Molecular characterization and phylogenetic relationships among microsporidian isolates infecting silkworm, Bombyx mori using small subunit rRNA (SSU-rRNA) gene sequence analysis
Authors: S K Gupta
A K Bajpai
B Surendra Nath
Journal: Acta Parasitologica (2012)
Discipline: MICROBIOLOGY
Keywords: life cycle; spore morphology; pathogenicity; tissue specificity; mode of transmission
Affiliations: Molecular Pathology Division, Seribiotech Research Laboratory, Central Silk Board, CSB Campus, Carmelram Post, Kodathi, Bangalore, Karnataka, India. 

Abstract:  The life cycle, spore morphology, pathogenicity, tissue specificity, mode of transmission and small subunit rRNA (SSU-rRNA) gene sequence analysis of the five new microsporidian isolates viz., NIWB-11bp, NIWB-12n, NIWB-13md, NIWB-14b and NIWB-15mb identified from the silkworm, Bombyx mori have been studied along with type species, NIK-1s_mys. The life cycle of the microsporidians identified exhibited the sequential developmental cycles that are similar to the general developmental cycle of the genus, Nosema. The spores showed considerable variations in their shape, length and width. The pathogenicity observed was dose-dependent and differed from each of the microsporidian isolates; the NIWB-15mb was found to be more virulent than other isolates. All of the microsporidians were found to infect most of the tissues examined and showed gonadal infection and transovarial transmission in the infected silkworms. SSU-rRNA sequence based phylogenetic tree placed NIWB-14b, NIWB-12n and NIWB-11bp in a separate branch along with other Nosema species and Nosema bombycis; while NIWB-15mb and NIWB-13md together formed another cluster along with other Nosema species. NIK-1s_mys revealed a signature sequence similar to standard type species, N. bombycis, indicating that NIK-1s_mys is similar to N. bombycis. Based on phylogenetic relationships, branch length information based on genetic distance and nucleotide differences, we conclude that the microsporidian isolates identified are distinctly different from the other known species and belonging to the genus, Nosema. This SSU-rRNA gene sequence analysis method is found to be more useful approach in detecting different and closely related microsporidians of this economically important domestic insect. 

Retracted: No

PubPeer comments:
 Figs 1 and 2 contain much of interest. ![file] 1(e) contains repeated stripes along the left and repeated sections at the bottom. More to the point, the main section of the panel ( Binucleate sporont)) appears to be a rescaled version of 1(d) ( Binucleate dividing sporonts ). ![file] Fig 1(g). Many repeating sections of the background stand out with boosted contrast. ![file] 2(a). Repeating motifs in the background. ![file] , 
 #1 Figures 1(f), 2(f). Very similar, including the texture in the background, part from some smeary, blurry areas in 2(f). Both depict  Elongate sporonts with nuclei arranged in diplokarya, but genetically different isolates. ![file] Here I have rotated 1(c) through 180 deg and enlarged it to facilitate comparison with 2(c), marking a few repeated areas. ![file] 2(d) and 2(e) ( Binucleate dividing sporonts and  Binucleate sporont ) have identical backgrounds. ![file] More identical backgrounds: 2(b) and 2(g). ![file] ,