Plant growth-promoting trait of rhizobacteria isolated from soil contaminated with petroleum and heavy metals.

Three hundred and seventy-four rhizobacteria were isolated from the rhizosphere soil (RS) or rhizoplane (RP) of Echinochloa crus-galli, Carex leiorhyncha, Commelina communis, Persicaria lapathifolia, Carex kobomugi, and Equisetum arvense, grown in contaminated soil with petroleum and heavy metals. The isolates were screened for plant growth-promoting potential (PGPP), including indole acetic acid (IAA) productivity, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, and siderophore(s) synthesis ability. IAA production was detected in 86 isolates (23.0%), ACC deaminase activity in 168 isolates (44.9%), and siderophore(s) synthesis in 213 isolates (57.0%). Among the rhizobateria showing PGPP, 162 rhizobacteria had multiple traits showing more than two types of PGPP. The PGPP-having rhizobateria were more abundant in the RP (82%) samples than the RS (75%). There was a negative correlation (-0.656, p < 0.05) between the IAA-producers and the ACC deaminase producers. Clustering analysis by principal component analysis showed that RP was the most important factor influencing ecological distribution and physiological characterization of PGPP-possesing rhizobateria.