Abstract
An in vitro study was conducted to assess the impact of organochlorine pesticides (OCPs) on cellular growth, morphology, cell viability, biofilm-formation activity, and growth-regulating substances of a soil bacterium. Phosphate-solubilizing EAM 35 isolated from rhizosphere soil was molecularly identified as Enterobacter cloacae (accession number MT672578.1). Strain EAM 35 tolerated varying levels of OCPs, viz., benzene hexachloride (BHC), chlorpyrifos (CP), dieldrin (DE), and endosulfan (ES). The toxicity of OCPs to strain EAM 35 was displayed in a concentration-dependent manner. Among the OCPs, ES at a concentration of 200 mu M showed a higher toxicity, where it maximally reduced the bacterial synthesis of indole-3-acetic acid (IAA), salicylic acid (SA), and 2,3-dihydroxy-benzoic acid (DHBA) by 73% (p <= 0.001), 85% (p <= 0.005), and 83% (p <= 0.001), respectively, over the control. While comparing the toxicity of OCPs to P-solubilizing activity of E. cloacae after 10 days of growth, the toxicity pattern followed the order ES (mean value = 82.6 mu g mL(-1)) > CP (mean value = 93.2 mu g mL(-1)) > DE (mean value = 113.6 mu g mL(-1)) > BHC (mean value = 127 mu g mL(-1)). Furthermore, OCP-induced surface morphological distortion in E. cloacae EAM 35 was observed as gaps, pits on both cellular facets, and fragmented and disorganized cell structure under a scanning electron microscope (SEM). The membrane-compromised cells increased as the concentrations of OC pesticides increased from 25 to 200 mu M. Additionally, microbial counts (log(10) CFU/mL) were also affected after pesticide exposure and decreased with increasing concentrations. While assessing the impact of OCPs on inhibition (%) of log(10) in CFU/mL, 150, 175, and 200 mu M concentrations of ES completely reduced the growth of E. cloacae. Similarly, while comparing the toxicity of higher concentrations of OCPs to bacterial growth, sensitivity followed the order ES > DE > CP > BHC. In addition, the biofilm-formation ability of strain EAM 35 was inhibited in a pesticide-dose-dependent manner, and it was statistically (p <= 0.05, p <= 0.005, and p <= 0.001) significant. Conclusively, the present study clearly suggests that before applying pesticides to soil, their recommended dose should carefully be monitored.