Addition Of Organic Nutrients Research Articles

Does long-term soil warming affect microbial element limitation? A test by short-term assays of microbial growth responses to labile C, N and P additions.

Increasing global temperatures have been reported to accelerate soil carbon (C) cycling, but also to promote nitrogen (N) and phosphorus (P) dynamics in terrestrial ecosystems. However, warming can differentially affect ecosystem C, N and P dynamics, potentially intensifying elemental imbalances between soil resources, plants and soil microorganisms. Here, we investigated the effect of long-term soil warming on microbial resource limitation, based on measurements of microbial growth (18 O incorporation into DNA) and respiration after C, N and P amendments. Soil samples were taken from two soil depths (0-10, 10-20 cm) in control and warmed (>14 years warming, +4°C) plots in the Achenkirch soil warming experiment. Soils were amended with combinations of glucose-C, inorganic/organic N and inorganic/organic P in a full factorial design, followed by incubation at their respective mean field temperatures for 24h. Soil microbes were generally C-limited, exhibiting 1.8-fold to 8.8-fold increases in microbial growth upon C addition. Warming consistently caused soil microorganisms to shift from being predominately C limited to become C-P co-limited. This P limitation possibly was due to increased abiotic P immobilization in warmed soils. Microbes further showed stronger growth stimulation under combined glucose and inorganic nutrient amendments compared to organic nutrient additions. This may be related to a prolonged lag phase in organic N (glucosamine) mineralization and utilization compared to glucose. Soil respiration strongly positively responded to all kinds of glucose-C amendments, while responses of microbial growth were less pronounced in many of these treatments. This highlights that respiration-though easy and cheap to measure-is not a good substitute of growth when assessing microbial element limitation. Overall, we demonstrate a significant shift in microbial element limitation in warmed soils, from C to C-P co-limitation, with strong repercussions on the linkage between soil C, N and P cycles under long-term warming.

Effect of organic nutrients on bioleaching of low-grade copper concentrate at different temperatures

The goal of the present work was to study the effect of different organic nutrients (yeast extract and molasses) on the biooxidation of copper concentrate containing chalcopyrite, tennantite, sphalerite, and pyrite in batch experiments at different temperatures (of 40 to 55°C). For the experiments, representatives of microbial groups predominant in biohydrometallurgical processes, bacterium of the genus Sulfobacillus, Acidithiobacillus caldus, and archaea of the genus Acidiplasma, were used. It was shown that both temperature and addition of organic nutrients in the medium affected the activity of the bioleaching. In the same time, the effect of organic nutrients was significant only at high temperatures (50 and 55°C). In all experiments, biooxidation rate decreased at the highest temperature, 55°C. Since among the strains used in the study, only A. caldus MBC-1 is autotroph, which is able to provide the population with organic nutrients and is not active at 55°C, at this temperature it was not able to maintain activity of other strains. Therefore at 55°C, biooxidation activity strongly depended on the presence of organic nutrients. Despite temperature and presence of organic nutrient affected activity of concentrate biooxidation that was revealed by the differences in pH, Eh values and iron ions concentrations in the medium, copper, zinc and arsenic extraction rates depended on these factors to a lesser extent.

Response of pico-nano-eukaryotes to inorganic and organic nutrient additions

Organic nutrient loading in coastal waters has considerably increased due to anthropogenic activities over the last decades. In particular, the increase in the proportion of organic vs. inorganic nitrogen may have an impact on microbial plankton communities, particularly within the small size classes, where mixotrophy is likely to be widespread. Here we explore the change in taxonomic composition of small eukaryotes (<20 μm) populating a productive coastal system in response to inorganic and/or organic nutrient amendments using 18S rRNA gene sequencing. Major changes in the community were observed in the mixed treatment, containing both inorganic and organic nutrients, which mostly affected phytoplankton taxa. Adding mixed nutrients had a positive effect on pigmented groups, when compared to additions of inorganic nutrients. The responding pigmented groups included dinoflagellates, cryptophyceans, chrysophyceans, bolidophyceans or dictyochophyceans, which comprise mixotrophic species, but also groups that are considered to be strictly autotrophs, such as diatoms or mamiellophyceans. Our results highlight the importance of organic nutrients for growth of small phytoplankton. The combination of both, autotrophic and heterotrophic capabilities, is possibly an advantage for small phytoplankton to thrive when inorganic nutrients or light are limiting or suboptimal.

Effect of Organic Nutrient Addition to the Biodegradation of Hydrocarbon Contaminated Marine Sediment in Malaysia

The effect of organic nutrient on the biodegradation of hydrocarbon contaminated marine sediment in Malaysia was investigated. Biodegradation was assessed in microcosm experiments containing 10% (w/w) of crude oil amended with fertilizers in three ways, which were with inorganic nutrients (NP), organic matter in the form of plant-based (Elaeis guineensis) and fish-amendments (Scomber australasicus). It was observed that hydrocarbon degradation occurred in all treatments, with the highest biodegradation rates inS. australasicussupplemented sediment. The addition of S. australasicus managed to reduce the oil concentration to 48% while the addition ofE. guineensisand inorganic NP reduced the final oil concentration to 66% and 63% respectively. All three amendments show faster degradation rate compared to the control. Isolation of the soil sample on specific nutrient agar, centrimide, revealed the presence of Pseudomonas aeruginosa that are well known for its ability to degrade hydrocarbon in crude oil.

Herbaceous perennial biomass production on frequently saturated marginal soils: Influence on N2O emissions and shallow groundwater

Warm season perennial grasses grown for biomass have been suggested as alternative cropping systems on marginal soils to increase farm profit, reduce nitrous oxide (N2O) emissions, and improve water quality. The objectives of this study were to determine: 1) how warm season perennial grasses, switchgrass (Panicum virgatum) and Miscanthus (Miscanthus x giganteus), compare to cool season grasses as streamside buffers on poorly drained marginal soils 2) if inorganic or organic nutrient additions improve biomass yield and affect environmental outcomes? 3) which soil variables influence N2O emissions in situ? We measured soil N2O emissions, soil solution nitrate (NO3−), ammonium (NH4+), O2, moisture, and temperature, along with shallow groundwater NH4+, NO3−, and ortho-phosphate during two growing seasons (2012–2013). N2O emissions were similar across unfertilized warm season grasses and cool season grasses. However, when switchgrass was fertilized with ammonium sulfate or broiler manure, N2O emissions increased significantly. N2O emissions were weakly correlated with soil solution NO3− concentrations and water filled pore space. Shallow groundwater N was elevated under switchgrass fertilized with ammonium sulfate, broiler manure, and when grown with the legume (Desmodium canadense) when compared to unfertilized switchgrass, Miscanthus, and cool season grasses. In 2013 dry aboveground biomass production did not differ among switchgrass treatments which averaged 10 Mg ha. Biomass production was significantly higher for Miscanthus (18.5 Mg ha). The results indicate that unfertilized switchgrass and Miscanthus are as effective as cool season grasses at mitigating N2O emissions and improving water quality, and that Miscanthus has potential production advantages over switchgrass grown on frequently saturated soils.

Responses of arbuscular mycorrhizal fungi to long-term inorganic and organic nutrient addition in a lowland tropical forest.

Improved understanding of the nutritional ecology of arbuscular mycorrhizal (AM) fungi is important in understanding how tropical forests maintain high productivity on low-fertility soils. Relatively little is known about how AM fungi will respond to changes in nutrient inputs in tropical forests, which hampers our ability to assess how forest productivity will be influenced by anthropogenic change. Here we assessed the influence of long-term inorganic and organic nutrient additions and nutrient depletion on AM fungi, using two adjacent experiments in a lowland tropical forest in Panama. We characterised AM fungal communities in soil and roots using 454-pyrosequencing, and quantified AM fungal abundance using microscopy and a lipid biomarker. Phosphorus and nitrogen addition reduced the abundance of AM fungi to a similar extent, but affected community composition in different ways. Nutrient depletion(removal of leaf litter) had a pronounced effect on AM fungal community composition, affecting nearly as many OTUs as phosphorus addition. The addition of nutrients in organic form (leaf litter) had little effect on any AM fungal parameter. Soil AM fungal communities responded more strongly to changes in nutrient availability than communities in roots. This suggests that the 'dual niches' of AM fungi in soil versus roots are structured to different degrees by abiotic environmental filters, and biotic filters imposed by the plant host. Our findings indicate that AM fungal communities are fine-tuned to nutrient regimes, and support future studies aiming to link AM fungal community dynamics with ecosystem function.

Farm management, not soil microbial diversity, controls nutrient loss from smallholder tropical agriculture

Tropical smallholder agriculture is undergoing rapid transformation in nutrient cycling pathways as international development efforts strongly promote greater use of mineral fertilizers to increase crop yields. These changes in nutrient availability may alter the composition of microbial communities with consequences for rates of biogeochemical processes that control nutrient losses to the environment. Ecological theory suggests that altered microbial diversity will strongly influence processes performed by relatively few microbial taxa, such as denitrification and hence nitrogen losses as nitrous oxide, a powerful greenhouse gas. Whether this theory helps predict nutrient losses from agriculture depends on the relative effects of microbial community change and increased nutrient availability on ecosystem processes. We find that mineral and organic nutrient addition to smallholder farms in Kenya alters the taxonomic and functional diversity of soil microbes. However, we find that the direct effects of farm management on both denitrification and carbon mineralization are greater than indirect effects through changes in the taxonomic and functional diversity of microbial communities. Changes in functional diversity are strongly coupled to changes in specific functional genes involved in denitrification, suggesting that it is the expression, rather than abundance, of key functional genes that can serve as an indicator of ecosystem process rates. Our results thus suggest that widely used broad summary statistics of microbial diversity based on DNA may be inappropriate for linking microbial communities to ecosystem processes in certain applied settings. Our results also raise doubts about the relative control of microbial composition compared to direct effects of management on nutrient losses in applied settings such as tropical agriculture.

Response of prokaryotic and eukaryotic community structure to inorganic and organic nutrient additions in a eutrophic coastal ecosystem

Event Abstract Back to Event Response of prokaryotic and eukaryotic community structure to inorganic and organic nutrient additions in a eutrophic coastal ecosystem Marta Hernández-Ruiz1*, Esther Barber-Lluch1, Xosé A. Álvarez-Salgado2, Mar Nieto-Cid2, Francisco G. Figueiras2, Belén Arbones2, Isabel G. Teixeira2, Cristina Sobrino1, Emilio Fernández1 and Eva Teira1 1 University of Vigo, Departamente de Biología y Ecología Animal, Spain 2 IIM-CSIC, Instituto de Investigaciones Marinas, Spain Coastal oceans are known to receive increasing inputs of reactive N as a result of the anthropogenic alteration of N cycling at the global scale, which may greatly alter nutrient supply to microbial plankton communities. The influence of nutrient availability (mainly inorganic N and P and/or organic C) on species composition has been widely reported for both eukaryotes and prokaryotes. The Ría de Vigo is a eutrophic embayment located in the coastal system of the NW Iberian Peninsula. Previous studies in the area revealed a highly variable response of microbial plankton to nutrient additions, a strong stimulation of phytoplankton growth after inorganic (N and P) and organic (C and N) nutrient addition and a strong carbon limitation of bacterial activity. To gain understanding on the effect of nutrient inputs on the functioning of this coastal ecosystem, the short-term effects of inorganic N and P (nitrate, ammonium, phosphate) and organic C and N (glucose, amino acids) inputs, added separately as well as jointly, on eukaryotic and prokaryotic community composition were studied in microcosm experiments conducted under contrasting hydrographic conditions. Changes in microbial diversity were analyzed by ARISA (automatic rRNA intergenic spacer analysis) and two sets of primers specific for bacteria and eukaryotes. The results obtained in these experiments showed that changes in microbial communities were clearly determined by the initial microbial assemblage. Changes in prokaryotic and eukaryotic community composition were closely related to changes in metabolic rates. In contrast to previous observations, prominent changes in bacterial community composition occurred only after inorganic and organic nutrient additions, which suggest a C and P co-limitation of bacteria during the sampling periods. Major eukaryotic community composition changes were observed in response to inorganic additions. Keywords: eukaryotic diversity, prokaryotic diversity, ARISA, Nutrient additions, Microcosm Experiment Conference: IMMR | International Meeting on Marine Research 2014, Peniche, Portugal, 10 Jul - 11 Jul, 2014. Presentation Type: Poster Presentation Topic: BIODIVERSITY, CONSERVATION AND COASTAL MANAGEMENT Citation: Hernández-Ruiz M, Barber-Lluch E, Álvarez-Salgado XA, Nieto-Cid M, Figueiras F, Arbones B, Teixeira I, Sobrino C, Fernández E and Teira E (2014). Response of prokaryotic and eukaryotic community structure to inorganic and organic nutrient additions in a eutrophic coastal ecosystem. Front. Mar. Sci. Conference Abstract: IMMR | International Meeting on Marine Research 2014. doi: 10.3389/conf.fmars.2014.02.00094 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 26 Apr 2014; Published Online: 18 Jul 2014. * Correspondence: Miss. Marta Hernández-Ruiz, University of Vigo, Departamente de Biología y Ecología Animal, Vigo, Pontevedra, 36200, Spain, marta.hdezr@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Marta Hernández-Ruiz Esther Barber-Lluch Xosé A Álvarez-Salgado Mar Nieto-Cid Francisco G. Figueiras Belén Arbones Isabel G. Teixeira Cristina Sobrino Emilio Fernández Eva Teira Google Marta Hernández-Ruiz Esther Barber-Lluch Xosé A Álvarez-Salgado Mar Nieto-Cid Francisco G. Figueiras Belén Arbones Isabel G. Teixeira Cristina Sobrino Emilio Fernández Eva Teira Google Scholar Marta Hernández-Ruiz Esther Barber-Lluch Xosé A Álvarez-Salgado Mar Nieto-Cid Francisco G. Figueiras Belén Arbones Isabel G. Teixeira Cristina Sobrino Emilio Fernández Eva Teira PubMed Marta Hernández-Ruiz Esther Barber-Lluch Xosé A Álvarez-Salgado Mar Nieto-Cid Francisco G. Figueiras Belén Arbones Isabel G. Teixeira Cristina Sobrino Emilio Fernández Eva Teira Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Biodegradation of Benzo[a]pyrene by Arthrobacter oxydans B4

A bacterial strain, Arthrobacter oxydans (B4), capable of degrading benzo[a]pyrene (BaP) in water body, was isolated from a polycyclic aromatic hydrocarbons-contaminated site. Effects of different factors, such as reaction time, pH value, temperature and organic nutrients, on BaP biodegradation by the strain B4 were studied. After 5 d treatment, the concentration of BaP in mineral salts medium was reduced to 0.318 mg L−1, compared to the initial concentration of 1.000 mg L−1. There was a process of acid formation during the degradation with pH falling from initial 7.01 to 4.61 at 5 d, so keeping the water body under slightly alkaline condition was propitious to BaP degradation. Strain B4 efficiently degraded BaP at 20 to 37 °C with addition of organic nutrients. The biodegradation and transformation of BaP mainly occurred on cell surfaces, and extracellular secretions played an important role in these processes. Fourier transform infrared spectroscopy and gas chromatograph-mass spectrometer analyses of metabolites showed that ring cleavage occurred in the BaP degradation process and the resulting metabolically utilizable substrates were generated as sole carbon sources for B4 growth. Furthermore, mineralization extent of metabolites was verified by determining the total organic carbon and inorganic carbon in the degradation system.

Effect of inorganic and organic nutrient addition on coral–algae assemblages from the Northern Red Sea

Previous studies in fringing reefs of the Northern Red Sea demonstrated that the in-situ competition of corals and algae in natural assemblages is highly variable between seasons displaying fast overgrowth of corals by benthic reef algae in fall that follows close to equilibrium between both groups of organisms in summer. This may be caused by up to 5-fold higher inorganic nutrient and 6-fold higher organic nutrient concentrations in fall and winter, thereby potentially promoting algae and cyanobacteria growth with concomitant phase shift. A long term mesocosm experiment (duration: 90 days) was conducted in order to study the effect of dissolved inorganic (ammonium, phosphate, nitrate, and mix of all three) and organic (glucose) nutrient addition onto the competitive process in the dominant coral–algae assemblages of the Northern Red Sea involving branching corals of the genus Acropora and a typical consortium of benthic turf algae. Nutrients were added in 3-fold higher concentrations compared to the annual averages, and the parameters algal growth, extension of bleached area on corals, tissue colour change and chlorophyll a concentrations were monitored at regular intervals over experimental duration. This revealed that elevated ammonium concentrations and elevated organic nutrient concentrations stimulate algal growth, while coral tissue pigmentation and chlorophyll a content were significantly decreased. But only in the elevated organic nutrient treatment all effects on corals were significantly pronounced when assembled with benthic turf algae. Supplementary logger measurements revealed that O 2 water concentrations were significantly lower in the elevated organic nutrient mesocosm compared to all other treatments, confirming side-effects on microbial activity. These findings indicate that organic nutrient input into coral reefs can affect physiology and metabolism of both corals and benthic turf algae. Reinforcing interaction between both groups of organisms along with involvement of microbes may facilitate phase shifts in coral reef ecosystems.

Assessment of Bacterial and Fungal Growth on Natural Substrates: Consequences for Preserving Caves with Prehistoric Paintings

The most representative bacterium (Pseudonocardia sp.) and fungus (Fusarium sp.) from the microbial communities of a cave containing paleolithic paintings were isolated and their growth on natural substrates assessed. Growth was tested at the in situ and optimal, laboratory growth temperature. Development was analyzed with and without supplemented nutrients (glucose, ammonium, phosphate, peptone). Results showed that the assayed bacterium on natural substrate was able to develop best at in situ temperature and the addition of organic nutrients and/or phosphate enhanced its growth. The growth of the assayed fungus, however, was limited by low temperature and the availability of ammonium. These results confirm a differential behavior of microorganisms between the laboratory and the natural environments and could explain previous invasion of fungi reported for some caves with prehistoric paintings.

Bio-Degradation of Pristane in Mixed Alkanes by a Mixed Culture Containing Nocardia corynebacterioides

Gram-positive bacterium identified as Nocardia cotynebacterioides L29-2 was isolated from a diesel oil contaminated site in southern Taiwan. The bacterium was found able to degrade both straight and branched alkanes in diesel oil. Inorganic nutrients were not able to enhance the growth of the cells but the cell growth and hydrocarbon biodegradation could be accelerated by adding yeast extract. It was found that this bacterium was able to degrade pristane at high efficiency. However, the ability of pristane biodegradation was severely inhibited by the presence of normal alkanes. The diesel oil biodegradation was significantly improved by introducing another bacterium, Rhodococcus globerulus H425-2, found in the same contaminated site. Rhodococcus globerulus H425-2 was found to degrade normal alkanes at a much higher rate than Nocardia corynebacterioides L29-2. In this study, the biodegradation of pristane and n-pentadecane in single substrate and mixed substrate experiments were compared. The cooperation of Nocardia corynebacterioides L29-2 and Rhodococcus globerulus H425-2 was also under investigation. It appeared that the 1:1 ratio was close to the optimum inoculation ratio of these two species for degrading the mixture of pristane and n-pentadecane at 1:1 ratio. The results indicate that the addition of organic nutrients and the proper control of the population ratio according to the alkane composition in the contaminated site are crucial for effective bioremediation of diesel spill.

Nutrient stimulation of lytic phage production in bacterial populations of the Gulf of Mexico

The effect of nutrient addition on prophage induction in marine water samples was investigated during a 2001 research cruise in the Gulf of Mexico. To test the hypothesis that prophage induction could be stimulated by nutrient addition, water samples were treated with inorganic and organic nutrients in combination with mitomycin C (1.0 µg ml -1 ) or with the nutrient alone as controls. An increase in phage abundance was observed at 3 stations in response to additions of PO4 3- (mesotrophic Mississippi River plume, oligotrophic surface-water, and Dry Tortugas stations), NH4 + (oligotrophic surface-water station), and several organic compounds (oligotrophic surface-water station). Augmented phage production occurred in both the presence and absence of mitomycin C, indicating that inorganic and organic nutrient addition did not appear to stimulate prophage induc- tion. These results suggest that nutrient amendment of environmental samples caused a stimulation of lytic phage production that may have resulted from a stimulation of host-cell growth. However, these results do not preclude nutrient stimulation of prophage induction at other times of the year or in other oceanic environments, which were not examined in this study.

Effects of inorganic and organic nutrient addition on a coastal microbial community (Isefjord, Denmark)

Using flow cytometry (FCM), microbial populations were followed in a mesoscosm experiment manipulated with daily additions of mineral nutrients (as phosphates and nitrates in Red- field equilibrium), of degradable organic carbon (as glucose-C), or with the 2 treatments combined. Intensive sampling was performed in order to assess the short time-scale variability of the microbial community. Five autotrophic groups (including Synechococcus spp. and cryptophytes), 2 groups of heterotrophic bacteria, and 2 groups of viruses could be discriminated by FCM. The control enclosure (no addition) revealed that heterotrophic bacteria were carbon-limited. Synechococcus spp. abun- dance increased in the control, presumably because they experienced little competition from hetero- trophic bacteria (which were C-limited) and from larger phytoplankton (which were not as efficient in nutrient uptake at low nutrient concentration and could not, therefore, sustain high growth rates). When N and P were added, however, larger-celled autotrophic populations were favoured. When glucose was added, alone or together with inorganic elements, the abundance of Synechococcus spp. and small eukaryotes was reduced, suggesting that, when released from C-limitation, heterotrophic bacteria are the best competitors for mineral nutrients. The addition of both inorganic and organic nutrients also enhanced cryptophytes in contrast to all other autotrophs, probably because of their heterotrophic capacity. Our results agree with recent evidence suggesting that heterotrophic bac- teria are limited by both carbon and mineral nutrients, and demonstrate how this has important con- sequences for the success of their trophic neighbours in the microbial food web.

Does shelterwood harvesting have less impact on forest floor nutrient availability and microbial properties than clearcutting?

Chemical and microbial properties of the forest floor were measured in 4-year-old shelterwood treatment plots in the montane coastal western hemlock biogeoclimatic zone of British Columbia, Canada, and compared to those in adjacent old-growth and 4-year-old clearcut plots. Forest floor pH, exchangeable Mg, total C and total N concentrations were similar in all three treatments. Bray-extractable P was significantly lower in humus from shelterwood plots, exchangeable Ca was significantly lower in humus from clearcut plots, and exchangeable K was significantly higher in humus from old-growth plots. Indices of available C (basal respiration rate, microbial biomass and metabolic quotient) were significantly higher in old-growth plots than in the two harvested treatment plots. The relative increase in maximum microbial metabolic rate due to the addition of organic nutrients was significantly greater in clearcut plots. Principal component analysis (PCA) ordination of humus samples based on C source utilization patterns of microbial communities (i.e., Biolog assay) showed distinctive clustering by treatment, although indices of substrate richness, evenness and diversity were the same in all three treatments. The relative utilization rates of substrates with the highest factor loadings on PCA axes 1 and 2 were dissimilar in each treatment. We conclude that forest floors can develop under shelterwood harvested stands to exhibit chemical and microbial properties atypical of either clearcut or old-growth plots.

Biodegradation of [ 14C]-4-nitrophenol in a sediment–water simulation test

A laboratory simulation test with natural water and sediments to study biodegradability of low concentrated chemicals in surface waters was evaluated by measuring the mineralisation and fate of 0.37 μg kg −1 [ 14C]-4-nitrophenol. The effects of the sediment type, the time of sediment collection, temperature, illumination and the method of aeration on the feasibility of the test, the mineralisation of 4-nitrophenol, the distribution of radioactivity between the different compartments and the physicochemical and biological state of the sediment–water systems were studied. During 35 days of incubation, non-reducing conditions prevailed in the test reactors and the overall microbial activity did not vary substantially. The aeration method, the sediment and water origin and temperature significantly influenced mineralisation, whereas illumination only slightly affected mineralisation and the addition of organic nutrients had almost no effect on the test systems. These results, together with those of experiments with lindane were used to propose a test guideline for standardised testing.

Partitioning and mineralization of [14C]lindane in a laboratory sediment–water system

AbstractTo develop a guideline for a simulation test for aerobic degradability in surface water, the fate of [14C]lindane (γ‐hexachlorocyclohexane) was studied in laboratory systems using natural river water and sediments. No sterilized controls were set up. Thus, measured data reflect the sum of biotic and abiotic processes. Tests were carried out under various experimental conditions to investigate which of these would affect the feasibility of the test, the fate of lindane, the physicochemical state, and the biological activity within the sediment–water systems. Lindane (37.7 nmol) was applied either to the water (3 L) or the sediment (0.33 L). Sediments remained nonreducing, and there was no serious decline of nutrients nor enzymatic activities. In one experiment up to 14.1% of the applied lindane was mineralized to14CO2within 50 d and in a second one up to 35.3%. At day 91 of the latter experiment up to 46.8% were found to have been mineralized. Among the experimental factors tested, the method of lindane application and temperature predominantly affected mineralization. The type of aeration and the semicontinuous addition of organic nutrients were of minor importance. Sediments and water collected at the same site but at different times showed variation in carbon content as well as in esterase and dehydrogenase activities. Nevertheless, these parameters could not be correlated with mineralization of lindane during the tests. Between 1 and 9% of the radioactivity volatilized during the tests. At the end, 23 to 66% were bound to sediments and 15 to 45% of the total activity was neither extractable by water nor by cyclohexane.

Study of sorption, biodegradation and isomerization of HCH in stimulated sediment/water system

This paper reported the sorption, biodegradation and isomerization of hexachlorocyclohexane (HCH) in laboratory sediment/water system under aerobic and anaerobic conditions , respectively. The effect of organic nutrient addition to the sorption of HCH was also investigated. It indicates that HCH is highly adsorbed on sediments under both conditions. During the tests, the biodegradation and isomerization of HCH were dramatically speeded up after organic nutrient additions, especially in the case of the observation under aerobic condition. It was found, β-HCH was the most persistent in the environment, that is due to the isomerization of α-HCH in a big amount to β-HCH, besides its chemical stability.

Plasma glucose turnover and oxidation during hemodialysis: nutritional effect of dialysis fluid

Mass transfer of glucose from dialysis fluid into patients is a source of energy and a form of nutrition during hemodialysis. The effect of glucose mass transfer on endogenous glucose metabolism and the overall nutritional importance of glucose transfer is not known. Rates of plasma glucose turnover and oxidation were determined by radioisotope-dilution techniques in patients with chronic renal failure (CRF) in the basal state, during hemodialysis, and during the infusion of glucose at a rate similar to the mass transfer rate (Mt: 6.6 +/- 0.7 mumol.min-1.kg-1). Rates of plasma glucose turnover (11.8 +/- 0.8 mumol.min-1.kg-1) and oxidation (4.0 +/- 0.4 mumol.min-1.kg-1) and contribution of glucose oxidation to the metabolic rate were similar to those of control subjects both in the basal state and during glucose infusion. During hemodialysis with acetate and glucose, the plasma glucose turnover rate was similar to that in the basal state, but the energy from glucose oxidation was less (P < or = 0.02) even though energy expenditure was increased by 21%. Immediate oxidation of plasma glucose and acetate accounted for 65% of the patients' energy expenditure. Energy (1172 kJ) from acetate Mt and glucose Mt surpassed the patients' energy requirements, offsetting the utilization of endogenous fuels, a sparing effect equivalent to 31 g fat or 70 g carbohydrate. Rates of plasma glucose turnover and oxidation during bicarbonate-glucose and glucose-free acetate hemodialysis were similar to that during acetate-glucose hemodialysis. However, without glucose or acetate in the bath fluid, a deficit as much as 669 kJ must be met by the oxidation of endogenous fuels. Addition of organic nutrients that supply energy to dialysis fluids may over time be a beneficial supplemental treatment for the malnutrition and body wasting commonly observed in CRF.

Characterization of marine prokaryotic communities via DNA and RNA

We know very little about species distributions in prokaryotic marine plankton. Such information is very interesting in its own right, and ignorance of it is also beginning to hamper process studies, such as those on viral infection. New DNA- and RNA-based approaches avoid many prior limitations. Here we discuss four such applications: (1) cloning and sequencing of 16S rRNA genes to produce lists of what types of organisms are present; (2) quantification of these individual types in marine samples by nucleic acid hybridization, including single cell fluorescence; (3) quantitative comparison by DNA-DNA hybridization of entire microbial communities in terms of shared common types, without knowledge of community components; and (4) finding cultures that are representative of native communities. Several previously uncharacterized types of bacteria and archaea (probably including novel phyla) are present in marine plankton. Evidence from both the Atlantic and Pacific suggests that as-of-yet uncultivated archaea may dominate the deep sea, and thus may be the most abundant group of organisms on Earth. Such archaea are in surface waters as well, and can be visualized with fluorescent probes and enriched at room temperature with addition of organic nutrients. Community hybridization shows that variability of microbial community compositions in time and space is high. Although most native bacteria do not grow in culture, some proteobacterial cultures appear by genomic hybridization to be representative of certain communities. These and other results indicate the utility of DNA- and RNA-based methods.