Higher Bacterial Biomass Research Articles

Seasonal Variations in Suspended Particulate Matter in the Marennes-Oléron Bay, France, using Lipids as Biomarkers

In the most important oyster-producing area in France, an investigation was conducted to determine the origin of particulate organic matter (POM) of the size, <100 μm, available to oysters. Suspended particulate matter (SPM) was sampled monthly over 1 year at one estuarine station in the Bay, Fort Boyard, and at one river station in the Charente at St. Savinien. Lipid-class and fatty-acid profiles were determined in the SPM. At Fort Boyard, variations in amounts of SPM and its ratio of both POC:Chlorophyll aand C:N were associated with changes in river discharge rates, local resuspension and phytoplankton proliferation. High concentrations of mineral and detrital particles were observed in winter, and low levels during the rest of the year, when phytoplankton blooms occur frequently. Lipid-class and fatty-acid profiles varied in relation to seasonal changes in both weather and hydrology. The terrestrial contribution to SPM was highest in winter, when river outflow and resuspension in the Bay were also maximal. High bacterial biomass occurred in association not only with river detritus, but also with early-spring blooms. Microalgal fatty acids were predominant from spring to autumn and, by using compounds shown to be of taxonomic significance, the presence of diatoms could be discerned from that of other microalgae. In winter, the estuarine and freshwater stations showed similar lipid compositions, with dominance by terrestrial and bacterial biomarkers. In summer, however, fatty-acid profiles were very different at the two sites, showing clear temporal variations, which suggest that the Bay and the River then function as separate systems and follow different biological patterns.

Effects of phenol feeding pattern on microbial community structure and cometabolism of trichloroethylene

Cometabolism of trichloroethylene (TCE) by phenol-fed enrichments was evaluated in four reactors with distinct phenol feeding patterns. The reactors were inoculated from the same source, operated at the same average dilution rate, and received the same mass of phenol over time. Only the timing of phenol addition differed. Reactor C received phenol continuously; reactor SC5 received phenol semicontinuously--alternating between 5 h of feed and 3 h without feed; reactor SC2 alternated between 2 h of feed and 6 h without feed; and reactor P received a single pulse every 24 h. The structure of the enrichments and their capacity for TCE transformation were analyzed. In long-term operation, reactors C and SC5 were dominated by fungi, had higher levels of predators, were more susceptible to biomass fluctuations, and exhibited reduced capacity for TCE transformation. Reactors P and SC2 were characterized by lower levels of fungi, higher bacterial biomass, higher concentrations of TCE-degrading organisms, and higher rates of TCE transformation. After 200 days of operation, rates of TCE transformation increased 10-fold in reactor P, resulting in TCE transformation rates that were 20 to 100 times higher than the rates of the other reactor communities. The cause of this shift is unknown. Isolates capable of the highest rates of TCE transformation were obtained from reactor P. We conclude that cometabolic activity depends upon microbial community structure and that the community structure can be manipulated by altering the growth substrate feeding pattern.

Ecology of diatom and bacterial assemblages in water associated with melting summer sea ice in the Weddell Sea, Antarctica

The fate of ice biota released via meltwater into pools of seawater trapped between melting ice floes (crack pools) was followed in late January in the southern Weddell Sea. Low salinity crack pools shared the following features: nitrate exhaustion, high pH and POC/PON ratios, high bacterial biomass composed of large cells, and a dense algal assemblage dominated to over 90% by only two diatom species. It is suggested that this “climax stage” evolved from a nutrient rich, moderate biomass situation prevailing in high salinity crack pools, and is representative of summer succession of sea ice biota. “Overflow” production following nitrate exhaustion by the algae resulted in internal (lipid) and external (presumably mucus) carbon pools. The latter must fuel bacterial biomass build-up, as algal mortality appeared to be low. The large algal and bacterial stocks point to low grazing pressure exerted by phagotrophic protists, presumably due to poor food quality (e.g. high C/N ratios) and/or excessive mucus production. It is concluded that environmental selection of the abundant ice algal species occurs under conditions prevailing in the disintegrating ice cover during summer, which differ drastically from those generally referred to as characteristic of the sea ice habitat at large (a combination of low temperature, low light and high salinity).

Comparison of ciliate communities in the anoxic hypolimnia of three lakes: general features and the influence of lake characteristics

The ciliate communities and their food sources were investigated in the anoxic hypolimnia of three lakes with differing water chemistry. Bacterial biomass and, as a result, the biomass of bactenvor- ous ciliates were correlated with lake trophy. Additionally, high sulfate and sulfide concentrations led to high bacterial biomass of sulfate reducers and anaerobic phototrophic and heterotrophic bacteria, which in turn sustained large ciliate populations. The anaerobic ciliate communities of the lakes shared many characteristics. They were comprised of the same or closely related species; this was attributed to a low diversity of food sources. Ciliate to prey biomass ratios were 1.2-3.8% which is consistent with a low theoretical growth efficiency of anaerobic metabolism. Grazing pressure on anaerobic ciliates by metazoa was insignificant. In all three lakes, ciliate populations showed distinct vertical non-random distribution patterns which were often correlated with the distribution of the corresponding food sources. It is suggested that the microbial communities in anoxic water bodies are largely influenced by few common environmental conditions and are therefore often inhabited by similarly structured ciliate communities.

The dynamics of heterotrophic nanoflagellates and bacterioplankton in a large ultra-oligotrophic Antarctic lake

The abundance of both heterotrophic nanoflagellates (HNAN) and bacterioplankton in a large (9km2) ultraoligotrophic Antarctic lake (Crooked Lake) were investigated from December 1992 until November 1993. HNAN abundance peaked in spring, summer and autumn, falling to lowest numbers during the winter. Numbers ranged between 0 and 50.9×104 l−1. Bacterioplankton abundance was highest during the late summer and then fell progressively towards winter and autumn (range 1.19–4.46×106 l−1) In contrast to numbers, mean cell volumes (MCV) of the bacteria reached their highest in spring, and consequently highest bacterial biomass occurred at this time. MCV ranged between 0.052 and 0.224μm3. Bacterial production measurements following the incorporation of [3H] thymidine into DNA and [14C] leucine into protein using a doubling-labelling procedure were undertaken in January, June, August, October and November. Rates varied between 2.8 and 52 ng C l1 h1. On occasions, a significant difference in production rates based on the uptake of leucine and thymidine was observed, suggesting unbalanced growth. Highest rates of production coincided with times of high dissolved organic carbon levels in the water column and lowest production with low levels of DOC. HNAN grazing rates were measured by following the uptake of fluorescently labelled bacteria and averaged 4.8 bacterial cells individual1 day1 at 2 and 4°C. Specific growth rates (h1) ranged around 0.00070–0.00077 in both the field and laboratory, giving doubling times of 37.3 and 41.0 days, respectively. These low rates of grazing and growth indicate that there is no adaptation to low temperatures in these freshwater protists. Based on these data, the gross production efficiency is 24%. HNAN removed between 0.1 and 9.7% of bacterial production per day.

Reduction of bacterial growth by a vesicular-arbuscular mycorrhizal fungus in the rhizosphere of cucumber (Cucumis sativus L.)

Cucumber was grown in a partially sterilized sand-soil mixture with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum or left uninoculated. Fresh soil extract was places in polyvinyl chloride tubes without propagules of mycorrhizal fungi. Root tips and root segments with adhering soil, bulk soil, and soil from unplanted tubes were sampled after 4 weeks. Samples were labelled with [3H]-thymidine and bacteria in different size classes were measured after staining by acridine orange. The presence of VAM decreased the rate of bacterial DNA synthesis, decreased the bacterial biomass, and changed the spatial pattern of bacterial growth compared to non-mycorrhizal cucumbers. The [3H]-thymidine incorporation was significantly higher on root tips in the top of tubes, and on root segments and bulk soil in the center of tubes on non-mycorrhizal plants compared to mycorrhizal plants. At the bottom of the tubes, the [3H]-thymidine incorporation was significantly higher on root tips of mycorrhizal plants. Correspondingly, the bacterial biovolumes of rods with dimension 0.28–0.40×1.1–1.6 μm, from the bulk soil in the center of tubes and from root segments in the center and top of tubes, and of cocci with a diameter of 0.55–0.78 μm in the bulk soil in the center of tubes, were significantly reduced by VAM fungi. The extremely high bacterial biomass (1–7 mg C g-1 dry weight soil) was significant reduced by mycorrhizal colonization on root segments and in bulk soil. The incorporation of [3H]-thymidine was around one order of magnitude lower compared to other rhizosphere measurements, probably because pseudomonads that did not incorporate [3H]-thymidine dominated the bacterial population. The VAM probably decreased the amount of plant root-derived organic matter available for bacterial growth, and increased bacterial spatial variability by competition. Thus VAM plants seem to be better adapted to compete with the saprophytic soil microflora for common nutrients, e.g., N and P, compared to non-mycorrhizal plants.

Bacterial 5′‐nucleotidase activity in estuarineand coastal marine waters: Role in phosphorus regeneration

5′‐Nucleotidase (5PN) activity was measured with [γ‐32P]ATP, and related measurements were made by conventional techniques. Our results suggest that 5PN activity was more closely correlated with high algal and bacterial biomass and growth rates (eutrophic environments) than with phosphate depletion. 5PN was also potentially important in phosphate regeneration, even when dissolved nucleotide concentrations of a few nanomolar were assumed. If nuclease hydrolysis of dissolved nucleic acids also contributes to the dissolved nucleotide pool, then phosphate regeneration by 5PN activity would be significantly greater. In the high‐phosphate environments studied, most of the phosphate regenerated by 5PN was not taken up immediately.

Evidence of enhanced microbial activity in the interstitial space of branched corals: possible implications for coral metabolism

Water samples from the interstitial space of 4 Indo-Pacific coral species (Acropora sp., Echinopora horrida, Psammocora digita and Pavona clavus) and a Mediterranean coral (Cladocora cespitosa) were analysed for NO 3 - +NO 2 - , NH 4 + , molybdate reactive phosphorus, bacterial and flagellate biomass and dissolved organic matter (DOM) and compared with ambient water concentrations. Higher values of NO 3 - +NO 2 - , bacterial and flagellate biomass were observed within the interstitial space of the corals. The lower DOM pool in the interstitium in combination with the high bacterial biomass suggests high bacterial activity and efficient substrate utilization, necessary to compensate for nanoflagellate predation. Since corals may be able to feed on bacteria, the high microbial biomass (bacterial and flagellate) may be utilized either directly as an additional heterotrophic food source, or indirectly in that microbes may act as attractants for microbe-feeding zooplankters, which in turn serve as food for the corals. The combined effect of reduced flow velocities between the coral branches and its associated fauna are probably the main factors in creating a specific environment more or less independent of the nutritive stage of the surrounding water.

Nutrient Regeneration by Fly Larvae in Cattle Dung

The effect of fly larvae on bacterial population growth in cow dung was studied. We measured bacterial density and NH'concentration in laboratory cultures of 0, 25, and 100 Orthellia caesarion larvae /50 g dung, and in dung pats in the field within aggregations of sarcophagid and muscid larvae. In the laboratory, larvae increased bacterial turnover and decreased bacterial numbers as larval density increased. In the field, larvae were associated with higher bacterial density, and larvae increased bacterial turnover when feeding at high density but not when feeding at low density. If increased bacterial turnover benefited individual larvae, it might be expected that pupal weights of larvae feeding at high density would be greater than those of larvae feeding at low density. Pupal weights, however, showed no increase in response to density, but simply declined as the density at which they were reared increased. We conclude that increases in bacterial turnover or density are too small relative to high bacterial biomass in dung to benefit individual larvae.

Sterols in interstitial waters of marine sediments

In order to attempt to elucidate the nature of biogeochemical processes occurring at the water-sediment interface, sterols have been analysed in near bottom sea and interstitial waters collected in the eastern and western intertropical Atlantic ocean. Free and esterified sterol concentrations range from 0.2 to 82 μg l −1 and are much higher than those found in overlying sea water, which range from 0.2 to 1.7 μg l −1 for the dissolved fraction and from 0.01 to 0.07 μg l −1 for the particulate fraction. Cholest-5-en-3β-ol and 24-ethylcholest-5-en-3β-ol are the dominant sterols in sea and interstitial waters. The variability encountered for the relative importance of minor sterols such as 24-methylcholesta-5,24(28)-dien-3β-ol and stanols, 5α-cholest-22(E)-en-3β-ol, 5α-cholestan-3β-ol and 24-ethyl-5α-cholestan-3β-ol in interstitial water and their variation with depth is discussed in terms of diversity of inputs and bacterial activity. For sediments cored off the Mauritanian coast, a productive area characterized by an intense upwelling, the chemical signatures observed in interstitial water through stanol/stenol ratios occur at levels of very high heterotrophic aerobic bacterial biomass estimations. The study of the sterol composition of interstitial water could constitute a valuable tool in appreciating the intensity of chemical and biological processes occurring in the first few metres of recent marine sediments.

Fatty acid components of nine species of molluscs of the littoral zone from Australian waters

1. 1. There is evidence that differences in algal diet are reflected in the component fatty acid compositions of the limpets found at two sites. 2. 2. The tropical species of gastropods lacking macroscopic algae in their diet suggest in several component acids a high bacterial biomass intake. 3. 3. Seasonal variations are reflected in varying proportions of saturated, monoenoic and especially polyunsaturated fatty acids. A sub-tidal gastropod although in a stable environment relative to the intertidal zone still reflected a seasonal change which is presumably metabolic in origin. 4. 4. Nonmethylene-interrupted fatty acids were detected in relatively high concentration levels in all the molluscs examined.