Genetic diversity of native Pseudomonas spp. isolated from maize plant

CORDERO, P.; FISCHER, SE.; JOFRÉ, EC.; MORI, GB.

Villa Carlos Paz, Córdoba

Workshop; II Argentine Workshop in Pseudomonas and Burkholderia Research; 2009

The genus Pseudomonas is one of the best-studied bacterial groups in soil, and includes numerous species of environmental interest. Some species exhibit plant growth-promoting and pathogen-suppressing functions and may be exploited for use in biological control. The PGPR traits and persistence of bacteria in the roots may be affected by biotic and abiotic factors. Therefore the assessment of the genetic structures of microbial populations is important for understanding their ecological role in natural environments. In our lab, we isolated bacterial strains on King B and Gould‟s mS1 media from maize plants (at two stages of growth: young and old plants). Several isolates identified as belonging to Pseudomonas genus showed PGPR traits, such as production of indole acetic acid, siderophores and extracellular enzymes or solubilization of phosphates. In this work ERIC and BOX-PCR (rep-PCR) were performed to estimate the genetic differences among 53 strains of Pseudomonas spp. In addition, the bacterial strains isolated were evaluated by an amplified ribosomal DNA restriction analysis (ARDRA) with the enzymes: HaeIII, TaqI, HinfI, RsaI. Gel images were digitized, converted, normalized with DNA size markers, and analyzed with GelComparII software (version 5.1; Applied Maths, Kortrijk, Belgium). For rep-PCR fingerprint and ARDRA analysis, a band-matching algorithm (tolerance of 1% and 3% respectively) was used to calculate pairwise similarity matrices with the Dice coefficient. Cluster analyses of similarity matrices were performed by the unweighted pair group method using arithmetic averages (UPGMA). Cluster analysis from rep-PCR showed 29 unique Pseudomonas genotypes out of 53 isolates. These strains were clustered into five major groups: A, B, C, D and E. Group A included only strains isolated from young plants while group E only strains of the old plant. Most isolates from both growth stages fell within the B and C groups. D group have only one strain (DGE5). The restriction analyses (ARDRA) revealed two main groups A and B. The strains DKR6 and DKR11 shared a high similarity (100%), and DKS4 and Pseudomonas putida KT2440 were closely related with an 80% of similarity.