Heterotrophic bacterioplankton production and grazing mortality rates in an Ethiopian rift-valley lake (Awassa)

SUMMARY. 1. Heterotrophic bacterioplankton growth and production rates were estimated in a tropical lake by various methods. Mean growth rates, determined by tritiated thymidine incoporation into DNA, frequency of dividing cells and increase in cell density varied between 0.013 and 0.014 (with a range of 0.006–0.026) h⁻¹ corresponding to bacterial production of 1.16–1.22 (0.34–3.63) mg C m⁻³ h⁻¹.
2. Heterotrophic bacterial production estimated from oxygen and inorganic carbon consumption in the dark were compared with these values. The oxygen method gave similar results, while values from dark carbon uptake were as much as 2.5 times higher.
3. Although the different estimates of rates of bacterial production showed different patterns, the existence of spatial (vertical) and temporal (diel and seasonal) variation was demonstrated. Bacterial production was 13–41% of the net primary production and 10–30% of gross primary production.
4. Bacterial grazing mortality rate was estimated from size-fractionation and metablic inhibitor experiments. Average grazing rates were between 0.34 and 3.77 mg C m⁻³ h⁻¹ corresponding to 76–120% of the mean bacterial production rate. Organisms 1–12 μm in size, possibly mainly ciliates. were implicated as important bacterial grazers.     

Covariation of stream community structure and biomass of algae, invertebrates and fish with forest cover at multiple spatial scales

1. To evaluate the spatial extent of the effects of forest cover on stream ecosystems, we measured algae, invertebrate, and fish biomass and invertebrate and fish community structure in 38 small first- to third-order streams in the National Capital Region of Canada along with forest cover at different spatial scales.
2. We considered 55 spatial scales of forest cover including several buffer widths (doubling 10–320 m) and lengths (doubling 10–1280 m, entire riparian distance upstream from sampling area) and entire catchments to determine which spatial scale maximized the correlation with biomass and metrics of community structure.
3. The proportion of variability in biomass and structural metrics explained by forest cover generally increased with increasing scale, suggesting that catchment-wide disturbances are the most influential determinants of benthic and fish communities.
4. Catchment forest cover explained more variation in algal (adjusted r ²   =   0.54), invertebrate (adjusted r ²   =   0.51) and fish (adjusted r ²   =   0.33) biomass than structural metrics of invertebrates and fish (adjusted r ²   =   0.08–0.27).
5. Analyses of the partial effects of forest cover at three scales (reach, riparian and the entire catchment) on biomass and community structure metrics identified catchment and reach scales as being most influential and never detected a significant partial effect of forest cover at the riparian scale.
6. These results suggest that maintenance or protection of reach and riparian buffers alone will not sufficiently protect stream function and structure from catchment-wide impacts.     

Alterations in the major heterotrophic bacterial populations isolated from a still bottled mineral water

M orais , P.V. & D a C osta , M.S. 1990. Alterations in the major heterotrophic bacterial populations isolated from a. still bottled mineral water. Journal of Applied Bacteriology 69 , 750–757.
The heterotrophic bacterial population of a bottled mineral water stored in returnable glass bottles and in polyvinyl chloride (PVC) bottles at room temperature was studied over 9–12 months. The plate counts in R₂A medium incubated at 22 and 37C were low initially, increasing to 10⁴-10⁵ cfu/ml within a few days of bottling. The number of bacteria recovered at 22C from PVC bottles was fairly constant during the storage period, but the population isolated at 37C decreased markedly after storage for 1 year. The major components of the population were Pseudomonas strains, one of which was identified as Pseudomonas vesicularis . Major changes took place during storage; two groups of bacteria (B and C) were dominant initially, but during the latter period of storage other groups (F, G and H) increased in number.     

The distribution of some freshwater planktonic bacteria in two stratified eutrophic lakes

SUMMARY. Changes in bacterial populations and certain physical and chemical variables in Esthwaite Water between June and September 1975 were studied and compared with results obtained from 1972 to 1974 in the hypolimnia of Blelham Tarn and the Lund tubes. The counts of total bacteria ranged between 1 and 7 × 10⁶ml⁻¹ and were highest in the anoxic hypolimnion. The bacterial genera examined in more detail constituted only a small percentage of this count and included Ochrobium (10⁴ml⁻¹), Naumanniella (10³ml⁻¹), Leptothrix (10²ml⁻¹), Planctomyces (10³ml⁻¹), and Metallogenium (10²ml⁻¹). The iron bacteria appear to grow best in the oxycline where there was not only sufficient oxygen for aerobic growth but also a plentiful supply of reduced iron. Planctomyces numbers increased as the thermocline became depressed in September. The results from Blelham Tarn might be interpreted as further evidence of growth by iron bacteria in the absence of dissolved oxygen, but other explanations are possible. Examination of the results by multiple regression analysis showed that it was possible to explain a significant proportion of the bacterial variation (with the notable exception of the Planctomyces counts) in spite of considerable intercorrelation of the regressor variables.     

Single-cell vs. bulk activity properties of coastal bacterioplankton over an annual cycle in a temperate ecosystem

The connections between single-cell activity properties of heterotrophic planktonic bacteria and whole community metabolism are still poorly understood. Here, we show flow cytometry single-cell analysis of membrane-intact (live), high nucleic acid (HNA) content and actively respiring (CTC+) bacteria with samples collected monthly during 2006 in northern Spain coastal waters. Bulk activity was assessed by measuring ³H-Leucine incorporation and specific growth rates. Consistently, different single-cell relative abundances were found, with 60–100% for live, 30–84% for HNA and 0.2–12% for CTC+ cells. Leucine incorporation rates (2–153 pmol L⁻¹ h⁻¹), specific growth rates (0.01–0.29 day⁻¹) and the total and relative abundances of the three single-cell groups showed marked seasonal patterns. Distinct depth distributions during summer stratification and different relations with temperature, chlorophyll and bacterial biovolume suggest the existence of different controlling factors on each single-cell property. Pooled leucine incorporation rates were similarly correlated with the abundance of all physiological groups, while specific growth rates were only substantially explained by the percentage of CTC+ cells. However, the ability to reduce CTC proved notably better than the other two single-cell properties at predicting bacterial bulk rates within seasons, suggesting a tight linkage between bacterial individual respiration and biomass production at the community level.     

Use of flow cytometry for enumeration of Mycoplasma mycoides subsp. mycoides large-colony type in broth medium

Aims:  The potential of using flow cytometry (FC) in combination with a fluorescent dye (SYBR green-I) for rapidly estimating Mycoplasma mycoides subSPS. mycoides large-colony type (MmmLC) in broth culture was examined.
Methods and Results:  The FC analysis was performed by staining the MmmLC cells with a fluorescent dye, SYBR green-I (SYBR), and the results were compared with plate count method (colony forming units, – CFUs). There was a good correlation (linear regression, r ² = 0·93) between mycoplasma counts determined by FC (cells ml⁻¹) and by traditional plate count method (CFU ml⁻¹). The lowest bacterial concentration detected by FC and traditional plate count was of the order of 10⁴ cells ml⁻¹ and 10³ CFU ml⁻¹, respectively. FC method allowed results in 20–30 min, whereas at least 24 h were necessary to obtain results with the traditional plate count method (CFU).
Conclusion:  Growth rates of MmmLC in broth medium determined by FC were highly reproducible and correlated well with mycoplasma counts assessed by the plate count method.
Significance and Impact of the Study:  These findings suggest that FC could be a good alternative to replace other time-consuming techniques that are currently used to enumerate mycoplasma in broth medium, such as plate count method (CFU).     

Bacterivory by starved marine heterotrophic nanoflagellates of two species which feed differently, estimated by uptake of dual radioactive-labelled bacteria

Abstract: The rates of ingestion of bacteria and of accumulation of bacterial biomass by hungry Pteridomonas danica and Paraphysomonas imperforata were measured using dual radioactive-labelled bacteria in experiments lasting 4–8 h. Pteridomonas continuously consumed 4–5 bacteria h⁻¹ throughout experiments lasting 8 h, irrespective of bacterial concentration above a threshold of about 5 × 10⁵ bacteria ml⁻¹, and continued to catch bacteria even below this density. The clearance rate of about 1 nl cell⁻¹ h⁻¹ at higher bacterial concentrations increased three or four times as bacterial numbers fell. Paraphysomonas cells, with only half the biomass of Pteridomonas , ingested up to 10 bacteria h⁻¹ at high bacterial concentrations, and gradually reduced the feeding rate, effectively ceasing to feed at 10⁶ bacteria ml⁻¹; their initial clearance rate of 1–2.5 nl cell⁻¹ h⁻¹ subsequently fell as low as 0.1 nl cell⁻¹ h⁻¹. Estimation of feeding rate by extrapolation from short-term experiments on such flagellates requires extreme caution. These flagellates, starved to levels typical of the natural environment, accumulated ingested bacterial biomass at an efficiency of between 16 and 21%, indicating that in nature they would recycle 80% or more of the nutrients contained in their food.     

Post-processing microflora and the shelf stability of gari marketed in Port Harcourt

Gari was examined for its post-processing microbial content. Aerobic mesophilic bacteria and fungi were isolated from all samples. The total viable bacterial counts ranged from 2.0 × 10² to 8.0 × 10⁴ cfu/g. Fungal counts ranged from 1.0 × 10² to 1.5 × 10⁴ cfu/g. The total viable counts of fresh samples were much lower than those of market and packaged samples. Bacillus, Micrococcus and Proteus spp. were the bacteria isolated, Aspergillus niger, Aspergillus flavus and Penicillium spp. the fungi. Food borne parasites and pathogens such as Staph. aureus and Clostridium perfringens were not found. The gari samples were quite stable, having a shelf life of 3–6 months. The water activities of the samples ranged from 0.52 to 0.68. Based on the microbial counts of the samples, the critical upper limit for the safety of gari was set at 10⁴ cfu/g dry sample.     

The bacterial population of a blanket peat

The number of aerobic bacteria in a blanket peat decreased with depth from 26 times 10⁶/g dry peat in the surface layers to 0.5 times 10⁶/g dry peat at 30–40 cm down the profile, thereafter remaining roughly constant. Obligate psychrophiles comprised <2.5% of this population. Anaerobes were most numerous, 9 times 10⁶/g dry peat at 6–10 cm depth, decreasing to 0.5 times 10⁶/g at 20–30 cm. Calculations indicated that these counts, 10³–10⁴-fold lower than the direct counts, substantially underestimated the active microbial population. Gram negative rods, the predominant aerobes in the surface layers, were replaced by unidentified Bacillus strains at 10–20 cm depth but became increasingly more numerous further down the profile. The Gram negative rods were the most numerous organisms/m² but the Bacillus strains, one third of which were present as spores, made the largest contribution to the biomass/m². Gram positive cocci, Arthrobacter and, infrequently, Nocardia were also isolated. Actinomyces -like forms were the predominant obligate anaerobes and were approximately three times more numerous than clostridia and a curved Gram negative rod.     

Bacterial production measured by leucine and thymidine incorporation rates in French lakes

1. Production of heterotrophic bacterioplankton was estimated monthly by the tritiated thymidine and leucine incorporation methods during the draining and filling of the mesotrophic Lake Pareloup (over a 2.5-years sampling program).
2. Rates of ³H-leucine (leu) and ³H-thymidine (thy _DNA) incorporation generally paralleled each other but the ratio of leu/thy _DNA incorporation rates was higher for the draining period (34.5 mean) than during and after filling (11.5 mean).
3. After draining, the highest ratios were observed during periods of low temperature and low bacterial specific activity, while DNA labeling by ³H-thymidine was reduced. However, bacterial production estimates obtained by ³H-leucine (BPL) and ³H-thymidine (BPT) incorporation methods were generally well correlated and the average BPL/BPT ratio was equal to 0.78.
4. In addition, both methods were applied during a diel cycle in three lakes of different trophic status. An increase of leu/thy _DNA incorporation rates was noted from the oligotrophic to the eutrophic system. In the absence of Cyanobacteria, BPL and BPT values were quite concordant on average.
5. In situations of unbalanced growth, BPL and BPT values can diverge but when considered over a sufficient period of time they were found to be in agreement.     

Real-time quantification of Pseudomonas fluorescens cell removal from glass surfaces due to bacteriophage varphiS1 application

Aims:  To study the efficacy of the lytic phage φS1 in eliminating Pseudomonas fluorescens in the early stage of biofilm formation, using an in situ and real time methodology for cell quantification.
Methods and Results:  Cell adhesion and phage infection studies were carried out in a parallel plate flow chamber under laminar conditions. Cells were allowed to adhere until reaching 1·7–1·8 × 10⁶ cells cm⁻² and phage infection was performed with two different phage concentrations (2 × 10⁹ PFU ml⁻¹ and 1 × 10¹⁰ PFU ml⁻¹). Phage concentration clearly affects the speed of infection. The less concentrated phage solution promoted a three times slower rate of cell removal but did not affect the overall percentage of cell removal. In fact, after a longer infection period the less concentrated phage solution reached the same 93% cell removal value.
Conclusions:  Phages are efficient in the eradication of bacterial cells at the early stage of biofilm formation and their presence at the surface did not allow bacterial recolonization of the surface.
Significance and Impact of the Study:  To date, no published studies have been made concerning in situ and real time quantification of cell removal from surfaces due to phage action.     

Environmental factors affecting the occurrence of mycobacteria in brook sediments

The occurrence of mycobacteria was studied in aerobic brook sediments from 39 drainage areas in Finland. The culturable counts of mycobacteria were related to climatic conditions, characteristics of the drainage area, chemical characteristics of the sediment and water, culturable counts of other heterotrophic bacteria, and microbial respiration rate in the sediment. The counts of mycobacteria varied from 1·1 × 10² to 1·5 × 10⁴ cfu g⁻¹ dry weight of sediment. They correlated positively with the proportion of the drainage area consisting of peatland, total content of C, content of Pb, microbial respiration rate in the sediment, and chemical oxygen demand of the water. The correlations of the mycobacterial counts with pH of sediment and alkalinity of water were negative. The results of the present sediment study and of the forest soil study published earlier strongly suggest that an increase in acidity increases the counts of mycobacteria and decreases the counts and activity of other heterotrophic bacteria. Mycobacterial counts were more than 100 times higher (per dry weight) in forest soils with pH 3·5–4·3 than in sediments with pH 4·5–6·3.     

The relation between bacterial carbon and dissolved humic compounds in oligotrophic lakes

Abstract The mean annual biomass of planktonic bacteria showed large variations both within and between lakes. The lowest bacterial biomass was found in acidified lakes (7.8–12.1 μg C · 1⁻¹), and tended to increase with increasing water colour (up to 44.1 μg C · 1⁻¹). The highest recorded bacterial biomass was 138 μg C · 1⁻¹. The mean annual bacterial biomass equalled 23–45% of the algal biomass. Zooplankton biomass was high, compared to algal biomass (40–50%). Multiple regression analysis of 10 variables showed a strong positive correlation between bacterial biomass and humic content ( r = 0.74, P < 0.001), while other parameters, except pH, showed no correlation. The observation thus strongly supports the role of humic compounds in aquatic secondary production.     

Seasonal heterotrophic flagellate and bacterial plankton dynamics in a large oligotrophic lake– Loch Ness, Scotland

1. Bacterial production in the 0–30 m water column of Loch Ness was measured using a dual labelling procedure with [³H] thymidine and [¹⁴C] leucine between May 1993 and June 1994. In most cases the uptake of the two labels did not covary, suggesting unbalanced growth. Rates of bacterial production varied from undetectable to 46.2 μg C l^–1 day^–1. Highest production coincided with the period of highest primary production, but carbon derived from this source was insufficient to meet the bacterial carbon demand, which was met by allochthonous humic inputs to the system.
2. Heterotrophic flagellate (HNAN) grazing rates, measured using fluorescently labelled bacteria, ranged between 10.3 and 24.5 bacteria cell^–1 day^–1 at temperatures between 5 and 15 °C. They removed up to 27% of the bacterial production per day.
3. Heterotrophic flagellate specific growth rates ranged from 0.043 to 0.093 h^–1 between 5 and 15 °C, giving generation times of 7.4–16.1 h.
4. bacterial and HNAN abundances were not coupled, but the highest HNAN grazing impact related to a time of high bacterial productivity.     

DEPTH DISTRIBUTIONS OF DNA DAMAGE IN ANTARCTIC MARINE PHYTO- AND BACTERIOPLANKTON EXPOSED TO SUMMERTIME UV RADIATION

During a survey from January to March 1998, the occurrence of UV-B radiation (UVBR)- induced DNA damage in Antarctic marine phytoplankton and bacterioplankton was investigated. Sampling was done in Ryder Bay, off the British base Rothera Station, 67°S, 68°W (British Antarctic Survey). Samples were taken regularly during the survey period at fixed depths, after which DNA damage was measured in various plankton size fractions (>10, 2–10, and 0.2–2 μm). Incident solar radiation was measured using spectroradiometry, whereas attenuation of biologically effective UVBR was studied using a DNA dosimeter. A diatom bloom was found in the bay during the research period, judging from microscopic observations and HPLC analyses of taxon-specific pigments. The high phytoplankton biomass likely caused strong attenuation of DNA effective UVBR (K_bd-eff). K_bd-eff values ranged from 0.83·m ^{− 1} at the peak of the bloom to 0.47·m ^{− 1} at the end of the season. UVBR-mediated DNA damage, as measured by cyclobutane pyrimidine dimer (CPD) abundance, was detected in all plankton size fractions. Highest levels were found in the smallest size fraction, mainly consisting of heterotrophic bacteria. Clear CPD depth profiles were found during mid-summer (January, beginning of February) with surface levels exceeding 100 CPDs per million nucleotides in the bacterioplankton fraction. At that time, melting of the continuously present shelf ice caused strong salinity gradients in the upper meters, thereby stimulating water column stabilization. At the end of February and beginning of March, this phenomenon was less pronounced or absent. At that time, DNA damage was homogeneously distributed over the first 10 m, ranging between 20 and 30 CPDs per million nucleotides for the smallest size fraction.     

Seasonal dynamics of free and attached heterotrophic nanoflagellates in an oligomesotrophic lake

1. The seasonal development of heterotrophic nanoflagellates (HNF), bacteria, rotiferans and crustacean zooplankton was studied in the epilimnion of Lake Pavin, an oligomesotrophic lake in the Massif Central of France.
2. HNF abundance varied from 0.1 to 2.5 × 10³ mL^–1. Free-living HNF reached their highest density in spring when the copepod Acanthodiaptomus denticornis dominated the metazooplankton. They were present in low numbers when rotifers and cladocerans were numerous.
3. Attached HNF, consisting of bicoecids and choanoflagellates, were fixed to large diatoms and to the colonial cyanobacterium Anabaena flos-aquae . The abundance of attached HNF was significantly correlated to bacterial abundance, which fluctuated between 1.1 and 2.7 × 10⁶ mL^–1. Highest abundance of these epiphytic protists was recorded when free-living heterotrophic nanoflagellates declined.
4. The comparison of the dynamics of heterotrophic nanoflagellates, bacteria, and the impact of zooplankton grazing suggested that prey abundance, the presence of suitable attachment sites and limited competition from the free-living forms were the main factors controlling the development of the epiphytic flagellate protists. In contrast, the low abundance of free-living forms during the period of rotiferan and cladoceran development suggests the prevalence of a top-down control by predation of the metazoopankton.     

Mixotrophic cryptophytes and their predators in the Dry Valley lakes of Antarctica

1. The ingestion rates of planktonic, mixotrophic cryptophytes in two perennially ice-covered Antarctic lakes in the McMurdo Dry Valleys, were investigated during the summer of 1997–1998.
2. In Lake Fryxell, which is meromictic, ingestion rates increased with depth in November and were highest in a cryptophyte maximum close to the chemocline. In Lake Hoare, which is unstratified and freshwater, there was no significant difference in ingestion rates with depth. In both lakes, the highest ingestion rates occurred in early summer, decreasing in December and January. Ingestion rates varied between 0.2 bacteria cell⁻¹ h⁻¹ and 3.6 bacteria cell⁻¹ h⁻¹.
3. During November, mixotrophic cryptophytes removed up to 13% of bacterial biomass day⁻¹ and had a greater grazing impact than heterotrophic nanoflagellates (HNAN). As summer progressed, the grazing impact of cryptophytes and HNAN became similar.
4. The maximum depth of cryptophytes in Lake Fryxell was predated by a population of the ciliate Plagiocampa. Plagiocampa had an ingestion rate of 0.13–0.19 cryptophytes cell⁻¹ h⁻¹. The grazing impact on the cryptophyte community was insignificant. However, the ciliate appeared to be indulging in temporary mixotrophy, sequestering the cryptophytes for a number of weeks before digesting them.
5. It is suggested that mixotrophy is an important survival strategy in the extreme lake ecosystems of the McMurdo Dry Valleys.     

Vertical distribution and abundance of invertebrates within the sandy substrate of a low-gradient headwater stream

SUMMARY. 1 The vertical distribution of invertebrates (>0.053 mm) was studied in a sandy-bottomed, first-order stream on the Coastal Plain of Virginia, U.S.A. Invertebrate species composition, abundance and bio-mass were determined monthly over one year at sediment depth intervals of 0–1, 1–5, 5–15,15–30 and 30–40 cm.
2. The subsurface community was numerically dominated by species of Chironomidae, Nematoda and Crustacea, while much of the biomass was due to early instars of several species of Trichoptera.
3. Invertebrate density and biomass decreased significantly with depth in the substrate (ANOVA; P <0.05). Annual mean density decreased from 1,346,844 individuals m⁻³ at the surface to 13,578 individuals m⁻³ at 15–30 cm. Annual mean biomass decreased from 66.30 g m⁻³ at the surface to 0.44 g m⁻³ at 15–30 cm.
4. Dissolved oxygen decreased markedly from the surface to the 5 cm depth in the substrate, anaerobic conditions often occurring below 10 cm. Density and biomass both showed a significant positive relationship with dissolved oxygen concentration (Linear regression; P <0.05).
5. Physical forces were important in structuring the subsurface invertebrate community. Besides low dissolved oxygen concentration, sediment scouring resulting from storm discharge dramatically reduced density and biomass     

Bacterial microflora in the gastro-intestinal tract of Dover sole (Solea solea L.), with emphasis on the possible role of bacteria in the nutrition of the host

Abstract There was a progressive increase in the size of the aerobic heterotrophic bacterial populations along the gastro-intestinal tract of farmed Dover sole. Moreover, higher counts were recorded in juvenile than in adult animals. Thus, in juvenile fish, 5.2 × 10⁵, 8.0 × 10⁵ and 9.8 × 10⁶ aerobic heterotrophs/g were recovered from the stomach/foregut, midgut and hindgut/rectum, respectively. In adult fish, comparative samples revealed the presence of only 3.0 × 10⁴, 7.0 × 10⁴ and 2.3 × 10⁵ bacteria/g, respectively. There bacteria were equated with Acinetobacter, Alcaligenes , Enterobacteriaceae representatives, Flavobacterium, Micrococcus, Photobacterium, Staphylococcus and Vibrio . Of the compounds tested, many isolates, particularly those recovered from the hindgut/rectum, degraded p -nitrophenyl- β - N -acetylglucosaminide, chitin and collagen. Consequently, it is likely that such organisms may contribute to nutritional processes within Dover sole.     

Rates of sulfate reduction and thiosulfate consumption in a marine microbial mat

Abstract The sulfur cycle in a microbial mat was studied by determining viable counts of sulfate-reducing bacteria, chemolithoautotrophic sulfur bacteria and anoxygenic phototrophic bacteria. All three functional groups of sulfur bacteria revealed a maximum population density in the uppermost 5 mm of the mat: 1.1 × 10⁸ cells of sulfate reducers cm⁻³ sediment, 2.0 × 10⁹ cells of chemolithoautotrophs cm⁻³ sediment, and 4.0 × 10⁷ cells of anoxygenic phototrophs cm⁻³ sediment. Bacterial dynamics were studied by sulfate reduction rate measurements, both under anoxic conditions (dark incubation) and oxic conditions (incubation in the light), and determination of the vertical distribution of the potential rate of thiosulfate consumption under oxic conditions. Sulfate reduction rates in the top 5 mm of the sediment were 566 nmol cm⁻³ d⁻¹ in the absence of oxygen, and 123 nmol cm⁻³ d⁻¹ in the presence of oxygen. In the latter case, the maximum rate was found in the 5–10-mm depth horizon (361 nmol cm⁻³ d⁻¹). Biological consumption of amended thiosulfate was rapid and decreased with depth, while in the presence of molybdate, thiosulfate consumption decreased to 10–30% of the original rate.