Biofilm Producing Rhizobacteria With Multiple Plant Growth-Promoting Traits Promote Growth of Tomato Under Water-Deficit Stress

Abstract

Plant growth-promoting rhizobacteria (PGPR) not only enhance plant growth but also control phytopathogens and mitigate abiotic stresses, including water-deficit stress. In this study, 21 (26.9%) rhizobacterial strains isolated from drought-prone ecosystems of Bangladesh were able to form air–liquid (AL) biofilms in the glass test tubes containing salt-optimized broth plus glycerol (SOBG) medium. Based on 16S rRNA gene sequencing, Pseudomonas chlororaphis (ESR3 and ESR15), P. azotoformans ESR4, P. poae ESR6, P. fluorescens (ESR7 and ESR25), P. gessardii ESR9, P. cedrina (ESR12, ESR16, and ESR23), P. veronii (ESR13 and ESR21), P. parafulva ESB18, Stenotrophomonas maltophilia ESR20, Bacillus cereus (ESD3, ESD21, and ESB22), B. horikoshii ESD16, B. aryabhattai ESB6, B. megaterium ESB9, and Staphylococcus saprophyticus ESD8 were identified. Fourier transform infrared spectroscopy studies showed that the biofilm matrices contain proteins, polysaccharides, nucleic acids, and lipids. Congo red binding results indicated that these bacteria produced curli fimbriae and nanocellulose-rich polysaccharides. Expression of nanocellulose was also confirmed by Calcofluor binding assays and scanning electron microscopy. In vitro studies revealed that all these rhizobacterial strains expressed multiple plant growth-promoting traits including N2 fixation, production of indole-3-acetic acid, solubilization of nutrients (P, K, and Zn), and production of ammonia, siderophores, ACC deaminase, catalases, lipases, cellulases, and proteases. Several bacteria were also tolerant to multifarious stresses such as drought, high temperature, extreme pH, and salinity. Among these rhizobacteria, P. cedrina ESR12, P. chlororaphis ESR15, and B. cereus ESD3 impeded the growth of Xanthomonas campestris pv. campestris ATCC 33913, while P. chlororaphis ESR15 and B. cereus ESD21 prevented the progression of Ralstonia solanacearum ATCC® 11696TM. In a pot experiment, tomato plants inoculated with P. azotoformans ESR4, P. poae ESR6, P. gessardii ESR9, P. cedrina ESR12, P. chlororaphis ESR15, S. maltophilia ESR20, P. veronii ESR21, and B. aryabhattai ESB6 exhibited an increased plant growth compared to the non-inoculated plants under water deficit-stressed conditions. Accordingly, the bacterial-treated plants showed a higher antioxidant defense system and a fewer tissue damages than non-inoculated plants under water-limiting conditions. Therefore, biofilm-producing PGPR can be utilized as plant growth promoters, suppressors of plant pathogens, and alleviators of water-deficit stress.

Screening and identification of novel halotolerant bacterial strains and assessment for insoluble phosphate solubilization and IAA production

“…The IAA production capability of PSB is remarkable in the application of the isolated PSB to phytostabilization (Park et al 2011). The reactions most frequently invoked to describe the direct effects of plant growth-promoting bacteria on plants is the production of phytohormones, including auxins such as indole acetic acid or IAA (Patten and Glick 2002;Haque et al 2020). B. amyloliquefaciens, a gram-positive bacterium is capable to produce and secrete a significant amount of IAA.…”

Multi-Trait Wheat Rhizobacteria from Calcareous Soil with Biocontrol Activity Promote Plant Growth and Mitigate Salinity Stress

“…Further, a study with mutant deficient in biofilm should be developed for comparative analysis to explore the exact contribution of biofilm in root colonization under the natural soil-plant system [ 79 ]. Researchers proved that biofilm-producing PGPR could be utilized as plant growth promoters, suppressors of plant pathogens, and alleviators of water-deficit stress at tomato plant pot experiments [ 80 ]. These selected strains could strengthen their role as excellent root colonizers that can be viable for long on the plant, even at high temperatures.…”

Characterization and Diversity of plant growth promoting Endophytic and Rhizosphere Bacteria isolated from theRhizosphere and tissues of Pepper and their effect on plant growth promotion and disease suppression of Phytophthora capsici

“…Among them, 16 (51.8%) strains showed strong bio lm production. 66 reported on bio lm production of rhizobacterial strains isolated from rhizosphere of tomato plants, and found that from 78 tasted strains 21 (26.9%) were found to form bio lms... All these bio lm-producing rhizobacterial strains are nonpathogenic to human and animals based on the hemolytic test using 5% sheep blood.…”