Isolation and partial characterization of culturable endophytic Arthrobacter spp. from leaves of maize (Zea mays L.)

The presence and diversity of the endophytic Arthrobacter species are relatively uninvestigated. We determined the genotypic and physiological diversity of the endophytic Arthrobacter spp. isolated from the interior leaf tissues of four out of six maize cultivars tested, all of which were collected under field conditions. Strains A7 and A9 isolated from Król cultivar and strain A23 isolated from KB1902 cultivar were identified as A. nicotinovorans. Strains A18, A22 and A34 identified as A. nitroguajacolicus were isolated from KB1903, KB1902 and Cyrkon cultivars respectively. Isolated strains tolerate the presence of o-coumaric, p-coumaric, chlorogenic, and ferulic acids in a concentration of at least two times higher than naturally occurring in maize tissue. The presence of the nitrogenase reductase gene nifH, a marker of biological nitrogen fixation, was determined in only two strains of A. nitroguajacolicus A18 and A34. None of the tested strains released compounds inhibiting in vitro the growth of the fungi Fusarium moniliforme and F. graminearum, pathogenic to maize. Seed inoculations with the A. nicotinovorans strain A7 suppressed the development of seedlings of four maize cultivars, which were not colonized by this species of bacteria, but stimulated the development of seedlings of the host-cultivar Król. Also, the A. nitroguajacolicus strain A18, which was applied as seed treatment, suppressed the development of seedlings of three maize cultivars, which were not colonized by this species of bacteria. The occurrence of endophytic A. nicotinovorans and A. nitroguajacolicus inhabiting interior tissues of maize leaves of specific maize cultivars is a first report in literature.