Bacterial Production Rates Research Articles

Organic priority substances and microbial processes in river sediments subject to contrasting hydrological conditions

Flood and drought events of higher intensity and frequency are expected to increase in arid and semi-arid regions, in which temporary rivers represent both a water resource and an aquatic ecosystem to be preserved. In this study, we explored the variation of two classes of hazardous substances (Polycyclic Aromatic Hydrocarbons and Nonylphenols) and the functioning of the microbial community in river sediments subject to hydrological fluctuations (Candelaro river basin, Italy). Overall, the concentration of pollutants (∑PAHs range 8–275ngg−1; ∑NPs range 299–4858ngg−1) suggests a moderate degree of contamination. The conditions in which the sediments were tested, flow (high/low) and no flow (wet/dry/arid), were associated to significant differences in the chemical and microbial properties. The total organic carbon contribution decreased together with the stream flow reduction, while the contribution of C-PAHs and C-NPs tended to increase. NPs were relatively more concentrated in sediments under high flow, while the more hydrophobic PAHs accumulated under low and no flow conditions. Passing from high to no flow conditions, a gradual reduction of microbial processes was observed, to reach the lowest specific bacterial carbon production rates (0.06fmolCh−1cell−1), extracellular enzyme activities, and the highest doubling time (40h) in arid sediments.In conclusion, different scenarios for the mobilization of pollutants and microbial processes can be identified under contrasting hydrological conditions: (i) the mobilization of pollutants under high flow and a relatively higher probability for biodegradation; (ii) the accumulation of pollutants during low flow and lower probability for biodegradation; (iii) the drastic reduction of pollutant concentrations under dry and arid conditions, probably independently from the microbial activity (abiotic processes). Our findings let us infer that a multiple approach has to be considered for an appropriate water resource exploitation and a more realistic prevision of the impact of pollutants in temporary waters.

Priming in the microbial landscape: periphytic algal stimulation of litter-associated microbial decomposers.

Microbial communities associated with submerged detritus in aquatic ecosystems often comprise a diverse mixture of autotrophic and heterotrophic microbes, including algae, bacteria, protozoa, and fungi. Recent studies have documented increased rates of plant litter mass loss when periphytic algae are present. We conducted laboratory and field experiments to assess potential metabolic interactions between natural autotrophic and heterotrophic microbial communities inhabiting submerged decaying plant litter of Typha angustifolia and Schoenoplectus acutus. In the field, submerged plant litter was either exposed to natural sunlight or placed under experimental canopies that manipulated light availability and growth of periphytic algae. Litter was collected and returned to the laboratory, where algal photosynthesis was manipulated (light/dark incubation), while rates of bacterial and fungal growth and productivity were simultaneously quantified. Bacteria and fungi were rapidly stimulated by exposure to light, thus establishing the potential for algal priming of microbial heterotrophic decay activities. Experimental incubations of decaying litter with 14C- and 13C-bicarbonate established that inorganic C fixed by algal photosynthesis was rapidly transferred to and assimilated by heterotrophic microbial decomposers. Periphytic algal stimulation of microbial heterotrophs, especially fungal decomposers, is an important and largely unrecognized interaction within the detrital microbial landscape, which may transform our current conceptual understanding of microbial secondary production and organic matter decomposition in aquatic ecosystems.

The Effects of Ocean Acidity and Elevated Temperature on Bacterioplankton Community Structure and Metabolism

By the end of the 21st century, mean sea surface temperatures are expected to increase 4?C, while atmospheric CO2 concentrations are predicted to triple causing seawater to become acidic. These compounding effects will undoubtedly have major consequences for the organisms and processes in the oceans. Bacterioplankton play a vital role in the marine carbon cycle and the oceans’ ability to sequester CO2. We utilized pCO2 perturbation experiments to investigate the effects of ocean acidity and elevated temperature on bacterioplankton community structure and metabolism. Terminal-restriction fragment length polymorphism (T-RFLP) of small subunit ribosomal (SSU) genes revealed that bacterioplankton incubated in lower pH conditions exhibited a reduction of species richness, evenness, and overall diversity, relative to those incubated in ambient pH conditions. Non-metric multidimensional scaling (MDS) of T-RFLP data resulted in clustering by pH suggesting that pH influenced the structure of these communities. Shifts in the dominant members of bacterioplankton communities incubated under different pH were observed in both T-RFLP and SSU clone library analyses. Both ambient and low pH communities were dominated by Gammaproteobacteria and Alphaproteobacteria, although abundance of Alphaproteobacteria increased in communities incubated at lower pH. This was expressed by the gamma to alpha ratio dropping from ~9 to 4, respectively. In general, the representative taxa from these two classes were distinctly different between the treatments, with a few taxa found to be persistent in both treatments. Changes in the structure of bacterioplankton communities coincided with significant changes to their overall metabolism. Bacterial production rates decreased, while bacterial respiration increased under lower pH conditions. This study highlights the ability of bacterioplankton communities to respond to ocean acidification both structurally and metabolically, which may have significant implications for their ecological function in the marine carbon cycle and the ocean’s response to global climate change.

Chemical properties and fluorescence of DOM in relation to biodegradation in the interconnected Marmara–North Aegean Seas during August 2008

The dynamics of dissolved organic matter (DOM) in the Marmara Sea–Dardanelles Straits–North Aegean Sea were investigated using measurements of dissolved organic carbon and nitrogen (DOC, DON), PARAFAC modeling of 3-D excitation–emission fluorescence spectra and bacterial production (BP) and respiration (BR) rates. In the surface brackish waters, chemical parameters showed an increase from the Aegean to the Marmara (DOC: 65–217μmolL−1; DON: 3.08–9.34μmolL−1; Dissolved Inorganic Nitrogen (DIN): 0.044–1.38), followed by an increase in BP rates (7.2–195nmolL−1d−1). In the subsurface waters, DIN also showed an increase in the Marmara basin (0.085–9.79μmolL−1) followed by an increase in BP rates (3.3–17.4nmolL−1d−1). PARAFAC modeling revealed three fluorescent components: λex/λem: <260(330)/464nm, humic-like; λex/λem: <(260) 285/364nm, quinone-like; λex/λem: 270/308nm, tyrosine-like. DOC:DON ratios were found similar for the Marmara (21±3) and the N. Aegean Sea (19±2). The slopes ΔDOC:ΔDON suggested that in the Marmara Sea mineralization processes require more carbon relative to nitrogen (22.3), whereas in the N. Aegean there is preferential removal of nitrogen over carbon (5.66). The lack of significant correlation between DOC and AOU (apparent oxygen utilization) in the deep Marmara waters indicates that particulate organic matter is important in deep mineralization processes.

Differential response of planktonic primary, bacterial, and dimethylsulfide production rates to static vs. dynamic light exposure in upper mixed-layer summer sea waters

Abstract. Microbial plankton experience short-term fluctuations in total solar irradiance and in its spectral composition as they are vertically moved by turbulence in the oceanic upper mixed layer (UML). The fact that the light exposure is not static but dynamic may have important consequences for biogeochemical processes and ocean–atmosphere fluxes. However, most biogeochemical processes other than primary production, like bacterial production or dimethylsulfide (DMS) production, are seldom measured in sunlight and even less often in dynamic light fields. We conducted four experiments in oligotrophic summer stratified Mediterranean waters, where a sample from the UML was incubated in ultraviolet (UV)-transparent bottles at three fixed depths within the UML and on a vertically moving basket across the same depth range. We assessed the response of the phyto- and bacterioplankton community with physiological indicators based on flow cytometry singe-cell measurements, fast repetition rate fluorometry (FRRf), phytoplankton pigment concentrations and particulate light absorption. Dynamic light exposure caused a subtle disruption of the photoinhibition and photoacclimation processes associated with ultraviolet radiation (UVR), which slightly alleviated bacterial photoinhibition but did not favor primary production. Gross DMS production (GPDMS) decreased sharply with depth in parallel to shortwave UVR, and displayed a dose-dependent response that mixing did not significantly disrupt. To our knowledge, we provide the first measurements of GPDMS under in situ UV-inclusive optical conditions.

Dark Carbon Fixation: An Important Process in Lake Sediments

Close to redox boundaries, dark carbon fixation by chemoautotrophic bacteria may be a large contributor to overall carbon fixation. Still, little is known about the relative importance of this process in lake systems, in spite the potentially high chemoautotrophic potential of lake sediments. We compared rates of dark carbon fixation, bacterial production and oxygen consumption in sediments from four Swedish boreal and seven tropical Brazilian lakes. Rates were highly variable and dark carbon fixation amounted up to 80% of the total heterotrophic bacterial production. The results indicate that non-photosynthetic carbon fixation can represent a substantial contribution to bacterial biomass production, especially in sediments with low organic matter content.

Diurnal variations in bacterial and viral production in Cochin estuary, India

Microbes play a central role in the decomposition and remineralization of organic matter and recycling of nutrients in aquatic environments. In this study, we examined the influence of physical, chemical, and biological parameters on the rate of bacterial production (BP) and viral production (VP) with respect to primary production over a diurnal period in Cochin estuary. Time series measurements were made every 2h for 12h (6a.m.-6p.m.) during periods of low and high salinities. The light intensity as photosynthetically active radiation, temperature, salinity, nutrients like NO3-N, SiO4-Si, and PO4-P, and chlorophyll a (Chl a) were measured along with BP, VP, and net primary production (NPP). NPP showed a strong positive correlation with light and Chl a (r (2) = 0.56 and 0.47, respectively), while VP showed a strong positive correlation with light, salinity, and Chl a (r (2) = 0.37, 0.58, and 0.37, respectively) and a negative correlation with BP (r (2) = -0.39) at P ≤ 0.05. We observed a diurnal pattern in BP but did not have any significant correlation with light. Similar diurnal pattern was seen in VP, the peak of which was in succession with BP, suggesting that virus-mediated lysis plays an important role in loss processes of bacteria in Cochin estuary. The results of our study highlight the light-dependent and physicochemical-dependent diurnal variation in virioplankton production in a tropical estuarine ecosystem.

Microbial carbon and nitrogen production under experimental conditions combining warming with increased ultraviolet-B radiation in Mediterranean coastal waters

The effects of warming and increased ultraviolet-B radiation (UVBR, 280–320nm) have been rarely studied at food web scale and very few studies have considered the effect of combining these two climatic stressors. Microbial carbon and nitrogen dynamics were studied under the single and combined conditions of +3°C warming and +20% UVBR above the natural levels (control) during a 10-day mesocosm experiment in coastal Mediterranean waters. The effect of increased UVBR on primary production (PP) and bacterial production (BP) rates was rarely significant during the experiment. Warming alone or combined with increased UVBR significantly reduced BP by about 30% but also significantly increased PP by an average of 90%. No accumulation of particulate organic matter was observed during the experiment but, in the warmed mesocosms, the cumulative carbon and nitrogen losses were greater (ca. +40%). The main short-term consequence of warming was, therefore, a shift of the food web dynamics leading to higher C and N losses. This suggests a more efficient transfer of the newly produced microbial production to the upper trophic levels and a greater exportation into deeper waters through settlement under warmer conditions in Mediterranean coastal waters in the future.

Different temperature adaptation in Arctic and Atlantic heterotrophic bacteria in the Barents Sea Polar Front region

In the northern Barents Sea, at and around the Polar Front, carbon cycle variables were investigated during 2weeks in late summer of 2007. Arctic Water primary production in the experimental period averaged 50mmol C m−2day−1, as estimated from satellite sensed chlorophyll. In Atlantic waters, which appeared to just have passed the culmination of a late summer bloom, primary production was 125mmol C m−2day−1. Total organic carbon (TOC) averaged 82.4μM C in the mixed layer, and the values showed a gradient with highest values to the southeast and lowest to the northwest. The distribution of TOC was not related to the distribution of Atlantic and Arctic waters, although the highest values were found in Atlantic Water. Integrated bacterial production in the mixed layer, as estimated from thymidine incorporation rates, averaged 6.3% of primary production. In Atlantic Water, over the depth of the mixed layer, bacterial production rate averaged 0.40mmol C m−3day−1, which was 6.6 times the average in Arctic Water and 2.3 times the average in the front regions. Below 30m depth, bacterial production rates were generally higher in the Arctic Water than in the Atlantic Water. Moreover, when production rates of bacteria were compared according to temperature, the rates in Arctic Water were systematically higher than the rates in Atlantic Water. This difference implies that the heterotrophic bacteria from the Arctic have adapted towards higher growth efficiency than the bacteria in Atlantic Water.

Temperature effects on the heterotrophic bacteria, heterotrophic nanoflagellates, and microbial top predators of the NW Mediterranean

Prokaryotes and protists are important players in the carbon biogeochemistry of mar- ine ecosystems, and temperature is one of the physical factors most influential in the metabolism and composition of plankton communities. Small changes in temperature can change the flow of carbon and the community structure of planktonic ecosystems, and climatological models predict a rise in temperature of 2 to 5°C toward the end of the century in the NW Mediterranean. Labora- tory culture experiments have shown that warming can increase the transfer of carbon between bacteria and protists and alter the community composition of microbial top predators (i.e. ciliates and dinoflagellates) by increasing the abundance of bacterivores and producing the extinction of herbivores. Here, we tested whether a small rise in temperature would produce these effects in the coastal Mediterranean. Between March 2003 and February 2004, we established 12 micro- cosm experiments with water from the Bay of Blanes. The samples were incubated for 48 h at ambient and warmer temperatures (~2.7°C higher than in situ values), and the net and gross growth rates of bacteria and heterotrophic nanoflagellates (HNF) were measured using unfiltered and 0.8 µm filtered treatments. Warming increased the rates of bacterial gross production and bacterial losses to grazing with a clear seasonality; the largest increments in the rates were observed during the cooler months of the year. Warming did not change the net growth rates of dinoflagellates. It decreased the net production of HNF and the net growth rates of ciliates but did not promote the extinction of herbivorous protists. Temperature changed the microbial food web function in NW Mediterranean waters, with small alterations in the community composition of microbial top predators.

Multiscale control of bacterial production by phytoplankton dynamics and sea ice along the western Antarctic Peninsula: A regional and decadal investigation

We present results on phytoplankton and bacterial production and related hydrographic properties collected on nine annual summer cruises along the western Antarctic Peninsula. This region is strongly influenced by interannual variations in the duration and extent of sea ice cover, necessitating a decade-scale study. Our study area transitions from a nearshore region influenced by summer runoff from glaciers to an offshore, slope region dominated by the Antarctic Circumpolar Current. The summer bacterial assemblage is the product of seasonal warming and freshening following spring sea ice retreat and the plankton succession occurring in that evolving water mass. Bacterial production rates averaged 20mgCm−2d−1 and were a low (5%) fraction of the primary production (PP). There was significant variation in BP between regions and years, reflecting the variability in sea ice, chlorophyll and PP. Leucine incorporation was significantly correlated (r2 ranging 0.2–0.7, p<0.001) with both chlorophyll and PP across depths, regions and years indicating strong phytoplankton–bacteria coupling. Relationships with temperature were variable, including positive, negative and insignificant relationships (r2<0.2 for regressions with p<0.05). Bacterial production is regulated indirectly by variations in sea ice cover within regions and over years, setting the levels of phytoplankton biomass accumulation and PP rates; these in turn fuel BP, to which PP is coupled via direct release from phytoplankton or other less direct pathways.

Distribution and metabolism of dimethylsulfoniopropionate (DMSP) and phylogenetic affiliation of DMSP‐assimilating bacteria in northern Baffin Bay/Lancaster Sound

We determined the distribution and bacterial metabolism of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) in the two dominant surface water masses in northern Baffin Bay/Lancaster Sound during September 2008. Concentrations of particulate DMSP (DMSPp; 5–70 nmol L−1) and the DMSPp:Chl a ratios (15–229 nmol μg−1) were relatively high, suggesting the presence of DMSP‐rich phytoplankton taxa. Photosynthetic picoeukaryotes and total prokaryotes were tenfold and threefold more abundant in Baffin Bay surface water (BBS) than in Arctic surface water (AS), respectively. Heterotrophic bacterial production (0.07–2.5μC L−1 d−1) and bacterial turnover rate constants for dissolved DMSP (DMSPd) were low (0.03–0.11 h−1) compared with the values previously reported in warmer and more productive environments. Nonetheless, a relatively large proportion (12%–31%) of the DMSP metabolized by the bacteria was converted into DMS. Additionally, between 40% and 65% of the total bacterial cells incorporated sulfur from DMSPd, with Gammaproteobacteriaand non‐Roseobacter Alphaproteobacteria (AlfR‐) contributing proportionally more to total DMSP‐incorporating cells. The contribution of AlfR‐ to the total prokaryotic community was 50% higher in BBS than in AS, while the bacterial rate constants for DMSPd turnover were 78% higher in BBS than in AS. These results show that the two different Arctic water masses host specific microbial assemblages that result in distinct affinity for DMSP.

Frothy bloat in ruminants: Cause, occurrence, and mitigation strategies

A number of pasture and feedlot management practices and feed additives have reduced, but not eliminated the occurrence of frothy bloat in cattle. Bloat occurs as a result of complex interactions among the feed, rumen microbial populations and the host. Factors such as soluble protein levels in the feed, rates of feed digestion, bacterial slime production and digesta passage rates, all play a role in the likelihood of bloat. Practices that lower soluble protein levels and retard the rate of feed digestion can reduce the risk of bloat as can grazing alfalfa at advanced stages of maturity. Similarly, processing grain to an optimal particle size, inclusion of ionophores in the diet and allowing a period of adaptation during the transition from forage to grain diets lowers the incidence of feedlot bloat. Pluronic detergents which disperse the stable froth in the rumen can be effective in the treatment and prevention of both pasture and feedlot bloat. The sporadic and unpredictable nature of frothy bloat often makes it unrealistic for preventative measures to be applied to all animals at risk. Genetic engineering of condensed tannin containing, bloat-safe varieties of alfalfa and clover may eliminate the occurrence of bloat in cattle grazing these forages. Understanding the factors that regulate intake and contribute to bacterial slime production could provide additional insight into feedlot bloat. Comparing of the rumen microbial metagenomes and metatrascriptomes of bloated and non-bloated animals should provide a fresh perspective on the role of rumen microbial populations in bloat. The key to the successful prevention of frothy bloat lies in a thorough understanding of the feed, microbial and host factors involved in the condition.

Viral and bacterial abundance and production in the Western Pacific Ocean and the relation to other oceanic realms

We completed a transect through the Western Pacific Warm Pool to examine how environmental variables may influence viral and bacterial abundance and production rates in this globally important oceanic region. Of the variables analyzed, viral abundance and production had the most significant relationship to bacterial cell abundance: viral parameters were not significantly correlated to the measured environmental variables, including temperature. Bacterial production rates were significantly correlated to temperature in open ocean waters, but not in waters close to land masses. Analyses of 16S rRNA gene by pyrosequencing indicated only minor changes in eubacterial community structure across the transect, with α-proteobacteria dominating all sampled populations. Diversity within the prokaryotic community did not correlate directly with viral abundance or activity. Comparisons to two other ocean-scale transects (> 8000 km of open ocean in total) in the Atlantic Ocean indicated that correlations between viral and bacterial abundance and production relative to environmental variables are regime dependent. In particular, correlations to temperature showed remarkable differences across the three transects. Collectively, our observations suggest that seemingly similar oceanic regions may have very different microbial community responses to environmental variables. Our observations and analyses demonstrate that ocean-scale generalizations may not apply in the case of viral ecology.

Response of a summertime Antarctic marine ­bacterial community to glucose and ammonium enrichment

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 64:205-220 (2011) - DOI: https://doi.org/10.3354/ame01519 Response of a summertime Antarctic marine ­bacterial community to glucose and ammonium enrichment Hugh W. Ducklow1,*, Kristen M. S. Myers1, Matthew Erickson1, Jean-François Ghiglione2,3, Alison E. Murray4 1Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA 2CNRS, UMR 7621, Laboratoire d’Océanographie Biologique de Banyuls, BP44, 66650 Banyuls-sur-Mer cedex, France 3UPMC Univ Paris 06, UMR 7621, Laboratoire ARAGO, Avenue Fontaulé, BP44, 66650 Banyuls-sur-Mer, France 4Desert Research Institute, Reno, Nevada 89512, USA *Email: hducklow@mbl.edu ABSTRACT: Along the western Antarctic Peninsula, marine bacterioplankton respond to the spring phytoplankton bloom with increases in abundance, production and growth rates, and a seasonal succession in bacterial community composition (BCC). We investigated the response of the bacterial community to experimental additions of glucose and ammonium, alone or in combination, incubated in replicate carboys (each: 50 l) over 10 d in November 2006. Changes in bulk properties (abundance, production rates) in the incubations resembled observations in the nearshore environment over 8 seasons (2001 to 2002 through 2008 to 2009) at Palmer Stn (64.8°S, 64.1°W). Changes in bulk properties and BCC in ammonium-amended carboys were small relative to controls, compared to the glucose-amended treatments. The BCC in Day 0 and Day 10 controls and ammonium treatments were >72% similar when assessed by denaturing-gradient gel electrophoresis (DGGE), length heterogeneity polymerase chain reaction (LH-PCR) and capillary electrophoresis single-strand conformation polymorphism (CE-SSCP) fingerprinting techniques. Bacterial abundance increased 2- to 10-fold and leucine incorporation rates increased 2- to 30-fold in the glucose treatments over 6 d. The BCC in carboys receiving glucose (with or without ammonium) remained >60% similar to that in Day 0 controls at 6 d and evolved to <20% similar to that in Day 0 controls after 10 d incubation. The increases in bacterial production rates, and the changes in BCC, suggest that selection for glucose-utilizing bacteria was slow under the ambient environmental conditions. The results suggest that organic carbon enrichment is a major factor influencing the observed winter-to-summer increase in bacterial abundance and activity. In contrast, the BCC was relatively robust, changing little until after repeated additions of glucose and prolonged (~10 d) incubation. KEY WORDS: Antarctica · Bacterial community composition · Bioassay · Marine bacterioplankton Full text in pdf format NextCite this article as: Ducklow HW, Myers KMS, Erickson M, Ghiglione JF, Murray AE (2011) Response of a summertime Antarctic marine ­bacterial community to glucose and ammonium enrichment. Aquat Microb Ecol 64:205-220. https://doi.org/10.3354/ame01519 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 64, No. 3. Online publication date: September 20, 2011 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2011 Inter-Research.

2,4,6-Trinitrotoluene mineralization and bacterial production rates of natural microbial assemblages from coastal sediments

The nitrogenous energetic constituent, 2,4,6-Trinitrotoluene (TNT), is widely reported to be resistant to bacterial mineralization (conversion to CO 2); however, these studies primarily involve bacterial isolates from freshwater where bacterial production is typically limited by phosphorus. This study involved six surveys of coastal waters adjacent to three biome types: temperate broadleaf, northern coniferous, and tropical. Capacity to catabolize and mineralize TNT ring carbon to CO 2 was a common feature of natural sediment assemblages from these coastal environments (ranging to 270+/−38 μg C kg −1 d −1). More importantly, these mineralization rates comprised a significant proportion of total heterotrophic production. The finding that most natural assemblages surveyed from these ecosystems can mineralize TNT ring carbon to CO 2 is consistent with recent reports that assemblage components can incorporate TNT ring carbon into bacterial biomass. These data counter the widely held contention that TNT is recalcitrant to bacterial catabolism of the ring carbon in natural environments.

Transparent exopolymer particle (TEP) dynamics in the eastern Mediterranean Sea

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 431:107-118 (2011) - DOI: https://doi.org/10.3354/meps09110 Transparent exopolymer particle (TEP) dynamics in the eastern Mediterranean Sea E. Bar-Zeev1, T. Berman2, E. Rahav1, G. Dishon1, B. Herut3, N. Kress3, I. Berman-Frank1,* 1Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat Gan, Israel 2Israel Oceanographic and Limnological Research, The Yigal Allon Kinneret Limnological Laboratory, Midgal, Israel 3Israel Oceanographic and Limnological Research, National Institute of Oceanography, Haifa, Israel *Corresponding author. Email: irfrank@mail.biu.ac.il ABSTRACT: Depth and spatial distribution patterns of transparent exopolymer particles (TEP) were measured during 2 east to west cruise transects across the ultra-oligotrophic Levantine basin, eastern Mediterranean Sea (SESAME, September 2008; ISRLEV, July 2009), and at 2 stations 20 and 50 km offshore (2008). TEP distribution was examined relative to chlorophyll a concentrations, bacterial production, and alkaline phosphatase activity (APA), taken as a measure of phosphorus (P) stress. During the stratified period, TEP levels were highest in a 5 m surface layer and correlated positively with APA as P concentrations decreased. On the transects, TEP concentrations from both surface and depth (1000 m) samples increased from west to east, corresponding to a pattern of increasing oligotrophy. In pelagic waters, maximal rates of bacterial production and TEP concentrations were consistently measured in surface samples. These contained abundant large (170 µm) TEP with numerous associated bacteria, possibly derived from algal or bacterial release or detritus. Lowest TEP concentrations were found in the deep chlorophyll maximum layer where TEP appeared as small (~4 µm) particles with only few attached bacteria. In deeper (300 to 1000 m) samples, both TEP concentrations and size increased, with most particles having associated bacteria. Our data augment previous studies on the formation of TEP and the subsequent utilization of this material by heterotrophic bacteria both in the euphotic zone and in deeper waters. Moreover, our study suggests that in ultra-oligotrophic environments such as the Levantine basin, TEP plays an especially important role in carbon cycling and transportation. KEY WORDS: TEP · Mediterranean Sea · Levantine basin · Bacterial production · Carbon cycling Full text in pdf format PreviousNextCite this article as: Bar-Zeev E, Berman T, Rahav E, Dishon G, Herut B, Berman-Frank I (2011) Transparent exopolymer particle (TEP) dynamics in the eastern Mediterranean Sea. Mar Ecol Prog Ser 431:107-118. https://doi.org/10.3354/meps09110 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 431. Online publication date: June 09, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Ultrahigh bacterial production in a eutrophic subtropical Australian river: Does viral lysis short‐circuit the microbial loop?

We studied trophic dynamics in a warm eutrophic subtropical river (Bremer River, Australia) to determine potential sources of dissolved organic carbon (DOC) and the fate of heterotrophic bacterial production. Sustained high rates of bacterial production suggested that the exogenous DOC was accessible (labile). Bacterial specific growth rates (0.2 h−1 to 1.8 h−1) were some of the highest measured for natural aquatic ecosystems, which is consistent with high respiration rates. Bacteria consumed 10 times more organic carbon than that supplied by the daily algal production, a result that implies that terrestrial sources of organic carbon were driving the high rates of bacterial production. Viruses (1011 L−1) were 10 times more abundant than bacteria; the viral to bacterial ratio ranged from 3.5 to 12 in the wet summer and 11 to 35 in the dry spring weather typical of eutrophic environments. Through a combination of high bacterial respiration and phage lysis, a continuous supply of terrestrial DOC was lost from the aquatic ecosystem in a CO2‐vented bacterial–viral loop. Bacterial processing of DOC in subtropical rivers may be contributing disproportionately large amounts of CO2 to the global carbon cycle compared to temperate freshwater ecosystems.

Reversible Hydrogen Electrode Application as Indicator Electrode for Real Time Kinetic Study of Microbial H2 Production

The Reversible Hydrogen Electrode (RHE) potential depends on the pH and the H2 pressure which determines the disolved hydrogen concentration according to the Henry law. RHE was applied as hydrogen sensor for real time bacterial hydrogen production rate evaluation employing the photosynthetic Rodobacter Capsulatus strain IR3 in 10 ml reactor containing RCV medium. The reliable determination of the produced H2 volume for determination of the process rate requires big reactor volumes since the H2 production rate is small, measured in mL/hour and the precise measurements of small gas volumes is very complicated. The RHE potential monitoring however allows real time determination of the generated H2 and hence the process rate without consumption of great reagent amounts.

Effects of alcohols on bacterial cellulose production by Acetobacter xylinum 186

To improve the yield of cellulose production in bacteria, we investigated the stimulatory effects of six different alcohols during fermentation of Acetobacter xylinum 186. Our study showed that after static fermentation at 30°C for 6 days, bacterial culture with 1.0% (v/v) of methanol added in the medium produced the highest bacterial cellulose (BC) yield at 103.5 mg/100 ml, which was 21.8% higher than the control group. Addition of 0.5% of ethylene glycol in the culture yielded 105.5 mg/100 ml BC, 24.1% higher than the control group. Adding 0.5% of n-propanol yielded 96.4 mg/100 ml BC, 13.4% higher; 3.0% of glycerol yielded 108.3 mg/100 ml BC, 27.4% higher; 0.5% of n-butanol yielded 132.6 mg/100 ml BC, 56.0% higher; and 4.0% of mannitol in the culture yielded 125.2 mg/100 ml BC, 47.3% higher, respectively. The rate of bacterial cellulose production increased with the growth rate of the bacteria. The stimulatory effects of these alcohols that we observed were significant in the later stage of fermentation, which was considered to be important for the biosynthesis of bacterial cellulose.