Natural occurrence of Pseudomonas aeruginosa, a dominant cultivable diazotrophic endophytic bacterium colonizing Pennisetum glaucum (L.) R. Br.

Endophytic microbial communities can have strong influence on the growth of their host plants. The present study reports a diazotrophic endophytic bacterial species that colonizes predominantly Pennisetum glaucum (pearl millet) and remains stabilized throughout the latter's various growth stages under field conditions. Qualitative and quantitative changes in the endophytic bacterial population structure were examined during the plant growth period at regular intervals of 7 days up to harvesting. DNA fingerprinting (ERIC-PCR) was used as a biomarker to track the identity of various isolates obtained at different time intervals. Identification of representative bacterial species corresponding to different ERIC types was made on the basis of 16S rRNA gene sequence analysis. Based on the colony forming unit (cfu) count of bacterial isolates observed at various growth stages, Pseudomonas aeruginosa PM389 was found to be the dominant diazotrophic species among the cultivable endophytes colonizing pearl millet. The population of P. aeruginosa was detected in the host 21 days after sowing (DAS), indicating its entry in plant roots from soil and suggesting its non-vertical transfer in pearl millet. Moreover, an upward migration of this dominant diazotrophic bacterial species to shoots was observed with the plant growth. Further evaluation of P. aeruginosa PM389 revealed its various plant growth promoting properties viz. nitrogen fixation, mineral phosphate solubilization, siderophore production and antagonistic properties.

► This work describes bacterial community dynamics at various growth stages of pearl millet plants growing in actual farming condition.
► Pseudomonas aeruginosa PM389 was identified as dominant cultivable diazotroph at various growth stages.
► Higher level of bacterial diversity of cultivable bacteria were observed in early (first 3 weeks) and late growth stages of plant (after 10th week of plant growth).
► Inoculation of P. aeruginosa PM389 significantly enhanced growth of wheat plant, a plant other than its original host.