Author
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Nakamura, Lawrence |
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Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/18/2000 Publication Date: N/A Citation: N/A Interpretive Summary: The bacterium named Bacillus sphaericus is potentially an environmentally, medically, and industrially important organism because it kills mosquitos. Unfortunately, because of the lack of good differentiating characteristics for identification, many organisms superficially similar to B. sphaericus have been classified as one of the mosquito killers. By comparing the genetic material and biochemical characteristics, this study showed that as many as seven different groups of organisms have been classified as B. sphaericus. Furthermore, the study showed that the mosquito pathogens should not be classified as B. sphaericus. The information obtained will provide means for correct identification of the pathogenic organisms. Beneficiaries of this study include consumers and commercial concerns interested in the production of an environmentally safe biological insecticide. Technical Abstract: Mesophilic round-spored organisms embrace three species, namely Bacillus sphaericus, B. fusiformis, and B. pasteurii. Although not displayed by all strains, mosquito pathogenicity is a noteworthy characteristic of B. sphaericus sensu lato. A phylogenetic analysis of the 16S rRNA DNA sequences from 58 strains identified as B. sphaericus was used to examine the genetic heterogeneity of the taxon. Results from sequence analysis were compared with whole-cell fatty acid profiles and other phenotypic determinations. The B. sphaericus-like strains segregated into seven distinct clusters in a phylogenetic tree generated from 16S sequences. One cluster represented B. sphaericus and another B. fusiformis. A third cluster containing all of the pathogenic strains was closely related to or was possibly part of the B. fusiformis group. The remaining four groups were distinct and represented unnamed taxa that are more closely related to B. sphaericus and B. fusiformis than to the psychrophilic, round-spored species, B. globisporus and B. psychrophilus. Groups based on phenotypic analyses corresponded to the 16S rDNA phylogenetic clusters. Data showed that B. sphaericus was genetically and phenotypically a highly heterogeneous taxon including at least seven genetically distinct taxa. The pathogenic strains were members of a distinct group and not of the species B. sphaericus sensu stricto. This heterogeneity partially accounts for the apparent variability of mosquito pathogenicity among B. sphaericus strains. |
