Bacterioplankton Growth Research Articles

Effect of signal compounds and incubation conditions on the culturability of freshwater bacterioplankton.

The effect of signal compounds and of different incubation conditions on the culturability (i.e., the fraction of all cells capable of growth) of natural bacterioplankton from the eutrophic lake Zwischenahner Meer was investigated over a period of 20 months. Numbers of growing cells were determined by the most-probable-number technique in liquid media containing low concentrations (10 micro M) of the signal compounds N-(oxohexanoyl)-DL-homoserine lactone, N-(butyryl)-DL-homoserine lactone, cyclic AMP (cAMP), or ATP. cAMP was the most effective signal compound, leading to significantly increased cultivation efficiencies of up to 10% of the total bacterial counts. Microautoradiography with [2,8-(3)H]cAMP, combined with fluorescence in situ hybridization, demonstrated that cAMP was taken up by 18% of all cells. The bacterial cAMP uptake systems had a very low K(m) value of </=1 nM. Analysis of the cultured bacteria by 16S rRNA gene fingerprinting showed that different bacterial phylotypes were recovered in the presence and in the absence of cAMP. Consequently, the addition of cAMP caused a stimulation of otherwise nonculturable bacteria. Phylogenetically different bacteria were also recovered at different temperatures and oxygen partial pressures. Throughout the study period, mainly members of the beta-subclass of the Proteobacteria were cultivated. In addition, some members of the Actinomycetales were enriched. Quantification by culture-independent fluorescence in situ hybridization demonstrated that beta-Proteobacteria and Actinomycetales also dominated the natural bacterioplankton assemblage. Sequence comparison revealed that two members of the Actinomycetales which reached high numbers in the natural bacterioplankton assemblage could actually be enriched by our cultivation approach.

Effect of appendicularians and copepods on bacterioplankton composition and growth in the English Channel

We compared the effects of the presence of the appendicularian Oikopleura dioica and the copepods Acartia clausii and Calanus helgolandicus on the coastal bacterioplankton community off Plymouth. Mesozooplankton were added to water samples and bacterioplankton growth was monitored by flow cytometry. Phylogenetic composition of bacterioplankton was analysed using fluorescence in situ hybridisation (FISH) with rRNA-targeted oligonucleotide probes. The bacterioplankton composition did not change in the presence of either appendicularians or copepods, and generally the same proportions of bacterioplankton groups were determined. In late spring, 15 ± 2% of cells hybridised with a probe specific to the Kingdom Archaea. The majority of cells (88 ± 2%) belonged to the Kingdom Bacteria, and 86% of cells were identified using group-specific probes. The Cytophage-Flavobacterium cluster dominated the community, comprising 64 ± 0.5% of cells. The g-proteobacteria were the second abundant group, comprising 11 ± 0.5% of cells, and the SAR86 cluster of g-proteobacteria accounted for 6 ± 5%. The a-proteobacteria comprised 10 ± 5% of bacterioplankton, and the Roseobacteria related cluster represented 9 ± 3% of cells. The reduction of bacterioplankton growth caused by appendicularian bacterivory was 0.4 to 14% ind.-1 l-1, and the total appendicularian population could reduce bacterial growth in coastal waters in late spring-summer by up to 9%. In contrast to the appendicularians the copepods stimulated bacterial growth, and in summer the bacterioplankton growth may be increased by up to 13% by the combined effect of dominant copepod populations. Thus, the appendicularians and copepods had an opposite but moderate effect on the bacterioplankton growth and no effect on the bacterioplankton composition.

Differential growth response of colony-forming alpha- and gamma-proteobacteria in dilution culture and nutrient addition experiments from Lake Kinneret (Israel), the eastern Mediterranean Sea, and the Gulf of Eilat.

Even though it is widely accepted that bacterioplankton growth in lakes and marine ecosystems is determined by the trophic status of the systems, knowledge of the relationship between nutrient concentrations and growth of particular bacterial species is almost nonexistent. To address this question, we performed a series of culture experiments with water from Lake Kinneret (Israel), the eastern Mediterranean Sea, and the Gulf of Eilat (northern Red Sea). In the initial water samples, the proportion of CFU was typically <0.002% of the 4',6'-diamidino-2-phenylindole (DAPI) counts. During incubation until the early stationary phase, the proportion of CFU increased to 20% of the DAPI counts and to 2 to 15% of the DAPI counts in unenriched lake water and seawater dilution cultures, respectively. Sequencing of the 16S ribosomal DNA of colony-forming bacteria in these cultures consistently revealed an abundance of alpha-proteobacteria, but notable phylogenetic differences were found at the genus level. Marine dilution cultures were dominated by bacteria in the Roseobacter clade, while lake dilution cultures were dominated by bacteria affiliated with the genera Sphingomonas and CAULOBACTER: In nutrient (glucose, ammonium, phosphate) addition experiments the CFU comprised 20 to 83% of the newly grown cells. In these incubation experiments fast-growing gamma-proteobacteria dominated; in the marine experiments primarily different Vibrio and Alteromonas species appeared, while in the lake water experiments species of the genera Shewanella, Aeromonas, and Rheinheimera grew. These results suggest that major, but different, gamma-proteobacterial genera in both freshwater and marine environments have a preference for elevated concentrations of nutrients and easily assimilated organic carbon sources but are selectively outcompeted by alpha-proteobacteria in the presence of low nutrient concentrations.

Nutrient limitation of bacterioplankton growth in three upland lakes

Nutrient limitation of bacterioplankton growth in three upland lakes

Seasonal and spatial variations in the nutrient limitation of bacterioplankton growth in the northwestern Mediterranean

Nutrient limitation of bacterioplankton growth was studied in the western Mediter- ranean Sea to determine its spatial and temporal variations. Shipboard microcosm experiments were performed in June 1995, June 1996 and September 1996. Seawater was amended with carbon (C, as glucose), nitrate (N) and phosphate (P), individually or in combination. The limiting nutrient was inferred from the combination that stimulated the highest bacterial production and generated the highest bacterial biomass in the experiments. The results of the experiments carried out along a coastal-to-open sea transect, with both surface and deep chlorophyll maximum depth waters (DCM), suggest that there is a strong variability in the factors limiting bacteria. While phosphorus was most often the limiting nutrient in the surface samples, at the DCM depths nitrogen or carbon limitation was also found. The surface waters of the open sea station were also studied during the 3 cruises to provide an estimate of seasonal variation of bacterial limitation. Phosphorus limitation was found in the 3 periods: very clear phosphorus limitation in September 1996, possible phosphorus limitation in June 1995 and possible co-limitation with carbon in June 1996. Our results show that phosphorus is the main nutrient limiting bacterioplankton growth in the NW Mediterranean. However, while phos- phorus was usually the limiting nutrient in the surface layers, nitrogen and carbon limitation also occurred at other depths. Thus, seasonal and spatial variability in the nutrient limiting bacterial growth should be expected.

Viral and bacterial production in the North Water: in situ measurements, batch-culture experiments and characterization and distribution of a virus–host system

Abstract Growth and viral lysis of bacterioplankton at subzero temperatures were measured in the North Water polynya in July 1998. In situ measurements of bacterial carbon consumption in surface waters ranged from 15 to 63 μg C l−1 d−1 in the eastern and 6 to 7 μg C l−1 d−1 in the northern part of the polynya. Both bacterial abundance and activity appeared to increase in response to the decay of the phytoplankton bloom that developed in the North Water. Organic carbon was the limiting substrate for bacteria in the polynya since addition of glucose, but not inorganic nutrients, to batch cultures increased both the carrying capacity of the substrate and the growth rate of the bacteria. Bacterial growth rates ranged from 0.11 to 0.40 d−1, corresponding to bacterial generation times of 1.7–6.3 d. The in situ viral production rate was estimated both from the frequency of visibly infected cells and from the rate of viral production in batch cultures; it ranged from 0.04 to 0.52 d−1 and from 0.25 to 0.47 d−1, respectively. From 6% to 28% of bacterial production was found to be lost due to viral lysis. The average virus–bacteria ratio was 5.1±3.1, with the abundance of viruses being correlated positively with bacterial production. A Pseudoalteromonas sp. bacterial host and an infective virus were isolated from the polynya; characteristics and distribution of the virus–host system were examined. The Pseudoalteromonas sp. showed psychrotolerant growth and sustained significant production of viruses at 0°C. The virus–host system was found throughout the polynya. Overall the results suggested that a large amount of organic carbon released during the development and breakdown of the spring phytoplankton bloom was consumed by planktonic bacteria and that the microbial food web was an important and dynamic component of the planktonic food web in the North Water.

Bacterioplankton dynamics in the Gulf of Aqaba and the northern Red Sea in early spring

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 239:263-276 (2002) - doi:10.3354/meps239263 Bacterioplankton dynamics in the Gulf of Aqaba and the northern Red Sea in early spring Hans-Peter Grossart*, Meinhard Simon Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, 26111 Oldenburg, Germany *E-mail: hgrossart@icbm.de ABSTRACT: The northern Red Sea, with its northernmost extension the Gulf of Aqaba, is an oligotrophic marine ecosystem, for which the growth and substrate dynamics of the heterotrophic bacterioplankton have not yet been studied. In 1999, we carried out a comprehensive investigation of bacterioplankton growth dynamics in early spring (February/March), a time of year when the Gulf waters are deeply mixed, while permanent stratification prevails in the northern Red Sea. Most of the parameters measured yielded low values (bacterial numbers: 0.5 to 12.8 x 105 ml-1; production: 0.9 to 56.8 ngC l-1 h-1; growth rates: <0.01 to 0.15 d-1; turnover rates of dissolved free amino acids, DFAA: 0.008 to 1.35 d-1; glucose: 0.001 to 0.14 d-1; and concentrations of dissolved free neutral monosaccharides: <2 to 86 nM). Glucose was the only monosaccharide detected in 93% of the samples. Concentrations of DFAA ranged from 13.2 to 176 nM, and those of dissolved combined amino acids and neutral monosaccharides from 0.42 to 3.69 µM and 0.05 to 3.31 µM, respectively. Uptake of glucose (as percent of bacterial production) in 93% of the samples was <50%, whereas that of DFAA was much higher, often exceeding 100% (the latter result may have been due to methodological biases). Most of the parameters measured were more variable and covered a wider range in the northern Red Sea than in the Gulf, where vertical patterns were more homogenous. Only concentrations of dissolved free neutral monosaccharides were systematically lower in the northern Red Sea. Bacterial production in this area was significantly correlated with turnover and uptake rates of DFAA, and with glucose turnover rates below 100 m. Aminopeptidase and β-glucosidase activities were fairly similar in both study areas, with means ranging from 19.4 to 29.9 nmol l-1 h-1. Whereas aminopeptidase hydrolysis rates were in the same range as values found in other oceanic regions, β-glucosidase hydrolysis rates were much higher, possibly due to the persistence of active β-glucosidase in the dissolved phase, as has been reported for alkaline phosphatase in this area. Analysis of the data indicates that in the northern Red Sea bacterioplankton growth dynamics were mainly controlled by biological processes, whereas in the Gulf hydrographic processes were more important. KEY WORDS: Bacteria · Bacterial production · Amino acids · Carbohydrates · Turnover rates · Aminopeptidase · Glucosidase · Gulf of Aqaba · Red Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 239. Online publication date: August 23, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Effects of hydrologically confined fishes on bacterioplankton and autotrophic picoplankton in a semiarid marsh

An enclosure experiment was conducted to assess the separate effects of exotic benthivorous (Cyprinus carpio L.), planktivorous (Gambusia holbrooki Gir.), and omnivorous (Lepomis gibbosus L.) fish on the dynamics of bacterioplankton (BAC) and autotrophic picoplankton (APP) in a semiarid Spanish marsh. Special emphasis was put on simulating the effect of natural fish density situations occur- ring under periods of hydrological confinement in the wet- land, i.e. during summer draw downs or artificial water-level reductions, when fish biomass can reach high levels. The resulting simulation of such a scenario (C. carpio, 5000 to 6000 kg ha -1 ; L. gibbosus, 1300 to 1700 kg ha -1 , and G. hol- brooki, 115 kg ha -1 ) revealed that C. carpio and L. gibbosus significantly increased the trophic level in the enclosures. This resulted in a significant increase of BAC in the respective treatments. G. holbrooki, on the other hand, failed to fuel BAC growth. Considering APP, composed of phycocyanin- rich picocyanobacteria Synechococcus sp., no fish treatment effects were detected, suggesting that the fishes, indepen- dent of biomasses used, were not important in driving APP. Results indicate that microbial communities respond in differ- ent ways to changes in fish biomass in fluctuating wetlands.

Coulometric carbonߚbased respiration rates and estimates of bacterioplankton growth efficiencies in Massachusetts Bay

Heterotrophic bacterioplankton production rates have been measured in many aquatic ecosystems over the last two decades, whereas measurements of bacterioplankton respiration rates have been scarce. This paper reports and discusses measurements of carbonߚbased plankton respiration rates made in a coastal ecosystem over an annual cycle. The coulometric technique was used to measure total inorganic carbon (TCO2) production rates in 0.8– µm filtered and unfiltered Massachusetts Bay surface seawater. Bacterioplankton respiration rates, defined as respiration in 0.8– µm filtered seawater, varied from 0.01 to 0.15 mmol C kg−1 h−1 (0.07 ±0.01 µmol C kg−1 h−1) (mean ±1 SE) and accounted for a high proportion (median 70%) of respiration in unfiltered seawater. Microplankton (unfiltered seawater) respiration rates varied from 0.04 to 0.24 µmol C kg−1 h−1 (0.12 ±0.02 µmol C kg−1 h−1). Bacterioplankton growth efficiencies (BGEs), estimated with concurrent measurements of bacterial production and respiration rates, varied from 0 to 69% (median 22%) and were well correlated with specific production rates (r2 = 0.67). To assess carbon flow in aquatic ecosystems, BGEs should be measured when possible because of their high variability. Compared with bacterioplankton specific production rates, bacterioplankton specific respiration rates were relatively constant (0.05 ±0.01 fmol CO2 cell−1 h−1). Given the apparent uncertainty in the values of respiratory quotients (Toolan 1996; Robinson and Williams 1999), carbonߚbased comparisons of microbial respiration and primary production rates will improve evaluations of the role of the coastal ocean in the global carbon cycle.

Linkage of small-scale spatial variations in DOC, inorganic nutrients and bacterioplankton growth with different coral reef water types

This study focuses on links of dissolved organic carbon (DOC), inorganic nutrients (DIN and DIP) and bacterioplankton growth with specific coral reef water types. At 5 reef stations along the SW coast of Curacao (Netherlands Antilles), 6 different water types (4 reef water types (live coral surface contact water, reef crevice water, reef bottom water, reef overlying water) and 2 reference water types collected offshore from each station at 2 and 8 m depth) were analysed for DOC, DIN and DIP, bacterial production and abundance. Consistent patterns were found: reef waters were enhanced in DIN, DIP and specific bacterial growth rate (µn) compared to offshore waters. DOC, DIP, and µn were higher close to the reef bottom than in the reef overlying water. Coral surface contact water was significantly enhanced in DOC compared to reef crevice and reef bottom water, suggest- ing that the major source of DOC in reef waters are the live corals. DIN concentration was highest in reef crevice water, suggesting that crevices are the major net N-regenerating spaces on reefs, more important than the reef bottom between corals. Small-scale DIP distribution suggested net P regen- eration in reef crevice and coral surface contact water. The highest specific growth rates of bacterio- plankton were found in the coral surface contact water, with slightly lower rates in reef crevice water. Experiments showed that the labile DOC fraction (LDOC) in reef crevice water was substantially smaller than in coral surface contact and reef overlying water, which suggests that crevices are apparently sinks of LDOC. In reef crevice and reef bottom water the low substrate LDOC:DIN ratios suggest that LDOC might be the growth-limiting factor of bacterioplankton in these water types. In coral surface contact and reef overlying water the substrate LDOC:DIN ratios of more than 40 (and LDOC:DIP ratios of over 800) and the significant relations between µn and DIN (DIP) suggest nutrient limitation of bacterioplankton growth in these water types. This study clearly illustrates the close link in reef waters between coral reef benthos and bacterioplankton trophodynamics.

The seasonal development of the bacterioplankton bloom in the Ross Sea, Antarctica, 1994–1997

We report on investigations of bacterioplankton growth dynamics and carbon utilization in the full water column of the Ross Sea, Antarctica carried out on six cruises in 1994–1997, using epifluorescence microscopy, thymidine and leucine incorporation to estimate bacterial abundance and production, respectively. The Ross Sea experienced a bacterial bloom with an amplitude equaling similar blooms observed in the North Atlantic and North Pacific, reaching 3 � 10 9 cells l � 1 or 35 mmol C m � 2 in late January. Increases in bacterial biomass were driven both by increases in abundance and in cell volume. Cell volumes ranged from 0.03mm 3 cell � 1 in early spring to over 0.15mm 3 cell � 1 in midsummer. Larger cells were associated with faster division rates. Bacterial growth rates ranged 0.02–0.3 divisions d � 1 , equal to rates at lower latitudes. Bacterial biomass accumulated steadily in the upper water column at a net rate of 0.03 d � 1 . While there is clear evidence of a bacterial bloom in the Ross Sea, equal to bacterioplankton blooms observed in other oceanic systems, the magnitude of bacterial response relative to the phytoplankton bloom was modest. For example, euphotic zone bacterial production (BP) rates were equivalent to 1–10% of particulate primary production (PP) except in April 1997 when PP was very low and BP : PP was sometimes >1. BP integrated over the upper 300 m was a more substantial fraction of the overlying PP than BP in the euphotic zone alone, with bacterial carbon demand in the upper 300 m about 30% of the seasonal PP. There was significant seasonal variation of bacterial biomass below the euphotic zone, indicating dynamic bacterial growth in the lower layer, and a supply of labile organic matter for bacteria. Bacterial metabolism is apparently limited by DOC flux in the upper layer. There is little evidence of temperature limitation, independent of substrate concentration. The relatively small diagenesis of phytoplankton biomass in the

Control of bacterioplankton growth in three oligotrophic lakes of differing humic content

Control of bacterioplankton growth in three oligotrophic lakes of differing humic content

Growth and production of bacterioplankton in a deep mesohumic boreal lake

Vertical distribution of bacterial biomass and production, as well as phytoplankton production, was studied in a deep, mesohumic lake in Southern Finland. In summer 1992 32-56 % of bacterial production but only ca. 17 % of biomass was found in the euphotic zone (0-5 m), which consists of 20 % of the total lake volume. In the deep central area of the lake, the production of bacteria varied between 63 and 121 mg C m -2 d -1 and that of phytoplankton 57-158 mg C m -2 d -1 . High bacterial production to primary production ratio (>0.5) indicates that the phytoplankton production alone was insufficient to sustain the total bacterial production, and that bacterioplankton utilised other carbon sources, such as allochthonous organic compounds. Factors controlling growth of bacteria in the aphotic zone (allochthonous and autochthonous dissolved organic matter (DOM), PO 4 -P, temperature and grazing) were studied in a laboratory experiment. The most pronounced increase in bacterial growth was achieved when allochthonous humic water originating from the catchment was added or when it was added together with PO 4 -P. Furthermore. PO 1 -P addition together with autochthonous organic carbon, resulted in higher bacterial growth rates than the addition of autochthonous DOC alone. The results suggest that despite the high concentration of dissolved organic carbon (DOC>10 mg C/L) in the lake, the quality of DOM and availability of PO 4 -P are the principal factors controlling the growth of bacterioplankton.

Nutrient stimulation of bacterioplankton growth in Tuamotu atoll lagoons

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 21:125-137 (2000) - doi:10.3354/ame021125 Nutrient stimulation of bacterioplankton growth in Tuamotu atoll lagoons J.-P. Torréton1,*, V. Talbot1, N. Garcia2 1Institut de Recherche pour le Développement, Laboratoire HEA, BP 5045, 34032 Montpellier cedex 1, France 2CNRS, Laboratoire d¹Océanographie et de Biogéochimie UMR 6535 (COM-OSU), Campus de Luminy, 13288 Marseille, France *Present address: Institut de Recherche pour le Développement, Université Montpellier II, UMR 5556, Case 093, 34095 Montpellier cedex 05, France. E-mail: torreton@ird.fr ABSTRACT: Knowledge of the factors regulating bacterioplankton growth is of considerable importance in attempts to understand the functioning of biogeochemical cycles and particularly their evolution after perturbation. We first tested the effect of nutrient additions on the growth of bacterioplankton assemblages collected from 10 atoll lagoons of various morphologies in the Tuamotu Archipelago and in oceanic surface waters surrounding them. Then, we examined these responses in relation to ambient nutrient concentrations and bacterioplankton community turnover rates in these lagoons. The lagoons studied exhibited a range of NH4 (~0 to 0.7 μM), NO2+NO3 (~0 to 0.5 μM), and PO4 (~0 to 0.3 μM) concentrations. Responses were assessed on bacterioplankton grown in seawater cultures during 2 seasons (end of rainy season, end of dry season) and amended with NH4-N, PO4-P or glucose-C in all possible combinations. The 10 lagoons investigated exhibited various responses to nutrient additions. Including co-stimulations, bacterioplankton growth was stimulated by C, N and P additions in 4, 10 and 4 cases, respectively. One atoll lagoon showed inconsistent responses during both cruises. Another one showed no response to any nutrient addition. On the other hand, the oceanic subsurface samples showed a systematic stimulation by glucose, in one case with a concomitant positive effect of N. Expressed as percentages of the unamended controls, responses to ammonium and phosphorus additions in the different lagoons investigated appeared to decrease with increasing ammonium and phosphorus concentrations, respectively. This correspondence suggests that in situ concentrations reflect the nutrient status of bacterioplankton in the sites visited. NH4-N appeared as the most frequently stimulatory nutrient in the atolls investigated. This is in agreement with the close log-log correlation (p < 0.001) observed between bacterioplankton turnover rates and DIN/PO4 ratio. KEY WORDS: Atoll lagoon · Bacterioplankton · Nutrient limitation · Ammonium · Phosphorus Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 21, No. 2. Publication date: March 31, 2000 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2000 Inter-Research.

Exposure of natural Antarctic marine microbial assemblages to ambient UV radiation: effects on bacterioplankton

Seasonal ozone depletion over Antarctica leads to enhanced UVB (280 to 320 nm) radiation throughout the period of greatest biological production. The effect of UV radiation on bacterioplankton has received little attention, and its effects on marine microheterotrophs and viruses, which mediate bacterial biomass, are poorly understood. This study examined the impact of ambient solar W radiation on bacterioplankton in natural Antarctic microbial communities. Following a lag of 2 d, bacterial concentrations increased all light treatments. Inhibition of bacterial growth increased with increasing UV irradiance and duration of exposure, reaching 27 % inhibition in hlgh UV treatments (c2.0 m equivalent depth) compared to controls after 7 d exposure. Bacterioplankton growth rates declined in all treatments during post-UV incubation, particularly at lower UV irradiances (23.0 m equivalent depth), indicating UV-induced inhibition of bacterial mortality during irradiation. Positive bacterial growth coincided with both phytoplankton mortality and increased microheterotroph concentrations following exposure to high UV irradiances. Exposure of Antarctic microbial communities to ambient UV is likely to increase microbial respiration of carbon in surface waters and reduce vertical carbon flux.

Bacterioplankton turnover of dissolved free monosaccharides in a mesotrophic lake

Concentrations and bacterioplankton uptake of dissolved free monosaccharides (DFCHO) in relation to bacter‐ioplankton production and phytoplankton biomass were studied in mesotrophic Lake Constance, Germany, from August 1995 to December 1996. Concentrations of total DFCHO, measured by high‐performance liquid chroma‐tography (HPLC) and pulsed amperometric detection, ranged from &lt;20 to 440 nM and exhibited pronounced spatiotemporal variations. Enhanced concentrations of DFCHO were often associated with the breakdown of phy‐toplankton blooms and periods of low phytoplankton growth. Bacterial uptake rates of DFCHO were also enhanced during such events, as well as at peaks of bacterioplankton production (BP). Ratios of uptake of DFCHO/BP, however, indicated that DFCHO concentrations were relatively more important as substrates during periods of low bacterial growth than during phases of intense bacterial growth. Ratios of bacterial uptake of DFCHO/BP from spring to fall ranged from 0.22 to 0.39 in the layer 0–10 m, from 0.17 to 0.56 at 20 m, and from 0.22 to 0.46 at 50 m, respectively. Glucose, galactose, and mannose dominated the DFCHO pool and constituted ∼55 to ∼70 mol%. The analysis of individual turnover times of five DFCHO concentrations from August to November 1995 at 3, 10, and 50 m revealed that the glucose pool turned over most rapidly, followed by galactose and mannose. Glucosamine and fructose always exhibited substantially longer turnover times. Comparisons to previous studies show that DFCHO concentrations are of similar significance for bacterioplankton growth as dissolved free amino acids (DFAA), even though temporal uptake patterns of both substrates are different.

Effects of nutrients (phosphorous, nitrogen, and carbon) and zooplankton on bacterioplankton and phytoplankton—a seasonal study

The effects of inorganic nutrients (P and N), organic C, and metazoan zooplankton on bacterioplankton production and abundance and on phytoplankton biomass were studied in five experiments (from May to September) in Lake Erken. In addition, the seasonal dynamics of bacterioplankton and phytoplankton were followed in the lake from April to November.Bacterioplankton production was P limited from May to August. N alone never stimulated bacterioplankton production, but bacterioplankton growth was close to colimited by P and N in July and August. Organic C stimulated bacterial production in June and September. Zooplankton enhanced bacterioplankton production in June, when bacterioplankton production was limited by P and C and the phytoplankton biomass in the lake was low. N alone stimulated phytoplankton growth in all experiments. In addition, P alone stimulated phytoplankton growth in May and July, and the combination of P and N stimulated phytoplankton growth in July and August. Zooplankton additions resulted in a decrease in phytoplankton biomass in May and September, mainly owing to grazing on Cryptophyceae.The experimental results indicate that bacterioplankton and phytoplankton growth were uncoupled during most of the open‐water period because P primarily limited bacterioplankton growth and N limited phytoplankton growth. The response of the bacterioplankton community was most likely a direct effect of nutrient additions. Primary production and bacterioplankton production were correlated during the season, but partial correlations analysis indicates that this relationship can be attributed to the fact that both primary production and bacterioplankton production showed strong positive correlations with temperature. We suggest that uncoupling of bacterioplankton production and phytoplankton production may be a common phenomenon in lakes.

Production of Epiphytic Bacteria and Bacterioplankton in Three Shallow Lakes

Secondary production of epiphytic bacteria and bacterioplankton was measured from May to September in three temperate, shallow and eutrophie Danish lakes. The biomass of bacteria attached to the submerged angiosperms Ceratophyllum demersum and Potamogeton pectinatus averaged 4.3 and 3.0 μg C cm 2 and the production measured by thymidine incorporation averaged 0.28 and 0.40 μg C cm -2 h -1 . In Lake Dystrup. Ceratophyllum demersum covers about 95% of the lake area and the epiphytic bacterial production (thymidine method) per lake surface area from mid-July to early September was twice the production of the bacterioplankton. With the lencine method the epiphytic bacterial production was seven-fold higher than the bacterioplankton production. A 20% area cover by Potamogeton pectinatus in Lake Stigsholm resulted in an epiphytic bacterial production equal to the bacterioplankton. The biafilms on macrophyte surfaces are hotspots with a bacterial per volume production 1000 times the bacterioplankton. Furthermore, the growth rates of the attached bacteria were from two to four times faster than in the bacterioplankton communities. A comparison of the twin lakes Dystrup and Ramten, respectively with and without submerged vegetation, showed bacterioplankton production of equal magnitude despite four-fold higher phytoplankton and bacterioplankton biomasses in Ramten. Higher bacterial growth rates in Dystrup almost compensated for the lower biomass, The total area production of the attached and free living bacteria in Dystrup was three to five times the total area production in Ramten. It is suggested that the higher bacterioplankton growth rates in vegetated areas may be explained both by an enhanced grazing pressure and by more favorable growth conditions due to exudation of DOC from the macrophytes.

Biomass, production and heterotrophic activity of bacterioplankton in the Great Astrolabe Reef lagoon (Fiji)

Biomass, production and heterotrophic activity of bacterioplankton were determined for two weeks in the Great Astrolabe Reef lagoon, Fiji. Bacterial and Bacterial activities were distributed homogeneously throughout the water column (20 to 40 m deep) and varied little from site to site inside the lagoon. Bacterioplankton biomass and production also varied little over a diel period with coefficients of variation of 9 and 22%, respectively. On average, over the whole study, bacterial abundance was 0.77×109 cells l-1 and bacterial production averaged 0.36 μg-at. C l-1 d-1. Bacterial abundance and production were greater in the lagoon than in oceanic waters. Attachment to particles seems to provide an advantage for bacterioplankton growth because specific growth rates for attached bacterioplankton were, on average, significantly greater than that of the free community. Growth efficiency, determined by correlating the net increase of bacterial biomass and the net decrease of dissolved organic carbon (DOC) in dilution cultures, was very low (average 6.6%). Using carbon growth efficiency and bacterial production rates, heterotrophic activity was estimated to average 5.4 μg-at. C l-1 d-1. The turn-over rate of DOC (average 114 μg-at. C l-1) due to bacterial consumption was estimated to be 0.048 d-1 during the period of study.

Pelagic processes in extensive shrimp ponds of the Mekong delta, Vietnam

Rates of pelagic primary production, respiration, and bacterioplankton dynamics were measured in relation to water quality parameters in three extensive shrimp ponds in the Mekong delta, Vietnam. There were few consistent differences in pelagic characteristics among different locations within these ponds, among the three ponds, or between the ponds and adjacent river water. Rates of primary production ( 14 C uptake) ranged from <1 to 94 mg C m −3 d −1. Rates of gross primary production (light–dark bottle technique) ranged from −184 to 2697 mg C m −3 d −1. Rates of pelagic respiration ranged from 60 to 3783 mg C m −3 d −1. Primary production rates measured by oxygen flux were greater than those measured via 14 C uptake, with P/ R ratios varying widely (−0.45 to 3.4), but the mean P/ R at each site was <1 with a grand mean among ponds of 0.7. Bacterioplankton numbers (mean range: 0.2 to 27.2×10 8 cells ml −1) and productivity (range: 2.5 to 297.3 mg C m −3 d −1) did not vary consistently among ponds with season. Mean bacterioplankton growth rates were fastest ( μ=0.29 d −1) in the pond with highest shrimp production and slowest in the poorest yielding pond ( μ=0.08 d −1). The primary production and respiration rates, and bacterioplankton dynamics, indicate that these pond waters are net heterotrophic. Plankton measurements rarely correlated with changes in physicochemistry (pH, dissolved O 2, salinity, temperature) or nutrient concentrations as within-site and temporal variability were large for most parameters. The diurnal cycles of physicochemical characteristics were similar to those measured in other unfertilized, low-alkalinity ponds, but these cycles were dampened by intense rainfall. Our data indicate that low net primary production, high rates of respiration, moderate rates of bacterioplankton production, high suspended solid and nutrient concentrations, low and very variable pH and dissolved O 2 concentrations, and variations in salinity due to intense rainfall episodes limit shrimp production in these extensive ponds.