Identification And Characteristics Of Six Pathogens Of Silkworm, Bombyx Mori

Harm of silkworm diseases are major instability factor of sericulture production,directly affects the harvest of sericulture, the production of cocoon and quality of silk.There are many kinds of silkworm disease which can be divided into infectious disease andnon-infectious two broad categories according to the cause of the treatment. Infectiousdiseases were caused by pathogenic microorganisms, such as bacteria, fungi, virus andparasite.Silkworm bacterial disease is a common silkworm disease.It’s commonly occurredless in spring, but more in summer and fall for the high temperature and high humidity.Silkworm bacterial disease is diversity, but all bcause of the rapid parasitic bacteriabreeding result in death and the dead body can quickly soften and decay, so it’s usuallyknown as flacherie, Silkworm bacterial disease can be divided into sotto disease, sepsis andbacterial intestinal disease according to its cause and condition.Silkworm fungal diseases are caused by pathogenic bacteria percutaneous intosilkworm body. Except yeast disease, the dead body have hardening phenomenon after thedeath, thus fungus disease is customarily called sclerosis or muscardine. It’s occurred morein wet seasons and wet areas. There are many kinds of mulberry silkworm fungal disease,among them, white muscardine and yellow muscardine is most serious.Due to the Paecilomyces farinosus and Beauveria bassiana have little differences onmorphology, most scholars believed that Paecilomyces farinosus and Beauveria bassianabelong to the same genera and species, just have different serotype. However, the specificsituation is not clear.4new pathogenic bacteria strains were isolated from naturally occurring disease ofsilkworm (temporarily named SY-1, ZJ-1, ZJ-2and DT-1). The author have studied thestrains’ morphological, physiological and biochemical characteristics and molecularidentification indicators, in order to determine their specific genera and species.Bacteriology experiment results showed that:4pathogenic bacteria strains weregram-negative bacteria, the cells are short rod, straight shape, with round ends, full offlagella, and that were motile. But the colony morphology, physiological and biochemicalindicators have significant differences. By sequencing the16S rRNA gene, phenotypic andgenotypic analyses revealed that: SY-1is identified as Providencia rettgeri, this is the first strain of Providencia rettgeri which has been identified as againsting the silkworm; ZJ-1and ZJ-2are closely related to Serratia marcescens, with over99%sequence similarity.After culturing the strains on nutrient agar for48h, with the culture temperature increased,the red color（prodigiosin）of ZJ-2strain produced is always deeper than ZJ-1.And ZJ-2strains showed a certain degree of red color in37°C,while ZJ-1strain nearly can not see,This result indicated that the temperature both has an impact on the prodigiosin productionof these two strains. Furthermore, some important morphological and biochemical featuresare different between strain ZJ-1and ZJ-2, for example，ZJ-2can use malonate，thephenomenon of citrate utilization is producing acid， VP react is negative and soon.Finally,ZJ-1was identified as the isolate strain of Serratia marcescens and ZJ-2wasidentified as a new subspecies of S. marcescens. The possibility of DT-1strain asSerratia marcescens was except because it can not produce prodigiosin.It was justidentified as a isolated strain of Serratia. However, they have different pathogenicity,ZJ-2> DT-1>ZJ-1. The results of this paper demonstrated that the Serratia marcescens wasnot the only insect pathogens of Serratia，It proved that the ability of produce pigment isdifferent in different in different S. marcescens. Laid the foundation for the developmentand utilization of the high pigment production strain seclected.it’s also indicated that theSerratia infecting silkworm is diverse.Comparison results between STH2, STH3and SHB showed that: Spores are differentcolors; Spore production quantity were extremely significant difference. However, theyhave the same size and the hyphae growth rate is consistent. ITS sequence is nearly100%similarity, therefore, we can conclude that both STH2and STH3are all belong to the samegenera and species on the molecular biology level. In addition, STH1is a Beauveriabassiana strains containing grouplintron.In this paper, we had isolated and identified4new pathogenic bacteria strains and2yellow muscardine strains. For the first time, we found that Providencia rettgeri can causesepticemia of silkworm. The results of this paper demonstrated that the Serratiamarcescens was not the only insect pathogens of Serratia，it’s also indicated that theSerratia infecting silkworm is diverse.Both STH2and STH3are belong to the same generaand species on the molecular biology level. Comprehensive the above results, in order toprovide a scientific basis for the diagnosis and treatment of bacterial disease and fungaldisease silkworm.