Ecological significance of bacterial polyphosphate metabolism in sediments

The purpose of this study was to find theoretical evidence that bacteria, in particular those capable of polyphosphate (polyP) metabolism, are directly implicated in sediment phosphorus (P) dynamics and control P metabolism of freshwater ecosystems. The specific attributes and functional role of such bacteria were investigated on successive levels of ecological organization: individual microorganism, microbial community, freshwater ecosystem. The results of this systematic approach have been formulated as a number of hypotheses.

1. PolyP metabolism is the mechanism which enables individual polyP bacteria to survive and grow under the fluctuating redox conditions characteristic of their habitat at the sediment-water interface.
2. PolyP metabolism together with anaerobic Mn and/or Fe respiration is the mechanism that confers upon polyP bacteria the advantage required to fill a unique ecological niche within the microbial community to which they belong.
3. To the freshwater ecosystem as a whole bacterial polyP metabolism is a homeostatic mechanism which limits P availability and makes ecosystem productivity self-correcting as a function of oxygen availability. Bacterial polyP pools in the sediment are vital components of the P cycle. It was suggested that the impact of this bacterial mechanism should be tested with regard to the eutrophication issue.

     

Studien über die Testaceenbesiedlung der Seen und Tümpel des Abisko-Gebietes (Schwedisch-Lappland)

1. From 40 waters of the Abisko-district (Sweden, Lapland) 58 samples were collected (essentially samples from sediments).
2. It is not possible to clear the origin of all discovered tests of sediments. The bottom of most waters was covered with mosses, from which vegetation, tests can come into the sediments. But also tests from other biotopes, can be found at the bottom.
3. Nevertheless we can recognize typical characters of those species living in sediments. The prevalent type is the “Difflugia-type”. Those species of Centropyxis which immigrated into sediments demonstrate a trend towards the “Difflugia-type”. The immigration is possible from Aufwuchs, mosses and soils. 62,7% of the recorded tests belong to Difflugia, 17,8% to Centropyxis.
4. The prevalent species in the sediments of the Abisko-district is Difflugia elegans var. teres, the next is D. glubolosa.
5. A great number of investigated waters contained the oligotrophic species Centropyxis aërophila. Only one lake (Ruontenjaure) shows the association of dystrophic lakes.
6. Some species are described taxonomically, for instance: Centropyxis nauwercki n.sp. C. nauwercki is very much like Difflugia, but is also connected with C. platystoma. The new species shows a trend from Centropyxis to Difflugia.
7. C. aërophila can also immigrate into the Aufwuchs. There the species has membraneous tests.
8. Geographical aspects of the sediment colonization are discussed.

     

The role of microorganisms in mobilization and fixation of phosphorus in sediments

Cycling of phosphorus (P) at the sediment/water interface is generally considered to be an abiotic process. Sediment bacteria are assumed to play only an indirect role by accelerating the transfer of electron from electron donors to electron acceptors, thus providing the necessary conditions for redox-and pH-dependent, abiotic sorption/desorption or precipitation/dissolution reactions. Results summarized in this review suggest that

1. in eutrophic lakes, sediment bacteria contain as much P as settles with organic detritus during one year
2. in oligotrophic lakes, P incorporated in benthic bacterial biomass may exceed the yearly deposition of bioavailable P several times
3. storage and release of P by sediment bacteria are redox-dependent processes
4. an appreciable amount of P buried in the sediment is associated with the organic fraction
5. sediment bacteria not only regenerate PO₄, they also contribute to the production of refractory, organic P compounds, and
6. in oligotrophic lakes, a larger fraction of the P settled with organic detritus is converted to refractory organic compounds by benthic microorganisms than in eutrophic lakes.

From this we conclude that benthic bacteria do more than just mineralize organic P compounds. Especially in oligotrophic lakes, they also may regulate the flux of P across the sediment/water interface and contribute to its terminal burial by the production of refractory organic P compounds.     

Nitrogen limitation on land and in the sea: How can it occur?

The widespread occurrence of nitrogen limitation to net primary production in terrestrial and marine ecosystems is something of a puzzle; it would seem that nitrogen fixers should have a substantial competitive advantage wherever nitrogen is limiting, and that their activity in turn should reverse limitation. Nevertheless, there is substantial evidence that nitrogen limits net primary production much of the time in most terrestrial biomes and many marine ecosystems. We examine both how the biogeochemistry of the nitrogen cycle could cause limitation to develop, and how nitrogen limitation could persist as a consequence of processes that prevent or reduce nitrogen fixation. Biogeochemical mechansism that favor nitrogen limitation include:

the substantial mobility of nitrogen across ecosystem boundaries, which favors nitogen limitation in the “source” ecosystem — especially where denitrification is important in sediments and soils, or in terrestrial ecosystems where fire is frequent;

differences in the biochemistry of nitrogen as opposed to phosphorus (with detrital N mostly carbon-bonded and detrital P mostly ester-bonded), which favor the development of nitrogen limitation where decomposition is slow, and allow the development of a positive feedback from nitrogen limitation to producers, to reduced decomposition of their detritus, and on to reduced nitrogen availability; and

other more specialized, but perhaps no less important, processes.

A number of mechanisms could keep nitrogen fixation from reversing nitrogen limitation. These include:

energetic constraints on the colonization or activity of nitrogen fixers;

limitation of nitrogen fixers or fixation by another nutrient (phosphorus, molybdenum, or iron) — which would then represent the ultimate factor limiting net primary production;

other physical and ecological mechanisms.

The possible importance of these and other processes is discussed for a wide range of terrestrial, freshwater, and marine ecosystems.     

Paläolimnologische Studien an Testaceen aus Bohrkernen des Latnjajaure (Abisko-Gebiet; Schwedisch-Lappland)

1. Rhizopod tests from 16 cores of sediments from lake Latnjajaure, in Swedish Lapland, were studied and found to show the development of the lake since its formation. Latnjajaure is a oligotrophic mountain lake.
2. All cores contained many remains of rhizopods, most of them intact. Most broken tests could be reconstructed. Postglacial development of a lake could thus be elucidated for the first time.
3. The sediment cores contained 24 species of Testacea, 41.6% of the recent fauna. The rank order of species forming 1 % or more of the total number in the cores is nearly identical with the rank order of recent species.
4. The history of lake Latnjajaure is characterized by Centropyxis aërophila, an oligotrophic species. Periods of beginning eutrophication are indicated by a decrease of Centropyxis aërophila and an increase of Difflugia species, but typical eutrophic species were absent. A dystrophic phase in the development could not be ascertained by means of rhizopods.

     

Development and efficiency of a new generation of bioreactors

The development and investigation of high-efficiency bioreactors is one of the primary problems bioprocess engineers have to solve. With increasing efficiency of the bioreactor the downstream processes will be much simplified, energy and costs will be substantially reduced. According to fundamental research on the properties of stirred tank bioreactors the following rules for the design of bioreactors should be observed:

1. Prevent rotational motion of the biosuspension.
2. Generate motion of the biosuspension in the radial and axial direction.
3. Prevent fluid flow in big spaces.

These design rules are in general observed in the development of high-efficiency bioreactors. A selected group of such bioreactors is described.     

Growth of a floating aquatic weed,Salvinia under standard conditions

1. Growth of the floating aquatic weed, Salvinia, in sterile culture was exponential for at least 2 weeks under standardized conditions.
2. Increase in light intensity or in CO₂ resulted in increases in growth rate, but did not extend the exponential period of growth.
3. This aquatic plant, like many others, discriminates against calcium relative to strontium.
4. In culture Salvinia exhibited luxury consumption of N and P.
5. Because of high C/N ratios, Salvinia may not be a favorable source of animal food, but might be useful in nutrient removal schemes.
6. In sterile culture, S. molesta produced fewer leaves than S. minima, but maintained a significant increase in leaf area and dry weight. This may be correlated with the ability of the first species to rapidly spread over tropical waterways.

     

Development and efficiency of a new generation of bioreactors

The development and investigation of high-efficiency bioreactors is one of the primary problems bioprocess engineers have to solve. With increasing efficiency of the bioreactor the downstream processes will be much simplified, energy and costs will be substantially reduced. According to fundamental research on the properties of stirred tank bioreactors the following rules for the design of bioreactors should be observed:

1. Prevent rotational motion of the biosuspension.
2. Generate motion of the biosuspension in the radial and axial direction.
3. Prevent fluid flow in big spaces.

These design rules are in general observed in the development of high-efficiency bioreactors. A selected group of such bioreactors is described.     

The use of toxicokinetics for the safety assessment of drugs acting in the brain

Pharmacological and toxicological studies undertaken on drugs that affect the brain are frequently performed in disparate species under various experimental conditions, at doses often greatly in excess of those expected to be administered to humans, and the findings are extrapolated implicitly or explicitly with scant regard to differences in the biodisposition of the drugs. Such considerations are necessary since:

1. Species;
2. Strain;
3. Gender;
4. Route;
5. Dose;
6. Frequency and time of administration;
7. Temperature;
8. Coadministration of drugs; and
9. Surgical manipulation

are but some of the factors that have been shown to influence the kinetics and metabolism of drugs. This article, using MDMA and other phenylethylamines as examples, provides evidence for the need to measure the exoosure of the drugs and their active metabolites in blood and brain (toxicokinetics) in order that conclusions based only on dynamic, biochemical, or histological evidence are more pertinent. Further, the combined use of toxicokinetic-dynamic modeling can lead to a better appreciation of the mechanisms involved and a more useful approach to the calculation of safety margins.     

Effects of the discharge of thermal effluent from a power station on Lake Wabamun,Alberta, Canada — The epipelic and epipsamic algal communities

1. The epipelic algal standing crops were increased by the discharge of thermal effluent into Lake Wabamun, particularly in the discharge canal at station (03–04) and 05.
2. The increase in the standing crop size of the epipelon was due to Oscillatoria amoena and O. borneti in the heated area, while the discharge canal provided the inoculum of the algae for the heated area of the lake.
3. At station (03–04) the increased standing crop size was also a function of increased light penetration to the sediment due to the heated effluent keeping an area of the lake free of ice during the winter.
4. The species composition of the diatoms was similar at all stations except in the discharge canal where there was a reduction in the number of diatom species.
5. Navicula cuspidate developed best in the discharge canal in the summer where water temperatures of 31°C were recorded.
6. Amphora ovalis var. pediculus was the dominant diatom species during the winter under ice-cover.
7. The heated effluent had no effect upon the standing crop or species composition of the epipsammon.
8. Results obtained from the sediment core study showed that the shallow littoral zone of the lake is very disturbed due to wind-induced wave action.

     

Effet des androgènes sur l’activité sportive

Androgenic hormones seem to be of beneficial effects on sports performance:

- they increase motivation, will, aggressiveness, resistance to the stress and to the fatigue, leading to an increase of the training quantity,

- they increase bone mineralization and probably mechanical resistance,

- they stimulate the bone marrow and so, with the erythropoietin, the erythropoiesis,

- they increase the tendancy to hyperglycemia, but with a decrease of the tolerance to the glucose,

- they stimulate the fatty acids mobilization from the adipose tissue, for their utilization in the muscle during the exercise,

- they participate, for the trained sportmen, to a better gestion of the muscle glycogen storage: their utilization during exercise is decreased,

- they increase the lean body mass, with an increase of the protein synthesis and a decrease of the protein catabolism, leading also to an increase of the muscle force under training. There is no beneficial effect upon the tendons,

- they have an immunomodulation action.

     

Effect of feeding on the respiration rate of the rotifer Brachionus plicatilis

The effect of feeding on the respiration rate of Brachionus plicatilis was studied. Oxygen consumption was determined under two feeding regimes, duplicate feeding and constant feeding. Oxygen consumption rate increased during feeding. The oxygen consumption profile is discussed in relation to the following processes:

1. filtration, mastication, and locomotion during feeding
2. specific dynamic action (SDA)
3. egg formation and routine metabolism.

     

Seasonal changes in ambient phosphate and phosphatase activities of the cyanobacterium Rivularia atra in intertidal pools at Tyne Sands, Scotland

1. A study was made of Rivularia atra at a sheltered bay in S-E. Scotland, where it is frequent in summer in pools of the upper eulittoral. Monthly measurements of water chemistry and phosphate activities were made at the same stage in the tidal cycle during April 1992–October 1993, together with other short intensive studies.
2. Drift seaweed deposited at high tide levels (>4.9 m) released high concentrations of inorganic nutrients to adjacent pools, where the water sometimes exceeded 6000 µg l^?1 PO₄?P. Combined inorganic N was, however, always low and the N:P ratio fell to 0.001–0.003:1 (by weight) in August, when the temperature was relatively high: much N was lost to the atmosphere as ammonia.
3. Total P concentrations in the Rivularia pools (mostly covered by 4.5–4.8 m tides) were much lower than in the drift seaweed pools, but similar to the sea, though with higher % organic P in the former (means of 50% v. 28%): total N concentrations were much lower in the Rivularia pools than in seawater, leading to a very low N:P for most of the time. Aqueous organic P tended to increase (in summer) during the period between tidal cover, even in pools lacking input drainage, suggesting that much of the organic P may be autochthonous.
4. All 9 Rivularia pools showed high concentrations of P in June in one or both years. At the same time the Rivularia colonies formed abundant hormogonia, followed 4–8 weeks later by a marked increase in macroscopically obvious colonies.
5. Assays of ‘surface’ phosphomonoesterase activity by Rivularia colonies showed different results according to whether p-nitrophenyl phosphate (pNPP) or 4-methylumbelliferyl phosphate (4-MUP) was used as substrate. Both substrates indicated obvious activity at intervals during the year. Using pNPP, activity was very low in June, usually followed by a very high value in July or August; use of 4-MUP showed a different response, with a high value one or two months later than with pNPP.

     

Survival,osmoregulatory ability,and respiration of idotea chelipes (Crustacea,Isopoda) from lake veere in different salinities and temperatures

1. An ecological and physiological study ofI. chelipes from Lake Veere, The Netherlands, was made.
2. Both osmoregulatory capacity and survival decrease with increasing temperature as well as with decreasing salinity.
3. Respiration experiments suggest that the need of energy by osmoregulatory activity may be supplied at the cost of other physiological processes, at any rate at temperatures of 10°C and higher.
4. It may be expected that, if temperatures higher than 15°C and salinities lower than 8‰ coincide, the population ofI. chelipes will be affected negatively.

     

Les prélèvements testiculaires dans les azoospermies sécrétoires: indications et bilan andrologique

The management of patients with nonobstructive azoospermia must not be limited to testicular biopsy. A complete andrological assessment must be performed to adapt treatment to each patient, in order to:

-avoid testicular biopsy by screening for “azoospermia-like” syndromes and treat any etiological factors (pituitary hypogonadism, varicoceles, cryptorchidism), and concomitant aggravating factors (spermatic cord infection, obstructive factor of the epididymis or vas deferens).

-screen for clinical or subclinical testicular tumors and demonstrate genetic anomalies involving risks for the offspring.

-establish a prognosis regarding the possible use of medically-assisted reproduction by ICSI (intracytoplasmic sperm injection) with testicular spermatozoa.

     

Erecteur a dépression (Vacuum erection device): Mise au point

The vacuum erection device (VED) is a nonsurgical alternative for the treatment of erectile dysfunction. This method is based on 2 phenomena:

1. an erection-like state occurs when the penis is placed in a vacuum
2. this state can be maintained by a constricting band placed around the base of the penis

The erection-like state thus obtained differs from a normal erection in the following ways:

1. blood flow into the penis decreases
2. penile skin temperature falls
3. congestion of extra-corporeal penile tissues occurs
4. the penis pivots at its base
5. the ejaculate is trapped in the proximal urethra

About 30 to 60% of men who trie the device at home purchase it for continued use. The others are unable to achieve sufficient rigidity, experience side-effects or dislike the use of the device despite good result. About 60 to 80% of the men who purchased the device continue to use it regulary at short or middle term. The VED seems to have lesser drop-out rate than the self injection therapy. The most frequently encountered side-effects of the device are pain, petechiaes, bruising and ecchymosis.     

Neurotransmitters of cephalopods

1. ACh, dopamine, noradrenaline, 5-HT,l-glutamate, and GABA are widely distributed in cephalopods and probably all function as neurotransmitters; octopamine also occurs and at one site is known to act as a neuromodulator.
2. Several peptides are also present, as well as nitric oxide synthase.
3. In the brain and sense organs cholinergic, aminergic, serotonergic and glutamatergic systems seem to be the most important.
4. ACh is also active in the gut, vascular system and some body muscles: it is generally inhibitory. The ACh receptors are similar to the vertebrate nicotinic type.
5. The catecholamines are important in the gut and vascular system: they are generally excitatory. The NA receptors are like the α-adrenergic subtype of vertebrates, but the nature of the DA and OA receptors is less certain.
6. 5-HT is important in the gut but is endogenous in some chromatophore nerves and acts on receptors that seem like the vertebrate 5-HT₁ type.
7. l-glutamate is an excitatory transmitter at the chromatophore (and probably at other) nerve-muscle junctions and is an extremely strong candidate for being the excitatory transmitter at the squid giant synapse. There are NMDA receptors on Schwann-cells but the receptors on neurons and muscles are like the vertebrate kainate type.
8. Little is known about the mode of action of cephalopod peptides; nor has it ever been shown that they co-exist with conventional transmitters in these animals.
9. The structure of one (FMRFamide) receptor has been elucidated, but apart from this nothing is known of the molecular biology of receptors in cephalopods.