Interpreting the SDS-PAGE protein patterns with self-organizing maps: application for the characterization of mosquito-pathogenic Bacillus strains.

AIMS To present the pairwise comparison of potential mosquito-pathogenic Bacillus strains based on their SDS-PAGE protein patterns and to evaluate their characteristic toxicity patterns. METHODS AND RESULTS In this work, 20 Bacillus strains were subjected to qualitative toxicity tests against Aedes aegypti and Culex quinquefasciatus larvae. The selected strains were then characterized by SDS-PAGE protein profiles. The highly heterogeneous multiple protein components of protein patterns were analysed using self-organizing map (SOM), a 'visualization and clustering' tool. Members of mosquitocidal Bacillus species were classified in four distinct clusters, and then toxicity patterns were examined. Cluster (1, 1) comprised of three highly toxic strains of Bacillus sphaericus: SPH88, 1593 and KSD-4; cluster (1, 2) consisted of two B. sphaericus strains: SSII-1 and Bsp-R that showed weak larvicidal activity; cluster (2, 1) constituted two B. sphaericus strains: WHO2297 and ISPC-5 that possessed moderate toxicity; and cluster (2, 2) contained four B. thuringiensis ssp. israelensis strains: ONR-60A, HD500, IPS70 and IPS82 belonging to serotype H14 but exhibited moderate to high mosquito larvicidal toxicity. CONCLUSIONS SOM served as a colour-coded alternate for easy visualization of similarities or dissimilarities between the strains even at the infra subspecies level. Furthermore, characteristic toxicity patterns of Bacillus strains of different clusters were determined. SIGNIFICANCE AND IMPACT OF THE STUDY Analysis of electrophoretic protein patterns using SOM provides a better insight into the inter-relationships of bacterial strains through similarity-based clustering and pairwise comparison of two strains.