Fatty acid composition and microbial activity of benthic marine sediment from McMurdo Sound, Antarctica

Abstract Signature lipids from the phospholipid esterlinked fatty acids (PELFA) of cell membranes were used to describe benthic microbial communities of 4 Antarctic sediments. Metabolic activities of the communities were determined by incorporation of [³H]thymidine into bacterial DNA and sodium [¹⁴C]acetate into membrane lipids. Biomass measurements from extractable phospholipid fatty acids per g dry wt. ranged between 6 to 76 nmol, or when converted to number of bacteria, 3.7 × 10⁸ to 4.5 × 10⁹ cells per g dry wt. The West Sound site at New Harbor contained the lowest biomass, while Cape Evans on the East Sound contained the greatest. A marked difference was also noted between sites in their sediment microbial community structure. The East Sound sites at Cape Armitage and Cape Evans contained a greater abundance of diatom marker lipids, whilst both sides of the Sound contained approximately the same relative amounts of bacterial groups distinguished using PELFA. Activity of sediment microorganisms measured by radiolabel incorporation under ambient conditions followed the trends of the biomass measurements. The East Sound sites were more active by an average of 45–73% for [³H]thymidine and possibly also for sodium [¹⁴C]acetate.     

Oligotrophic properties of heterotrophic bacteria and in situ heterotrophic activity in pelagic seawates

Abstract The distribution of heterotrophic bacteria in polluted coastal and unpolluted pelagic seawaters was studied using a ¹⁴C-MPN method with either five of seven kinds of ¹⁴C-organic compounds as substrates. The total number of heterotrophic bacteria in pelagic waters ranged from 9.2 × 10³ to 5.4. ¢ 10⁴ cell/ml and more than 85% of the heterotrophic bacteria were represented by obligate oligotrophs. In coastal waters, the number of heterotrophs was one order of magnitude higher (av. 3.5 ¢ 10⁵ cells/ml), and eutrophic and facultatively oligotrophic bacteria were predominant. Oligotrophs in pelagic waters had a high specificity for the utilization of amino acids, especially glycine, and acetate-utilizing bacteria were scarce. The in situ maximum uptake rates of glutamate and glycine were much higher than those of glycolate and acetate. Acetate uptake rates were extremely low or not detectable in pelagic waters. The specificity of uptake kinetics is assumed to depend on the existence of obligate oligotrophs as dominant bacteria in pelagic seawater.     

DEPTH DISTRIBUTIONS OF DNA DAMAGE IN ANTARCTIC MARINE PHYTO- AND BACTERIOPLANKTON EXPOSED TO SUMMERTIME UV RADIATION

During a survey from January to March 1998, the occurrence of UV-B radiation (UVBR)- induced DNA damage in Antarctic marine phytoplankton and bacterioplankton was investigated. Sampling was done in Ryder Bay, off the British base Rothera Station, 67°S, 68°W (British Antarctic Survey). Samples were taken regularly during the survey period at fixed depths, after which DNA damage was measured in various plankton size fractions (>10, 2–10, and 0.2–2 μm). Incident solar radiation was measured using spectroradiometry, whereas attenuation of biologically effective UVBR was studied using a DNA dosimeter. A diatom bloom was found in the bay during the research period, judging from microscopic observations and HPLC analyses of taxon-specific pigments. The high phytoplankton biomass likely caused strong attenuation of DNA effective UVBR (K_bd-eff). K_bd-eff values ranged from 0.83·m ^{− 1} at the peak of the bloom to 0.47·m ^{− 1} at the end of the season. UVBR-mediated DNA damage, as measured by cyclobutane pyrimidine dimer (CPD) abundance, was detected in all plankton size fractions. Highest levels were found in the smallest size fraction, mainly consisting of heterotrophic bacteria. Clear CPD depth profiles were found during mid-summer (January, beginning of February) with surface levels exceeding 100 CPDs per million nucleotides in the bacterioplankton fraction. At that time, melting of the continuously present shelf ice caused strong salinity gradients in the upper meters, thereby stimulating water column stabilization. At the end of February and beginning of March, this phenomenon was less pronounced or absent. At that time, DNA damage was homogeneously distributed over the first 10 m, ranging between 20 and 30 CPDs per million nucleotides for the smallest size fraction.     

Allocation of carbon to growth, storage and respiration in the vegetative barley plant

Abstract. It is proposed that the growing plant can be divided into three compartments with reference to carbon: soluble, storage and structural. Experiments carried out at 10, 15, 20 and 30°C in the light followed changes in size of these compartments in barley plants 10–24 days old. The redistribution of ^I4C photo-assimilated by 10 day old plants was monitored simultaneously. The soluble and storage compartments are a higher percentage of plant weight at lower temperatures, and are turned over rapidly at all temperatures; they form the source of respired ¹⁴C. About 30% of the ¹⁴C fixed enters structural material; in the first 24 h after labelling, for each unit of ¹⁴C entering the structural compartment, between 0–9 (at 15°C) and 3.2 (at 30°C) units of ¹⁴C are lost by respiration. At 15°C in the dark, respiratory loss of ¹⁴C is initially from soluble and storage compartments; thereafter respiration of ^I4C occurs at the expense of structural material.     

Constitutive mineralization of low concentrations of the herbicide linuron by a Variovorax sp. strain

The mineralization of the herbicide linuron at concentrations of μg and mg L⁻¹ was studied in liquid batch experiments with Variovorax sp. strain SRS16. The strain was highly efficient at mineralizing a range of linuron concentrations (0.002–10 mg L⁻¹) with 20–60% of the added ¹⁴C-ring-labeled linuron metabolized to ¹⁴CO₂ within hours to days depending on the initial linuron concentration and incubation period. At mg L⁻¹ linuron concentrations the mineralization activity by SRS16 was inducible and a shift to constitutive mineralization activity was apparent with a reduction in the linuron concentration to μg L⁻¹ levels. This study revealed that strain SRS16 is a promising candidate for bioaugmentation of water or soil resources contaminated with low linuron concentrations.     

Random mutagenesis of Legionella pneumophila with mini-Tn10

Abstract The degradation of sheets of poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (BIOPOL^®) by aerobic sewage sludge was analyzed. Degradation of the polymer was highly dependent on the pH of the culture medium and was maximal between pH 7 and pH 8.5. Below pH 6 and above pH 9 the degradation rate was very low. Agitation of the culture fluid had relatively little influence on the rates of degradation. 1.2×10⁵ aerobic polymer-degrading bacteria per ml sewage sludge were identified by halo formation on solid poly(3-hydroxybutyrate) (PHB)-containing media. The number of PHB-degrading bacteria in other ecosystems amounted to 3.8×10³ per ml sludge of a fresh-water lake, 9.2×10⁵ per g garden-soil, 1.3×10⁶ per g field-soil and 4.3×10⁶ per g compost.     

Growth of a facultative anaerobe under oxygen-limiting conditions in pure culture and in co-culture with a sulfate-reducing bacterium

Abstract The occurrence and properties were studied of glucose-metabolizing bacteria present in the anaerobic sediment 5–10 cm below the surface of an estuarine tidal mud-flat. Of all these bacteria (10⁴– 10⁵ per g wet sediment) 80–90% were facultatively anaerobic species. Chemostat enrichments on glucose under aerobic, oxygen-limited and alternately aerobic-anaerobic conditions also yielded cultures dominated by facultative anaerobes. One of the dominant species, tentatively identified as a Vibrio sp., was studied in more detail under oxygen-limiting conditions. Fermentative and respiratory metabolisms were found to operate simultaneously, and the ratio between the two was regulated by the extent of oxygen limitation. A small fraction of the acetate formed under such growth conditions was shown to be subsequently respired. A co-culture was established of the Vibrio sp. and a sulfate-reducing bacterium ( Desulfovibrio HL21 ) in an aerated chemostat. The importance of these observations is discussed in relation to the role of facultative anaerobes in anaerobic habitats.     

Distribution and biodegradation potential of oil-degrading bacteria in North Eastern Japanese coastal waters

Abstract The distribution of oil-degrading microorganism in samples of surface water and sediment from North Eastern Japanese coastal waters was studied. Modified natural sea water (NSW) agar supplemented with emulsified crude oil (Arabian light, 5 g 1⁻¹) was used to enumerate oil-degrading bacteria. In addition, filtered samples were inoculated into NSW broth containing weathered crude oil. Incubation was carried out at 20°C for 7–10 days. Populations of oil-degrading microorganisms ranged from 3–230 CFU 100 ml⁻¹ in surface waters and 2.9 × 10³ to 1.2 × 10⁵ CFU g⁻ in sediment samples. Analysis of variance showed that oil-degraders were heterogenously distributed. Six mixed populations selected from 20 samples were studied to determine which of the constituent microflora were capable of crude oil biodegradation. Among 51 strains selected for identification, only 61% could be identified which formed 17 different bacterial species. Acinetobacter species (14 strains), Psychrobacter immobilis (9 strains) and Gram-positive cocci (10 strains) were the predominant types. Oil-degrading activity by various mixed populations (three each from water and sediment samples) was determined by using a conventional total weight reduction technique. Reduction in amount of various aliphatic and aromatic hydrocarbon substrates was verified using gas chromatography and high pressure liquid chromatography. Biodegradation of crude oil ranged from 35–58%. One mixed population of the sediment samples degraded more hydrocarbon (both aliphatic and aromatic) and the biodegradation of the aromatic hydrocarbon reached as high as 48%.     

The planktonic and benthic bacterial populations of Lough Neagh

The planktonic and benthic bacterial populations of Lough Neagh, Northern Ireland, were studied over a one-year period. Direct counts of bacteria in the water column averaged 6 times 10⁷/ml with limited spatial or temporal variation; viable counts, however, showed a pronounced late spring maximum of 1.7 times 10⁶/ml and were consistently higher at a littoral sampling station. Direct counts of bacteria in the profundal sediments averaged 8 times 10⁹/ml whilst viable benthic counts rose steeply during spring to reach a June maximum of 1 times 10⁸/ml. Direct: viable count ratios were much greater in the more sandy littoral zone. The predominant benthic isolate was an Aeromonas sp. which was also common in samples from the water column. These results confirm the eutrophic status of Lough Neagh indicated by other biological and chemical surveys.     

Distribution and metabolism of root-applied cytokinins in Pisum sativum

When N ⁶ [8–¹⁴C] furfuryladenine was applied to the intact root system of Pisum sativum L. cv. Meteor seedlings it was almost completely metabolised to other compounds within 24 h. Of the total activity recovered from the plants 94.5% was retained in the root system itself. ¹⁴C was recovered in a number of ethanol-soluble compounds and in ribonucleic acid, deoxyribonucleic acid and protein fractions of roots, stems, leaves and axillary buds. In rapidly growing axillary buds released from apical dominance by removal of the shoot apex the combined nucleic acid fractions accounted for 63.3% of the total ¹⁴C recovered from these organs. Xylem exudate collected from decapitated plants 0 to 12 h after supplying N ⁵[8–¹⁴C]furfuryladenine to the roots consistently contained a single major ¹⁴C-labelled compound which, in three different solvent systems, had the same Rf values as a major endogenous cytokinin isolated from the xylem of unlabelled plants. The content of N ⁶ [8–¹⁴C] furfuryladenine itself in the xylem exudate was always low and in some experiments it could not be detected.
It is suggested that part of the label from N ⁶ [8- ¹⁴CJfurfuryladenine taken up by the intact root system may have become incorporated in an endogenous cylokinin before export to the shoot.     

Seasonal heterotrophic flagellate and bacterial plankton dynamics in a large oligotrophic lake– Loch Ness, Scotland

1. Bacterial production in the 0–30 m water column of Loch Ness was measured using a dual labelling procedure with [³H] thymidine and [¹⁴C] leucine between May 1993 and June 1994. In most cases the uptake of the two labels did not covary, suggesting unbalanced growth. Rates of bacterial production varied from undetectable to 46.2 μg C l^–1 day^–1. Highest production coincided with the period of highest primary production, but carbon derived from this source was insufficient to meet the bacterial carbon demand, which was met by allochthonous humic inputs to the system.
2. Heterotrophic flagellate (HNAN) grazing rates, measured using fluorescently labelled bacteria, ranged between 10.3 and 24.5 bacteria cell^–1 day^–1 at temperatures between 5 and 15 °C. They removed up to 27% of the bacterial production per day.
3. Heterotrophic flagellate specific growth rates ranged from 0.043 to 0.093 h^–1 between 5 and 15 °C, giving generation times of 7.4–16.1 h.
4. bacterial and HNAN abundances were not coupled, but the highest HNAN grazing impact related to a time of high bacterial productivity.     

COMPARTMENTATION AND LABELLING OF AMINO ACIDS IN THE DEVELOPING RAT BRAIN AFTER INJECTION OF [U-14C]RIBOSE

Abstract— [U-¹⁴C]Ribose was given by subcutaneous injection to young rats aged 2–56 days. During the first week after birth ¹⁴C in the brain was found mainly combined in glucose, fructose and sedoheptulose which contained 46–57 per cent of the ¹⁴C in the acid soluble metabolites in the rat brain. In contrast, during the critical period (10–15 days after birth) the ¹⁴C in the free sugars decreased from 24 to 3 per cent, while the ¹⁴C content of amino acids in the brain increased from 11 to 44 per cent of the total perchloric acid-soluble ¹⁴C. The increase in labelling of amino acids during the critical period was attributed to increased glycolysis and increased oxidation of pyruvate. The relative specific radioactivity of y -aminobutyrate and aspartate in the rat brain at 28 days after birth was equal to or greater than the relative specific radioactivity of glutamate. Assuming that the increase in amino acid content following the cessation of cell proliferation in the brain is located mainly in cell processes (cytoplasm of axons, dendrites, glial processes and nerve terminals), tentative values were estimated for the pool sizes of glutamate, glutamine, aspartate and y -amino butyrate.     

Physiological mechanisms of buoyancy in eggs from brackish water cod

Newly fertilized eggs of brackish water (Gotland, Baltic Sea) and marine (Lofoten, Norway) cod were investigated with regard to specific gravity, wet and dry weight, water content, chorion weight, and content of protein, free amino acids (FAA), and ions. The eggs had neutral buoyancies equivalent to a salinity of 14^.3% (range 11^.5–16^.2%) in brackish water, and 33^.0% (range 31^.8–34^.5%) in the marine environment. A buoyancy model was developed and showed that this difference was mainly caused by differences in egg water content which was 96.6 ± 0^.47% and 92.7 ± 0.45% in the brackish and marine eggs, respectively. The higher water content of the brackish eggs resulted from increased water uptake during final oocyte maturation due to higher intracellular contents of FAA, Cl ^– and NH₄⁺. SDS polyacrylamide gel electrophoresis of eggs and oocytes, and measurements of egg protein content suggested that the FAA pool of both egg types originated from hydrolysis of specific yolk proteins. The main contributor seemed to be a protein with a molecular weight of 100 kDa.     

Anaerobic degradation of benzene in BTX mixtures dependent on sulfate reduction

Abstract Enrichment cultures from marine sediments mineralized benzene while using sulfate as the terminal electron acceptor. Parallel cultures using river marsh sediment displayed no activity. Mineralization was confirmed by release of ¹⁴CO₂ from radiolabeled benzene. The dependence on sulfate reduction was demonstrated by stoichiometric balances and the use of specific inhibitors. This work supports recent observations that anaerobic benzene degradation takes place coupled to sulfate reduction.     

Growth characteristics of low-nutrient bacteria from the north-east and central Pacific Ocean

Abstract Low-nutrient, or oligotrophic, marine bacteria, defined operationally as those which grow well in the dilute nutrient concentrations typical of natural seawaters, were found in waters of the eastern and central Pacific Ocean. All isolates tested grew in sterile unsuplemented seawater, ultraviolet-irradiated seawater, artificial seawater and charcoal-treated artificial seawater. Under optimal conditions, doubling times for low-nutrient bacteria were generally 2–5 h. Low-nutrient bacteria are heterotrophs responding to added organic substrates including glucose, proline, acetate, peptone, algal extract and yeast extract. Organic substrate concentrations ( K _s values) necessary to yield half the maximum growth rates of low-nutrient bacteria ranged from 0.8–12 μg · 1⁻¹ (0.2–4.9 μg C · 1⁻¹). Bacterial inoculum size had little effect on doubling times, whereas low oxygen tensions and low temperatures reduced growth rates. Surfaces (glass beads) increased growth rates and maximum cell densities. The results of these laboratory studies indicate that low-nutrient bacteria play a major role in marine heterotrophic transformations of dissolved organic matter.     

Environmental factors affecting the occurrence of mycobacteria in brook sediments

The occurrence of mycobacteria was studied in aerobic brook sediments from 39 drainage areas in Finland. The culturable counts of mycobacteria were related to climatic conditions, characteristics of the drainage area, chemical characteristics of the sediment and water, culturable counts of other heterotrophic bacteria, and microbial respiration rate in the sediment. The counts of mycobacteria varied from 1·1 × 10² to 1·5 × 10⁴ cfu g⁻¹ dry weight of sediment. They correlated positively with the proportion of the drainage area consisting of peatland, total content of C, content of Pb, microbial respiration rate in the sediment, and chemical oxygen demand of the water. The correlations of the mycobacterial counts with pH of sediment and alkalinity of water were negative. The results of the present sediment study and of the forest soil study published earlier strongly suggest that an increase in acidity increases the counts of mycobacteria and decreases the counts and activity of other heterotrophic bacteria. Mycobacterial counts were more than 100 times higher (per dry weight) in forest soils with pH 3·5–4·3 than in sediments with pH 4·5–6·3.     

Bacterivory by the ciliate Euplotes in different states of hunger

Abstract: The feeding of the marine ciliate Euplotes mutabilis was studied using bacteria ( Vibrio natriegens ) doubly labelled with ³H-thymidine and ¹⁴C-leucine. In the presence of abundant bacteria (30 × 10⁶ bacteria ml⁻¹), an average Euplotes cell (initially without food vacuoles) with a protein content of 12 ng consumed 16 × 10³ bacteria in the first hour and 27 × 10³ bacteria over four hours, accumulating about 60% of the bacterial protein into ciliate macromolecules. Euplotes which had been starved or under-fed to reduce cell protein biomass to 7 or 9 ng consumed significantly fewer bacteria, but the gross growth efficiency for protein did not change. The rate of consumption of bacteria by large Euplotes of protein content 15 ng was initially less than that of 12 ng cells, and it decreased markedly before the end of a 4-hour experiment. Recently divided cells ingested bacteria rapidly, but showed a reduced gross growth efficiency of about 40%. At low bacterial concentrations (6 × 10⁶ bacteria ml⁻¹) the rates of ingestion were markedly reduced to between     and     of maximal levels; the smallest cells could not sustain feeding activity at the low prey concentration and gross growth efficiency fell from 43 to 20% during a 4-hour experiment. The strategy adopted by Euplotes in response to local fluctuations in food supply involves rapid consumption with high growth efficiency in times of plenty, but slow shrinkage without cell division to survive in times of shortage.     

The effect of water status and season on the incorporation of 14CO2 and [14C]-acetate into resin and rubber fractions in guayule

The effects of drought stress and season on both allocation of photosynthates to stems and leaves and potential for stem rubber synthesis were studied in guayule ( Parthenium argentatum Gray USDA line 11604). Two-year-old plants grown under field conditions in the Negev desert of Israel were subjected to different irrigation regimes, and water status was assessed by measuring the relative water content (RWC). Undetached plant tips were exposed to a 1 h pulse of ¹⁴CO₂, followed by a 24 h chase. ¹⁴C fixed and translocated to different plants parts and notably ¹⁴C incorporation into rubber and resin fractions was determined. The potential of detached branch slices to incorporate [¹⁴C]-acetate into rubber was also studied. A higher percentage of fixed ¹⁴C was translocated from shoot tips in winter (28–30%) than in summer (15–18%). The percentage of [¹⁴C]-acctate incorporated into the rubber fraction by stem slices was maximal in winter (20%) and minimal in summer (3–5%) in both cases in the absence of drought stress. In summer the translocation of photosynthates into stems was inversely related to plant RWC, dropping from 18% three days after irrigation to 3% 14 days later, and the potential of stems to synthesise rubber was high under drought conditions and low in well irrigated plants.     

Post-processing microflora and the shelf stability of gari marketed in Port Harcourt

Gari was examined for its post-processing microbial content. Aerobic mesophilic bacteria and fungi were isolated from all samples. The total viable bacterial counts ranged from 2.0 × 10² to 8.0 × 10⁴ cfu/g. Fungal counts ranged from 1.0 × 10² to 1.5 × 10⁴ cfu/g. The total viable counts of fresh samples were much lower than those of market and packaged samples. Bacillus, Micrococcus and Proteus spp. were the bacteria isolated, Aspergillus niger, Aspergillus flavus and Penicillium spp. the fungi. Food borne parasites and pathogens such as Staph. aureus and Clostridium perfringens were not found. The gari samples were quite stable, having a shelf life of 3–6 months. The water activities of the samples ranged from 0.52 to 0.68. Based on the microbial counts of the samples, the critical upper limit for the safety of gari was set at 10⁴ cfu/g dry sample.     

Effect of algal deposition on acetate and methane concentrations in the profundal sediment of a deep lake (Lake Constance)

Abstract In the profundal sediment ot Lake Constance (143 m depth) the temperature is constant at 4 °C. Despite the constant temperature, CH₄ concentrations changed with season between about 120 μM in winter and about 750 μM in summer, measured down to 30 cm depth. The acetate concentration profiles also varied between seasons. In summer, acetate concentration reached a maximum at about 100 μM in 2 or 4 cm depth. In winter, maximal concentrations of about 5 μM were observed over the entire depth. Input of organic material in late spring may be the reason for the seasonal change of both compounds. To simulate such a sedimentation event, intact sediment cores were covered with suspensions of Porphyridium aerugenium or Synechococcus sp. The addition of the phytoplankton material resulted in a drastic increase of acetate concentrations with a maximum at 2 cm depth, similar to in situ acetate concentrations measured in summer. The same applies for CH₄ for which increased concentrations were observed down to 6 cm depth. H₂ concentrations, on the other hand, showed no distinct increase. Treatment of intact sediment cores with ¹⁴C-labeled Synechococcus cells resulted in the formation of ¹⁴C-acetate, ¹⁴CH₄ and ¹⁴CO₂. Maximum concentrations of ¹⁴CH₄ were found at 4 cm depth, i.e. just above the depth to which ¹⁴C-acetate penetrated. The results show that phytoplankton blooms may cause a seasonal variation of acetate and CH₄ in profundal sediments of deep lakes despite the constant low temperature. They also indicate that acetate is the dominant substrate for methanogenic bacteria in the profundal sediments of Lake Constance.