safety limits, especially at Mundhwa. Out of 16 initial Cd-tolerant isolates, three highly resistant strains were identified as Bacillus tropicus, Pseudomonas laurentiana, and Exiguobacterium indicum. Pseudomonas laurentiana showed the highest biosorption capacity, absorbing 78.5 mg/g of Zn and 62.3 mg/g of Cd. FTIR analysis showed shifts in hydroxyl/amino (3400 cm⁻¹), carboxyl (1650 cm⁻¹), and phosphate (1080 cm⁻¹) groups, indicating their involvement in metal sequestration. PCR confirmed the presence of the czc A gene in all three isolates. These findings underscore the heavy metal pollution in Mula-Mutha river sediments and discover indigenous bacteria carrying the czc A gene, providing essential data for environmental risk assessments and microbial remediation approaches.

PMID:
42440184
Bibliographic data and abstract were imported from PubMed on 13 Jul 2026.

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