Abstract
Compatible interaction between commonly used plant growth promoting rhizobacteria (PGPR) in biofilm mode in vitro and in the rhizosphere is expected to provide better understanding for the development of effective consortium. With the above hypothesis, the present study evaluated two characterized PGPR (Pseudomonas fluorescens FAP2 and Bacillus licheniformis B642) for their biofilm-related functions using standard protocols. The interaction between the FAP2 and B642 in planktonic mode was studied by plate spot/overlay method and competitive growth assessment. Biofilm development on a microtitre plate and a glass surface was studied by standard methods. Biofilm formation was characterized by SEM. Rhizosphere and rhizoplane colonization of wheat seedlings by both isolates individually and by co-inoculation was studied by determining CFU/g of soil/root samples. Biofilm development on the root surface was further analyzed by SEM. Both isolates demonstrated multiple plant growth promoting (PGP) traits (production of IAA, siderophore, and ammonia; phosphate solubilization) and biofilm-related functions such as production of EPS, alginate, cell surface hydrophobicity and swarming motility. Both strains formed strong biofilms on a glass cover slip in vitro. Interaction between the two strains under the planktonic mode revealed no antagonism in terms of growth inhibition and competitive growth kinetics. Similarly, FAP2 and B642 strains formed a mixed biofilm on a glass cover slip as well as on seedling roots. Wheat rhizosphere and rhizoplane were colonized by both isolates as evidenced from their viable counts in single and co-inoculation. The effect of single and co inoculation revealed the significant enhancement of vegetative growth and photosynthetic parameters such as chlorophyll content, transpiration rate (E), internal CO2 concentration (Ci), stomatal conductance (gs), and net photosynthetic rate (PN) and leaf water potential (LWP) as compared to uninoculated control. Indigenous Pseudomonas fluorescens FAP2 strain and Bacillus licheniformis B642 are compatible PGPR in both planktonic and biofilm modes of growth and threfore could be developed effective consortium of PGPR. Further indepth investigation is required to understand molecular mechanism of the interaction in biofilm mode of growth under natural condition.
Highlights
Soil microbial diversity and their functions are of prime importance to soil fertility
It is hypothesized that promising plant growth promoting rhizobacteria (PGPR) exhibiting compatibility in planktonic and biofilm modes can deliver consistence performance in plant growth promotion
Further investigation relates to their interaction and significance in root and rhizosphere colonization, plant growth enhancement including some physiological attributes of photosynthesis
Summary
Soil microbial diversity and their functions are of prime importance to soil fertility. The interaction between microbial inoculant in planktonic and biofilm modes may be positive for effective rhizosphere colonization and performance in the soil-plant system. The potential compatibility between Pseudomonas and Bacillus has been explored in planktonic and biofilm mode of growth. Both positive and negative interactions in mixed-species biofilms have been demonstrated[3]. It is hypothesized that promising PGPR exhibiting compatibility in planktonic and biofilm modes can deliver consistence performance in plant growth promotion. Our main objective in this study is to evaluate two promising PGPRs; Pseudomonas fluorescens FAP2 and Bacillus licheniformis B642 and their interaction in planktonic and biofilm modes. Further investigation relates to their interaction and significance in root and rhizosphere colonization, plant growth enhancement including some physiological attributes of photosynthesis
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