L. Harold Stevenson

The dynamics of the bacterial population associated with a salt marsh

Abstract The distribution and temporal fluctuations in the density of bacteria in the water covering a high-salinity marsh were investigated employing epifluorescence microscopy for quantification as well as by transmission and scanning electron microscopy. The observed densities ranged from about 1 to 19 × 10 6 bacteria/ml during the course of the study. High-marsh sampling sites had an average population level of 7.8 × 10 6 bacteria/ml which was more than double the mean density recovered from large creeks near the mouth of the marsh system. Bacteria associated with seston varied tidally and seasonally, whereas the population of free planktonic bacteria varied only seasonally. Very small fluorescing bodies were commonly observed during epifluorescent observation of samples. These small bodies were observed at densities two orders of magnitude higher than easily recognized bacteria. In a salt marsh, the relative density of epibacteria was influenced by short-term tidal effects, and the population of planktobacteria was apparently controlled by long-term seasonal phenomena.

Transport of microbial biomass through the North Inlet ecosystem

Tidal fluctuations and transports of total microbial biomass (measured as adenosine triphosphate [ATP]) were investigated at three marsh creeks comprising the major transfer points between the North Inlet marsh and the adjoining aquatic ecosystems. Two creeks, Town Creek and North Jones Creek, form the inlet mouth and are the only marsh-ocean exchange points. The third creek, South Jones Creek, connects to a brackish water embayment. The creeks were simultaneously sampled every 1.5 hours for 50 consecutive hours during neap tides (four tidal cycles) and 50 consecutive hours during spring tides of each season. At the inlet, ATP concentration fluctuated in phase with the tide during winter and fall and out of phase with the tide during the spring. Fluctuation patterns at South Jones Creek were irregular. The highest ATP concentrations were during the spring (mean=2.17 mg of ATP per m3) and the lowest concentrations were during the winter (mean=0.65 mg of ATP per m3). Net transports of ATP varied from tidal cycle to tidal cycle with regard to direction of transport (import or export) and magnitude. Net transports were small compared to large instantaneous transports and only 4 of 22 determinations of net transport were different from zero transport.

Environmental factors associated with proteolytic activity of estuarine bacteria

Abstract The effects of various parameters on the extracellular hydrolysis of protein by salt marsh bacteria were examined using an agar plate assay technique. Maximum activity was observed at pH 8 and 18 C. Elimination of salts and nutrients from the growth media had little effect on activity; while, incubation in a reduced oxygen atmosphere markedly restricted proteolysis by laboratory stocks and random isolates. The availability of oxygen appeared to be one of the important factors controlling extracellular protease production by salt marsh bacteria.

Variability in total microbial biomass measurements made in cross-sections of salt-marsh creeks

Abstract The temporal fluctuation and distribution of microbial biomass were studied at two salt-marsh creeks having different salinities and hydrographic features. One creek, North Jones Creek, is adjacent to the marsh inlet, while the second creek, South Jones Creek, interfaces with a brackish-water embayment. Samples for analysis of microbial biomass, measured as adenosine 5′-triphosphate (ATP), were collected synoptically for 25 h from three depths at each of three sites within each creek cross-section. The temporal fluctuation pattern of ATP at North Jones Creek followed a tidal rhythm with maximum concentrations occurring at high tide. The temporal fluctuation pattern at South Jones Creek was somewhat erratic with highest concentrations of ATP recovered from samples collected during flooding tides. The distribution of mean ATP densities as well as net flux through each interface proved to be complex which suggests that sampling depth and station placement are critical in determining net fluxes through marsh creeks.

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ACTIVITY OF BACTERIA IN THE ESTUARINE ENVIRONMENT

ABSTRACT Water in near-shore and estuarine environments characteristically contains a large number of bacteria and a generally high “activity” or heterotrophic potential. The bacteria in near-shore waters do not represent a uniform population and the density probably does not reflect growth and multiplication. The population consists of those bacteria that are adapted to function in the environment together with those that are simply surviving. Studies with pure cultures are often suspect and there are also inherent problems involved with metabolic studies of mixed populations. The enhanced metabolic activity in estuarine areas may be a simple reflection of the favorable nutritional status of the water, however, it may also represent increased activities of freshwater and marine forms in an attempt to compensate for the adverse impact of some perturbation. No single factor can account for the demise or survival of bacteria in these environments. A variety of both structural and physiological explanations may be put forth to explain how bacteria have adapted to the near-shore areas. The structural adaptations may include modification of the cell surface, membrane permiability and transport, and enzyme structure. The physiological responses may include changes in metabolic rate, metabolite pools, proteins and nucleic acid synthesis, and growth patterns.

Influence of freshwater intrusion on microbial biomass in salt-marsh creeks

Adenosine triphosphate (ATP), particulate organic carbon (POC), pH, temperature, and salinity associated with the water column of several salt marsh creeks were monitored at 5 stations for 8 months. A gradient in mean salinity of 11.5‰ to 32.7‰ was observed in the creeks. No significant correlations (Pearson’s r) could be found among the variables measured at the station with the highest salinity. ATP and POC were found to be positively correlated at all other stations. Salinity was found to be negatively correlated with both ATP and POC only at a station with the second highest mean salinity (28.8‰) and could account for only 45.7‰ of the variation in ATP. The lack of significant correlations between salinity and ATP as well as the inability of salinity to account for a large portion of the variation in ATP suggested that salinity had little relationship to the level of total microbial mass.

Short-Term Fluxes Through Major Outlets of the North Inlet Marsh in Terms of Adenosine 5′-Triphosphate

Transects across three major creeks joining the North Inlet marsh system to the neighboring ocean and bay environments were characterized in terms of the temporal fluctuations, distribution, and short-term transport of total microbial biomass (measured as adenosine 5′-triphosphate [ATP]). The mean ATP density ranged from 0.865 to 1.357 mg per m3. Highest densities were recovered during flood tides. The distribution of mean ATP densities as well as net flux through each interface proved to be complex with both vertical and horizontal stratification apparent at some locations. A net import of ATP at a rate of about 40 mg per s was noted at the two creeks that interfaced directly with the oceanic environment. A net export was noted through the creek that emptied into the bay. The results indicate that the characterization of a tidal creek interface in terms of ATP, or similar parameters, requires the simultaneous measurement of both the component of interest and directional velocity.

Tidal and diel fluctuations in the temporal concentrations of chlorophyll a and pheophytin at a station monitoring a high-marsh creek

Abstract The temporal distribution of chlorophyll a and pheophytin at a transect monitoring the flow at a high-marsh creek was investigated. The observed fluctuations in chlorophyll a concentration consisted of complex, superimposed, tidal and diel rhythms; pheophytin variability, on the other hand, was controlled by the tides. Transport measurements and correlation analyses supported the hypothesis that tidal forces have a major influence on the temporal fluctuation of chlorophyll a and phaeophytin concentrations in high-marsh creeks. The data indicate that it is important to consider tidal flux when designing programs to study seasonal effects, primary productivity, and phytoplankton species composition.