Discrimination between two Perkinsus spp. isolated from the softshell clam, Mya arenaria, by sequence analysis of two internal transcribed spacer regions and the 5.8S ribosomal RNA gene.

The internal transcribed spacer (ITS-1 and ITS-2) regions and the 5.8S ribosomal RNA gene of 2 Perkinsus spp. (G117 and H49) originating from the softshell clam, Mya arenaria, of the Chesapeake Bay were cloned and sequenced to obtain evidence for their genetic divergence. A high level of heterogeneity in both regions, probably resulting from deletions, insertions, and base substitutions, was evident from alignments of the sequences of the 2 isolates with published sequences of other Perkinsus spp. The isolate G117 and other Perkinsus spp. were highly divergent (13-26% and 19-20% sequence divergence in ITS-1 and ITS-2, respectively). These regions in the isolate H49 and Perkinsus marinus were similar (99.07% and 99% for ITS-1 and ITS-2, respectively). Evidence obtained from a phylogenetic analysis using the aligned sequences suggests that G117 and H49 belong to 2 distinct species of Perkinsus. The isolate G117 possibly belongs to an as yet undescribed species of Perkinsus, and H49 belongs to the species P. marinus. The conclusions drawn from the genetic analysis of H49 and G117 are supported by previously reported morphological characteristics (McLaughlin & Faisal, 1998b). Isolates H49 and G117 originated from the same molluscan species demonstrating that at least 2 different species of Perkinsus can co-exist in 1 host.

Characterization of two Perkinsus spp. from the softshell clam, Mya arenaria using the small subunit ribosomal RNA gene.

Sequence analysis and riboprinting of the small subunit ribosomal RNA genes were used to characterize two morphologically different Perkinsus species isolates from the gill (G117) and the hemolymph (H49) of the softshell clam, Mya arenaria. Sequence data of the polymerase chain reaction amplified ribosomal RNA loci of G117 and H49 indicated that these genes are 1803 and 1806 base-pair long, respectively. A sequence similarity of > 98.9% was calculated among ribosomal RNA sequences of the two isolates of this study and the published sequences of Perkinsus marinus from the American eastern oyster, Crassostrea virginica, and Perkinsus sp. from the blood cockle of the Australian mollusc, Anadara trapezia. From a phylogenetic tree obtained from Jukes-Cantor distances of the aligned ribosomal RNA gene sequences of 13 eukaryotic taxa using the Neighbor-Joining method, we showed that G117 and H49 clustered within the genus Perkinsus. Guided by the sequence data of Perkinsus marinus (accession # X75762) and Perkinsus sp. (accession # L07375), restriction endonucleases were selected for restriction fragment analysis of polymerase chain reaction products of the small subunit ribosomal RNA genes (riboprinting). Riboprinting was used to distinguish the four members of the genus Perkinsus from each other.

Essential role of the consensus nucleotide-binding site of PtlH in secretion of pertussis toxin from Bordetella pertussis.

PtlH is a member of a specialized set of transport proteins that is essential for secretion of pertussis toxin (PT) from Bordetella pertussis. Previously, PtlH was shown to contain a consensus nucleotide-binding motif. Here, we demonstrate that introduction of plasmids containing mutant forms of ptlH, altered in the putative nucleotide-binding region, into a wild-type strain of B. pertussis resulted in inhibition of PT secretion. Thus, this region of PtlH appears to be essential for protein function. Moreover, the observed dominant negative phenotype suggests that PtlH either functions as a multimer or interacts with another component necessary for secretion of PT.

Localization of the promoter for the ptl genes of Bordetella pertussis, which encode proteins essential for secretion of pertussis toxin.

The ptl locus of Bordetella pertussis, which encodes proteins necessary for the secretion of pertussis toxin into the extracellular medium, is located directly downstream from the ptx locus, which encodes the structural subunits of the toxin. We have found that the ptx promoter is essential for expression of the ptl genes. A strain of B. pertussis which lacked only the ptx promotor region but which retained all other portions of the ptx-ptl region did not produce PtlF. Moreover, insertion of a functional ptx promoter from B. pertussis at the 5' end of the ptx region of Bordetella bronchiseptica resulted in the production of PtlF in B. bronchiseptica, a species which normally does not produce PtlF. These results suggest that the ptx operon is larger than originally proposed and contains both the ptx and ptl genes.

Homogentisic acid is the primary precursor of melanin synthesis in Vibrio cholerae, a Hyphomonas strain, and Shewanella colwelliana.

The enzyme p-hydroxyphenylpyruvate hydroxylase (HPPH) is involved in pigmentation (pyomelanin) via homogentisic acid (HGA). Pyomelanin formation is correlated with HGA production and expression of HPPH in three disparate marine species: Vibrio cholerae, a Hyphomonas strain, and Shewanella colwelliana. Induction of pigmentation in V. cholerae 569B by nutrient limitation also correlated with production of HGA.

Genotypic Diversity among Strains of Bradyrhizobium japonicum Belonging to Serogroup 110.

Thirty-three strains of Bradyrhizobium japonicum within serogroup 110 were examined for genotypic diversity by using DNA-DNA hybridization analyses. The analysis of the DNA from 15 hydrogen-uptake-negative strains with the bradyrhizobial uptake hydrogenase probe pHU52 showed variation in degree of homology and restriction fragment length polymorphism of EcoRI-restricted DNA. Clustering analysis of the 33 strains on the basis of DNA-DNA hybridization analysis with four restriction enzymes and with the bradyrhizobial nodulation locus, pRJUT10, as probe indicated the existence of four groups of strains, which were less than 70% similar. Restriction digestion of genomic DNA with BamHI and DNA-DNA hybridization with pRJUT10 permitted classification of each of the strains according to a specific fingerprint pattern.

Phenotypic Diversity among Strains of Bradyrhizobium japonicum Belonging to Serogroup 110.

Thirty-four strains of Bradyrhizobium japonicum within serogroup 110 were examined for phenotypic diversity. The strains differed in their abilities to nodulate and fix dinitrogen with Glycine max (L.) Merr. cv. Williams. Thirteen strains expressed uptake hydrogenase activity when induced as free-living cultures in the presence of 2% hydrogen and oxygen. Six bacteriophage susceptibility reactions were observed. Each of the strains produced either a large, mucoid or a small, dry colony morphology, but colony type was not related to effectiveness for nitrogen fixation.