Influence of macrophyte decomposition on growth rate and community structure of okefenokee swamp bacterioplankton

Dissolved substances released during decomposition of the white water lily (Nymphaea odorata) can alter the growth rate of Okefenokee Swamp bacterioplankton. In microcosm experiments dissolved compounds released from senescent Nymphaea leaves caused a transient reduction in the abundance and activity of water column bacterioplankton, followed by a period of intense bacterial growth. Rates of [H]thymidine incorporation and turnover of dissolved d-glucose were depressed by over 85%, 3 h after the addition of Nymphaea leachates to microcosms containing Okefenokee Swamp water. Bacterial activity subsequently recovered; after 20 h [H]thymidine incorporation in leachate-treated microcosms was 10-fold greater than that in control microcosms. The recovery of activity was due to a shift in the composition of the bacterial population toward resistance to the inhibitory compounds present in Nymphaea leachates. Inhibitory compounds released during the decomposition of aquatic macrophytes thus act as selective agents which alter the community structure of the bacterial population with respect to leachate resistance. Soluble compounds derived from macrophyte decomposition influence the rate of bacterial secondary production and the availability of microbial biomass to microconsumers.     

Spatial and Seasonal Variation in a Reservoir Sedimentary Microbial Community as Determined by Phospholipid Analysis

Sediment samples were collected monthly from Acton Lake, a eutrophic reservoir located in an agricultural region of southwestern Ohio, from three stations (River, Middle, and Dam) during the period May 1995 through January 1997. Sedimentary microbial biomass and community structures from these stations were studied using phospholipid analysis. At the River and Middle stations, the water column remained aerobic throughout the year, whereas the water overlying the Dam station sediments became anaerobic during summer stratification. Sedimentary microbial biomass at the River and Middle stations, as measured by the phospholipid phosphate (PLP) method, ranged from 225 to 450 nmol PLP g?1 d.w. (dry weight). Sedimentary microbial biomass at the Dam station was typically greater and ranged from 500 to 1,500 nmol PLP g?1 d.w. Principal component analysis of phospholipid fatty acid (PLFA) profiles indicated that the sedimentary microbial communities at all three stations displayed seasonal patterns of change. Among these patterns of change was a shift from aerobic microorganisms during times of cold water to anaerobic microorganisms during times of warm water. The Dam station differed from the River and Middle stations in that sediments from this station had disproportionately more polyenoic fatty acids, whereas sediments from the River and Middle stations had disproportionately more bacterial fatty acids. These data suggest that the Dam station may be a depositional zone for microeukaryotic phytoplankton produced in the overlying water column. These findings have implications for the understanding of carbon flux in reservoirs and preservation of organic matter in aquatic systems.     

Annual Cycle of Bacterial Secondary Production in Five Aquatic Habitats of the Okefenokee Swamp Ecosystem

Rates of bacterial secondary production by free-living bacterioplankton in the Okefenokee Swamp are high and comparable to reported values for a wide variety of marine and freshwater ecosystems. Bacterial production in the water column of five aquatic habitats of the Okefenokee Swamp was substantial despite the acidic (pH 3.7), low-nutrient, peat-accumulating character of the environment. Incorporation of [³H]thymidine into cold-trichloroacetic acid-insoluble material ranged from 0.03 to 2.93 nmol liter⁻¹ day⁻¹) and corresponded to rates of bacterial secondary production of 3.4 to 342.2 μg of carbon liter⁻¹ day⁻¹ (mean, 87.8 μg of carbon liter⁻¹ day⁻¹). Bacterial production was strongly seasonal and appeared to be coupled to annual changes in temperature and primary production. Bacterial doubling times ranged from 5 h to 15 days and were fastest during the warm months of the year, when the biomass of aquatic macrophytes was high, and slowest during the winter, when the plant biomass was reduced. The high rates of bacterial turnover in Okefenokee waters suggest that bacterial growth is an important mechanism in the transformation of dissolved organic carbon into the nutrient-rich bacterial biomass which is utilized by microconsumers.     

Dynamics of microbial biomass and activity in five habitats of the Okefenokee Swamp ecosystem

A variety of freshwater marsh and swamp habitats are found interspersed in a mosaic pattern throughout the Okefenokee Swamp, Georgia, USA. We examined spatial and temporal patterns in standing stocks and activity in the microbial community of five habitats within this heterogeneous ecosystem. Standing stock dynamics were studied by measuring microbial biomass (ATP) and bacterial numbers (AODC) in both water and sediments over a 14 month period. Abundance varied temporally, being generally lower in winter months than in spring and summer months. However, a large proportion of the measured variability was not correlated with temporal patterns in temperature or with bulk nutrient levels. Spatial variability was characteristic of the Okefenokee at a variety of large and small scales. Habitat-level heterogeneity was evident when microbial standing stocks and activity (measured as [¹⁴C]lignocellulose mineralization) were compared across the five communities, although abundance differences among sites were restricted to nonwinter months when microbial biomass was high. Spatial variation within habitats was also found; patches of surface sediment with differing microbial activity or abundance were measured at scales from 30 cm to 150 m.     

Microbial methanogenesis and acetate metabolism in a meromictic lake.

Methanogenesis and the anaerobic metabolism of acetate were examined in the sediment and water column of Knaack Lake, a small biogenic meromictic lake located in central Wisconsin. The lake was sharply stratified during the summer and was anaerobic below a depth of 3 m. Large concentrations (4,000 mumol/liter) of dissolved methane were detected in the bottom waters. A methane concentration maximum occurred at 4 m above the sediment. The production of (14)CH(4) from (14)C-labeled HCOOH, HCO(3) (-), and CH(3)OH and [2-(14)C]acetate demonstrated microbial methanogenesis in the water column of the lake. The maximum rate of methanogenesis calculated from reduction of H(14)CO(3) (-) by endogenous electron donors in the surface sediment (depth, 22 m) was 7.6 nmol/h per 10 ml and in the water column (depth, 21 m) was 0.6 nmol/h per 10 ml. The methyl group of acetate was simultaneously metabolized to CH(4) and CO(2) in the anaerobic portions of the lake. Acetate oxidation was greatest in surface waters and decreased with water depth. Acetate was metabolized primarily to methane in the sediments and water immediately above the sediment. Sulfide inhibition studies and temperature activity profiles demonstrated that acetate metabolism was performed by several microbial populations. Sulfide additions (less than 5 mug/ml) to water from 21.5 m stimulated methanogenesis from acetate, but inhibited CO(2) production. Sulfate addition (1 mM) had no significant effect on acetate metabolism in water from 21.5 m, whereas nitrate additions (10 to 14,000 mug/liter) completely inhibited methanogenesis and stimulated CO(2) formation.     

Microbial community structure and biomass estimates of a methanogenic Antarctic Lake ecosystem as determined by phospholipid analyses

Phospholipid analyses were performed on water column particulate and sediment samples from Ace Lake, a meromictic lake in the Vestfold Hills, Antarctica, to estimate the viable microbial biomass and community structure in the lake. In the water column, methanogenic bacterial phospholipids were present below 17 m in depth at concentrations which converted to a biomass of between 1 and 7×10⁸ cells/liter. Methanogenic biomass in the sediment ranged from 17.7×10⁹ cells/g dry weight of sediment at the surface to 0.1×10⁹ cells/g dry weight at 2 m in depth. This relatively high methanogenic biomass implies that current microbial degradation of organic carbon in Ace Lake sediments may occur at extremely slow rates. Total microbial biomass increased from 4.4×10⁸ cells/ liter at 2 m in depth to 19.4×10⁸ cells/liter at 23 m, near the bottom of the water column. Total nonarchaebacterial biomass decreased from 4.2 ×10⁹ cells/g dry weight in the surface sediment (1/4 the biomass of methanogens) to 0.06×10⁸ cells/g dry weight at 2 m in depth in the sediment. Phospholipid fatty acid profiles showed that microeukaryotes were the major microbial group present in the oxylimnion of the lake, while bacteria dominated the lower, anoxic zone. Sulfate-reducing bacteria (SRB) comprised 25% of the microbial population at 23 m in depth in the water column particulates and were present in the surface sediment but to a lesser extent. Biomass estimates and community structure of the Ace Lake eco-system are discussed in relation to previously measured metabolic rates for this and other antarctic and temperate ecosystems. This is the first instance, to our knowledge, in which the viable biomass of methanogenic and SRB have been estimated for an antarctic microbial community.     

Temporal relationship between the deposition and microbial degradation of lignocellulosic detritus in a Georgia salt marsh and the Okefenokee Swamp

Temperature dependence and seasonal variations in rates of microbial degradation of the lignin and polysaccharide components of specifically radiolabeled lignocelluloses were determined in sediment and water samples from a Georgia salt marsh and the nearby Okefenokee Swamp. Although temperature regimes in the two ecosystems were similar, rates of mineralization ofSpartina alterniflora lignocellulose in salt marsh sediments increased eightfold between winter and summer, whereas rates of mineralization of lignocellulose from an analogous freshwater macrophyte,Carex walteriana, in Okefenokee sediments increased only twofold between winter and summer. Temperature was the major factor influencing seasonal variations in rates of lignocellulose degradation in both environments. At any given temperature, no substantial differences in lignocellulolytic potential were observed with sediment samples collected at each season. In both ecosystems, the bulk of the lignocellulosic detritus was not degraded at the time of its peak deposition during the fall and winter. Instead, the periods of maximal decomposition occurred during the following spring and summer. These results suggest that periods of maximal nutrient regeneration from the mineralization of lignocellulosic detritus coincide with periods of highest primary production, and that, depending on hydrologic conditions, significant horizontal transport of essentially intact lignocellulosic material is possible due to the lag period between deposition and microbial degradation.     

Microbial processes of the carbon and sulfur cycles in the Chukchi Sea

The research performed in August 2004 within the framework of the Russian-American Long-term Census of the Arctic (RUSALCA) resulted in the first data concerning the rates of the key microbial processes in the water column and bottom sediments of the Bering strait and the Chukchi Sea. The total bacterial counts in the water column varied from 30 x 10(3) cells ml(-1) in the northern and eastern parts to 245 x 10(3) cells ml(-1) in the southern part. The methane content in the water column of the Chukchi sea varied from 8 nmol CH4 l(-1) in the eastern part of the sea to 31 nmol CH4 l(-1) in the northern part of the Herald Canyon. Active microbial processes occurred in the upper 0-3 cm of the bottom sediments; the methane formation rate varied from 0.25 to 16 nmol CH4 dm(-3) day(-1). The rates of methane oxidation varied from 1.61 to 14.7 nmol CH4 dm(-3) day(-1). The rates of sulfate reduction varied from 1.35 to 16.2 micromol SO4(2-) dm(-3) day(-1). The rate of methane formation in the sediments increased with depth, while sulfate reduction rates decreased (less than 1 micromol SO4(2-) dm(-3) day(-1)). These high concentrations of biogenic elements and high rates of microbial processes in the upper sediment layers suggest a specific type of trophic chain in the Chukchi Sea. The approximate calculated balance of methane emission from the water column into the atmosphere is from 5.4 to 57.3 micromol CH4 m(-2) day(-1).     

Temporal dynamics and spatial variation of algae in relation to hydrology and sediment characteristics in the Okefenokee Swamp,Georgia

In a 20-month study, phytoplankton and periphyton chl a, and dry mass of macroscopic algal aggregates in four marshes and a lake within the Okefenokee Swamp (Georgia, USA) were comparable to other wetlands and lake littoral areas. Chlorophyll levels in two marshes were inversely related to water level and phytoplankton at three marshes developed unimodal maxima following macrophyte dieback. Standing stocks in a vernally inundated marsh were greater than a nearby marsh which was permanently inundated; chlorophyll levels displayed longer blooms in the inundated marsh during periods of low rainfall or after drought. Field dynamics, sediment sorption characteristics and algal bioassays suggest that evaporative drawdown stimulates algae by release of nutrients from exposed peat, while high water levels reduce nutrient release from sediments and disperse phytoplankton through flushing. Equilibrium phosphate concentrations of sediments and algal levels were higher at an abandoned rookery than a nearby non-rookery area, indicating nutrient enrichment from residual guano deposits.     

Effects of shelter and enrichment on the ecology and nutrient cycling of microbial communities of subtidal carbonate sediments

The interactions between physical disturbances and biogeochemical cycling are fundamental to ecology. The benthic microbial community controls the major pathway of nutrient recycling in most shallow-water ecosystems. This community is strongly influenced by physical forcing and nutrient inputs. Our study tests the hypotheses that benthic microbial communities respond to shelter and enrichment with (1) increased biomass, (2) change in community composition and (3) increased uptake of inorganic nutrients from the water column. Replicate in situ plots were sheltered from physical disturbance and enriched with inorganic nutrients or left without additional nutrients. At t(0) and after 10?days, sediment-water fluxes of nutrients, O(2) and N(2) , were measured, the community was characterized with biomarkers. Autochthonous benthic microalgal (BMA) biomass increased 30% with shelter and a natural fivefold increase in nutrient concentration; biomass did not increase with greater enrichment. Diatoms remained the dominant taxon of BMA, suggesting that the sediments were not N or Si limited. Bacteria and other heterotrophic organisms increased with enrichment and shelter. Daily exchanges of inorganic nutrients between sediments and the water column did not change in response to shelter or nutrient enrichment. In these sediments, physical disturbance, perhaps in conjunction with nutrient enrichment, was the primary determinant of microbial biomass.     

Comparison of diffusion and reaction rates in anaerobic microbial aggregates

The ability of hydrogen diffusion to account for the rates of methane production in microbial aggregates was studied in a defined coculture consisting of a sulfate reducer grown as a syntrophic hydrogen producer in the absence of sulfate and a methanogen. The hydrogen uptake kinetics of the methanogen were determined using the infinite dilution technique. The maximum hydrogen uptake velocity was 7.1 nmol/min/μg protein and the half saturation constant for hydrogen uptake was 386 nmol/liter. A threshold of 28 nmol/liter below which no further hydrogen consumption occurred was observed. The reconstituted co-culture was shown to produce methane at rates similar to mixed culture enrichments grown on lactate. The diffusion model demonstrated that for the particular system studied, the rates of hydrogen diffusion could account for the overall rate of methane production.     

Phylogenetic comparison of methanogen diversity in different wetland soils

Aspects of archaeal diversity in peat soil samples from climatically and geographically distinct wetlands (subarctic: West Siberia Bog, Russia; temperate: Akaiyachi Mire, Japan; subtropical: Okefenokee Swamp, USA) were studied by molecular phylogenetic techniques. DNA was extracted directly from the soil samples and 16S rRNA genes were amplified by polymerase chain reaction. Partial sequences of the amplified 16S rDNAs (total 426 clones) were compared with known sequences from GenBank and the Ribosome Database Project (RDP). Peat-derived sequences were mostly related to Euryarchaeota, principally methanogens. Sets of sequences (operational taxonomic unit; OTU) were created for each wetland (21 OTUs for West Siberia; 22 OTUs for Akaiyachi; 33 OTUs for Okefenokee). The majority of the OTUs clustered in and showed low similarities to the Methanosarcinales family (West Siberia) or the Methanomicrobiales family (Akaiyachi and Okefenokee). In terms of the Shannon-Weaver diversity index, the archaeal community diversity in Okefenokee Swamp was greater than that of the other wetlands.     

Effects of Acid Stress on Aerobic Decomposition of Algal and Aquatic Macrophyte Detritus: Direct Comparison in a Radiocarbon Assay

Radiolabeled phytoplankton and macrophyte lignocelluloses were incubated at pHs 4 and 7 in water from a naturally acidic freshwater wetland (Okefenokee Swamp; ambient pH, 3.8 to 4.2), a freshwater reservoir (L-Lake; pH 6.7 to 7.2), and a marine marsh (Sapelo Island; pH ~7.8). The data suggest that acidity is an important factor in explaining the lower decomposition rates of algae in Okefenokee Swamp water relative to L-Lake or Sapelo Island water. The decomposition of algal substrate was less sensitive to low pH (~5 to 35% inhibition) than was the decomposition of lignocellulose (~30 to 70% inhibition). These substrate-dependent differences were greater and more consistent in salt marsh than in L-lake incubations. In both freshwater sites, the extent to which decomposition was suppressed by acidity was greater for green algal substrate than for mixed diatom or blue-green algal (cyanobacteria) substrates. The use of different bases to adjust pH or incubation in a defined saltwater medium had no significant effect on substrate-dependent differences. Although pH differences with lignocellulose were larger in marine incubations, amendment of lakewater with marine bacteria or with calcium, known to stabilize exoenzymes in soils, did not magnify the sensitivity of decomposition to acid stress.     

Microbiological studies in the deepwater area of the Southern Caspian Sea

For the first time, microbiological monitoring was performed in the deepwater area of the Southern Caspian Sea. It revealed seasonal and interannual variations in total microbial content and concentrations of saprophytes and other physiological groups of bacteria in water and bottom sediments. The biomass, generation time, and bacterial production were determined. The most profound variations in microbial content, biomass, and production were found to occur in the water column and in bottom sediments at depths to 200–250 m.     

Microbiological studies in the deepwater area of the Southern Caspian Sea

For the first time, microbiological monitoring was performed in the deepwater area of the Southern Caspian Sea. It revealed seasonal and interannual variations in total microbial content and concentrations of saprophytes and other physiological groups of bacteria in water and bottom sediments. The biomass, generation time, and bacterial production were determined. The most profound variations in microbial content, biomass, and production were found to occur in the water column and in bottom sediments at depths to 200-250 m.     

Contributions of three subsystems of a freshwater marsh to total bacterial secondary productivity

Rates of bacterial production were measured in the water column, on the surface of plant detritus, and in the surface sediments of a freshwater marsh in the Okefenokee Swamp, Georgia, USA. Bacterioplankton production rates were not correlated with several measures of quantity and quality of dissolved organic matter, including an index of the relative importance of vascular plant derivatives. Bacterioplankton productivity was high (mean: 63 g C liter^–1 day^–1) compared with rates reported for other aquatic ecosystems. Somewhat paradoxically, bacterial productivity on plant detritus (mean: 13 g C g^–1 day^–1) and sediments (mean: 15 g C g^–1 day^–1) was low relative to other locations. On an a real basis, total bacterial productivity in this marsh ecosystem averaged 22 mg C m^–2 day^–1, based on sample dates in May 1990 and February 1991. Marsh sediments supported the bulk of the production, accounting for 46% (May) and 88% (February) of the total. The remainder was contributed approximately equally by bacteria in the water column and on accumulated stores of plant detritus. Send offprint requests to: M. A. Moran.     

Kinetics of bacterial processes in natural aquatic systems based on biomass as determined by high-resolution flow cytometry

The two primary kinetic constants for describing the concentration dependency of nutrient uptake by microorganisms are shown to be maximal rate of substrate uptake and, rather than the Michaelis constant for transport, specific affinity. Of the two, the specific affinity is more important for describing natural aquatic microbial processes because it can be used independently at small substrate concentrations. Flow cytometry was used to evaluate specific affinities in natural populations of aquatic bacteria because it gives a convenient measure of biomass, which is an essential measurement in the specific-affinity approach to microbial kinetics. Total biomass, biomass in various filter fractions, and the specific affinity of the bacteria in each fraction were determined in samples from a near-arctic lake. The partial growth rate of the pelagic bacteria from the 25 micrograms/liter of dissolved amino acids present (growth rate from the amino acid fraction alone) was determined to be 0.78 per day. By measuring activity in screened and whole-system populations, the biomass of the bacteria associated with particles was computed to be 427 micrograms/liter.     

Bacterioplankton and bacteriobenthos of some floodplain lakes in the course of the lower Amur river

The main structural and functional characteristics of bacterioplankton and bacteriobenthos of three lakes in the lower course of the Amur River are presented: the total number of bacteria (TNB), biomass, the numbers of bacteria of certain aerobic and anaerobic groups; the intensities of methanogenesis (MG), methane oxidation (MO), assimilation of 14C-compounds, sulfate reduction (SR); and gross estimate of organic matter decomposition (D). Depending on the reservoir type and the anthropogenic load, TNB constituted (2.27 to 16.1) x 10(6) cells/ml in water and (1.06 to 10.35) x 10(9) cells/ml in sediments; MO was 0 to 0.28 ml CH4/(1 day) in water and 0 to 8.4 ml CH4/(dm3 day) in sediments; MG in sediments was 0.001 to 40 ml CH4/(dm3 day); SR varied from 0.001 to 24.8 mg S/(dm3 day); D was 0.3 to 25 g C/(m2 day) in water and 0.2 to 4.9 g C/(m2 day) in sediments. The role of anaerobic microbial processes of organic matter decomposition was shown to increase with an increase in the anthropogenic load, attaining 95% of the total D in the ecosystem of an accumulating pond.     

Single cell oil (SCO) production by Mortierella isabellina grown on high-sugar content media

Mortierella isabellina cultivated in nitrogen-limited media presented remarkable cell growth (up to 35.9 g/l) and high glucose uptake even with high initial sugar concentrations (e.g. 100 g/l) in media. After nitrogen depletion, significant fat quantities were accumulated inside the fungal mycelia (50-55%, wt/wt oil in dry biomass), resulting in a notable single cell oil production of 18.1 g/l of culture medium. Total dry biomass and lipid yields presented greatly increased values (0.34 and 0.17 g respectively per gram of glucose consumed). The microbial lipid produced contained gamma-linolenic acid (GLA) at a concentration of 3.5+/-1.0%, wt/wt, which corresponded to 16-19 mg GLA per gram of dry microbial mass and a maximum concentration of 0.801 g GLA per liter of culture medium.     

Sedimentary microbial community dynamics in a regulated stream: East Fork of the Little Miami River,Ohio

A field study was conducted in the Lower East Fork of the Little Miami River, a regulated stream in Clermont county, Ohio, to determine how changes in streamflow, water temperature and photo-period affect sediment microbial community structure. Surface sediment cores were collected from sampling stations spanning 60 river kilometers three to four times per year between October 1996 and October 1999. During the final year of the field study, water temperature, water depth, conductivity, total suspended solids, dissolved organic carbon, instantaneous streamflow velocity, sediment grain size and sediment organic matter were determined. Total microbial biomass was measured using the phospholipid phosphate technique (PLP) and ranged between 2 and 134 nmol PLP * g(-1) dry weight sediment with a mean of 25 nmol PLP * g(-1). Microbial community structure was determined using the phospholipid fatty acid analysis and indicated seasonal shifts in sedimentary microbial community composition. January to June sedimentary microbial biomass was predominately prokaryotic (60% +/- 2), whereas microeukaryotes dominated samples collected during the late summer (55% +/- 2.4) and fall (60% +/- 2). These changes were correlated with stream discharge and water temperature. Microbial community structure varied spatially about a reservoir with prokaryotic biomass dominant at upstream stations and eukaryotic biomass dominant at downstream stations. These findings reveal that sedimentary microbial communities in streams are dynamic responding to the seasonal variation of environmental factors.