Molecular characterization and phylogenetic relationships among microsporidian isolates infecting silkworm, Bombyx mori using small subunit rRNA (SSU-rRNA) gene sequence analysis

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 NIWB14b, NIWB-12n and NIWB-11bp in a separate branch along with other Nosema species and Nosema bombycis; while NIWB15mb 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.

Marteilia refringens and Marteilia pararefringens sp. nov. are distinct parasites of bivalves and have different European distributions

“…This approach has been used many times in protistology at species level and below (e.g. Wright et al 1997 ; Amato et al 2007 ; Bass et al 2009 ; Rynearson et al 2009 ; Nath et al 2012 ) and at higher taxonomic levels (Cavalier-Smith and Chao, 2003 ; Karpov et al 2006 ; Burki et al 2010 ). Sequence signatures are also used in bacteriology and metazoan parasitology (Pettersson et al 1996 ; Egyed et al 2001 ; Tung et al 2007 ).…”

Sequence and phylogenetic analysis of Intergenic spacer (IGS) region of ten microsporian isolates infecting Indian vanya silkworms (Samia cynthia ricini and Antheraea assamensis).

“…Ten microsporidians isolated from S. c. ricini and A. assamensis were relatively characterised by using IGS region sequence and phylogenetic analysis. NIK-1s_mys a Nosema Bombycis standard strain from India, used in this study was previously characterized using SSU r-RNA gene analysis (Nath et al 2012), that showed 99.90% of sequence homology with N. bombycis (GenBank accession number-D85503) (isolated from host B. mori), maintained at the Sericultural Experimentation Station, Tokyo, Japan.…”

Gaps in the thread: Disease, production, and opportunity in the failing silk industry of South Sulawesi

“…Serious diseases that can destroy silk cocoon harvest include pebrine and grasserie (JICA, 1985;Yup-lian, 1991;Etebari et al, 2007;Hussain and Buhroo, 2011;Nath et al, 2012). The Pebrine disease was responsible for sericulture collapse in several European countries and resulted in drastic drops in global silk production in the 19 th century (Singh et al, 2012), which originated in France and Italy and spread to Spain, Syria and Romania (Bhat et al, 2009).…”