Study On The Pathogenicity Of Serratia Marcescens Nonpigmented Mutants In Silkworm,Bombyx Mori

Serratia marcescens is a Gram-negative bacteria are widely distributed in nature, belonging to Proteobacteria, Enterobacteriaceae, Serratia. Serratia marcescens is part of arthropods and vertebrates opportunistic pathogen that can lead to infection or tissue caused by arthropod invertebrates such as insects, suffering fatal septicemia. In sericulture, Serratia marcescens is one of the main pathogenic bacteria silkworm, infection can occur after acute sepsis and death in a relatively short period of time led to the silkworm, called bleeding septicemia. Serratia marcescens produces a red surface of secondary metabolites that red spots after prodigiosin, silkworm disease death, and then covered the entire body of the silkworm, the industry generally judged as sepsis, bleeding in accordance with. Prodigiosin has anti-bacterial, anti-fungal, anti-protozoal activity of a variety of biological, anti-malarial, anti-tumor and immune suppression, but its physiological activity and significance of Serratia marcescens is currently still not very clear.Studies have shown that the pigment produced by pathogenic microorganisms usually affect its appeal and lethal force, but it remains unclear Serratia marcescens produce prodigiosin will affect its virulence silkworm. In this study, continuous passage through separation,separation of red pigment recession mutant SM-R2 and do not produce pigment mutants SM-RW from the production of silkworm prodigiosin pathogen Serratia marcescens wild-type strain SM-R, SM -WW and verified using 16S rDNA analysis. Further research will be different mutant strains infect healthy silkworm to the wild-type strain as a positive control, negative control E. coli, a statistical analysis of its appeal and lethal force.The main findings are as follows:1. The separation and verificationSM-R wild-type strain after long-term subculture occasionally observed decline in the ability to produce pigment pink colonies and completely white colonies do not produce pigment. After re-isolated colony morphology continued to show a circular, convex, smooth, neat edges, in addition to color outside consistent with the wild-type strain. Identified by Gram-negative bacilli, no spores, microscopic morphology consistent with the wild-type strain. Further analysis of mutant strains of 16S rDNA showed strain SM-R2,SM-RW and SM-WW indeed Serratia marcescens.2. Analysis of the amplified Serratia marcescens synthesis prodigiosin of key genes pigCSerratia marcescens in prodigiosin synthesis pathway, the final step is 2-methyl-3-pyrrole (MAP) and 4-methoxy-2,2’-bipyrrole-5-carbaldehyde(MBC) condensation, thus pigC entire biosynthetic pathway enzyme is the rate-limiting enzyme. Has been reported in laboratory culture conditions pigC prone to mutations, especially deletions will not directly lead to the production of pigment. This study was amplified and analyzed three mutant strains pigC gene, silkworm explore pathogen Serratia marcescens SM-R no pigment mutants mutation type.3. Research virulence of S. marcescens silkwormTo study the impact of prodigiosin Silkworm pathogen Serratia marcescens virulence, the study of different mutant infected through injecting healthy silkworm fifth instar to the wild-type strain as a positive control, negative control E. coli, and a separate survey of prodigiosin silkworm toxicity. The results showed that the wild-type strain and three mutants could cause silkworm suffer from acute septicemia and rapid death, but does not lead to dead mutant silkworm red, even if cultured silkworm black was not observed any red spots. Strain SM-R, SM-R2, SM-RW and SM-WW for silkworm LD50was 50.9 ±5.2,46.9 ±7.7,54.7 ± 5.5 and 54.4 ±3.2, and Statistics analysis showed no significant difference. In addition, the strain SM-R, SM-R2, SM-RW and SM-WW silkworm median lethal timeLT 50was 23.5±2.4,24.6 ±1.1,24.3 ±1.5 and 24.1 ±1.7 The difference was not significant, Feeding prodigiosin (10 mg/head) or injection prodigiosin (16.15 μg/head) does not show any acute toxicity, prodigiosin and SM-WW will not be enhanced by co-injection without pigment mutants death force. Accordingly, this study found no pigment mutants silkworm pathogen Serratia marcescens also can lead to acute sepsis, infectious and lethal force is consistent with the wild-type strain, so prodigiosin of Serratia marcescens pathogenicity no significant effect.