Fates of dissolved free amino acids in groundwater discharged through stream bed sediments

Laboratory simulations were used to investigate the immobilization of dissolved free amino acids (DFAAs) from groundwater discharged up through cores of stream-bed sediments from a first order stream. At natural concentrations, 99% of DFAAs supplied in groundwater were immobilized, with 14–25% of this material respired and the remainder retained in the lower layers of the cores (depth = 7.5 cm). Immobilization efficiencies increased with increasing groundwater DFAA concentrations and discharge rates. Moderate enrichments (up to 1 mg l^–1) appeared to stimulate biotic immobilization of DFAAs, while abiotic processes accounted for much of the increased immobilization at higher enrichments (tested up to 100 mg l^–1). Variability in groundwater discharge rates induced no changes in the proportional contribution of biotic and abiotic immobilization processes. Thus relative contributions of DFAA concentration and groundwater discharge rate to a given DFAA load (concentration × discharge rate) influenced the degree to which immobilized DFAAs were retained (as microbial biomass or adsorbed to the biofilm) or respired. Results showed that DFAAs in groundwater discharged through the stream-bed are in a highly dynamic state of flux, suggesting that these compounds may be more significant to the transfer of organic matter to the benthic trophic structure than their normally low concentrations in groundwater would imply.     

Immobilization and mineralization of dissolved free amino acids by stream-bed biofilms

1. Radiolabelled (¹⁴C) amino acids were used to investigate the influence of sediment size as well as dissolved free amino acid (DFAA) concentration and composition on immobilization and mineralization of DFAAs by biofilms from a first-order stream. 2. Over time (240 min), biofilms on stony substrata immobilized a DFAA mixture more effectively than those on sandy substrata, however proportional mineralization of immobilized DFAAs was higher for sandy substrata (36 v 20%). 3. Using stony substrata, the DFAA mixture was immobilized more rapidly than glycine alone at ‘near-natural’ amino acid concentrations (c. 37 μgl^?1), as well as enriched concentrations (1 and 100 mg 1-^?1). Instantaneous rates of glycine immobilization and mineralization were not saturated at glycine enrichments of up to 980 mgl^?1. 4. With both the amino acid mixture and glycine alone, proportional mineralization of the immobilized amino acids increased on enrichment to Img 1-^?1 (DFAA mixture: from 25 to 37%; glycine alone: from 50 to 54%), but then fell on further enrichment to 100mgl^?1 (DFAA mixture: 11%; glycine alone: 7%). 5. Results are discussed in terms of the potential trophic utility of immobilized DFAAs as well as the apparent roles of biotic and abiotic immobilization mechanisms. Immobilization and mineralization responses to variables investigated in this study give an insight into potential variability of carbon immobilization and retention in stream-bed sediments. This is fundamental to an understanding of how DOC may become available to higher trophic levels.     

Annual Cycle of Bacterial Secondary Production in Five Aquatic Habitats of the Okefenokee Swamp Ecosystem

Rates of bacterial secondary production by free-living bacterioplankton in the Okefenokee Swamp are high and comparable to reported values for a wide variety of marine and freshwater ecosystems. Bacterial production in the water column of five aquatic habitats of the Okefenokee Swamp was substantial despite the acidic (pH 3.7), low-nutrient, peat-accumulating character of the environment. Incorporation of [³H]thymidine into cold-trichloroacetic acid-insoluble material ranged from 0.03 to 2.93 nmol liter⁻¹ day⁻¹) and corresponded to rates of bacterial secondary production of 3.4 to 342.2 μg of carbon liter⁻¹ day⁻¹ (mean, 87.8 μg of carbon liter⁻¹ day⁻¹). Bacterial production was strongly seasonal and appeared to be coupled to annual changes in temperature and primary production. Bacterial doubling times ranged from 5 h to 15 days and were fastest during the warm months of the year, when the biomass of aquatic macrophytes was high, and slowest during the winter, when the plant biomass was reduced. The high rates of bacterial turnover in Okefenokee waters suggest that bacterial growth is an important mechanism in the transformation of dissolved organic carbon into the nutrient-rich bacterial biomass which is utilized by microconsumers.     

An Outbreak of Nonflocculating Catabolic Populations Caused the Breakdown of a Phenol-Digesting Activated-Sludge Process

Activated sludge was fed phenol as the sole carbon source, and the phenol-loading rate was increased stepwise from 0.5 to 1.0 g liter⁻¹ day⁻¹ and then to 1.5 g liter⁻¹ day⁻¹. After the loading rate was increased to 1.5 g liter⁻¹ day⁻¹, nonflocculating bacteria outgrew the sludge, and the activated-sludge process broke down within 1 week. The bacterial population structure of the activated sludge was analyzed by temperature gradient gel electrophoresis (TGGE) of PCR-amplified 16S ribosomal DNA (rDNA) fragments. We found that the population diversity decreased as the phenol-loading rate increased and that two populations (designated populations R6 and R10) predominated in the sludge during the last several days before breakdown. The R6 population was present under the low-phenol-loading-rate conditions, while the R10 population was present only after the loading rate was increased to 1.5 g liter⁻¹ day⁻¹. A total of 41 bacterial strains with different repetitive extragenic palindromic sequence PCR patterns were isolated from the activated sludge under different phenol-loading conditions, and the 16S rDNA and gyrB fragments of these strains were PCR amplified and sequenced. Some bacterial isolates could be associated with major TGGE bands by comparing the 16S rDNA sequences. All of the bacterial strains affiliated with the R6 population had almost identical 16S rDNA sequences, while the gyrB phylogenetic analysis divided these strains into two physiologically divergent groups; both of these groups of strains could grow on phenol, while one group (designated the R6F group) flocculated in laboratory media and the other group (the R6T group) did not. A competitive PCR analysis in which specific gyrB sequences were used as the primers showed that a population shift from R6F to R6T occurred following the increase in the phenol-loading rate to 1.5 g liter⁻¹ day⁻¹. The R10 population corresponded to nonflocculating phenol-degrading bacteria. Our results suggest that an outbreak of nonflocculating catabolic populations caused the breakdown of the activated-sludge process. This study also demonstrated the usefulness of gyrB-targeted fine population analyses in microbial ecology.     

Assessing Phytoplankton and Bacterioplankton Production During Early Spring in Lake Erken, Sweden

The spring development of both phytoplankton and bacterioplankton was investigated between 18 April and 7 May 1983 in mesotrophic Lake Erken, Sweden. By using the lake as a batch culture, our aim was to estimate, via different methods, the production of phytoplankton and bacterioplankton in the lake and to compare these production estimates with the actual increase in phytoplankton and bacterioplankton biomass. The average water temperature was 3.5°C. Of the phytoplankton biomass, >90% was the diatom Stephanodiscus hantzchii var. pusillus, by the peak of the bloom. The ¹⁴C and O₂ methods of estimating primary production gave equivalent results (r = 0.999) with a photosynthetic quotient of 1.63. The theoretical photosynthetic quotient predicted from the C/NO₃ N assimilation ratio was 1.57. The total integrated incorporation of [¹⁴C]bicarbonate into particulate material (>1 μm) was similar to the increase in phytoplankton carbon determined from cell counts. Bacterioplankton increased from 0.5 × 10⁹ to 1.52 × 10⁹ cells liter⁻¹ (~0.5 μg of C liter⁻¹ day⁻¹). Estimates of bacterioplankton production from rates of [³H]thymidine incorporation were ca. 1.2 to 1.7 μg of C liter⁻¹ day⁻¹. Bacterial respiration, measured by a high-precision Winkler technique, was estimated as 4.8 μg of C liter⁻¹ day⁻¹, indicating a bacterial growth yield of 25%. The bulk of the bacterioplankton production was accounted for by algal extracellular products. Gross bacterioplankton production (production plus respiration) was 20% of gross primary production, per square meter of surface area. We found no indication that bacterioplankton production was underestimated by the [³H]thymidine incorporation method.     

Rapid Degradation of Isolated Lignins by Phanerochaete chrysosporium

Phanerochaete chrysosporium degraded purified Kraft lignin, alkali-extracted and dioxane-extracted straw lignin, and lignosulfonates at a similar rate, producing small-molecular-weight (~1,000) soluble products which comprised 25 to 35% of the original lignins. At concentrations of 1 g of lignin liter⁻¹, 90 to 100% of the acid-insoluble Kraft, alkali straw, and dioxane straw lignins were degraded by 1 g of fungal mycelium liter⁻¹ within an active ligninolytic period of 2 to 3 days. Cultures with biomass concentrations as low as 0.16 g liter⁻¹ could also completely degrade 1 g of lignin liter⁻¹ during an active period of 6 to 8 days. The absorbance at 280 nm of 2 g of lignosulfonate liter⁻¹ increased during the first 3 days of incubation and decreased to 35% of the original value during the next 7 days. The capacity of 1 g of cells to degrade alkali-extracted straw lignin under optimized conditions was estimated to be as high as 1.0 g day⁻¹. This degradation occurred with a simultaneous glucose consumption rate of 1.0 g day⁻¹. When glucose or cellular energy resources were depleted, lignin degradation ceased. The ability of P. chrysosporium to degrade the various lignins in a similar manner and at very low biomass concentrations indicates that the enzymes responsible for lignin degradation are nonspecific.     

Modulation of Affinity of a Marine Pseudomonad for Toluene and Benzene by Hydrocarbon Exposure

Trace (microgram liter⁻¹) quantities of either toluene or benzene injected into an amino-acid-limited continuous culture of Pseudomonas sp. strain T2 were utilized immediately with affinities of 2.6 and 6.8 liters g of cells⁻¹ h⁻¹, respectively, and yielded large amounts of organic products, carbon dioxide, and cells. The immediate utilization of hydrocarbons by hydrocarbon-deprived organisms helps to establish the nutritional value of nonpolar substrates in the environment. The observation of small Michaelis constants for toluene transport led to tests of metabolic competition between hydrocarbons; however, competitive inhibition of toluene metabolism was not found for benzene, naphthalene, xylene, dodecane, or amino acids. Benzene and terpenes were inhibitory at milligram liter⁻¹ concentrations. Toluene was metabolized by a strongly inducible system when compared with benzene. The capacity of toluene to effect larger affinity values increased with exposure time and concentration. The kinetics of induction suggested saturation phenomena, resulting in an induction constant, K_ind, of 96 μg of toluene liter⁻¹. Maximal induction of amino-acid-grown cells required about 80 h, with the affinity reaching 317 liters g of cells⁻¹ h⁻¹.     

Initial Effects of the Mount St. Helens Eruption on Nitrogen Cycle and Related Chemical Processes in Ryan Lake

Ryan Lake, a 1.6-hectare basin lake near the periphery of the tree blowdown area in the blast zone 19 km north of Mount St. Helens, was studied from August to October 1980 to determine the microbial and chemical response of the lake to the eruption. Nutrient enrichment through the addition of fresh volcanic material and the organic debris from the surrounding conifer forest stimulated intense microbial activity. Concentrations of such nutrients as phosphorus, sulfur, manganese, iron, and dissolved organic carbon were markedly elevated. Nitrogen cycle activity was especially important to the lake ecosystem in regulating biogeochemical cycling owing to the limiting abundance of nitrogen compounds. Nitrogen fixation, both aerobic and anaerobic, was active from aerobic benthic and planktonic cyanobacteria with rates up to 210 nmol of N₂ cm⁻¹ h⁻¹ and 667 nmol of N₂ liter⁻¹ h⁻¹, respectively, and from anaerobic bacteria with rates reaching 220 nmol of N₂ liter⁻¹ h⁻¹. Nitrification was limited to the aerobic epilimnion and littoral zones where rates were 43 and 261 nmol of NO₂ liter⁻¹ day⁻¹, respectively. Potential denitrification rates were as high as 30 μmol of N₂O liter⁻¹ day⁻¹ in the anaerobic hypolimnion. Total bacterial numbers ranged from 1 × 10⁶ to 3 × 10⁸ ml⁻¹ with the number of viable sulfur-metal-oxidizing bacteria reaching 2 × 10⁶ ml⁻¹ in the hypolimnion. A general scenario for the microbial cycling of nitrogen, carbon, sulfur, and metals is presented for volcanically impacted lakes. The important role of nitrogen as these lakes recover from the cataclysmic eruption and proceed back towards their prior status as oligotrophic alpine lakes is emphasized.     

Bacterial Contribution to Dissolved Organic Matter in Eutrophic Lake Kasumigaura,Japan

Incubation experiments using filtered waters from Lake Kasumigaura were conducted to examine bacterial contribution to a dissolved organic carbon (DOC) pool. Bacterial abundance, bacterial production, concentrations of DOC, total dissolved amino acids (TDAA), and total dissolved neutral sugars (TDNS) were monitored during the experiments. Bacterial production during the first few days was very high (20 to 35 μg C liter⁻¹ day⁻¹), accounting for 40 to 70% of primary production. The total bacterial production accounted for 34 to 55% of the DOC loss during the experiment, indicating high bacterial activities in Lake Kasumigaura. The DOC degradation was only 12 to 15%, whereas the degradation of TDAA and TDNS ranged from 30 to 50%, suggesting the preferential usage of TDAA and TDNS. The contribution of bacterially derived carbon to a DOC pool in Lake Kasumigaura was estimated using d-amino acids as bacterial biomarkers and accounted for 30 to 50% of the lake DOC. These values were much higher than those estimated for the open ocean (20 to 30%). The ratio of bacterially derived carbon to bulk carbon increased slightly with time, suggesting that the bacterially derived carbon is more resistant to microbial degradation than bulk carbon. This is the first study to estimate the bacterial contribution to a DOC pool in freshwater environments. These results indicate that bacteria play even more important roles in carbon cycles in freshwater environments than in open oceans and also suggests that recent increases in recalcitrant DOC in various lakes could be attributed to bacterially derived carbon. The potential differences in bacterial contributions to dissolved organic matter (DOM) between freshwater and marine environments are discussed.     

Primary and Bacterial Secondary Production in a Southwestern Reservoir

Rates of primary and bacterial secondary production in Lake Arlington, Texas, were determined. The lake is a warm (annual temperature range, 7 to 32°C), shallow, monomictic reservoir with limited macrophyte development in the littoral zone. Samples were collected from six depths within the photic zone from a site located over the deepest portion of the lake. Primary production and bacterial production were calculated from NaH¹⁴CO₃ and [methyl-³H]thymidine incorporation, respectively. Peak instantaneous production ranged between 14.8 and 220.5 μg of C liter⁻¹ h⁻¹. There were two distinct periods of high rates of production. From May through July, production near the metalimnion exceeded 100 μg of C liter⁻¹ h⁻¹. During holomixis, production throughout the water column was in excess of 100 μg of C liter⁻¹ h⁻¹ and above 150 μg of C liter⁻¹ h⁻¹ near the surface. Annual areal primary production was 588 g of C m⁻². Bacterial production was markedly seasonal. Growth rates during late fall through spring were typically around 0.002 h⁻¹, and production rates were typically 5 μg of C liter⁻¹ h⁻¹. Growth rates were higher during warmer parts of the year and reached 0.03 h⁻¹ by August. The maximum instantaneous rate of bacterial production was approximately 45 μg of C liter⁻¹ h⁻¹. Annual areal bacterial production was 125 g of C m⁻². Temporal and spatial distributions of bacterial numbers and activities coincided with temporal and spatial distributions of primary production. Areal primary and bacterial secondary production were highly correlated (r = 0.77, n = 15, P < 0.002).     

Fungal Growth, Production, and Sporulation during Leaf Decomposition in Two Streams

I examined the activity of fungi associated with yellow poplar (Liriodendron tulipifera) and white oak (Quercus alba) leaves in two streams that differed in pH and alkalinity (a hardwater stream [pH 8.0] and a softwater stream [pH 6.7]) and contained low concentrations of dissolved nitrogen (<35 μg liter⁻¹) and phosphorus (<3 μg liter⁻¹). The leaves of each species decomposed faster in the hardwater stream (decomposition rates, 0.010 and 0.007 day⁻¹ for yellow poplar and oak, respectively) than in the softwater stream (decomposition rates, 0.005 and 0.004 day⁻¹ for yellow poplar and oak, respectively). However, within each stream, the rates of decomposition of the leaves of the two species were not significantly different. During the decomposition of leaves, the fungal biomasses determined from ergosterol concentrations, the production rates determined from rates of incorporation of [¹⁴C]acetate into ergosterol, and the sporulation rates associated with leaves were dynamic, typically increasing to maxima and then declining. The maximum rates of fungal production and sporulation associated with yellow poplar leaves were greater than the corresponding rates associated with white oak leaves in the hardwater stream but not in the softwater stream. The maximum rates of fungal production associated with the leaves of the two species were higher in the hardwater stream (5.8 mg g⁻¹ day⁻¹ on yellow poplar leaves and 3.1 mg g⁻¹ day⁻¹ on oak leaves) than in the softwater stream (1.6 mg g⁻¹ day⁻¹ on yellow poplar leaves and 0.9 mg g⁻¹ day⁻¹ on oak leaves), suggesting that effects of water chemistry other than the N and P concentrations, such as pH or alkalinity, may be important in regulating fungal activity in streams. In contrast, the amount of fungal biomass (as determined from ergosterol concentrations) on yellow poplar leaves was greater in the softwater stream (12.8% of detrital mass) than in the hardwater stream (9.6% of detrital mass). This appeared to be due to the decreased amount of fungal biomass that was converted to conidia and released from the leaf detritus in the softwater stream.     

Seasonal Variation and Indirect Monitoring of Microcystin Concentrations in Daechung Reservoir, Korea

Physicochemical and biological water quality, including the microcystin concentration, was investigated from spring to autumn 1999 in the Daechung Reservoir, Korea. The dominant genus in the cyanobacterial blooming season was Microcystis. The microcystin concentration in particulate form increased dramatically from August up to a level of 200 ng liter⁻¹ in early October and thereafter tended to decrease. The microcystin concentration in dissolved form was about 28% of that of the particulate form. The microcystins detected using a protein phosphatase (PP) inhibition assay were highly correlated with those microcystins detected by a high-performance liquid chromatograph (r = 0.973; P < 0.01). Therefore, the effectiveness of a PP inhibition assay for microcystin detection in a high number of water samples was confirmed as easy, quick, and convenient. The microcystin concentration was highly correlated with the phytoplankton number (r = 0.650; P < 0.01) and chlorophyll-a concentration (r = 0.591; P < 0.01). When the microcystin concentration exceeded about 100 ng liter⁻¹, the ratio of particulate to dissolved total nitrogen (TN) or total phosphorus (TP) converged at a value of 0.6. Furthermore, the microcystin concentration was lower than 50 ng liter⁻¹ at a particulate N/P ratio below 8, whereas the microcystin concentration varied quite substantially from 50 to 240 ng liter⁻¹ at a particulate N/P ratio of >8. Therefore, it seems that the microcystin concentration in water can be estimated and indirectly monitored by analyzing the following: the phytoplankton number and chlorophyll-a concentration, the ratio of the particulate and the dissolved forms of N and P, and the particulate N/P ratio when the dominant genus is toxigenic Microcystis.     

Zooplankton induced changes in dissolved free amino acids and in production rates of freshwater bacteria

This study examined the importance of zooplankton in the flux of dissolved free amino acids (DFAA) in the water and into bacteria. DFAA release rates were followed in laboratory grazing experiments usingDaphnia galeata andEudiaptomus graciloides as grazers, andScenedesmus acutus andSynechococcus elongatus as food sources. Except for minor initial peaks, DFAAs were released continuously during the first 2 hours and made up 6–12% (in one experiment 50%) of the calculated ingestion rates. During three diel studies in lakes, effects of removal and increase of the density of zooplankton (>200m) on the pools of DFAA as well as on the bacterial production were followed. During two of the diel studies, higher DFAA pools were measured when 3–4 times the natural zooplankton density was present, and in one study a minor increase also occurred in the bacterial production, compared with results from experiments without zooplankton and with a natural zooplankton density. The increase in bacterial growth coincided with a decline in DFAA. During the third study, neither DFAA nor the bacterial production changed significantly when the zooplankton density was increased 3 times. Removal of zooplankton, however, caused a decline in both DFAA and bacterial production. Our data suggest a close relationship between occurrence of zooplankton and release of DFAA, but the factors regulating the amount of DFAA released and its effect on bacterial growth are not yet understood.     

Environmental Dissolved Organic Matter Governs Biofilm Formation and Subsequent Linuron Degradation Activity of a Linuron-Degrading Bacterial Consortium

It was examined whether biofilm growth on dissolved organic matter (DOM) of a three-species consortium whose members synergistically degrade the phenylurea herbicide linuron affected the consortium''s integrity and subsequent linuron-degrading functionality. Citrate as a model DOM and three environmental DOM (eDOM) formulations of different quality were used. Biofilms developed with all DOM formulations, and the three species were retained in the biofilm. However, biofilm biomass, species composition, architecture, and colocalization of member strains depended on DOM and its biodegradability. To assess the linuron-degrading functionality, biofilms were subsequently irrigated with linuron at 10 mg liter⁻¹ or 100 μg liter⁻¹. Instant linuron degradation, the time needed to attain maximal linuron degradation, and hence the total amount of linuron removed depended on both the DOM used for growth and the linuron concentration. At 10 mg liter⁻¹, the final linuron degradation efficiency was as high as previously observed without DOM except for biofilms fed with humic acids which did not degrade linuron. At 100 μg liter⁻¹ linuron, DOM-grown biofilms degraded linuron less efficiently than biofilms receiving 10 mg liter⁻¹ linuron. The amount of linuron removed was more correlated with biofilm species composition than with biomass or structure. Based on visual observations, colocalization of consortium members in biofilms after the DOM feed appears essential for instant linuron-degrading activity and might explain the differences in overall linuron degradation. The data show that DOM quality determines biofilm structure and composition of the pesticide-degrading consortium in periods with DOM as the main carbon source and can affect subsequent pesticide-degrading activity, especially at micropollutant concentrations.     

Dimethylsulfoniopropionate Turnover Is Linked to the Composition and Dynamics of the Bacterioplankton Assemblage during a Microcosm Phytoplankton Bloom

Processing of the phytoplankton-derived organic sulfur compound dimethylsulfoniopropionate (DMSP) by bacteria was studied in seawater microcosms in the coastal Gulf of Mexico (Alabama). Modest phytoplankton blooms (peak chlorophyll a [Chl a] concentrations of ~2.5 μg liter⁻¹) were induced in nutrient-enriched microcosms, while phytoplankton biomass remained low in unamended controls (Chl a concentrations of ~0.34 μg liter⁻¹). Particulate DMSP concentrations reached 96 nM in the enriched microcosms but remained approximately 14 nM in the controls. Bacterial biomass production increased in parallel with the increase in particulate DMSP, and nutrient limitation bioassays in the initial water showed that enrichment with DMSP or glucose caused a similar stimulation of bacterial growth. Concomitantly, increased bacterial consumption rate constants of dissolved DMSP (up to 20 day⁻¹) and dimethylsulfide (DMS) (up to 6.5 day⁻¹) were observed. Nevertheless, higher DMSP S assimilation efficiencies and higher contribution of DMSP to bacterial S demand were found in the controls compared to the enriched microcosms. This indicated that marine bacterioplankton may rely more on DMSP as a source of S under oligotrophic conditions than under the senescence phase of phytoplankton blooms. Phylogenetic analysis of the bacterial assemblages in all microcosms showed that the DMSP-rich algal bloom favored the occurrence of various Roseobacter members, flavobacteria (Bacteroidetes phylum), and oligotrophic marine Gammaproteobacteria. Our observations suggest that the composition of the bacterial assemblage and the relative contribution of DMSP to the overall dissolved organic sulfur/organic matter pool control how efficiently bacteria assimilate DMSP S and thereby potentially divert it from DMS production.     

Bacterioplankton Secondary Production Estimates for Coastal Waters of British Columbia, Antarctica, and California

The principal objective of this study was to quantify the rate of heterotrophic bacterioplankton production. Production was estimated by two approaches: (i) measurement of increasing bacterial abundance with time in filtered (3-μm pore size) seawater and (ii) estimation of bacterial deoxyribonucleic acid synthesis by tritiated thymidine incorporation in unfractionated seawater. The two approaches yielded comparable results when used at the Controlled Ecosystem Population Experiment (Saanich Inlet, British Columbia, Canada), at McMurdo Sound (Antarctica), and off Scripps Pier (La Jolla, Calif.). Estimated bacterioplankton production was lower in Antarctic samples (ranging from ~0 to 2.9 μg of C liter⁻¹ day⁻¹) than in those from the other two sites (ranging from 0.7 to 71 μg of C liter⁻¹ day⁻¹). In all three regions studied, it appeared that a significant fraction of the total primary production was utilized by the bacterioplankton and that substantial growth could occur in the absence of large particles. These results support the conclusion that bacterioplankton are a quantitatively important component of coastal marine food webs.     

Polysaccharides and Proteins Added to Flowing Drinking Water at Microgram-per-Liter Levels Promote the Formation of Biofilms Predominated by Bacteroidetes and Proteobacteria

Biopolymers are important substrates for heterotrophic bacteria in (ultra)oligotrophic freshwater environments, but information about their utilization at microgram-per-liter levels by attached freshwater bacteria is lacking. This study aimed at characterizing biopolymer utilization in drinking-water-related biofilms by exposing such biofilms to added carbohydrates or proteins at 10 μg C liter⁻¹ in flowing tap water for up to 3 months. Individually added amylopectin was not utilized by the biofilms, whereas laminarin, gelatin, and caseinate were. Amylopectin was utilized during steady-state biofilm growth with simultaneously added maltose but not with simultaneously added acetate. Biofilm formation rates (BFR) at 10 μg C liter⁻¹ per substrate were ranked as follows, from lowest to highest: blank or amylopectin (≤6 pg ATP cm⁻² day⁻¹), gelatin or caseinate, laminarin, maltose, acetate alone or acetate plus amylopectin, and maltose plus amylopectin (980 pg ATP cm⁻² day⁻¹). Terminal restriction fragment length polymorphism (T-RFLP) and 16S rRNA gene sequence analyses revealed that the predominant maltose-utilizing bacteria also dominated subsequent amylopectin utilization, indicating catabolic repression and (extracellular) enzyme induction. The accelerated BFR with amylopectin in the presence of maltose probably resulted from efficient amylopectin binding to and hydrolysis by inductive enzymes attached to the bacterial cells. Cytophagia, Flavobacteriia, Gammaproteobacteria, and Sphingobacteriia grew during polysaccharide addition, and Alpha-, Beta-, and Gammaproteobacteria, Cytophagia, Flavobacteriia, and Sphingobacteriia grew during protein addition. The succession of bacterial populations in the biofilms coincided with the decrease in the specific growth rate during biofilm formation. Biopolymers can clearly promote biofilm formation at microgram-per-liter levels in drinking water distribution systems and, depending on their concentrations, might impair the biological stability of distributed drinking water.     

Impact of Different In Vitro Electron Donor/Acceptor Conditions on Potential Chemolithoautotrophic Communities from Marine Pelagic Redoxclines

Anaerobic or microaerophilic chemolithoautotrophic bacteria have been considered to be responsible for CO₂ dark fixation in different pelagic redoxclines worldwide, but their involvement in redox processes is still not fully resolved. We investigated the impact of 17 different electron donor/acceptor combinations in water of pelagic redoxclines from the central Baltic Sea on the stimulation of bacterial CO₂ dark fixation as well as on the development of chemolithoautotrophic populations. In situ, the highest CO₂ dark fixation rates, ranging from 0.7 to 1.4 μmol liter⁻¹ day⁻¹, were measured directly below the redoxcline. In enrichment experiments, chemolithoautotrophic CO₂ dark fixation was maximally stimulated by the addition of thiosulfate, reaching values of up to 9.7 μmol liter⁻¹ CO₂ day⁻¹. Chemolithoautotrophic nitrate reduction proved to be an important process, with rates of up to 33.5 μmol liter⁻¹ NO₃⁻ day⁻¹. Reduction of Fe(III) or Mn(IV) was not detected; nevertheless, the presence of these potential electron acceptors influenced the development of stimulated microbial assemblages. Potential chemolithoautotrophic bacteria in the enrichment experiments were displayed on 16S ribosomal complementary DNA single-strand-conformation polymorphism fingerprints and identified by sequencing of excised bands. Sequences were closely related to chemolithoautotrophic Thiomicrospira psychrophila and Maorithyas hadalis gill symbiont (both Gammaproteobacteria) and to an uncultured nitrate-reducing Helicobacteraceae bacterium (Epsilonproteobacteria). Our data indicate that this Helicobacteraceae bacterium could be of general importance or even a key organism for autotrophic nitrate reduction in pelagic redoxclines.     

Ammonium Removal by the Oxygen-Limited Autotrophic Nitrification-Denitrification System

The present lab-scale research reveals the potential of implementation of an oxygen-limited autotrophic nitrification-denitrification (OLAND) system with normal nitrifying sludge as the biocatalyst for the removal of nitrogen from nitrogen-rich wastewater in one step. In a sequential batch reactor, synthetic wastewater containing 1 g of NH₄⁺-N liter⁻¹ and minerals was treated. Oxygen supply to the reactor was double-controlled with a pH controller and a timer. At a volumetric loading rate (B_v) of 0.13 g of NH₄⁺-N liter⁻¹ day⁻¹, about 22% of the fed NH₄⁺-N was converted to NO₂⁻-N or NO₃⁻-N, 38% remained as NH₄⁺-N, and the other 40% was removed mainly as N₂. The specific removal rate of nitrogen was on the order of 50 mg of N liter⁻¹ day⁻¹, corresponding to 16 mg of N g of volatile suspended solids⁻¹ day⁻¹. The microorganisms which catalyzed the OLAND process are assumed to be normal nitrifiers dominated by ammonium oxidizers. The loss of nitrogen in the OLAND system is presumed to occur via the oxidation of NH₄⁺ to N₂ with NO₂⁻ as the electron acceptor. Hydroxylamine stimulated the removal of NH₄⁺ and NO₂⁻. Hydroxylamine oxidoreductase (HAO) or an HAO-related enzyme might be responsible for the loss of nitrogen.     

Nitrification Rates in the Baltic Sea: Comparison of Three Isotope Techniques

Simultaneous measurements of nitrification in the Baltic Sea were made at 10- to 30-m intervals in the months of June and November by three isotope techniques: [¹⁵N]nitrate dilution, N-serve sensitive [¹⁴C]bicarbonate incorporation, and [¹⁵N]ammonium oxidation to nitrite and nitrate. Nitrification rates of 1 to 280 nmol liter⁻¹ day⁻¹ were recorded, and each method showed that the highest rates of nitrification occurred below the halocline. Even in the presence of ammonium, dark incubations of mixed layer (above ca. 50 m) waters never yielded nitrification rates exceeding 45 nmol liter⁻¹ day⁻¹. The rates measured by the ammonium oxidation method were two- to sevenfold greater than those obtained by ¹⁴C incorporation or ¹⁵N dilution. The merits of each technique are discussed, and it is suggested that the [¹⁵N]ammonium oxidation method should be used in conjunction with the [¹⁴C]bicarbonate incorporation method.