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. 2019 Mar 14;9(1):4547.
doi: 10.1038/s41598-019-40864-4.

Fluorescent Pseudomonas -FAP2 and Bacillus licheniformis interact positively in biofilm mode enhancing plant growth and photosynthetic attributes

Firoz Ahmad Ansari  1 , Iqbal Ahmad  2
Affiliations

Fluorescent Pseudomonas -FAP2 and Bacillus licheniformis interact positively in biofilm mode enhancing plant growth and photosynthetic attributes

Firoz Ahmad Ansari et al. Sci Rep. .

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.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Positive interaction between Pseudomonas fluorescens FAP2 and Bacillus licheniformis B642 on the solid agar media at different time intervals using co-cultured plate method. The centers of the initial cell suspensions were placed 0.5 cm away from each other.
Figure 2
Figure 2
Competitive growth assessment of Pseudomonas fluorescens FAP2 and Bacillus licheniformis B642. (a) Filtered supernatant of FAP2 supplemented at 0% to 50% in NB medium to check the growth of B642 at different time interval (b) Filtered supernatant of B642 supplemented at 0% to 50% in NB medium to check the growth of FAP2 at different time interval.
Figure 3
Figure 3
Scanning electron micrograph of biofilm formation on glass surface by Pseudomonas fluorescens FAP2 (A) and Bacillus licheniformis B642 (B) individually and in consortium (C).
Figure 4
Figure 4
Scanning electron micrograph of Triticum aestivum seedling roots colonized by Pseudomonas fluorescens FAP2 (A) and Bacillus licheniformis B642 (B) individually and in consortium (C).
Figure 5
Figure 5
Rhizoplane colonization by consortium of FAP2 and B642 under microcosm soil system at different days after transplantation.
Figure 6
Figure 6
Rhizosphere colonization by mixed culture of FAP2 and B642 under microcosm soil system at different days after transplantation.
Figure 7
Figure 7
Effect of plant growth promoting rhizobacteria FAP2 and B642 individually and in consortium on the attributes of photosynthesis (A) SPAD chlorophyll value, (B) net photosynthetic rate [PN], (C) stomatal conductance [gs], (D) internal CO2 concentration [Ci], (E) transpiration rate [E] and (F) water use efficiency [WUE].
Figure 8
Figure 8
Effect of FAP2 and B642 alone and in consortium on plant growth attributes, (A) shoot dry weight [SDW] and root dry weight [RDW]; (B) shoot fresh weight [SFW], root fresh weight [RFW] and number of leaf per plant [NLPP].
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