Systematics of Insect Pathogenic Bacilli: Uses in Strain Identification and Isolation of Novel Pathogens

Distribution and characterization of mosquitocidal toxin genes in some strains of Bacillus sphaericus

“…High toxicity to mosquito larvae is generally associated with B. sphaericus strains of serotype 5a5b, which are by far the most common mosquitocidal B. sphaericus strains isolated (15). However, we show here that high toxicity is by no means limited to this serotype and that binary toxin genes can be detected in six of the nine described serotypes of mosquitocidal B. sphaericus, including serotype 1a, which was previously thought to contain only weakly toxic strains.…”

“…Such lateral transfer could also explain the generation of hybrid genes such as the new type 4 btx, which could have arisen through recombination between types 1 or 2 and 3 or, alternatively, by convergent evolutionary change. Strains of serotype 5a5b, on the other hand, illustrate an interesting ecological adaption in that the several hundred known strains of this serotype probably represent a successful clone of identical strains that has become established in the absence of significant genetic interchange (15). Future screening programs could usefully concentrate on excluding serotype 5a5b strains and attempt to isolate rare or novel serotypes.…”

“…Given the variation in the types of toxins synthesized by mosquitocidal B. sphaericus strains, it was important to develop typing systems for strain identification. Flagellar (H) serotyping, similar to that for B. thuringiensis strains, has been used to allocate entomocidal strains to nine different serotypes (10), which, because of early confusion about B. sphaericus classification, are not in strict numerical order (15). In early studies, toxicity and serotype appeared to correlate; high-toxicity strains were classified largely in serotypes 5a5b, 6, and 25, and low-toxicity strains were classified in serotypes 1a, 2a2b, and 9a9c (8,10).…”

Evaluation of an rRNA-targeted oligonucleotide probe for the detection of mosquitocidal strains of Bacillus sphaericus in soils: characterization of novel strains lacking toxin genes

“…Nevertheless, strains lacking toxin genes have been described, such as strains 2173 and 2315 from serotype 26a26b [S], although it had not been confirmed that they belonged to group IIA. This is therefore the first full description of strains which belong to group IIA, as judged by ribotyping and ADH mobility, but lack both toxin genes, and it is notable that at least one of theses strains belongs to serotype 26a26b (strain R-4a), while strain Gt-Id belongs to serotype 2a2b (normally associated with strains bearing the Mtx toxin only) and strains Gt-la and R-la to serotype 6, normally associated with strains possessing both toxin genes [5]. It is thought that the binary toxin contributes to the success of group IIA strains by killing the larva following ingestion of the spore/crystal toxin combination and providing the spore with a nutrient-rich cadaver in which to germinate and grow [21].…”

“…which are toxic towards mosquito larvae are taxonomically distinct from non-toxic types and have been allocated to a 41.9 kDa and 5 1.2 kDa components [4], and its high toxicity masks the activity of Mtx in strains which contain and express both genes. To date, group IIA strains containing only the Mtx protein, only the binary toxin or both toxins have been described (reviewed in [5]).…”