Living apart together-bacterial volatiles influence methanotrophic growth and activity.

Volatile organic compounds play an important role in microbial interactions. However, little is known about how volatile-mediated interactions modulate biogeochemical processes. In this study, we show the effect of volatile-mediated interaction on growth and functioning of aerobic methane-oxidizing bacteria, grown in co-culture with five different heterotrophs. Both growth and methane oxidation of Methylobacter luteus were stimulated by interaction with specific heterotrophs. In Methylocystis parvus, we observed significant growth promotion, while methane oxidation was inhibited. Volatolomics of the interaction of each of the methanotrophs with Pseudomonas mandelii, revealed presence of a complex blend of volatiles, including dimethylsulfide, dimethyldisulfide, and bicyclic sesquiterpenes. Although the ecological role of the detected compounds remains to be elucidated, our results provide unprecedented insights into interspecific relations and associated volatiles for stimulating methanotroph functioning, which is of substantial environmental and biotechnological significance.

Fourier phase parameters with possible diagnostic importance as obtained from the radionuclide ventriculograms of normal baboons with and without cardiac catheterization and under prolonged anaesthesia.

The possible diagnostic importance of parameters defined from radionuclide ventriculograms and Fourier phase analysis was investigated for data from normal baboons (Papio ursinus) under prolonged anaesthesia (7 hours). Of the 14 animals, 7 were studied using indwelling cardiac catheters. Phase angle differences between the electromechanical activation of the septum and left lateral wall (LLW), and again between the activation of the septum and the apex indicated no significant differences (p greater than 0.05) for the consecutive hourly values for both catheterized and non-catheterized baboons. Consequently, average values and their ranges (mean +/- 1 S.D.) were obtained for these parameters in each group, and they did not differ significantly between the two groups. As could be expected, the activation delays between the septum and LLW, and the septum and apex differed with the latter being significantly longer. The phase angle histogram parameters of atrial peak width, left ventricular plus right ventricular peak width, (LV + RV), LV-to-RV peak separation and LV-to-atrial peak separation were similarly analysed and found not to change significantly between hourly measurements or because of catheterization. Therefore mean normal values and ranges were also obtained for these parameters, possibly to serve as baselines in the diagnosis of subtle conduction pathology.

Evaluation of the clinical validity of the "integral spleen" method of renography analysis from parameter changes induced by pharmacological and surgical intervention.

A set of controlled experimental animal procedures involving pharmacological and surgical interventions was carried out to assess the clinical validity of the parameters calculated by the "integral spleen" method of renography analysis. There appeared to be a good correlation between the observed changes of these parameters and current pathophysiological information. In particular, the described method includes an original calculation of the filtration fraction without blood and urine sampling or a second tracer injection. This calculation was experimentally validated here.

Comparison of blood flow parameters measured by Doppler ultrasound and radionuclide techniques in the baboon (Papio ursinus).

Ascending aortic blood velocity was measured in the baboon (Papio ursinus) by using continuous wave Doppler ultrasound. The blood flow parameters thus obtained were compared to those by the standardized radionuclide technique. It appears that, due to the anatomical position of the ascending aorta and brachiocephalic trunks in relation to the ultrasound beam, Doppler ultrasound does not provide an accurate method of measuring aortic blood velocity in the baboon, which could be the reason for the poor correlation of the results from the two techniques.

Estimation of bacterial nitrate reduction rates at in situ concentrations in freshwater sediments.

A method was developed to follow bacterial nitrate reduction in freshwater sediments by using common high-performance liquid chromatographic equipment. The low detection limit (14 pmol) of the method enabled us to study concentration profiles and reaction kinetics under natural conditions. Significant nitrate concentrations (1 to 27 muM) were observed in the sediment of Lake Vechten during the nonstratified period; the concentration profiles showed a successive depletion of oxygen, nitrate, and sulfate with depth. The profiles were restricted to the upper 3 cm of the sediment which is rich in organics and loosely structured. Nitrate reduction in the sediment-water interface followed first-order reaction kinetics at in situ concentrations. Remarkably high potential nitrate-reducing activity was observed in the part of the sediment in which nitrate did not diffuse. This activity was also observed throughout the whole year. Estimates of K(m) varied between 17 and 100 muM and V(max) varied between 7.2 and 36 mumol cm day for samples taken at different depths. The diffusion coefficient of nitrate ([10 +/- 0.4] x 10 cm s) across the sediment-water interface was estimated by a constant-source technique and applied to a mathematical model to estimate the net nitrate reduction during the nonstratified period. In this period, observed nitrate reduction rates by the model, 0.2 to 0.4 mmol m day, were lower than those found for oxygen (27 mmol m day) and sulfate (0.4 mmol m day). During the summer stratification, nitrate was absent in the sediment and reduction could not be estimated by the model.