Heavy Metals Induced Modulations in Growth, Physiology, Cellular Viability, and Biofilm Formation of an Identified Bacterial Isolate

Abstract

The release of untreated tannery effluents comprising biotoxic heavy metal (HM) compounds into the ecosystem is one of our society’s most serious environmental and health issues. After discharge, HM-containing industrial effluents reach agricultural soils and thus negatively affect the soil microbial diversity. Considering these, we assessed the effect of HMs on identified soil beneficial bacteria. Here, the effects of four heavy metals (HMs), viz., chromium (Cr), cadmium (Cd), nickel (Ni), and lead (Pb), on cellular growth, physiology, cell permeability, and biofilm formation of Enterobacter cloacae MC9 (accession no.: MT672587) were evaluated. HMs in a concentration range of 25–200 μg mL–1 were used throughout the study. Among HMs, Cd in general had the maximum detrimental effect on bacterial physiology. With increasing concentrations of HMs, bacterial activities consistently decreased. For instance, 200 μgCr mL–1 concentration greatly and significantly (p ≤ 0.05) reduced the synthesis of indole-3-acetic acid (IAA) by 70% over control. Furthermore, 200 μg mL–1 Cd maximally and significantly (p ≤ 0.05) reduced the synthesis of 2,3-dihydroxybenzoic acid (2,3-DHBA), salicylic acid (SA), 1-aminocyclopropane 1-carboxylate (ACC) deaminase, and extra polymeric substances (EPSs) of E. cloacae MC9 by 80, 81, 77, and 59%, respectively, over control. While assessing the toxic effect of HMs on the P-solubilizing activity of E. cloacae, the toxicity pattern followed the order Cr (mean value = 94.6 μg mL–1) > Cd (mean value = 127.2 μg mL–1) > Pb (mean value = 132.4 μg mL–1) > Ni (mean value = 140.4 μg mL–1). Furthermore, the colony-forming unit (CFU) count (Log10) of strain MC9 was completely inhibited at 150, 175, and 200 μg mL–1 concentrations of Cr and Cd. The confocal laser scanning microscopic (CLSM) analysis of HM-treated bacterial cells showed an increased number of red-colored dead cells as the concentration of HMs increased from 25 to 200 μg mL–1. Likewise, the biofilm formation ability of strain MC9 was maximally (p ≤ 0.05) inhibited at higher concentrations of Cd. In summary, the present investigation undoubtedly suggests that E. cloacae strain MC9 recovered from the HM-contaminated rhizosphere endowed with multiple activities could play an important role in agricultural practices to augment crop productivity in soils contaminated with HMs. Also, there is an urgent need to control the direct discharge of industrial waste into running water to minimize heavy metal pollution. Furthermore, before the application of HMs in agricultural fields, their appropriate field dosages must be carefully monitored.

Unraveling the potential of pesticide-tolerant Pseudomonas sp. augmenting biological and physiological attributes of Vigna radiata (L.) under pesticide stress

“…Similar production and stress-induced reduction in siderophores synthesized by Enterobacter cloacae have recently been reported. 70 …”

Tolerance of pesticides and antibiotics among beneficial soil microbes recovered from contaminated rhizosphere of edible crops

“…As a result, there has been a surge in interest in finding EPS-producing organisms in recent years. Under controlled/stressed environmental conditions, numerous species of soil isolates recovered from different rhizosphere sources are reported to produce exopolysacchrides ( Syed et al., 2021 ; Khan and Bano, 2019 ; Naseem et al., 2018 ; Shahid and Khan, 2017 ).…”

PGPR Kosakonia Radicincitans KR-17 Increases the Salt Tolerance of Radish by Regulating Ion-Homeostasis, Photosynthetic Molecules, Redox Potential, and Stressor Metabolites

“…Biofilm formation ability of bacterial strain KR-17 in absence/presence of different NaCl concentrations was assessed by growing the cells in 96 well plates and treating with 1% crystal violet (CV), following the standard procedure of O'Toole ( 2011 ) (Syed et al, 2021 ) (see Supplementary Method Section S2.5 ). Furthermore, swimming and swarming motilities of strainKR-17 were assayed (Adler, 1966 ).…”