Diversity and abundance of culturable nitrogen-fixing bacteria in the phyllosphere of maize

The present study aimed at gaining an insight into the abundance and genetic diversity of culturable N-fixing epiphyte bacteria on the phyllosphere of maize in arid and semi-arid regions of Iran.

Leaf samples of the maize variety, 'single cross 704' (Zea mays L.) were collected from different locations in Iran. The community of culturable N-fixing epiphyte bacteria present was examined by 16S rRNA sequencing, BOXAIR-polymerase chain reaction (PCR) and restricted fragment length polymorphisms analysis of 16S rRNA gene (16S-RFLP). Approximately, 31·82% of the 242 isolates were identified as N-fixers by cultivation of bacteria in Rennie medium and detection of their nifH gene. The N-fixers were affiliated with four bacterial phyla: Firmicutes, Proteobacteria, Actinobacteria and Bacteroidetes. 16S rRNA sequencing detected 16 genera and 24 different species in the identified phyla. The most dominant genus was Bacillus and the species identified were B. pumilus, B. amyloliquefaciens, B. subtilis, B. paralicheniformis, B. licheniformis, B. niabensis and B. megaterium. In total, 22 RFLP groups were present among the isolates originally identified as N-fixing bacteria. BOXAIR-PCR showed that there was a low similarity level among the N-fixing bacteria isolates, and genetic differentiation of individual strains was relatively great.

Our findings suggest that nitrogen-fixing epiphyte bacteria on the phyllosphere of maize may provide significant nitrogen input into arid and semi-arid ecosystem.

This research implies that phyllosphere epiphyte diazotrophs have much to offer in sustainable agriculture and can be an alternative to chemical N-fertilizers for providing nitrogen to crops arid and semi-arid regions.