Genetic diversity among Curtobacterium flaccumfaciens pv. flaccumfaciens populations in the American high plains.

Curtobacterium flaccumfaciens pv. flaccumfaciens is a Gram-positive bacterium and has reemerged as an incitant of bacterial wilt in common (dry, edible) beans in western Nebraska, eastern Colorado, and southeastern Wyoming. Curtobacterium flaccumfaciens pv. flaccumfaciens is diverse phenotypically and genotypically and is represented by several different pathogen color variants. The population structure of 67 strains collected between 1957 and 2009, including some isolated from alternate hosts, was determined with 3 molecular typing techniques: amplified fragment length polymorphism (AFLP), repetitive extragenic palindromic polymerase chain reaction (rep-PCR), and pulsed-field gel electrophoresis (PFGE). All 3 typing techniques showed a great degree of population heterogeneity, but they were not congruent in cluster analysis of the C. flaccumfaciens pv. flaccumfaciens populations. Cluster analysis of a composite data set (AFLP, PFGE, and rep-PCR) using averages from all experiments yielded 2 distinct groups: cluster A included strains with colonies of yellow, orange, and pink pigments, and cluster B had strains of only yellow pigment. Strains producing purple extracellular pigment were assigned to both clusters. Thus, C. flaccumfaciens pv. flaccumfaciens is diverse phenotypically and genotypically.

Genetic diversity and population structure of Clavibacter michiganensis subsp. nebraskensis.

Clavibacter michiganensis subsp. nebraskensis (CMN) is a gram-positive bacterium and an incitant of Goss's bacterial wilt and leaf blight or "leaf freckles" in corn. A population structure of a wide temporal and geographic collection of CMN strains (n = 131), originating between 1969 and 2009, was determined using amplified fragment length polymorphism (AFLP) analysis and repetitive DNA sequence-based BOX-PCR. Analysis of the composite data set of AFLP and BOX-PCR fingerprints revealed two groups with a 60% cutoff similarity: a major group A (n = 118 strains) and a minor group B (n = 13 strains). The clustering in both groups was not correlated with strain pathogenicity. Group A contained two clusters, A1 (n = 78) and A2 (n = 40), with a linkage of 75%. Group A strains did not show any correlation with historical, geographical, morphological, or physiological properties of the strains. Group B was very heterogeneous and eight out of nine clusters were represented by a single strain. The mean similarity between clusters in group B varied from 13% to 63%. All strains in group B were isolated after 1999. The percentage of group B strains among all strains isolated after 1999 (n = 69) was 18.8%. Implications of the findings are discussed.

Genetic Characterization and Diversity of Rathayibacter toxicus.

ABSTRACT Rathayibacter toxicus is a nematode-vectored gram-positive bacterium responsible for a gumming disease of grasses and production of a highly potent animal and human toxin that is often fatal to livestock and has a history of occurring in unexpected circumstances. DNA of 22 strains of R. toxicus from Australia were characterized using amplified fragment length polymorphism (AFLP) and pulsed-field gel electrophoresis (PFGE). AFLP analysis grouped the 22 strains into three genetic clusters that correspond to their geographic origin. The mean similarity between the three clusters was 85 to 86%. PFGE analysis generated three different banding patterns that enabled typing the strains into three genotypic groups corresponding to the same AFLP clusters. The similarity coefficient was 63 to 81% for XbaI and 79 to 84% for SpeI. AFLP and PFGE analyses exhibited an analogous level of discriminatory power and produced congruent results. PFGE analysis indicated that the R. toxicus genome was represented by a single linear chromosome, estimated to be 2.214 to 2.301 Mb. No plasmids were detected.