Plant growth-promoting Rhizopseudomonas : expanded biotechnological purposes and antimicrobial resistance concern

The present study was conducted to characterize a collection of plant growth-promoting (PGP) Rhizopseudomonas isolated from date palm roots for their biosurfactant production ability, heavy metal tolerance, and antimicrobial susceptibility. A collection of 36 bacterial strains was evaluated for several plant growth-promoting abilities including indole acetic acid (IAA) production, mineral phosphate solubilization, siderophores and ammonia release, and protease and cellulase activity. Biosurfactant production was screened throughout hemolytic activity, bleu agar test, and drop collapse method. Strains exhibiting tolerance to heavy metals at high concentration were subjected to PCR for the detection of heavy metal gene tolerance. Moreover, antimicrobial susceptibility patterns were determined using the disk-diffusion method. High rates of plant growth promotion activities were registered among the isolated rhizopseudomonads, mainly, the indole acetic acid production (88.8%), phosphate solubilization (63.8%), siderophore release (83.3%), and ammonia synthesis (52.7%). Furthermore, biosurfactant production was recorded, using three distinct methods, on 77.7% of the tested strains. Particularly, two strains affiliated to Pseudomonas vancouverensis and Pseudomonas brassicacearum harboring copA-arsR and arsB genes, respectively, and producing biosurfactants, were selected. The evaluation of antibiotic resistance dissemination risk analysis in the environment revealed a low rate of resistance among the analyzed strains and the absence of known antibiotic resistance genes. This investigation could provide the basis for the development of microbial inoculums showing multifarious properties for biotechnological application while caring human health.