Oxygen consumption in Mediterranean octocorals under different temperatures

Ecosystem resilience to climate anomalies is related to the physiological plasticity of organisms. To characterize the physiological response of some common Mediterranean gorgonians to fluctuations in temperature, four species (Paramuricea clavata, Eunicella singularis, Eunicella cavolinii and Corallium rubrum) were maintained in aquaria, in which the temperature was increased every ten days with increments of 2-3 °C, starting at 14 °C, ending at 25 °C. Oxygen consumption, number of open/closed polyps and percentage of necrotic tissue were monitored. All species showed similar activity patterns with increasing temperature. P. clavata and E. singularis showed the highest respiration rate at 18 °C, E. cavolinii and C. rubrum at 20 °C. Above these temperatures, both oxygen consumption and polyp reactivity decreased in all species. The present data confirm a reduction of the metabolic activity in Mediterranean gorgonians during periods of high temperature. At temperatures above 18 °C, the percentage of open polyps (considered as a parameter to evaluate polyps reactivity) decreased, thus mirroring the trend of oxygen consumption. The average values of Q₁₀ indicated that gorgonians have a definite temperature limit over which the metabolism (oxygen consumption) stop to follow the temperature increase. After three days at 25 °C, metabolic activity in E. cavolinii, C. rubrum and P. clavata further decreased and the first signs of necrosis were observed. At this temperature, activity remained unchanged in E. singularis. This species seems to more resistant to thermal stress. The symbiotic zooxanthellae present in this species are likely to provide an alternative source of energy when polyps reduce their feeding activity.     

Oxygen consumption kinetics of Nitrosomonas europaea and Nitrobacter hamburgensis grown in mixed continuous cultures at different oxygen concentrations

Chemolithotrophic ammonium- and nitrite-oxidizing bacteria are dependent on the presence of oxygen for the production of nitrite and nitrate, respectively. In oxygen-limited environments, they have to compete with each other as well as with other organotrophic bacteria for the available oxygen. The outcome of the competition will be determined by their specific affinities for oxygen as well as by their population sizes. The effect of mixotrophic growth by the nitrite-oxidizing Nitrobacter hamburgensis on the competition for limiting amounts of oxygen was studied in mixed continuous culture experiments with the ammonium-oxidizing Nitrosomonas europaea at different levels of oxygen concentrations.The specific affinity for oxygen of N. europaea was in general higher than of N. hamburgensis. In transient state experiments, when oxic conditions were switched to anoxic, N. hamburgensis was washed out and nitrite accumulated. However, grown at low oxygen concentration, the specific affinity for oxygen of N. hamburgensis increased and became as great as that of N. europaea. Due to its larger population size, the nitrite-oxidizing bacterium became the better competitor for oxygen and ammonium accumulated in the fermentor. It is suggested that continuously oxygen-limited environments present a suitable ecological niche for the nitrite-oxidizing N. hamburgensis.     

Oxygen consumption by Metarhizium anisopliae during germination and growth on different carbon sources.

Respirometry was used to monitor the germination and growth of the entomopathogenic deuteromycete Metarhizium anisopliae on media containing carbon sources of different kinds (monosaccharides, polysaccharides, amino acids, and proteins). As also observed in several other species of fungi, M. anisopliae germination was found to be marked by a significant increase in O(2) consumption, which started a few hours before germ tube emergence. The exponential consumption of the carbon source and O(2) coincided with the exponential growth phase of the cultures. QO(2) reached a maximum value during the exponential growth phase and was drastically reduced after the depletion of the exogenous carbon source. Taking glucose as reference, we observed that casein, hydrolyzed casein, and N-acetylglucosamine accelerated germination, reduced the lag phase, and increased the growth rate. This fact demonstrates that the fungus can readily use amino acids and N-acetylglucosamine, which are the monomers of the major constituents of the insect cuticle (proteins and chitin), a property that represents an important physiological adaptation to entomopathogenicity.     

Blood ammonia and lactate concentrations during endurance exercise of differing intensities.

The purpose of this study was to examine the changes of blood ammonia concentration ([NH3]b) during endurance exercise of differing intensities on the cycle ergometer and to compare [NH3]b to the changes observed in the simultaneously monitored blood lactate acid concentrations ([la-]b) measurements. A group of 16 endurance-trained athletes participated in the first part of the study and performed exercise of 30 min duration in a randomized order at intensities of 85%, 95%, 100% and 105% of their individual anaerobic threshold (Th(an,ind); E85-E105) which had been determined beforehand by a cycle exercise test with stepwise increments in intensity. In the second part, 18 average endurance-trained sports students underwent exhausting intensive endurance exercise (IEE) with an intensity of 95% of Th(an,ind). An extensive endurance exercise (EEE) of the same duration at 85% of the Th(an,ind) was carried out 2 days later. The [NH3]b increased constantly with increasingly duration of all exercise. However, [la-]b only increased during exercise with intensities above the Th(an,ind) (E105). The increase of [NH3]b was higher with higher exercise intensities. At IEE, [NH3]b was significantly higher from the 30th min than at EEE, whereas [la-]b increased from the 5th min. In conclusion, [la-]b responded more sensitively to the intensity of exercise than [NH3]b, but it is conceivable that in the future measurements of [NH3]b could be used to advise on the duration of endurance training. At present, however, the lack of experience and lack of appropriate values still hinders the systematic use of [NH3]b measurements in the physiological monitoring of sports training.     

Oxygen consumption and sulfide detoxification in the lugworm Arenicola marina (L.) at different ambient oxygen partial pressures and sulfide concentrations

The lugworm Arenicola marina is a typical inhabitant of intertidal flats. In its L-shaped burrow the animal is exposed to varying concentrations of O₂ and toxic sulfide depending on the tides. The lugworm is able to detoxify sulfide through its oxidation to thiosulfate. When exposed to declining O₂ tensions Arenicola marina reacted as an oxyconformer. In the presence of 25 μmol · l⁻¹ sulfide the respiration was not affected. In contrast, the lugworm consumed significantly less O₂ at any Po₂ in the presence of 200 μmol · l⁻¹ sulfide. Without sulfide anaerobic metabolism started at a Po₂ of approximatedly 10 kPa. Even at high O₂ tensions animals exposed to sulfide produced significantly more anaerobic metabolites compared with the controls. Accordingly the critical value Pc_M, the ambient Po₂ below which anaerobic metabolism starts, was shifted towards normoxia. Since O₂ supply was sufficient for aerobic metabolism, anaerobiosis was induced by sulfide. An influx of sulfide was observed at 25 as well as at 200 μmol · l⁻¹ sulfide. The main product of sulfide detoxification in the lugworm was thiosulfate. Its synthesis increased with ambient Po₂ and depended on the sulfide concentration. Sulfide and thiosulfate were detected in the coelomic fluid, the blood, and the body wall of Arenicola marina. Only about 2% of the ambient O₂ was used for sulfide detoxification at 25 μmol · l⁻¹ sulfide and about 50% at 200 μmol · l⁻¹ sulfide, respectively. Even at the low sulfide concentration Arenicola marina's capacity to detoxify sulfide was too low to maintain a complete aerobic metabolism. Accepted: 19 February 1997