Loss of Estuarine Bacteria by Viral Infection and Predation in Microcosm Conditions

The bacterioplankton density in Ria de Aveiro, a shallow estuarine ecosystem, varied in the broad range of 1.9-10.6 109 cells L-1. The range of values was about 2 times higher in brackish water than in marine water. At high tide bacterial abundance was 2-3 times lower than at low tide. The overall variation in virioplankton was in the range of 2.4-25.0 1010 particles L-1. Brackish water was about 2 times richer in viral particles than the marine water. Near low tide the virioplankton was 2-3 times higher that at high tide. Viral density followed the pattern of bacterial abundance (it explained 40% of virioplankton variation). The viruses to bacterium ratio varied, throughout tidal cycles, by a factor of about 10 establishing the range 4.7-55.6 (average 17.6). This ratio was rather similar in the two estuarine zones. We compared the effects of infection and predation on the control of bacterioplankton size in the two zones of the estuary. The approach to this question was conducted in experimental microcosms, set up in six combinations of plankton variables affecting the presence/absence of predators, virus-to-bacterium ratio (10-fold increase), virus-to-bacterium distance (2.2-fold increase), and bacterial growth rate. The results showed that predation was similar, in a percent basis, in marine (69%) and brackish water (73%). Viral infection was, however, higher in brackish water (59%) than in the marine water (36%). We conclude that the bacterioplankton along the salinity gradient evolves under biological pressures that are in different balance in the marine and brackish water zones. The effect of viral lysis on bacterial communities with enhanced growth (after yeast extract addition) was masked even when the initial ratio was 10-fold greater than in the natural samples. The high density of the virioplankton did not preclude the large and rapid increase in bacterial density. We suggest that the dynamics of the equilibrium between bacteria and viruses in the environment is driven to higher numerical levels during periods of intensive bacterial growth. On the contrary, at low bacterial growth rates the temporarily increased virus-to-bacterium ratio may drive the equilibrium to its lowest levels.     

Short-Term Responses of the Natural Planktonic Bacterial Community to the Changing Water Properties in an Estuarine Environment: Ectoenzymatic Activity,Glucose Incorporation,and BiomassProduction

The possibility that two principlal bacterial communities expressing different levels of heterotrophic activity might coexist in an estuarine ecosystem (Ria de Aveiro, Portugal) and could quickly respond to tidal fluctuations of environmental factors was experimentally tested in diffusion chambers by swapping the dissolved components of the natural water between the two communities and comparing their reactivity against the unaltered controls. The results for ectoenzymatic activity (Leuaminopeptidase and β-glucosidase), glucose incorporation and biomass production after transference of the marine bacterial community to brackish water showed maxima in the range of 241–384% of the control values. The opposite transference of the brackish-water bacterial community to marine water produced maximal decreases to 0.14–0.58% of the control values. In a reverse experiment, designed as the return to the initial conditions after 2 hours of the first exposure, the marine community rapidly re-acquired the characteristic low profile of activity. Contrastingly, the negative effects of 2 hours of exposure to marine water on the activity of the brackish water bacteria persisted, at least for 4 hours, after return to their own water. The apparent short-term irreversibility of the decline in activity of the brackish water bacteria when exposed to marine water, in parallel with the quick and reversible positive response of the marine water bacteria to the brackish water, suggests the development of two distinct bacterioplankton communities adapted to the environmental conditions prevailing at distinct sections of the estuary. The reactivity to environmental changes demonstrated by the two communities allows the prediction of estuarine profiles of bacterial activity steeper than those expected from the conservative transport of bacterial cells associated with tidal currents.     

Compartments of oxygen consumption in a tidal mesotrophic estuary (Ria de Aveiro,Portugal)

Oxygen consumption rates were determined, in parallel with primary production and bacterial biomass production, as an approach to the analysis of carbon cycling in the estuarine community of the Ria de Aveiro. The water column of the marine zone was the major contributor (64–99 %) to the total aerobic carbon remineralisation in which O₂ uptake rates averaged from 80 to 127 mg O₂.m^–2.h^–1, respectively at low tide and high tide. The planktonic consumption of O₂ varied from 0.010 to 0.041 mg O₂.L^–1.h^–1 with the highest values in the brackish zone. Small water column depths in this zone, however, reduced the integrated average consumption of the plankton, per unit of surface area, to 57 (LT) and 66 % (HT) of that observed in the marine zone. Benthic O₂ consumption rates, 5.1 to 22.0 mg O₂.m^–2.h^–1, were two to four times higher in the brackish zone when compared to the rates in the marine zone. It represented 1–31 % of the total surface integrated values in different areas and at different tides. From the ratios of the primary production and bacterial biomass production, on a per surface unit basis, it is concluded that, in late autumn, the Ria de Aveiro was mostly a heterotrophic system with a feeble recovery of primary production at HT in the marine zone and at LT in the brackish water zone.     

Bacterial Productivity Distribution During a Rainy Year in an Estuarine System

Bacterial density and productivity were investigated along four salinity gradients within the estuary Ria de Aveiro. Bacterial variables and environmental parameters were measured at three to four stations spanning the entire salinity gradient of the four channels. The rather high variation in bacterial productivity (0.16–7.6 μg C L⁻¹ h⁻¹) along the profiles of salinity indicates that bacterial activity shows a reactive behavior to environmental changing. Bacterial density (0.5–11.2 × 10⁹ cells L⁻¹) with a comparative smaller variation showed a more conservative behavior, mainly reflecting the phytoplankton distribution. Contrary to expectation, minimal values of bacterial productivity were not observed in November–December but in June. In fact, in November–December, the deep zone near the mouth showed the highest values of bacterial activity. At the upper stations, the highest values were observed in October. The relatively high values of bacterial production during the cold rainy season suggest that allochthonous substrates leached out from the surroundings by rain controlled the distribution of bacterial activity in the estuarine system. The substantial decrease in salinity during the rainy season negatively affected bacterial productivity, namely in the marine zone, where water column was highly stratified. Salinity seems to play an indirect role in the regulation of estuarine bacteria because there are different bacterial communities adapted to a wide salinity range.     

Proportion of prokaryotes enumerated as viruses by epifluorescence microscopy

It is well known that there are prokaryotes small in size (e.g. ultra-microprokaryotes) that pass through a 0.2-μm filter. As bacterial and viral abundances are determined by epifluorescence microscopy and the differentiation between them is based on particle size, some bacteria can be erroneously enumerated as viruses, namely in marine waters where bacteria are small. However, there is no information on the proportion of prokaryotes that could be misidentified as viruses by epifluorescence microscopy. In this work, we assessed, in water samples collected in the estuarine system Ria de Aveiro (Portugal), the proportion of prokaryotes that could be counted as viruses by the current widespread epifluorescence microscopy and, for the first time, by fluorescence in situ hybridization (FISH). The total number of particles was determined on membranes of 0.2 and 0.02 μm after staining with 4′,6-diamidino-2-phenylindole (DAPI), and the number of prokaryotes (Bacteria and Archaea) was determined by FISH for both pore size membranes. The results show that, in the marine zone of the estuarine system, 28 % of particles enumerated as virus-like particles were prokaryotes, but, in the brackish water zone, only 13 % of the particles counted as viruses were actually prokaryotic cells. Epifluorescence microscopy overestimates viral abundance, and also the ratio viruses:prokaryotes, and this error must be taken into consideration because it can vary significantly within a system. In fact, in the marine zone of an estuarine system, the overestimation of viral abundance can be twice as high as in the brackish water zone.     

Relation between bacterial activity in the surface microlayer and estuarine hydrodynamics

Bacterial communities of the surface microlayer (SML) of the estuary Ria de Aveiro (Portugal) were characterized in terms of abundance and activity during a 2-year survey at two sites with distinct hydrodynamic properties (marine and brackish water zones). The hydrodynamic conditions were simulated using a bidimensional numerical model and related to the microbiological observations. The pattern of variation of bacterial biomass productivity (BBP) was distinct between the two sampling sites. At the outer site, BBP was significantly lower at the SML, whereas at the inner site, it was significantly enhanced at the SML. Although the total bacterial abundance was similar in the SML and underlying water (UW), the fraction of cells attached to particles was significantly higher at the SML (two to three times). The integration of microbiological results with environmental and hydrological variables shows that strong currents in the marine zone promote the vertical mixing, inhibiting the establishment of an SML bacterial community distinct from that of UW. In contrast, in the brackish water zone, lower current velocities provide conditions for enhancing the bacterial activity in the enriched SML. Estuarine dynamics influence the distribution and activity of microorganisms at the SML and in the water column, with anticipated impacts for the carbon cycle in the estuarine environment.     

Is bacterioplankton production in the Ria de Aveiro influenced by salt marshes and bed sediment?

The contribution of potential export of materials from bottom sedimentsand salt marshes into the water column of a shallow estuarine system of Ria deAveiro to the observed high bacterial productivity in the mid section of thisestuary was evaluated. Vertical profiles of physical, chemical and bacterialvariables were studied in the marine and brackish water zones, and oftransversal profiles in the brackish zone only. Although the concentrations ofseston (17–241 mg l^–1), particulate organiccarbon (3–15.5 mg l^–1) and chlorophyll(1.2–7.0 g l^–1) varied widely, thevertical and transversal profiles were without much variation. Total bacterialnumber (0.2–8.5 × 10⁹ cellsl^–1) and the number of particle-attached bacteria(0.02–2.50 × 10⁹ cellsl^–1)along vertical and transversal profiles did not differ much, but the rate ofbacterial production (0.05–14.2 g C l^–1h^–1) and dissolved organic carbon concentration(6.0–69.2 mg l^–1) were frequently highernear the salt marsh margin at the brackish water transect. The increase inproductivity could not be associated with runoff of particulate matter butcoincided with the inputs of dissolved organic carbon. The results of verticaland transversal profiles point to a minor role of particulate matter additionsfrom the salt marsh area or from bed sediments.     

Influence of incubation conditions on bacterial production estimates in an estuarine system

This study aimed to assess the influence of incubation conditions in the determination of bacterial production (BP). In order to achieve that goal, experimental setups were performed in situ and in the laboratory under both dark and light conditions. To test spatial and seasonal variations and the different natural light exposure of microorganisms, sampling was performed in two distinct zones of the estuary Ria de Aveiro (Portugal), typifying the marine and brackish water zones of the estuarine system. Denaturing gradient gel electrophoresis analysis of 16S rRNA gene fragments was used to monitor possible alterations in bacterial community composition induced by the incubation conditions. The results showed that BP determined in situ conditions significantly differed from in the laboratory. In the marine zone, a defined pattern of variation was detected, with consistent higher values of BP in laboratory dark conditions. This trend was not present in the brackish water zone. The seasonal and spatial variability of BP observed in field incubations was related to the physical–chemical proprieties of the water column, irradiance levels and the original community composition. The metabolic active profiles of bacteria were substantially different in the several incubation conditions, suggesting that methodological procedure influences the bacterial community composition, and the values of BP reported for aquatic ecosystems could be quite different from the real ones. In the light of these results, we suggest that BP determinations should be conducted under in situ conditions. However, due to execution limitations, BP needs to be frequently determined in the laboratory, and in this case, dark incubations provide more approximate values. This is the method routinely used, and although this incubation condition can cause stimulation of BP, the structure of the bacterial community is more similar to the one obtained with the in situ incubations.     

Response of Bacterial Metabolic Activity to Riverine Dissolved Organic Carbon and Exogenous Viruses in Estuarine and Coastal Waters: Implications for CO2 Emission

A cross-transplant experiment between estuarine water and seawater was conducted to examine the response of bacterial metabolic activity to riverine dissolved organic carbon (DOC) input under virus-rich and virus-free conditions, as well as to exogenous viruses. Riverine DOC input increased bacterial production significantly, but not bacterial respiration (BR) because of its high lability. The bioavailable riverine DOC influenced bulk bacterial respiration in two contrasting ways; it enhanced the bulk BR by stimulating bacterial growth, but simultaneously reduced the cell-specific BR due to its high lability. As a result, there was little stimulation of the bulk BR by riverine DOC. This might be partly responsible for lower CO₂ degassing fluxes in estuaries receiving high sewage-DOC that is highly labile. Viruses restricted microbial decomposition of riverine DOC dramatically by repressing the growth of metabolically active bacteria. Bacterial carbon demand in the presence of viruses only accounted for 7–12% of that in the absence of viruses. Consequently, a large fraction of riverine DOC was likely transported offshore to the shelf. In addition, marine bacteria and estuarine bacteria responded distinctly to exogenous viruses. Marine viruses were able to infect estuarine bacteria, but not as efficiently as estuarine viruses, while estuarine viruses infected marine bacteria as efficiently as marine viruses. We speculate that the rapid changes in the viral community due to freshwater input destroyed the existing bacteria-virus relationship, which would change the bacterial community composition and affect the bacterial metabolic activity and carbon cycling in this estuary.     

Microbial biomass and productivity in seagrass beds

Different methods for measuring the rates of processes mediated by bacteria in sediments and the rates of bacterial cell production have been compared. In addition, net production of the seagrass Zostera capricorni and bacterial production have been compared and some interrelationships with the nitrogen cycle discussed. Seagrass productivity was estimated by measuring the plastochrone interval using a leaf stapling technique. The average productivity over four seasons was 1.28 +/- 0.28 g C m-2 day-1 (mean +/- standard deviation, n = 4). Bacterial productivity was measured five times throughout a year using the rate of tritiated thymidine incorporated into DNA. Average values were 33 +/- 12 mg C m-2 day-1 for sediment and 23 +/- 4 for water column (n = 5). Spatial variability between samples was greater than seasonal variation for both seagrass productivity and bacterial productivity. On one occasion, bacterial productivity was measured using the rate of 32P incorporated into phospholipid. The values were comparable to those obtained with tritiated thymidine. The rate of sulfate reduction was 10 mmol SO4(-2) m-2 day-1. The rate of methanogenesis was low, being 5.6 mg CH4 produced m-2 day-1. A comparison of C flux measured using rates of sulfate reduction and DNA synthesis indicated that anaerobic processes were predominant in these sediments. An analysis of microbial biomass and community structure, using techniques of phospholipid analysis, showed that bacteria were predominant members of the microbial biomass and that of these, strictly anaerobic bacteria were the main components. Ammonia concentration in interstitial water varied from 23 to 71 micromoles. Estimates of the amount of ammonia required by seagrass showed that the ammonia would turn over about once per day. Rapid recycling of nitrogen by bacteria and bacterial grazers is probably important.     

Dynamics of nutrients and faecal bacteria in a macrotidal estuary,the Bay of Somme (France)

A stratified methodology for water sampling on tidal flats was adopted in 1988 and 1989 in the Bay of Somme. Analyses of nutrients, particulate matter and faecal germs showed the poor mixing of fresh and marine water and the weakness of stratification of the water column. Freshwater is pushed by marine water to the inner reaches of the bay and there are only a few lenses with true estuarine characteristics. In 1990, water was sampled simultaneously on the Somme river, the tidal flats and in the open sea, in order to point out estuarine gradients of several physical and chemical parameters and their evolution during a tidal cycle. The role of continental inputs was confirmed for faecal pollution, nitrate (20–25 mg l⁻¹), nitrite and silicate. The importance of ammonium excreted by the estuarine benthic populations was highlighted. High concentrations of continental chlorophyll (450 mg m⁻³) were also measured and contribute, with nitrates and ammonium, to eutrophication in the Bay of Somme. Pollution of the southern part of the bay by marine waters was regularly observed during the flow, raising doubts about the purifying capacity of sea-water and the conservation of faecal bacteria. A regular survey of fresh-water inputs and sea-water quality, offshore and within the bay, is considered to enable estimation of their respective influences in eutrophication processes in the Bay of Somme.     

The effect of temperature and algal biomass on bacterial production and specific growth rate in freshwater and marine habitats

We analyzed heterotrophic, pelagic bacterial production and specific growth rate data from 57 studies conducted in fresh, marine and estuarine/coastal waters. Strong positive relationships were identified between 1) bacterial production and bacterial abundance and 2) bacterial production and algal biomass. The relationship between bacterial production and bacterial abundance was improved by also considering water temperature. The analysis of covariance model revealed consistent differences between fresh, marine and estuarine/coastal waters, with production consistently high in estuarine/coastal environments. The log-linear regression coefficient of abundance was not significantly different from 1.00, and this linear relationship permitted the use of specific growth rate (SGR in day⁻¹) as a dependent variable. A strong relationship was identified between specific growth rate and temperature. This relationship differed slightly across the three habitats. A substantial portion of the residual variation from this relationship was accounted for by algal biomass, including the difference between marine and estuarine/coastal habitats. A small but significant difference between the fresh- and saltwater habitats remained. No significant difference between the chlorophyll effect in different habitats was identified. The model of SGR against temperature and chlorophyll was much weaker for freshwater than for marine environments. For a small subset of the data set, mean cell volume accounted for some of the residual variation in SGR. Pronounced seasonality, fluctuations in nutrient quality, and variation of the grazing environment may contribute to the unexplained variation in specific growth.     

Seasonal change in the proportion of bacterial and phytoplankton production along a salinity gradient in a shallow estuary

We intended to evaluate the relative contribution of primary production versus allochthonous carbon in the production of bacterial biomass in a mesotrophic estuary. Different spatial and temporal ranges were observed in the values of bacterioplankton biomass (31–273 g C l^–1) and production (0.1–16.0 g C l^–1 h^–1, 1.5–36.8 mg C m^–2 h^–1) as well as in phytoplankton abundance (50–1700 g C l^–1) and primary production (0.1–512.9 g C l^–1 h^–1, 1.5–512.9 mg C m^–2 h^–1). Bacterial specific growth rate (0.10–1.68 d^–1) during the year did not fluctuate as much as phytoplankton specific growth rate (0.02–0.74 d^–1). Along the salinity gradient and towards the inner estuary, bacterio- and phytoplankton biomass and production increased steadily both in the warm and cold seasons. The maximum geographical increase observed in these variables was 12 times more for the bacterial community and 8 times more for the phytoplankton community. The warm to cold season ratios of the biological variables varied geographically and according to these variables. The increase at the warm season achieved its maximum in the biomass production, particularly in the marine zone and at high tide (20 and 112 times higher in bacterial and phytoplankton production, respectively). The seasonal variation in specific growth rate was most noticeable in phytoplankton, with seasonal ratios of 3–26. The bacterial community of the marine zone responded positively – generating seasonal ratios of 1–13 in bacterial specific growth rate – to the strong warm season increment in phytoplankton growth rate in this zone. In the brackish water zone where even during the warm season allochthonous carbon accounted for 41% (on average) of the bacterial carbon demand, the seasonal ratio of bacterial specific growth rate varied from about 1 to 2. During the warm season, an average of 21% of the primary production was potentially sufficient to support the whole bacterial production. During the cold months, however, the total primary production would be either required or even insufficient to support bacterial production. The estuary turned then into a mostly heterotrophic system. However, the calculated annual production of biomass by bacterio- and phytoplankton in the whole ecosystem showed that auto- and heterotrophic production was balanced in this estuary.     

Comparison of bacterial production in sediments, epiphyton and the pelagic zone of a lowland river

1. The microbial metabolism of organic matter in rivers has received little study compared with that of small streams. Therefore, we investigated the rate and location of bacterial production in a sixth‐order lowland river (Spree, Germany). To estimate the contribution of various habitats (sediments, epiphyton, and the pelagic zone) to total bacterial production, we quantified the contribution of these habitats to areal production by bacteria. 2. Large areas of the river bottom were characterized by loose and shifting sands of relatively homogenous particle size distribution. Aquatic macrophytes grew on 40% of the river bottom. Leaf areas of 2.8 m² m^?2 river bottom were found in a 6.6 km river stretch. 3. The epiphyton supported a bacterial production of 5–58 ng C cm^?2 h^?1. Bacterial production in the pelagic zone was 0.9–3.9 μg C L^?1 h^?1, and abundance was 4.0–7.8 × 10⁹ cells L^?1. Bacterial production in the uppermost 2 cm of sediments ranged from 1 to 8 μg C cm^?3 h^?1, and abundance from 0.84 to 6.7 × 10⁹ cells cm^?3. Bacteria were larger and more active in sediments than in the pelagic zone. 4. In spite of relatively low macrophyte abundance, areal production by bacteria in the pelagic zone was only slightly higher than in the epiphyton. Bacterial biomass in the uppermost 2 cm of sediments exceeded pelagic biomass by factors of 6–22, and sedimentary bacterial production was 17–35 times higher than in the overlying water column. 5. On a square meter basis, total bacterial production in the Spree was clearly higher than primary productivity. Thus, the lowland river Spree is a heterotrophic system with benthic processes dominating. Therefore, sedimentary and epiphytic bacterial productivity form important components of ecosystem carbon metabolism in rivers and shallow lakes. 6. The sediments are focal sites of microbial degradation of organic carbon in a sand‐bottomed lowland river. The presence of a lowland river section within a river continuum probably greatly changes the geochemical fluxes within the river network. This implies that current concepts of longitudinal biogeochemical relationships within river systems have to be revised.     

Nitrate Regeneration Coupled to Degradation of Different Size Fractions of DON by the Picoplankton in the Elbe Estuary

Bacterial conversion of high (HMW > 3,000 Da) and low (LMW < 3,000 Da) molecular weight DON (dissolved organic nitrogen) was studied along the freshwater section of the Elbe estuary during the summer of 1997. Indigenous populations of picoplankton were incubated in a flow-through chamber that allowed a constant exchange of sterile, filtered Elbe water as the culture medium for the microorganisms, which remained within the chamber. Nitrogen conversion was followed by changes in the concentrations of total and low molecular weight DON and dissolved inorganic nitrogen compounds, the uptake of O2, and bacterial growth. Along the Elbe estuary, total DON concentrations varied between 0.69 and 1.1 mg N L-1, of which between 64 and 79% was LMW-DON. Ammonium was a minor nutrient present in the Elbe at concentrations below 0.26 mg N L-1. During incubation in the laboratory between 27 and 64% of the LMW-DON was consumed at rates ranging from 24 to 51 g N L-1 h-1. HMW-DON was used only when the degradable LMW-DON pool became exhausted and accounted for between 60 and 100% of the HMW-DON. This produced an increase in the DON consumption rate between 43 and 79 g N L-1 h-1. Nitrification rates were independent of the external ammonium concentration until it decreased to below 1 g N-NH4 L-1. Most of the N in the nitrification process originated as NH4 regenerated from DON. Between 75 and 100% of the LMW-DON and ammonium consumed was rapidly converted to nitrate. This amount decreased to between 65 and 85% when HMW-DON was consumed in addition to the LMW-DON. DON and ammonium consumption supported nitrification rates up to 71 g N L-1 h-1. The amount of DOC (dissolved organic carbon) degraded was not equivalent to the C:N ratio of the total dissolved organic matter. Calculations based on oxygen consumption for respiration and ammonium regeneration revealed that the substrates used during the incubations contained C:N at ratios of about 3:1. These results suggest that the nitrogen-rich compounds had been removed from the dissolved organic matter and subsequently consumed by bacteria, while the carbon skeleton remained mostly unaffected by the degradation processes.     

Bacterial activity and production in near-surface estuarine and freshwater sediments

Abstract: Two indices of bacterial production, thymidine incorporation and the frequency of divided and dividing cells were measured, along with a suite of measurements of aerobic and anaerobic bacterial activity, to investigate the relationship between bacterial cell production and organic carbon mineralisation at three different sediment sites: a sheltered intertidal estuarine mudflat (Kingoodie Bay), a riverside mudbank (Ashleworth Quay) and an intertidal mudflat in a hydraulically dynamic estuary (Aust Warth). Organic carbon mineralisation was dominated by anaerobic processes at all three sites: sulfate reduction at the two estuarine sites (equivalent to 76% and 61% of oxygen uptake) and methanogenesis at the freshwater site (56%). Although all three sites had similar bacterial population sizes, activities in Kingoodie Bay were 2–3 times higher than at Aust Warth or Ashleworth Quay. Thymidine incorporation rates and Numbers of Dividing and Divided Cells correlated strongly at all three sites. Thymidine incorporation rates were spatially uncoupled from zones of principal anaerobic activity, providing in situ evidence that sulfate-reducing bacteria and methanogens do not incorporate radiolabelled thymidine into DNA during growth. Cell yield was lower in the anaerobic zone, as subsurface peaks in anaerobic mineralisation were not matched by increases in bacterial productivity. However, as anaerobic degradation processes were so dominant, anaerobic productivity still accounted for the majority of cell production.     

Numérations bactériennes dans le lagon du grand Cul-de-Sac marin et sa zone côtière (guadeloupe)

Sixty sea-water and marine sediment samples have been collected in the clear and dredged coral waters of a lagoon in Guadeloupe. Total counts of 10 to 100 living bacteria were obtained by counting colonies on membranes after filtration and pour plate count techniques in the clear water coral zones. Living bacterial populations ranging from 2 × 10³ to 20 × 10³/ml of water were detected in the dredged coral zone. Suspended sandy particulate matter resulting from dredging seems to be the direct cause of the abnormal increase in bacteria. The mean values were ≈ 10³ living bacteria/ml for the coastal sea water and 10⁴ for the brackish waters of channels in the mangrove swamp. It seems that the bacterial sediment population has been under-estimated.     

A note on the enumeration of manganese-oxidizing bacteria in estuarine water and sediment samples

V ojak , P.W.L., E dwards , C. & J ones , M.V. 1985. A note on the enumeration of manganese-oxidizing bacteria in estuarine water and sediment samples. Journal at Applied Bacteriology 59, 375–379.
Media for the enumeration of manganese-oxidizing bacteria in estuarine water and sediment samples were compared. A peptone/yeast extract medium containing manganese sulphate and 30% (v/v) sea salts solution gave the highest percentage of manganese-oxidizers and high total viable counts. A survey of estuarine (River Tamar) and marine (English Channel) sites indicated that manganese-oxidizing bacteria comprise a significant but variable proportion (11–85%) of the total bacterial count.     

Bacterial secondary production on vascular plant detritus: relationships to detritus composition and degradation rate.

Bacterial production at the expense of vascular plant detritus was measured for three emergent plant species (Juncus effusus, Panicum hemitomon, and Typha latifolia) degrading in the littoral zone of a thermally impacted lake. Bacterial secondary production, measured as tritiated thymidine incorporation into DNA, ranged from 0.01 to 0.81 microgram of bacterial C mg of detritus-1 day-1. The three plant species differed with respect to the amount of bacterial productivity they supported per milligram of detritus, in accordance with the predicted biodegradability of the plant material based on initial nitrogen content, lignin content, and C/N ratio. Bacterial production also varied throughout the 22 weeks of in situ decomposition and was positively related to the nitrogen content and lignin content of the remaining detritus, as well as to the temperature of the lake water. Over time, production was negatively related to the C/N ratio and cellulose content of the degrading plant material. Bacterial production on degrading plant material was also calculated on the basis of plant surface area and ranged from 0.17 to 1.98 micrograms of bacterial C cm-2 day-1. Surface area-based calculations did not correlate well with either initial plant composition or changing composition of the remaining detritus during decomposition. The rate of bacterial detritus degradation, calculated from measured production of surface-attached bacteria, was much lower than the actual rate of weight loss of plant material. This discrepancy may be attributable to the importance of nonbacterial organisms in the degradation and loss of plant material from litterbags or to the microbially mediated solubilization of particulate material prior to bacterial utilization, or both.