Measurements Of Bacterial Production Research Articles

Organic matter availability drives the spatial variation in the community composition and activity of Antarctic marine bacterioplankton.

Carbon cycling by Antarctic microbial plankton is poorly understood but it plays a major role in CO2 sequestration in the Southern Ocean. We investigated the summer bacterioplankton community in the largely understudied Weddell Sea, applying Illumina amplicon sequencing, measurements of bacterial production and chemical analyses of organic matter. The results revealed that the patchy distribution of productive coastal polynyas and less productive, mostly ice-covered sites was the major driver of the spatial changes in the taxonomic composition and activity of bacterioplankton. Gradients in organic matter availability induced by phytoplankton blooms were reflected in the concentrations and composition of dissolved carbohydrates and proteins. Bacterial production at bloom stations was, on average, 2.7 times higher than at less productive sites. Abundant bloom-responsive lineages were predominately affiliated with ubiquitous marine taxa, including Polaribacter, Yoonia-Loktanella, Sulfitobacter, the SAR92 clade, and Ulvibacter, suggesting a widespread genetic potential for adaptation to sub-zero seawater temperatures. A co-occurrence network analysis showed that dominant taxa at stations with low phytoplankton productivity were highly connected, indicating beneficial interactions. Overall, our study demonstrates that heterotrophic bacterial communities along Weddell Sea ice shelves were primarily constrained by the availability of labile organic matter rather than low seawater temperature.

Incorporation characteristics of exogenous 15N-labeled thymidine, deoxyadenosine, deoxyguanosine and deoxycytidine into bacterial DNA.

Bacterial production has been often estimated from DNA synthesis rates by using tritium-labeled thymidine. Some bacteria species cannot incorporate extracellular thymidine into their DNA, suggesting their biomass production might be overlooked when using the conventional method. In the present study, to evaluate appropriateness of deoxyribonucleosides for evaluating bacterial production of natural bacterial communities from the viewpoint of DNA synthesis, incorporation rates of four deoxyribonucleosides (thymidine, deoxyadenosine, deoxyguanosine and deoxycytidine) labeled by nitrogen stable isotope (15N) into bacterial DNA were examined in both ocean (Sagami Bay) and freshwater (Lake Kasumigaura) ecosystems in July 2015 and January 2016. In most stations in Sagami Bay and Lake Kasumigaura, we found that incorporation rates of deoxyguanosine were the highest among those of the four deoxyribonucleosides, and the incorporation rate of deoxyguanosine was approximately 2.5 times higher than that of thymidine. Whereas, incorporation rates of deoxyadenosine and deoxycytidine were 0.9 and 0.2 times higher than that of thymidine. These results clearly suggest that the numbers of bacterial species which can incorporate exogenous deoxyguanosine into their DNA are relatively greater as compared to the other deoxyribonucleosides, and measurement of bacterial production using deoxyguanosine more likely reflects larger numbers of bacterial species productions.

Antecedent precipitation influences the bacterial processing of terrestrial dissolved organic matter in a North Carolina estuary

Estuaries and coastal waters ultimately receive the terrestrial dissolved organic matter (DOM) exported from coastal watersheds, more directly during extreme precipitation events. Recent work suggests DOM's degradation in coastal waters varies with its quality, which also might vary as a function of precipitation, activating contributions from different sources within a watershed. The aim of this study was to determine the extent to which microbial degradation of terrestrial DOM in the Newport River Estuary, eastern North Carolina, was influenced by precipitation events occurring within the preceding seven days from sampling. We hypothesized that DOM stored in forested wetlands (e.g., pocosins and Cypress swamps) that become connected to the main channel of the Newport River during high precipitation events was more labile than DOM flowing into the estuary under low precipitation events. DOM quality was assessed with optical and stable C isotope (δ13C) measurements, while DOM lability was assessed by measurements of bacterial production (BP) and mineralization of 14C-labeled phenanthrene (Pmin), a polyaromatic tracer compound. Aromatic content of DOM, assessed by specific ultraviolet absorbance at 254 nm (SUVA254) was highest in the river with values well over 5.0 L mg C−1 m−1, and decreased with salinity. Antecedent precipitation (AP) of at least 100 mm in the seven days prior to sampling resulted in dissolved organic carbon (DOC) concentrations >20 mg L−1, at salinities <10. Similarly, fluorescence humification index (HIX) values were highest in the estuary after the highest AP. Generally depleted δ13C-DOC values (−26 to −28‰) in the estuary up to a salinity of 30 indicated a substantial source of DOM likely originating from the forested swamps and tidal wetlands fringing the estuary. BP exhibited wide variability yet declined with salinity, while median values after higher AP (40 μg C L−1 d−1) were double that under lower AP. By contrast, aromatic mineralization (Pmin) rates increased as both DOC and CDOM concentrations, and SUVA254 and HIX values, declined with salinity. However, Pmin rates were highest after the highest AP for the three events sampled. Results indicate that flooding of coastal wetlands mobilizes a large pool of labile DOM which have a large impact on the carbon cycle in estuaries. By altering the quality, as well as quantity of terrestrial organic matter inputs to estuarine systems, extreme events may also affect utilization of aromatic organics by estuarine microbial assemblages, an intriguing research question worthy of further study.

Control of net community production by microbial community respiration at Station ALOHA

Abstract Net community production (NCP) constrains the amount of carbon that is available for storage within or export from, the photic zone of marine ecosystems. With the aim of studying the control exerted by microbial community respiration (MCR) and gross primary production (GPP) over NCP, short-term variability in rates of MCR, GPP and NCP were measured over a 13-day sampling period (August 23–September 4, 2012) at Station ALOHA. During this period, picoplankton abundances and concentrations of photosynthetic pigments demonstrated weak to moderate decreases coincident with the passage of a low salinity water mass through the sampling area. During the same period, rates of MCR, measured using the in vivo INT method, varied by 2.7-fold. Rates of primary production (PP) were estimated based on four different methodologies: Fast Repetition Rate Fluorometry (FRRF), 14C-bicarbonate assimilation, diel changes in mixed layer O2 concentrations based on Seaglider measurements, and isotopic composition (17ΔO2) of dissolved O2. Remarkably, these different methods for measuring microbial metabolism were consistent, suggesting that collectively these different approaches provide an accurate constraint on ecosystem metabolism, despite the different time and space scales over which these measurements integrate. FRRF-derived estimates of PP, which were similar in magnitude to 14C-based-PP, were significantly correlated with variability in mixed layer MCR. None of the other independent measurements of PP demonstrated significant relationships to MCR. Day-to-day variability in MCR and bacterial growth efficiency (BGE), derived based on measurements of bacterial production (as estimated by 3H-leucine incorporation) and MCR, were related to changes in NCP estimated from O2/Ar ratios (O2/Ar-NCP), suggesting short-term variability in the efficiency with which microorganisms consume dissolved organic matter exerts direct control on rates of NCP in this ecosystem. Our results highlight internal consistency among the derived rates of ecosystem metabolism using a suite of different methodologies to estimate productivity and respiration. Moreover, we find that rates of MCR can be as variable as PP and that variability in MCR may regulate NCP in this ecosystem.

New radioisotope-free method for measuring bacterial production using [15N5]-2′-deoxyadenosine and liquid chromatography mass spectrometry (LC–MS) in aquatic environments

This study proposed a non-radioactive quantitative measurement of bacterial production using stable isotope nitrogen-15-labeled deoxyadenosine ([15N5]-2′-deoxyadenosine; 15N-dA) by liquid chromatography mass spectrometry (LC–MS). The method of preparing 5N-dA described in this study included incubation of seawater or lake water with 15N-dA for 5–24 h, filtration onto a membrane filter, DNA extraction, enzymatic hydrolysis of DNA to nucleosides and quantification of 15N-dA by LC–MS. In the DNA extraction, the silica beads method was examined first, but a large amount of salts and enzymatic inhibitors used in the method caused failure of subsequent procedures, such as enzymatic hydrolysis and LC–MS analysis. On the other hand, the magnetic beads method showed much better results for the extraction. The incorporation rate of 15N-dA was significantly positively correlated to that of tritium-labeled thymidine (3H-TdR) in samples of coastal seawaters and lake waters. The average 15N-dA: 3H-TdR incorporation ratio for the seawater sample was 0.55 with 2.5 and 97.5 % confidence intervals of 0.51 and 0.58, respectively; the average ratio for the lake water sample was 0.28 with 2.5 and 97.5 % confidence intervals of 0.23 and 0.34, respectively. The results suggest that the 15N-dA method can be applied to the measurement of bacterial production in aquatic ecosystems, and that this method can accurately predict the DNA synthesis rates measured by the conventional method.

Plankton community and bacterial metabolism in Arctic sea ice leads during summer 2010

Microbial plankton metabolism was examined during summer 2010 in sea ice-influenced waters of the Fram Strait, eastern Arctic Ocean. Rates of gross primary production and community respiration were tightly coupled over a wide range of values (33±3–143±6 and 20±3–126±6mmol O2m−2−1, respectively) leading to a prevalence of positive net community production. The high variability in community respiration, similar to that of gross primary production, suggests that heterotrophic metabolism may exhibit a significant response to environmental change. Bacterial respiration was assessed at similar time scales to bacterial production measurements, by determining the in vivo INT reduction capacity without pre-filtering the community. Bacteria seem to play a major role in total community respiration, contributing between 5% and 61% of total community respiration, indicating that a high fraction of the organic carbon in Arctic planktonic food webs could flow through these microbes.

Bacterial diversity in relation to secondary production and succession on surfaces of the kelp Laminaria hyperborea.

Kelp forests worldwide are known as hotspots for macroscopic biodiversity and primary production, yet very little is known about the biodiversity and roles of microorganisms in these ecosystems. Secondary production by heterotrophic bacteria associated to kelp is important in the food web as a link between kelp primary production and kelp forest consumers. The aim of this study was to investigate the relationship between bacterial diversity and two important processes in this ecosystem; bacterial secondary production and primary succession on kelp surfaces. To address this, kelp, Laminaria hyperborea, from southwestern Norway was sampled at different geographical locations and during an annual cycle. Pyrosequencing (454-sequencing) of amplicons of the 16S rRNA gene of bacteria was used to study bacterial diversity. Incorporation of tritiated thymidine was used as a measure of bacterial production. Our data show that bacterial diversity (richness and evenness) increases with the age of the kelp surface, which corresponds to the primary succession of its bacterial communities. Higher evenness of bacterial operational taxonomical units (OTUs) is linked to higher bacterial production. Owing to the dominance of a few abundant OTUs, kelp surface biofilm communities may be characterized as low-diversity habitats. This is the first detailed study of kelp-associated bacterial communities using high-throughput sequencing and it extends current knowledge on microbial community assembly and dynamics on living surfaces.

Functional variation among polysaccharide-hydrolyzing microbial communities in the Gulf of Mexico

Marine polysaccharides are structurally diverse, as are the microbial communities capable of remineralizing them. Variations in the diversity, richness, and metagenome content of pelagic microbial communities are well documented, but variation in the spectrum of substrates accessible to those communities is less well understood. Here we investigate variability in the abilities of microbial communities to access specific polysaccharides along lateral and depth gradients in the Gulf of Mexico. Patterns of polysaccharide degradation during long-term incubations varied in ways that could not be predicted from bulk community measurements of bacterial production and glucose metabolism. There was greater diversity of function among epipelagic communities than among mesopelagic communities, and the communities in the two deepest water samples (700m and 905m) were more specialized in their abilities to access specific polysaccharide structures than were shallower-water communities. Timecourses of polysaccharide hydrolysis suggest that the capacity of communities to access specific polysaccharides may be influenced in part by variability in the composition or activity of the rare biosphere.

Contrasting ability to take up leucine and thymidine among freshwater bacterial groups: implications for bacterial production measurements

We examined the ability of different freshwater bacterial groups to take up leucine and thymidine in two lakes. Utilization of both substrates by freshwater bacteria was examined at the community level by looking at bulk incorporation rates and at the single-cell level by combining fluorescent in situ hybridization and signal amplification by catalysed reporter deposition with microautoradiography. Our results showed that leucine was taken up by 70–80% of Bacteria-positive cells, whereas only 15–43% of Bacteria-positive cells were able to take up thymidine. When a saturating substrate concentration in combination with a short incubation was used, 80–90% of Betaproteobacteria and 67–79% of Actinobacteria were positive for leucine uptake, whereas thymidine was taken up by < 10% of Betaproteobacteria and by < 1% of the R-BT subgroup that dominated this bacterial group. Bacterial abundance was a good predictor of the relative contribution of bacterial groups to leucine uptake, whereas when thymidine was used Actinobacteria represented the large majority (> 80%) of the cells taking up this substrate. Increasing the substrate concentration to 100 nM did not affect the percentage of R-BT cells taking up leucine (> 90% even at low concentrations), but moderately increased the fraction of thymidine-positive R-BT cells to a maximum of 35% of the hybridized cells. Our results show that even at very high concentrations, thymidine is not taken up by all, otherwise active, bacterial cells.

Lability of organic carbon in lakes of different trophic status

Summary1. We used first‐order kinetic parameters of biological oxygen demand (BOD), the constant of aerobic decomposition (k) and the asymptotic value of BOD (BODult), to characterise the lability of organic carbon pools in six lakes of different trophic state: L. Naroch, L. Miastro and L. Batorino (Belarus), L. Kinneret (Israel), L. Ladoga (Russia) and L. Mendota (U.S.A.). The relative contributions of labile and refractory organic carbon fractions to the pool of total organic carbon (TOC) in these lakes were quantified. We also determined the amounts of labile organic carbon within the dissolved and particulate TOC pools in the three Belarus lakes.2. Mean annual chlorophyll concentrations (used as a proxy for lake trophic state) ranged from 2.3 to 50.6 μg L−1, labile organic carbon (OCL = 0.3BODult) from 0.75 to 2.95 mg C L−1 and k from 0.044 to 0.14 day−1.3. Our data showed that there were greater concentrations of OCL but lower k values in more productive lakes.4. In all cases, the DOC fraction dominated the TOC pool. OCL was a minor component of the TOC pool averaging about 20%, irrespective of lake trophic state.5. In all the lakes, most (c. 85%) of the DOC pool was refractory, corresponding with published data based on measurements of bacterial production and DOC depletion. In contrast, a larger fraction (27–55%) of the particulate organic carbon (POC) pool was labile. The relative amount of POC in the TOC pool tended to increase with increasing lake productivity.6. Long‐term BOD incubations can be valuable in quantifying the rates of breakdown of the combined particulate and dissolved organic carbon pools and in characterising the relative proportions of the labile and recalcitrant fractions of these pools. If verified from a larger number of lakes our results could have important general implications.

Relationship of bacterial growth efficiency to spatial variation in bacterial activity in the Hudson River

Variation in bacterial production (BP) is used as an indicator of bacterial metabolism and carbon processing in the analysis of aquatic ecosystems. The allocation of carbon by bacteria to either BP or respiration (BR), however, is variable and may potentially influence the assessment of carbon cycling by bacteria in ecosystems. We studied 10 transects in the Hudson River estuary where there is a gradient in BP and BR along the flow path of the estuary. We measured BP and BR in filtered sam- ples to derive an estimate of bacterial growth efficiency (BGE) that we could compare with indepen- dent measurements of total BP (BPT) from unfiltered samples to evaluate the relationship of BGE to BP. We further tested the assumption that BGE derived from filtered samples is a good estimator of the ambient BGE on a subset of transects in the upriver section where bacteria dominate respiration. There was good agreement (near 1:1) between respiration measured in unfiltered samples and total BR estimated from BPT and BGE in the filtered fraction (total BR = (BPT/BGE) - BPT). BGE averaged 0.29 but varied from 0.07 to 0.61, and did not explain the general decline in BPT along the river. Rather, BGE was strongly correlated to the residuals of the BPT and specific BPT (i.e. growth) vs. flow path (= river kilometer) relationship, indicating that shifts in bacterial carbon allocation explained local variations in bacterial metabolic activity, and these shifts were superimposed on the larger scale decline in carbon consumption and BP. The pattern in BP along the Hudson River is clearly a combi- nation of changes in consumption as well as in BGE, to the point that the pattern in BPT or growth would be impossible to recreate from any one of these 2 components. We conclude that BGE indicates changes in carbon allocation of bacteria that reflect shifts in relative BR and BP at shorter time and space scales that are distinct from larger overall patterns in consumption and BP.

Biomass, composition and activity of organism assemblages along a salinity gradient in sea ice subjected to river discharge in the Baltic Sea

A study was undertaken to examine the activity and composition of the seasonal Baltic Sea land-fast sea-ice biota along a salinity gradient in March 2003 in a coastal location in the SW coast of Finland. Using a multi-variable data set, the less well-known algal and protozoan communities, and algal and bacterial production in relation to the physical and chemical environment were investigated. Also, the first coincident measurements of bacterial production and dissolved organic matter (DOM) in a sea-ice system are reported. Communities in sea ice were clearly autotrophy-dominated with algal biomass representing 79% of the total biomass. Protozoa and rotifers made up 18% of biomass in the ice and bacteria only 3%. Highest biomasses were found in mid-transect bottom ice. Water column assemblages were clearly more heterotrophic: 39% algae, 12% bacteria and 49% for rotifers and protozoa. Few significant correlations existed between DOM and bacterial variables, reflecting the complex origin of ice DOM. Dynamics of dissolved organic carbon, nitrogen and phosphorus (DOC, DON and DOP) were also uncoupled. A functional microbial loop is likely to be present in the studied ice. Existence of an under-ice freshwater plume affects the ecosystem functioning: Under-ice water communities are influenced directly by river-water mixing, whereas the ice system seems to be more independent—the interaction mainly taking place through the formation of active bottom communities.

A nonradioactive assay of bacterial productivity optimized for oligotrophic pelagic environments

The measurement of bacterial production is a cornerstone of research in aquatic biogeochemistry and microbial ecology, yet the standard radioisotope‐based techniques are threatened by increasing logistical obstacles. The two primary goals of this study were (1) the development of a reliable nonradioactive assay of bacterial productivity interpretable in the context of previous 3H‐thymidine (3H‐TdR)—based metrics, and (2) maximizing the sensitivity of the assay to allow routine measurement of bacterial productivity in open‐ocean and low‐productivity environments. We optimize existing methods for immunochemical detection of the incorporation of the thymidine analog 5‐bromo‐2′‐deoxyuridine (BrdU) to present a functional assay of community bacterial productivity comparable to radioisotope‐based assays in economy and field implementation and capable of consistently detecting bacterial production rates within the range of 0.1 to 10 pmol BrdU L−1 h−1. A standardization procedure provides complete separation of radioisotopes from the working methodology and gives statistically consistent results between calibrations with no degradation of the labeled DNA standards. Immunoassayed BrdU incorporation rates were highly correlated with parallel measurements of 3H‐TdR incorporation rates spanning a range of 0.1 to 10 pmol L−1 h−1 (r = 0.96, n = 20, P &lt; 0.001). Model II linear regression (BrdU = 0.65[3H‐TdR] + 0.12) yielded a conversion factor not significantly different from that reported previously comparing incorporation rates measured using radioisotope protocols (3H‐BrdU = 0.69[3H‐TdR] − 0.81). The assay is interpretable in the context of 3H‐TdR—based measures of production, providing continuity as a nonradioactive measure of bacterial production in low‐productivity aquatic ecosystems.

Major shift in bacterioplankton utilization of enantiomeric amino acids between surfacewaters and the ocean's interior

The peptidoglycan layer of the bacterioplankton cell wall contains four major amino acids (alanine, Ala; serine, Ser; aspartic acid, Asp; and glutamic acid, Glu) in a characteristic enantiomeric ratio (D/L ratio). It is assumed that bacterioplankton are the only biological source of significance for these four specific D‐amino acid species in the ocean. The concentrations of these dissolved total enantiomeric amino acids were measured throughout the water column of the Faroe Shetland Channel (North Atlantic). Concurrently, the uptake of D‐ versus L‐Asp and of L‐leucine (as a measure of bacterial production) by bacterioplankton was determined. The D/L ratios of the dissolved total Ala, Asp, Glu, and Ser did not exhibit any particular trend with depth, averaging 0.49 for Ala, 0.42 for Asp, 0.15 for Glu, and 0.09 for Ser. The ratio of D‐/L‐Asp uptake by bacteria, however, increased from surface (D‐/LAsp uptake ratio of ~0.03) to deeper layers reaching a D‐/L‐Asp uptake ratio of close to 1 at 1,000 m depth, indicating that mesopelagic bacteria utilize D‐Asp almost as efficiently as L‐Asp. Subsequent laboratory experiments with surface‐water bacterioplankton assemblages incubated in nutrient‐amended artificial seawater confirmed that bacterioplankton, in the absence of other utilizable organic carbon, efficiently utilize D‐amino acids. In these laboratory experiments, the D‐/L‐Asp uptake ratio increased within 8 d to values similar to those obtained for mesopelagic bacteria. Furthermore, the presence of flagellates stimulated the uptake of D‐Asp probably via enhanced release of D‐amino acids during bacterivory. Thus, our results indicate that dissolved D‐amino acids might be an important substrate for mesopelagic bacterioplankton. The efficient uptake of D‐amino acids in the deeper layers of the ocean might indicate that mesopelagic bacterioplankton are utilizing bacterial cell wall‐derived organic matter efficiently.

Regeneration of dissolved organic matter by viral lysis in marine microbial communities

The influence of viruses on bacterial net growth and respiration was investigated in batch cultures with natural assemblages of marine bacterioplankton, which were manipulated with respect to abundance of natural virioplankton. In 1 set of cultures (-virus), a virus-free water sample (0.02 μm filtered) was inoculated with a bacterioplankton concentrate, and in a parallel set of cultures (control) a virus-containing water sample (0.2 pm filtered) was inoculated with the bacterioplankton concentrate. The 0.02 pm filtration procedure reduced viral abundance by 62 to 92 % in the -virus cultures relative to the parallel control cultures with the natural density of viruses (i.e. the fraction of natural viruses <0.2 μm). This approach allowed us to examine the effects of reduced viral densities on the production of natural assemblages of bacteria and viruses and on the distribution of added 3 H-thymidine into size fractions (the bacterial size fraction, viral size fraction, dissolved size fraction and respired fraction). The results showed significantly higher bacterial net growth and growth efficiency in cultures with a reduced abundance of viruses relative to control cultures with natural viral abundance, and indicated viral regulation of bacterial abundance in the control cultures. We suggest that viral lysis significantly affected the bacterial carbon cycling in the cultures by liberating a fraction of the organic matter already taken up by the bacteria, thus stimulating recycling of bacterial carbon and reducing the net bacterial production. The implications of such regeneration of dissolved organic matter by viral lysis for pelagic carbon cycling and for measurements of bacterial production are discussed.

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.

Bacterial dissolved organic carbon demand in McMurdo Dry Valley lakes, Antarctica

The proximal substrate source of planktonic bacteria is dissolved organic carbon (DOC), and the combined sources of DOC (bulk, phytoplankton production, and advected) set an upper limit on how much C is available for bacterial respiration (BR). We compared measurements of bacterial production (BP) and estimates of BR to measurements of what we assumed to be the major DOC inputs for three permanently iceߚcovered lakes in Antarctica: Lakes Fryxell, Hoare, and Bonney. These measured inputs, which included phytoplankton extracellular release (ECR), stream input, and upward diffusion of DOC across the chemocline, sediments, and benthic microbial mats, were three to eight times smaller than planktonic BR, suggesting that a major source of bacterial C was unaccounted for. Despite overestimating DOC and doubling bacterial growth efficiency (BGE), BR in the lakes was 1.25ߚ2 times greater than our estimate of DOC supply. We hypothesize that a major source of organic C for planktonic bacteria in these lakes comes from drawdown of bulk DOC and/or decomposition of particulate material.

Regulation of bacterial growth efficiency in a large turbid estuary

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 20:31-38 (1999) - doi:10.3354/ame020031 Regulation of bacterial growth efficiency in a large turbid estuary Fabio Roland1,2, Jonathan J. Cole1,* 1Institute of Ecosystem Studies, Box AB, Millbrook, New York 12545, USA 2Institute of Biological Sciences - Biology Department/UFJF, Juiz de Fora, Minas Gerais, 36036-330, Brazil *Corresponding author. E-mail: colej@ecostudies.org ABSTRACT: Bacterial secondary production transforms organic C from the environment into new bacterial biomass. Bacterial respiration generates energy and converts assimilated organic C into CO2. Two decades of research have given us a good understanding of the magnitude and regulation of bacterial production in pelagic ecosystems, but much less is known about bacterial respiration. Bacterial growth efficiency [BGE = BP/(BP + BR)] relates measurements of bacterial production and respiration. Recent reviews demonstrate a large range in BGE among and within systems; the regulation of this variance is not well understood. We made direct measurements of both BP and BR over a full seasonal cycle in the Hudson River, New York, and in a series of manipulative experiments. BGE was well correlated with BP and ranged from 0.04 to 0.66, with a majority (69%) between 0.2 and 0.5. BR and BP were correlated (r = 0.65; p < 0.0001) but BR was less variable than BP. Thus, much of the variation in BGE could be explained by the variation in BP. The relationship (based on 24 h bioassays) between BP and BGE fit a rectilinear hyperbola [BGE = 0.10 + 0.68BP(5.21 + BP)] and explained 70% of the variation in BGE (p < 0.001). During the relatively long incubation (24 h) required to measure BR, conditions diverge from ambient. BP, BR and BGE all increase during this incubation period. We used the relationships between BGE and BP and BR (above) to calculate realistic ambient estimates of BGE from short-term measurements (<1 h) of BP. Based on this approach, modeled BGE for the Hudson averaged 0.16 ± 0.05 (range = 0.07 to 0.23), about 50% lower than the values based on 24 h bioassays. Using this relationship we estimate pelagic BR in the tidal, freshwater Hudson River to be between 176 and 229 g C m-2 yr-1. KEY WORDS: BGE · Bacterial metabolism · Production · Respiration · Estuary · River · Ecosystems Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 20, No. 1. Publication date: November 30, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

Suspended bacterial biomass and activity in full-scale drinking water distribution systems: Impact of water treatment

Bacterial regrowth in drinking water distribution systems is a source of concern since it could result in non-compliance with water quality regulations, taste and odor problems, and may be associated with an increased risk of gastrointestinal illnesses. Bacterial regrowth is dependent on several factors, including the amount of substrate available for growth, such as biodegradable dissolved organic carbon (BDOC), oxidant residuals and the presence of corrosion. To investigate the impact of nutrients levels and oxidant residual maintenance, a full-scale investigation of two distribution systems was completed. This study presents data obtained from two distribution systems (DS) fed by different treatment trains: one DS has low BDOC concentrations and no free oxidant residual (St. Rose plant, Quebec, Canada), and the other has a high BDOC concentration and moderate concentrations of free oxidant residual (Pont Viau plant, Quebec, Canada). Monitoring included heterotrophic plate counts (HPC), total direct count by epifluorescence after acridine orange staining (AODC), direct viable counts (DVC-CTC method) and the measurement of bacterial production by 3H-thymidine incorporation. Results show that bacterial biomass (AODC and DVC) and bacterial production are lower in the DS fed by the treatment plant with a low BDOC concentration in the plant effluent. This difference is observed in warm water but not in cold water. The results suggest that HPCs are not a good indicator of bacterial regrowth in DSs. Finally, statistical analysis demonstrated that the treatment type and cumulative surface to volume ratio are the significant factors affecting regrowth in the distribution systems studied in warm waters.

Adsorption of dissolved free amino acids on colloidal DOM enhances colloidal DOM utilization but reduces amino acid uptake by orders of magnitude in marine bacterioplankton

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 166:99-108 (1998) - doi:10.3354/meps166099 Adsorption of dissolved free amino acids on colloidal DOM enhances colloidal DOM utilization but reduces amino acid uptake by orders of magnitude in marine bacterioplankton Stefan Schuster1, Jesus Maria Arrieta2, Gerhard J. Herndl2,* 1Institute of Zoology, University of Vienna, Althanstr. 14, A-1090 Vienna, Austria 2Dept of Biological Oceanography, Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands *Addressee for correspondence. E-mail: herndl@nioz.nl In an attempt to quantify abiotic adsorption of easily metabolizable dissolved free amino acids (DFAA) to colloidal dissolved organic matter (CDOM) in the sea, laboratory experiments were performed using dextran of various molecular size ranging from 4.4 to 2000 kDa or phytoplankton-derived CDOM (>1 kDa) as model CDOM, and leucine or a DFAA mixture. Abiotic leucine adsorption to dextran was found to be independent of the molecular size of the dextran. Adsorption of leucine to dextran and phytoplankton-derived CDOM was saturated at ~7.5 nmol mg-1 dextran-C; other DFAA species reached higher saturating concentrations (maximum: serine, 48.6 nmol mg-1 dextran-C). Adsorption of DFAA to dextran and phytoplankton-derived CDOM led to an approximately 3 times more efficient utilization of dextran and CDOM by marine bacterioplankton than colloidal matter to which no DFAA were adsorbed. Bacterial uptake of CDOM-adsorbed leucine, however, was reduced by 2 to 3 orders of magnitude as compared to the uptake of 'truly' free (non-adsorbed) leucine offered simultaneously at the same concentration. This finding might also be relevant for bacterial production measurements if leucine or thymidine are used as a tracer in colloidal-matter-rich micro-environments such as marine snow. All the CDOM-adsorbed DFAA (except glycine and threonine) were detectable without prior hydrolysis by o-phthalaldialdehyde (OPA) derivatization in the HPLC. Adsorption of labile DFAA on otherwise refractory CDOM also has important implications for the biogeochemical flux of CDOM by forming 'semi-labile' molecules which are more readily degradable by bacterioplankton and thereby reducing the flux of CDOM to the deep ocean. Colloidal matter · Dissolved free amino acids · Leucine · Bacterioplankton · Dissolved organic matter · Bacterial uptake · Bacterial production measurements Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 166. Publication date: May 28, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.