Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2003
Publication Date: 10/1/2003
Citation: Zhang, Q., Weyant, R., Steigerwalt, A.G., White, L.A., Melcher, U., Bruton, B.D., Pair, S.D., Mitchell, F.L., Fletcher, J. 2003. Genotyping of Serratia marcescens strains associated with cucurbit yellow vine disease by repetitive elements-based polymerase chain reaction and DNA-DNA hybridization. Phytopathology. 93:1240-1246.
Interpretive Summary: Cucurbit yellow vine disease (CYVD) is an insect transmitted and serious disease of cucurbit crops in several areas of the U. S. It is caused by a bacterium that colonizes the plant vascular system and ultimately kills the plant. This bacterium has been identified as closely related to Serratia marcescens, a bacterium species that consists of many strains some of which are harmful to human health. Other strains are harmful to insects although some have proven useful as control agents for other organisms and are completely harmless. Thus, It is important to determine if the strain causing CYVD is closely related to other known strains or if it is new and unique. We used molecular techniques to examine and type the DNA composition of the known strains and compared them to the CYVD strain. Results showed the CYVD strain was indeed significantly different from those originating from biological systems other than cucurbit crops. This information combined with other biological studies strongly suggests that the CYVD strain differs genetically from all other strains and especially those affecting human health.
Technical Abstract: The bacterium that causes cucurbit yellow vine disease (CYVD) has been placed in the species Serratia marcescens based on 16S rDNA and groE sequence analysis. However, phenotypic comparison of the organism with S. marcescens strains isolated from a variety of ecological niches showed significant heterogeneity. In this study, we compared the genomic DNA of S. marcescens strains from different niches as well as type strains of other Serratia species through rep-PCR and DNA-DNA hybridization. With the former, CYVD strains showed identical banding patterns despite the fact that they were from different cucurbit hosts, geographic locations, and years of isolation. In the phylogenetic trees generated from rep-PCR banding patterns, CYVD strains were clearly differentiated from other strains but formed a loosely related group with S. marcescens strains from other niches. The homogeneity of CYVD strains was further supported by the DNA relatedness study in that labeled DNA from the cantaloupe isolate, C01-A, showed an average relative binding ratio (RBR) of 99% and 0.33 percent divergence to other CYVD strains. Used as a representative strain of CYVD, the labeled C01-A had a RBR of 76% and a 4.5 percent divergence to the S. marcescens type strain. These data confirm the previous placement of CYVD strains in species Serratia marcescens. Our investigations, including rep-PCR, DNA-DNA hybridization and previous phenotyping experiments, have demonstrated that CYVD associated strains of S. marcescens cluster together in a group significantly different from other strains of the species.