The molecular characterization of native plant growth-promoting bacteria of petrochemical-degraded soil for use as a soil conditioner

Abstract

Industrial activities are a significant environmental problem because of their degradation effects, which are associated with the reduction of soil productivity, microbial diversity, and the sustainability of ecosystems. Degraded soils can be restored to promote sustainable agriculture and the recovery of ecosystems, which contribute to Sustainable Development Goals (SDGs) 2 (Zero Hunger) and 15 (Life on Land). Soil conditioners are needed as microbial-based remediation approaches are less effective at reducing contaminants and increasing soil biological functions. The objective of the study was to evaluate the soil physicochemical properties and to isolate the native bacteria with plant growth-promoting (PGP) activity. The physicochemical properties of soil samples collected from four industrially impacted places were analyzed, followed by bacterial isolation, purification, and characterization based on colony morphology and Gram staining from the selected soil sample. The isolates were tested for the production of phosphate-solubilizing, indole-3-acetic acid (IAA), total antioxidant capacity (TAC), and exopolysaccharide (EPS) production. The selected isolates were identified by 16S rRNA gene sequencing and phylogenetic analysis. A total of 20 different bacterial isolates were isolated, and there was a significant difference (p ≤ 0.05) in TAC and IAA production. PEC018 exhibited the highest activity of TAC (2735.88 µg AAE/gm) while PEC019 exhibited the maximum activity of IAA (22063.95 µg/gm). There were 13 and 12 isolates found to be able to solubilize phosphate and produce EPS, respectively. The molecular identification confirmed Priestia megaterium (PEC008), Lysinibacillus varians (PEC019), Lysinibacillus sphaericus (PEC001), and Rhodococcus ruber (PEC018). These are native multifunctional strains with potential for use as microbial soil conditioners.