Abstract Purpose. The application of plant growth promoting rhizobacteria (PGPR) is considered to have the potential to improve plant development in water-stressed agroecosystems. The current study was designed to screen PGPR for a broad spectrum of functional traits that that can enhance plant growth and soil microbial activity under drought stress conditions. Methods. This study characterised selected indigenous bacterial strains isolated from the rhizosphere of Lactuca sativa , focusing on their ability to enhance nutrient bioavailability, phytostimulation and produce biofilms and exopolysaccharides. The isolates’ functional potential was validated under controlled conditions by evaluating plant biomass and soil enzymatic activity under two treatments: moderate drought stress and well-watered control. Results. Using the biological GEN III test, the strains tested were found to be metabolically diverse. Furthermore, the results indicate that all strains solubilize phosphate, fix nitrogen and synthesize indole-3-acetic acid (IAA) - like compounds. Most of them were active producers of siderophores and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Out of 15 strains, 3 were strong biofilm producers, while all strains were extracellular polymeric substances (EPS) producers. The results of the pot experiment showed that decreasing irrigation significantly reduced the total biomass of lettuce by 36.2%. Lettuce plants inoculated with Bacillus spp. and Variovorax spp. strains exhibited a significant increase in dry weight, by 63.9% and 59.9%, respectively, under drought conditions compared to non-inoculated plants. Moreover, soils inoculated with the Bacillus spp. and Variovorax spp. strains showed higher dehydrogenase and phosphatase activities compared to the non-inoculated control; however, these differences were not statistically significant. Conclusions. Screening of the indigenous isolates revealed unique microbial traits with potential technological applications, including phosphate solubilization, biofilm and EPS production, nitrogen fixation, IAA synthesis, ACC deaminase activity, siderophore production, and high metabolic activity. Meanwhile, newly identified strains were found to enhance the development of butterhead lettuce under both optimal and reduced water availability.
Woźniak et al. (Mon,) studied this question.