A collaboration with Cheryl Whistler (ude.hnu|reltsihw.lyrehc#ude.hnu|reltsihw.lyrehc) and Steve Jones (ude.hnu.xinusic|jhs#ude.hnu.xinusic|jhs)
PROJECT OBJECTIVES AND SCIENTIFIC HYPOTHESES
Our experimental approach will determine the interplay of salt and microbial interactions on the abundance of and genetic relationships among pathogenic Vibrios in oysters. We will examine the intraspecies population structure of oyster-associated Vibrios to determine the extent that pathogenic and non-pathogenic strains exchange genes. We will also survey the resident microbial community within oysters to identify those members that may antagonize or favor pathogenic strains. Identifying these microbes can add to our detection and management tools by serving as pathogen indicators. We will compare two field sites within the Great Bay Estuary: one with lower salinity and high nutrient load, conditions that favor Vibrio populations, and one with higher salinity and similar nutrient load compared to the first site, to examine the interplay of salinity and microbial interaction on pathogenic Vibrio populations. These experiments address two central hypotheses:
Hypothesis 1: Changing physical conditions promote changes in Vibrio abundance and population structure that favor pathogenic strains.
Hypothesis 2: Interspecies interactions within oyster polymicrobial communities influence Vibrio abundance.
These hypotheses encompass a series of more specific questions, as follows. 1) How do physical variables, such as salinity, temperature, and nutrient loading, alter the composition of microbial communities in shellfish, and the relative abundance of Vibrios 2) Is Vibrio population expansion the result of clonal expansion of all existing strains or does it involve selective amplification of certain, competitively superior genotypes, such as pathogenic strains? 3) Are successful Vibrio strains prone to share their mechanisms of success with other lineages within the community by genetic recombination? If so, how frequently do they undergo recombination, and can environmental stress increase recombination rates? Answering these questions is critical for understanding how environmental change alters the likelihood of ecological disruption or human disease (these are often driven by the same calamity, i.e. Hurricane Katrina in New Orleans). While bacteria are ubiquitous and at times overwhelmingly abundant and diverse, this focused survey on a limited group of potential pathogens using two very powerful genetic lenses promises to clarify the key variables. We propose two research objectives to determine the key environmental and biological factors that drive the population dynamics of pathogenic vibrios. Our specific objectives are:
1. Map the population genetic structure and virulence potential of V. vulnificus and V. parahaemolyticus and determine the extent of recombination between strains using multi-locus sequence typing (MLST). Of critical importance to understanding how virulent strains emerge is to quantify how frequently different lineages exchange genes, and in particular, whether the virulence genes themselves recombine. Broad maps of the population genetic structure of each of these species is lacking, so we will sequence 7-10 genes from approximately 350 strains collected under varying conditions and infer rates and effects of recombination.
2. Determine the correlated effects of the resident microbial community on the abundance and distribution of Vibrio populations in oysters.. Our preliminary data suggests that an interaction between water conditions and the resident microbial community may govern the presence and persistence of V. vulnificus and V. parahaemolyticus. We will therefore characterize the oyster microbiological community under two different abiotic conditions by sequencing the variable regions of the 16SrDNA gene from the metagenome.
