Genetic characterization of Mexican Frankia strains nodulating Casuarina equisetifolia

There is a need to increase the utilization of the Casuarina equisetifolia J.R. Forst. Br G. Forst. - Frankia symbiosis and be sure of its effectivene ss in Mexico. This may be facilitated by selecting appropriate bacterial st rains for which ecological characteristics are known. We tested various typ ing methods to develop genetic markers for ecological studies. DNA, extract ed from clonal cultures of native strains or from reference cultures of Cas uarina-infective Frankia strains, was used as the template in polymerase ch ain reactions (PCR) with primers targeting different DNA regions. nifH and 16S rDNA probes from the reference strain Frankin Br were utilized to authe nticate the isolates. Polymorphisms of the restricted fragments of the inte rgenetic spacer between the 16S-23S rDNAs were analyzed. Repetitive extrage nic palindromic sequences (rep-PCR) (BOXAIR primer) were used to generate g enomic fingerprints. All studied strains showed two copies of the ribosomal operon and a single copy of the nifH gene. PCR restriction fragment length polymorphism patterns of the 16S-23S intergenetic spacer (IGS) were simila r for all Frankia isolates; however, the rep-PCR technique was sensitive en ough to distinguish between some of these Frankia strains. The Mexican cult ured strains of Frankia nodulating C. equisetifolia appeared to be closely related to the isolated and nodular Frankia from trees growing outside Aust ralia.