Author
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Nakamura, Lawrence |
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Submitted to: American Society for Microbiology
Publication Type: Abstract Only Publication Acceptance Date: 6/3/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Mesophilic round-spored organisms embrace two species, namely Bacillus sphaericus and B. fusiformis. Although not displayed by all strains, mosquito pathogenicity is a noteworthy characteristic of B. sphaericus sensu lato. Entomopathogenic variability, DNA hybridization evidence, numerical taxonomic work, and RAPD analyses suggest strongly that B. sphaericus is a heterogeneous taxon. A phylogenetic study based on the DNA sequences of the 16S rRNA gene from 60 strains identified as B. sphaericus was used to examine the extent of taxon genetic heterogeneity. The strains were isolated from diverse geographical locations and substrates. The sequencing study was supplemented with whole-cell fatty acid profile assessments and phenotypic determinations. In a phylogenetic tree generated from 16S sequences, the B. sphaericus-like strains segregated into seven distinct clusters. One cluster represented B. sphaericus and another B. fusiformis strains. The remaining five groups are distinct and represent unnamed taxa that are more closely related to B. sphaericus and B. fusiformis than to the psychrophilic species, B. globisporus and B. psychrophilus. Groups based on fatty acid profiles and phenotypic analyses correspond to the phylogenetic clusters. The data show that B. sphaericus is genetically and phenotypically a highly heterogeneous taxon consisting of at least six genetically distinct taxa. The pathogenic strains are members of one of the unnamed taxa and not of the species B. sphaericus. This heterogeneity partially accounts for the apparent diversity of mosquito pathogenicity of B. sphaericus. |