Vibrio spp. are naturally occurring bacteria in marine and estuarine environments around the world. The genus includes several human and animal pathogens that can negatively impact human health, seafood and aquaculture. Vibrio spp. populations are capable of rapid adaptation in response to changing environmental conditions, making them dynamic over short-term and seasonal scales. Temperature, vertical mixing, tidal flushing, climate, precipitation and nutrient loading can change the estuarine environment and subsequently alter microbial community structure, including Vibrio spp., affecting estuarine water quality and public health. To describe these dynamics, Vibrio spp. concentrations and a range of microbial, physical and chemical measures were monitored every 2 weeks and after storm events for 19 months in the Neuse River Estuary (NRE). Results showed clear seasonal and geographic trends in Vibrio spp. abundance. Multiple regression analysis revealed a strong relationship to temperature and salinity, with additional minor influences of chlorophyll a and dissolved organic carbon. Similar models based on easily measured environmental parameters should be pursued for individual Vibrio species in the NRE and other estuarine environments. Predictive models provide useful information for managers, researchers and modellers of estuarine ecosystems.
Observations of microbial contamination and particle suspensions represent valuable inputs to water quality models that form the basis of regulatory decisions regarding the use of surface waters. The Neuse River Estuary in eastern North Carolina is experiencing a decline in water quality due to increasing anthropogenic inputs. Potentially serious consequences of these inputs are the introduction and persistence of bacterial pathogenic organisms from human and animal waste. A critical factor in determining human health risk is the partitioning of these organisms between particle-attached and free-living cells in the water column. Particle-associated bacteria are generally less mobile in the environment, settle faster, and may have different rates of mortality than their free phase counterparts. Surface and bottom water samples were collected during both dry weather and storm events throughout the summer of 2004 to gage changes in particle concentration, particulate organic carbon and nitrogen, and the partitioning of two indicators of fecal contamination: Enterococcus sp. ͑ENT͒ and E. coli ͑EC͒. Increases in concentrations of these indicators coincided with increases in particles in suspension following storm events. In surface waters, both ENT and EC exhibited similar patterns, controlled primarily by runoff inputs ͑i.e., storms͒. In bottom waters, resuspension of sediments was additional source of particles and both indicators. Partitioning of these indicators between particle attached and free living exhibited an overall average of 38% of bacteria associated with particles capable of settling out of the water column. This fraction compares well with previous estimates of attachment of indicators in stormwater. The ability to estimate attachment rates and characterize particle suspensions provides a powerful tool for management and assessment of water quality in estuaries.
Vibrio spp. are ubiquitous members of aquatic microbial food webs that can be pathogenic to humans and a range of other organisms. Previously published predictive models for Vibrio spp. concentrations in estuarine and coastal waters, based only on salinity and temperature, are 70 to 75% accurate during 'normal' conditions (e.g. not during storms or drought). We have conducted a preliminary comparison of the output from this type of model to the natural concentrations of both total Vibrio spp. and the potentially pathogenic Vibrio vulnificus when measured during tropical storms. Water samples were collected in situ from a deployed platform in the Neuse River Estuary (NRE), North Carolina, USA, during 2 storm events: Hurricane Ophelia and Tropical Storm Ernesto. Total Vibrio spp. concentrations were measured using culture-based methods and V. vulnificus levels were determined using a newly developed, rapid quantitative polymerase chain reaction (QPCR) assay. Results were analyzed in relation to environmental parameters and to concentrations of the fecal indicator bacteria Escherichia coli (EC) and Enterococcus spp. (ENT). Total concentrations of Vibrio spp. in the NRE were often orders of magnitude higher than those predicted by a previously published model. These large deviations from model predictions may indicate contributions from storm forcing (e.g. resuspension, surges) that are missing from the calm weather observations used to build these models.
Abstract. Bacterioplankton response to eutrophication is a critical part of the transition from phytoplankton blooms to bottom-water hypoxia in estuaries. This topic is of particular concern when endemic bacterial populations, such as Vibrio sp., may pose a health risk to local human populations using estuaries for recreation and food. The purpose of this study was to observe the dynamics of both Vibrio and phytoplankton in the Neuse River Estuary (NRE) in North Carolina, USA, during the summer of 2004. Vibrio concentrations, particle suspension characteristics, and chlorophyll a were measured in surface water collected at a series of stations along the estuarine gradient. Consistent with previous studies, a strong positive relationship between Vibrio concentration and salinity was found. Both Vibrio sp. and phytoplankton concentrations increased moving downstream, but beyond the salt front, phytoplankton declined while Vibrio sp. concentrations continued to increase. In surface waters, a large portion of suspensions was comprised of phytoplankton cells. The fraction of Vibrio cells attached to phytoplankton increased with phytoplankton concentration and decreased with increasing salinity. These observations of Vibrio dynamics in the NRE provide evidence that populations interact with phytoplankton populations in surface waters. This information may prove critical for models of estuarine bacterial dynamics in response to eutrophication.
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