Stress Response of Sulfur‐Oxidizing Bacteria to Pesticide Exposure: Growth Profiling and Functional Analysis

ABSTRACT The excessive use of agrochemicals, especially pesticides, has resulted in their accumulation in crops and the environment, raising concerns for both soil health and microbial inoculant performance. This study evaluated the tolerance and functional efficacy of functionally characterized heterotrophic sulfur‐oxidizing plant growth‐promoting bacteria (SOB) in the presence of five commercial pesticides—herbicides (pendimethalin and clodinafop), fungicides (bavistin and ridomil), and an insecticide (chlorpyrifos)—at recommended and sublethal concentrations (0.5 minimum inhibitory concentrations [MICs]). Three strains, Enterobacter ludwigii Remi_9, Enterobacter hormaechei AUH‐ENM30, and Bacillus sp. 5BM21Y12, were obtained from the Department of Microbiology, Punjab Agricultural University, Ludhiana, India. All strains exhibited good growth at recommended pesticide doses except with ridomil. Growth profiling revealed that Bacillus sp. achieved the highest OD 540 nm at clodinafop (2.09), isoproturon (2.44), bavistin (1.46), and chlorpyrifos (0.88), whereas E. hormaechei showed optimum growth (OD 540 nm 2.24) with pendimethalin. E. ludwigii recorded peak growth (OD 540 nm 1.68) at 0.5 MIC of ridomil. Functional characterization indicated that Bacillus sp. showed highest phosphate solubilization (1.76 µg/mL), IAA production (38.43 µg/mL), siderophore production (12.70 µg/mL), ammonia excretion (3.03 µg/mL), and sulfate production (0.12 mM). E. ludwigii excelled in qualitative phosphate and zinc solubilization, whereas E. hormaechei produced the highest siderophores. This study represents the first detailed reports from India on pesticide tolerance of functionally characterized heterotrophic SOB strains with multiple plant growth‐promoting traits, highlighting their potential as sustainable bioinoculants for improving crop productivity under pesticide‐impacted environments.