Exploring the bioremediation potential of <i>Citrobacter</i> spp. and <i>Klebsiella</i> spp. newly isolated from the industrial effluents of Eastern Shewa, Ethiopia

Abstract The research focused on investigating the bioremediation abilities of Citrobacter and Klebsiella species, newly isolated bacteria from industrial effluent in East Shewa, aiming to reduce environmental pollution caused by heavy metals (HM). Heavy metal resistant bacteria (HMRB) are isolated and characterized through Gram staining, biochemical assays, 16S rRNA gene sequencing, and scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM-EDX). We isolated approximately 60 HMRB, exhibiting diverse biochemical characteristics. Among them, 20 isolates (33.33%) were Gram-positive, while 40 isolates (66.67%) were Gram-negative. Molecular identification and 16S rRNA sequencing confirmed that the HMRBIs belong to the genera Citrobacter and Klebsiella and are recognized as versatile organisms capable of HM bioremediation. Furthermore, the minimum inhibitory concentration (MIC) results highlighted that Klebsiella spp. exhibited an MIC of 700 ppm, whereas Citrobacter spp. presented an MIC of 800 ppm. Moreover, the highest biodegradability efficiencies were noted at 89.74%, 85.21%, and 79.27% for HMRBI-14, HMRBI-5, and HMRBI-1, respectively. In addition, the SEM-EDX analysis demonstrated that the organelles of bacterial isolates were deformed due to various HM concentrations. The deformation of the bacterial cell revealed that HM was biosorbed into the cellular structure. Additional analysis showed that the isolate contained HMRG elements, including pcoC, cadD, and chrR. Therefore, the bacteria isolated in this study are strong candidates for HM bioremediation in East Shewa, particularly in areas impacted by industrial waste discharge.