Project description:For expression analysis of wild-type V. cholerae, hapR, and rpoS deletion mutants in mid-exponential or stationary phase, the strains were grown to either OD600 of 0.3 or for 11 h in LB media at 37 0C, and bacteria from 2-ml culture were quickly pelleted, resuspended in Trizol reagent (GIBCO/BRL, San Diego, California, United States), and frozen on dry ice. RNA was isolated from the Trizol agent, treated with DNaseI (Ambion, Austin, Texas, United States), and cleaned by using the RNeasy kit (Qiagen, Valencia, California, United States). Labeling of cDNA and microarray hybridizations were performed as described [Yiliz et al. 2001, Mol. Micro. 53: 497-515]. Microarrays were scanned with a GenePix 400A instrument (Axon Instruments), using the GENEPIX 5.0 software. At least four microarray experiments were performed for each of two biological replicates for the tested strains. Gene expression of V. cholerae, rpoS, and hapR deletion mutants in stationary phase LB cultures was analyzed and compared to the wild-type parent under identical conditions. Gene expression of the wild-type parent during stationary phase after 11 h growth in LB was analyzed using RNA from an exponentially growing culture as a reference.
Project description:The PFGRC has developed a cost effective alternative to complete genome sequencing in order to study the genetic differences between closely related species and/or strains. The comparative genomics approach combines Gene Discovery (GD) and Comparative Genomic Hybridization (CGH) techniques, resulting in the design and production of species microarrays that represent the diversity of a species beyond just the sequenced reference strain(s) used in the initial microarray design. These species arrays may then be used to interrogate hundreds of closely related strains in order to further unravel their evolutionary relationships. Many infectious agents that cause emerging and re-emerging diseases appear to evolve from non-virulent forms. We still lack a clear understanding about the natural history of various microbial agents that cause human infectious diseases and the events leading to acquisition of their pathogenic potential. There have been seven pandemics of V. cholerae throughout the history of the mankind. To date, the world population is still experiencing the seventh one which started in the early 1960s. From almost 200 recognized V. cholerae serotypes, the majority of these epidemics are associated with primarily O1 serotype. However there is evidence that this species is undergoing some phenotypic changes during the last decades. Such examples include shifts in some metabolic pathways used for biotyping, phage sensitivity profiling and the acquisition of plasmids that carry multiple genes conferring antimicrobial resistance. Furthermore, the recent emergence of a non-O1 serotype (‘Bengal strain’, classified serologically as O139) has prompted the experts to think that perhaps this genotype will be the predominant one in the upcoming (eighth) pandemic. Besides the O1 and O139, the non-O1 and non-O139 V. cholerae stains are occasionally associated with other severe forms of gastrointestinal disease in humans. Interestingly, many of these non-canonical strains lack the genes encoding the typical virulence factors for this species such as the Cholera-toxin (ctx) and toxin co-regulated pilus (tcpA). Therefore it has been hypothesized that this group of non-canonical V. cholerae pathogens consist of several sub-clones that elicit disease via unknown virulence determinants and underlying mechanisms. The flow of genetic information within this group motivated us to identify novel genes for the purpose of creating a "species" DNA microarray to better understand the ancestral relationships among its members. Based on preliminary genotyping (MLST, and CGH using a single-genome-based array), 10 diverse V. cholerae and one V. mimicus were selected for sequencing. Sequence information obtained from this project, and from other publicly available sources, led to the development of a comprehensive species microarray for V. cholerae group members. The availability of the V. cholerae species DNA microarray has allowed us to carry out a collaborative CGH genotyping project to validate this microarray as well as understand the phylogenomic relationships among members of V. cholerae group.