Does microbial stoichiometry modulate eutrophication of aquatic ecosystems?

The stoichiometry of prokaryotes (Bacteria and Archaea) can control benthic phosphorus (P) fluxes relative to carbon (C) and nitrogen (N) during organic matter remineralization. This paper presents the first experimental data on benthic microbial stoichiometry. We used X-ray microanalysis to determine C : N : P ratios of individual prokaryotes from C-limited Baltic Sea sediments incubated under oxic or anoxic conditions. At approximately 400:1, C : P ratios of prokaryotes from both oxic and anoxic incubations were higher than the Redfield ratio for marine organic matter (106:1), whereas prokaryotic C : N ratios (6.4:1) were close to the Redfield ratio. We conclude that high microbial C : P ratios contribute to the enhanced remineralization of P from organic matter relative to C and N observed in many low oxygen marine settings.

Counterintuitive carbon-to-nutrient coupling in an Arctic pelagic ecosystem.

Predicting the ocean's role in the global carbon cycle requires an understanding of the stoichiometric coupling between carbon and growth-limiting elements in biogeochemical processes. A recent addition to such knowledge is that the carbon/nitrogen ratio of inorganic consumption and release of dissolved organic matter may increase in a high-CO(2) world. This will, however, yield a negative feedback on atmospheric CO(2) only if the extra organic material escapes mineralization within the photic zone. Here we show, in the context of an Arctic pelagic ecosystem, how the fate and effects of added degradable organic carbon depend critically on the state of the microbial food web. When bacterial growth rate was limited by mineral nutrients, extra organic carbon accumulated in the system. When bacteria were limited by organic carbon, however, addition of labile dissolved organic carbon reduced phytoplankton biomass and activity and also the rate at which total organic carbon accumulated, explained as the result of stimulated bacterial competition for mineral nutrients. This counterintuitive 'more organic carbon gives less organic carbon' effect was particularly pronounced in diatom-dominated systems where the carbon/mineral nutrient ratio in phytoplankton production was high. Our results highlight how descriptions of present and future states of the oceanic carbon cycle require detailed understanding of the stoichiometric coupling between carbon and growth-limiting mineral nutrients in both autotrophic and heterotrophic processes.

Discovery of a dsRNA virus infecting the marine photosynthetic protist Micromonas pusilla.

We report the isolation of the first double-stranded (ds) RNA virus in the family Reoviridae that infects a protist (microalga Micromonas pusilla, Prasinophyceae). The dsRNA genome was composed of 11 segments ranging between 0.8 and 5.8 kb, with a total size of approximately 25.5 kb. The virus (MpRNAV-01B) could not be assigned to the genus level because host type, genome size, and number of segments smaller than 2 kb did not correspond to either of the two existing 11-segmented dsRNA genera Rotavirus and Aquareovirus. MpRNAV-01B has a particle size of 65-80 nm, a narrow host range, a latent period of 36 h, and contains five major proteins (120, 95, 67, 53, and 32 kDa). MpRNAV-01B was stable to freeze-thawing, resistant to chloroform, ether, nonionic detergents, chelating and reducing agents. The virus was inactivated at temperatures above 35 degrees C and by ionic detergent, ethanol, acetone, and acidic conditions (pH 2-5).

Isolation and characterization of two viruses with large genome size infecting Chrysochromulina ericina (Prymnesiophyceae) and Pyramimonas orientalis (Prasinophyceae).

Two lytic viruses specific for Chrysochromulina ericina (Prymnesiophyceae) and for Pyramimonas orientalis (Prasinophyceae) were isolated from Norwegian coastal waters in June 1998. The lytic cycle was 14-19 h for both viruses; the burst size was estimated at 1800-4100 viruses per host cell for the Chrysochromulina virus and 800-1000 for the Pyramimonas virus. Thin sections of infected cells show that both viruses replicate in the cytoplasm and that they have a hexagonal cross section, indicating icosahedral symmetry. The Chrysochromulina virus had a particle size of 160 nm and a genome size of 510 kbp; the size of the major polypeptide was 73 kDa. The Pyramimonas virus had a particle size of 220 x 180 nm and a genome size of 560 kbp; the size of the major polypeptide was 44 kDa. The genome sizes of these viruses are among the largest ever reported for viruses and they are larger than the minimum required for cellular life. The Chrysochromulina virus clone CeV-01B and the Pyramimonas virus clone PoV-01B described in this study have several properties in common with other viruses infecting microalgae, suggesting that they belong to the Phycodnaviridae.

Short-term physical training reduces left ventricular dilatation during exercise soon after myocardial infarction.

Coronary heart disease and beta-blocker treatment can increase the use of the Frank-Starling mechanism during exercise. The aim of the study was to assess whether this could be influenced by physical training. Male patients on beta-blocker treatment after myocardial infarction were randomised to four weeks of training (ET, n = 19) or to a control group (Ctr, n = 18). Cardiac output (CO) at rest and at identical submaximal exercise levels in each patient were determined by radionuclide ventriculography at baseline and after the intervention period. CO was calculated as end diastolic volume (EDV) x ejection fraction x heart rate, and deltaCO and deltaEDV as change in parameter from rest to exercise. The mean (SD) deltaCO decreased from 6.5 (2.1) L/min(-1) to 5.1 (2.4) in ET patients and increased from 5.0 (1.7) to 5.8 (2.7) in Ctr, p = 0.004. deltaEDV decreased from 30 (30) mL to 12 (35) in ET and increased from 11 (20) to 36 (33) in Ctr, p = 0.005. When adjusting for baseline dissimilarities between the groups in a multivariate linear regression analysis, these differences were still statistically significant, p = 0.018 and p = 0.044, respectively. Physical training reduces the CO increase needed to perform identical submaximal exercise, and this is accompanied by less left ventricular dilatation, with a potential for reducing exercise-induced ischaemia.

Randomised training after myocardial infarction: short and long-term effects of exercise training after myocardial infarction in patients on beta-blocker treatment. A randomized, controlled study.

In this study we assessed the short- and long-term effects of 4-weeks of exercise training (MI) soon after myocardial infarction in patients on beta-blocker treatment. Thirty-seven male patients < or = 65 years of age were included in the study, 19 of them randomized to exercise training (ET) and 18 to a control group (Ctr). Cumulated work (CW), calculated in kiloJoules (kJ), was recorded before immediately after the intervention period and again six months after the MI. In the short term the mean (SD) CW increased by 22% (from 65(20) to 79(25) kJ) in the ET group, compared with no change in the Ctr patients (65(24) vs 65(21) kJ) (p = 0.009). At late follow-up CW was 14% above baseline in the ET patients (65(20) vs 74(20) kJ) p = 0.036, compared with only 6% in the 15 Ctr patients who were still available for follow-up (68(24) vs 72(29) kJ), but without a significant between-group difference. In post-MI patients on beta-blocker treatment, and with a high baseline exercise capacity, physical training improved exercise capacity in the short term, but there was no significant between-group difference at long-term follow-up.

The inorganic ion content of native aquatic bacteria.

In this study we have quantified the ionic content and volume of native aquatic, and two cultured bacteria, by X-ray microanalysis (XRMA) in the transmission electron microscope (TEM). The cellular concentrations of magnesium (means of 630 and 710 mM) were more than an order of a magnitude higher than the outside concentrations. The internal concentrations of sodium were on average 50-180 mM, and the [K+]/[Na+] ratios were in the range of 0.1-0.5; lowest for apparently nonactive bacteria. Magnesium and chloride probably act as the major components of cell turgor, since no other inorganic ions were present in comparable amounts. Our carbon and nitrogen measurements indicated that organic solutes are not likely to be present at significant concentrations. The estimated charge of inorganic ions (Na, Mg, P, Cl, K, and Ca) gave a positive net internal charge for most cells. However, in cultures of Vibrio natriegens, the high internal chloride concentration made the net inorganic charge negative in these cells. Our results suggest that growing marine bacterioplankton have an internal environment in which magnesium is the dominating cation. These results suggest that actively growing marine bacteria are physiologically adapted to high internal concentrations of both magnesium and chloride.

Occurrence of virus-like particles in the Dead Sea.

Electron-microscopic examination of water samples from the hypersaline Dead Sea showed the presence of high numbers of virus-like particles. Between 0.9 and 7.3 x 10(7) virus-like particles ml(-1) were enumerated in October 1994 in the upper 20 m of the water column during the decline of a bloom of halophilic Archaea. Virus-like particles outnumbered bacteria by a factor of 0.9-9.5 (average 4.4). A variety of viral morphologies were detected, the most often encountered being spindle-shaped, followed by polyhedral and tailed phages. In addition, other types of particles were frequently found, such as unidentified algal scales, and virus-sized star-shaped particles. Water samples collected during 1995 contained low numbers of both bacteria and virus-like particles (1.9-2.6 x 10(6) and 0.8-4.6 x 10(7) ml(-1) in April 1995), with viral numbers sharply declining afterwards (less than 10(4) ml(-1) in November 1995-January 1996). It is suggested that viruses may play a major role in the decline of halophilic archaeal communities in the Dead Sea. an environment in which protozoa and other predators are absent.

Bacterial population dynamics in a meromictic lake.

Polyclonal antibodies against nine different bacteria isolated from Lake Saelenvannet in western Norway were produced, and the population dynamics of these strains in the lake were monitored through two spring seasons by immunofluorescence staining. The total counts of bacteria varied over time and space from 1.5 x 10(6) to 1.5 x 10(7) cells ml-1. The counts of specific bacteria were in the range of 10(3) to 10(4) cells ml-1 or less; in sum, they generally made up less than 1% of the bacterial community. Some populations showed significant changes in abundance, with blooms lasting 1 to 3 weeks. The rate of change (increase and decrease) in abundance during blooms was estimated to be 0.2 to 0.6 day-1. The average virus-to-bacteria ratio was 50, and there was a significant correlation between the abundances of virus and bacteria. Both protozoan grazing and lytic virus infection were assessed as possible mechanisms driving the variations in bacterial population density.

Simple clinical data are useful in predicting effect of exercise training after myocardial infarction.

OBJECTIVES: The aim of the present study was to determine whether simple clinical variables can predict the effect of intensive exercise training in an unselected population early after myocardial infarction. METHODS: Starting 5 weeks after the qualifying myocardial infarction, 105 patients, 68 years old or younger, completed a 4 week period of intensive exercise training. The training effect was defined as an absolute increase in cumulative work at bicycle ergometry. Using univariate and multivariate analysis, 28 variables were tested against the training effect. RESULTS: The mean exercise capacity increased from 46.7 +/- 22.7 kJ to 69.5 +/- 31.1 kJ (P = 0.0001). Multivariate analysis identified five independent predictors of the training effect. Myocardial infarct size was associated with a better training effect (P = 0.0018), as was male gender (P = 0.0042) and ability to exercise to exhaustion at the baseline exercise test (P = 0.0124). Older age (P = 0.0017) and treatment with beta-adrenergic blocking agents (P = 0.0241) were associated with a lower effect from training. These five variables explained 33% of the variations in effect from training. Patients suffering in-hospital cardiac complications or congestive heart failure achieved a training effect at least as great as patients without cardiac complications. CONCLUSIONS: Five simple clinical variables, including infarct size, can assist in the selection of patients for exercise training after myocardial infarction.

[Radiofrequency ablation of heart arrhythmias. Results in the first 150 patients treated at the Arrhythmia center in Oslo]. / Radiofrekvensablasjon av hjertearytmier. Resultater hos de første 150 pasienter behandlet ved Arytmisenteret i Oslo.

The authors review the first 150 patients with cardiac arrhythmias who were treated with radio-frequency ablation at a Norwegian arrhythmia centre. The clinical success rate (either electrophysiological cure or a dramatic reduction in the severity and frequency of the attacks) was 97%. 11 patients were treated for two or more arrhythmias. In 27 patients two, occasionally three, sessions were required to obtain a satisfactory clinical result. Repeat ablation is scheduled for three cases where the treatment was unsuccessful. Among 190 ablations, 13 complications occurred, none of which resulted in permanent sequelae. The time spent on each procedure, and particularly the long time spent on fluoroscopy during the earlier procedures, demonstrates the existence of a learning curve for ablation. This lends support to the authorities' restriction of treatment of arrhythmias by ablation to only two laboratories in a population of four million.

Light element analysis of individual bacteria by x-ray microanalysis.

A method based on X-ray microanalysis (XRMA) with the transmission electron microscope for measurement of total amounts of elements in single microbial cells has been developed. All major elements in cells except hydrogen can be measured simultaneously. XRMA provided N/C ratios (means (plusmn) standard errors of the mean) for stationary-phase and growing Escherichia coli of 0.23 (plusmn) 0.01 and 0.30 (plusmn) 0.01, respectively, while CHN analysis gave values of 0.276 and 0.307, respectively, for samples from the same cultures. Analyses of free coccoliths from Emiliana huxleyi provided weight fractions close to those of CaCO(inf3): 0.35 (plusmn) 0.01, 0.15 (plusmn) 0.01, and 0.47 (plusmn) 0.01 for calcium, carbon, and oxygen, respectively. Calibration is based on monodisperse latex beads and on microdrops of defined compounds. Elements in particles in the size range from 5 fg to 500 pg are measured with a relative precision between 500 and 5,000 ppm, depending on size. As a single-cell method, XRMA avoids the shortcomings of commonly used fractionation techniques associated with bulk methods, which are based on centrifugation or filtration. On the basis of morphology and XRMA, particles may be classified more precisely into groups (e.g., biotic versus abiotic) than is possible by bulk methods. Single-cell elemental analysis may provide insight into topics like nutritional and energetic status, macromolecular composition, and (by multivariate statistics) community structure.

Effects of intensive exercise training on lipid levels in high risk post-MI patients.

One hundred and two patients participated in a 4 week programme of intensive exercise training early after myocardial infarction. Lipid levels were measured before and after exercise training. The mean exercise capacity increased by 49% (P = 0.0001). Twenty-one patients who continued smoking and 25 non-beta-blocked patients were considered to have an increased risk of recurrent cardiac events, as were patients with high initial lipid levels. In the smokers and non-beta-blocked patients total cholesterol decreased by 0.30 mmol.l-1 (P = 0.031) and 0.37 mmol.l-1 (P = 0.042) respectively and triglycerides by 0.28 mmol.l-1 (P = 0.058) and 0.13 mmol.l-1 (P = 0.11). Patients with high initial cholesterol and triglyceride levels had the largest cholesterol and triglyceride decrease, r = 0.43 (P = 0.0001) and r = 0.38 (P = 0.001) respectively. After adjusting for initial lipid levels, cholesterol (P = 0.036) as well as triglycerides (P = 0.034) decreased in patients without beta-blocker treatment whereas smoking no longer had an independent effect on lipid level decrease. HDL-cholesterol did not change in any group. Thus, after 4 weeks of exercise training lipid profiles were improved in patients with an increased risk of recurrent cardiac events. Beta-blocker treatment, however, seemed to hinder the beneficial effects of exercise training on lipid levels.

Viruses and the microbial loop.

The abundance of viral-like particles in marine ecosystems ranges from <104 ml(-1) to >10(8) ml(-1). Their distribution in time and space parallels that of other biological parameters such as bacterial abundance and chlorophyll a. There is a lack of consensus between methods used to assess viral activity, i.e., rate of change in viral abundance (increase or decrease). The highest rates, 10-100 days(-1), are observed in experiments with short sampling intervals (0.2-2 h), while lower rates, on the order of 1 day(-1), are observed in experiments with longer sampling intervals (days). Few studies have been carried out, but viruses appear, at least in some cases, to have a significant impact on carbon and nutrient flow in microbial food webs. Viruses have also been demonstrated to exert a species specific control of both bacteria and phytoplankton populations in natural waters.

Deep vein thrombosis: a 7-year follow-up study.

OBJECTIVES: To study the sequelae of deep venous thrombosis (DVT) in terms of symptoms and objective signs of deep venous insufficiency (DVI) and their relationship to the initial extension of DVT, and to assess the control legs in the same way. DESIGN: Follow-up study after an average of 89 (range 79-102) months. SETTING: Out-patient clinic, University Hospital, Oslo. SUBJECTS: Seventy-six patients with DVT 7 years previously. At follow-up 41 patients were dead and 10 were not available for restudy, thus twenty-five patients were studied in all. MAIN OUTCOME MEASURES: Symptom rating. Objective verification of DVI by invasive pressure recordings (DVI-I) and by the Doppler ultrasound technique (DVI-D). RESULTS: At follow-up, 42% of the patients had symptoms, half of these severe, while 68% had DVI. Eighty-two per cent of symptomatic patients and 60% of the asymptomatic patients had DVI. There were no more symptoms in proximal than in distal DVT, but slightly more DVI. Control legs had neither symptoms nor DVI. CONCLUSIONS: Seven years after DVT few patients had severe symptoms, although objective signs of DVI were common. Symptoms were no more frequent after proximal than after distal DVT. We found no symptoms or DVI in control legs.

Effects of flecainide on termination of atrial flutter by rapid atrial pacing.

Rapid atrial pacing is effective in terminating atrial flutter, but often results in transient or permanent atrial fibrillation rather than sinus rhythm. Class Ia antiarrhythmic drugs have earlier been shown to facilitate the direct conversion of atrial flutter to sinus rhythm. The present study was performed to test the hypothesis that flecainide, a group 1c antiarrhythmic drug, increases the direct conversion to sinus rhythm. In a series of 30 consecutive clinical episodes of atrial flutter treated with rapid atrial pacing, 12 episodes were in patients on flecainide treatment (group A), while in 13 episodes no patients were on group I antiarrhythmic drugs (group B). Direct conversion to sinus rhythm was achieved more often in group A (75%) than in group B (31%) P = 0.034. Both the flutter rates and the pacing rates used were lower in group A, 240 vs 280 beat.min-1 and 375 vs 430 b.min-1, respectively. Patients with atrial flutter in whom rapid atrial pacing is to be performed should be considered for pretreatment with flecainide.

Are viruses important partners in pelagic fend webs?

Viruses have been assumed to play a rather negligible role as partners in microbial food web dynamics. However, recent discoveries suggest that the rate of virally induced lysis of marine microbial populations may be significant. This, in turn, may have important consequences for the developing conceptual framework of the microbial food web.

Changes in polyphosphate composition and localization in Propionibacterium acnes after near-ultraviolet irradiation.

Electron microscopy showed that electron-dense granules accumulated in Propionibacterium acnes in larger amounts when the bacteria were grown on a phosphate-rich medium. X-ray microanalysis demonstrated that the granules contained mostly phosphorus and potassium, indicating that the cells contained polyphosphate granules. When cells were grown on a complex Bacto-agar medium, the amount and the size of the polyphosphate granules were reduced. Polyphosphate was also detected with 31P nuclear magnetic resonance (31P-NMR). Of the polyphosphates observed with 31P-NMR, 20% seemed to be located outside the cell membrane. Broad-band near-ultraviolet irradiation (emission maximum 366 nm) corresponding to doses that killed 37% of the cells increased the amount of polyphosphate in cells grown on the phosphate-rich medium. The fluorescent chromophore 4',6-diamidino-2-phenylindole (DAPI) shifted the fluorescence emission from 478 to 538 nm when bound to polyphosphate and excited at 340 nm. DAPI was used to detect polyphosphates generated after near-ultraviolet irradiation of the cells. Nonirradiated cells showed no increased fluorescence at 538 nm, indicating no polyphosphate is presented in the cells. We conclude that DAPI did not have "access" to the intracellular polyphosphate as long as the cells were not light damaged. This observation is important for the interpretation of near-UV damage to cells.

Viruses as partners in spring bloom microbial trophodynamics.

Population sizes of algae, bacteria, heterotrophic flagellates, and viruses were observed through the 1989 spring diatom bloom in Raunefjorden in western Norway. The culmination of the diatom bloom was followed by a peak in the concentration of bacteria and an increase in the concentration of heterotrophic flagellates, a pattern consistent with the concept of a food chain from photosynthetically produced organic material, through bacteria, to bacterivorous flagellates. The concentration of viruses varied through the spring bloom from 5 x 10 in the prebloom situation to a maximum of 1.3 x 10 viruses ml 1 week after the peak of the diatom bloom. Coinciding with the collapse in the diatom bloom, a succession of bacteria and viruses was observed in the mucous layer surrounding dead or senescent diatoms, with an estimated maximum of 23% of the total virus population attached to the diatoms. The dynamic behavior observed for the virus population rules out the possibility that it is dominated by inactive species, and the viruses are suggested to be active members of the microbial food web as agents causing lysis in parts of the bacterial population, diverting part of the bacterial production from the predatory food chain.

Enumeration and biomass estimation of planktonic bacteria and viruses by transmission electron microscopy.

Bacteria and virus particles were harvested from water samples by ultracentrifugation directly onto Formvar-coated electron microscopy grids and counted in a transmission electron microscope. With this technique, we have counted and sized bacteria and viruses in marine water samples and during laboratory incubations. By X-ray microanalysis, we could determine the elemental composition and dry-matter content of individual bacteria. The dry weight/volume ratio for the bacteria was 600 fg of dry weight microns-3. The potassium content of the bacteria was normal compared with previous estimates from other bacterial assemblages; thus, this harvesting procedure did not disrupt the bacterial cells. Virus particles were, by an order of magnitude, more abundant than bacteria in marine coastal waters. During the first 5 to 7 days of incubation, the total number of viruses increased exponentially at a rate of 0.4 day-1 and thereafter declined. The high proliferation rate suggests that viral parasitism may affect mortality of bacteria in aquatic environments.