Electrochemical checking of aerobic isolates from electrochemically active biofilms formed in compost

AIMS

To design a cyclic voltammetry (CV) procedure to check the electrochemical activity of bacterial isolates that may explain the electrochemical properties of biofilms formed in compost.

METHODS AND RESULTS

Bacteria catalysing acetate oxidation in garden compost were able to form electrochemically active biofilms by transferring electrons to an electrode under chronoamperometry. They were recovered from the electrode surface and identification of the isolates using 16S rRNA sequencing showed that most of them were Gammaproteobacteria, mainly related to Enterobacter and Pseudomonas spp. A CV procedure was designed to check the electrochemical activity of both groups of isolates. Preliminary CVs suggested that the bacteria were not responsible for the catalysis of acetate oxidation. In contrast, both groups of isolates were found to catalyse the electrochemical reduction of oxygen under experimental conditions that favoured adsorption of the microbial cells on the electrode surface.

CONCLUSIONS

Members of the genera Enterobacter and Pseudomonas were found to be able to catalyse the electrochemical reduction of oxygen.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has shown the unexpected efficiency of Enterobacter and Pseudomonas spp. in catalysing the reduction of oxygen, suggesting a possible involvement of these species in biocorrosion, or possible application of these strains in designing bio-cathode for microbial fuel cells.

Developmental changes in ventilation and breathing pattern in unanesthetized kittens

Ventilation and the breathing pattern of 12 intact, unanesthetized, unrestrained kittens, were recorded at intervals from the second postnatal day to the end of the eighth month. Five of the animals were also studied at 12 months of age. Ventilation (VE) became stable by the 5th month, whereas body weight was still increasing. The relationship between tidal volume (VT) and breathing rate (BR) changed with age. During the 1st month, BR fell and VT increased, VE increasing slowly. From 1 to 5 months, BR remained nearly constant while VT increased. Finally, from 5 to 12 months, BR decreased slightly, VT increased slightly, and VE did not change. The results are compared with relevant data from the literature, especially those derived from interspecific analyses.

Hypoxemia, hypercapnia, and breathing pattern in patients with chronic obstructive pulmonary disease

The results of lung function tests (total and functional residual capacities, residual volume/total lung capacity ratio, forced expiratory volume in one second) breathing patterns and arterial PO2 and PCO2 were studied in 651 ambulatory male patients with chronic obstructive pulmonary disease, functionally and clinically stable. Function tests were only loosely correlated with gas tensions: abnormalities in mechanics and in gas exchange are not necessarily related. In patients matched for the degree of obstruction, the breathing pattern depended upon both PaO2 and PaCO2. Isolated hypoxemia was accompanied by increased respiratory frequency without any variation in tidal volume: this suggests that the chemoreceptive systems still responded to changes in PaO2. Isolated hypercapnia was accompanied by a decrease in tidal volume and an increase in respiratory frequency. Consequently, the dead space/tidal volume ratio increased, leading to a drop in alveolar ventilation and to CO2 retention.

Concomitant changes in function tests, breathing pattern And PaCO2 in patients with chronic obstructive pulmonary disease

151 ambulatory male patients with chronic obstructive pulmonary disease have been studied twice, at time intervals ranging from 2 to 36 months (average : 11), to determine the relationships between changes in lung function tests, pattern of breathing and arterial PCO2. This longitudinal analysis confirms the results of cross-sectional studies: variations in PaCO2 seem independent of the evolution of lung function tests (FEV1, VC, FEV1/VC, RV/TLC). Increases in PaCO2 are associated with a decrease in tidal volume and no change in respiratory frequency. These changes in breathing pattern result in a decreased minute ventilation and an increased VD/VT ratio.

Some limitations in the use of normal value tables

Analysis of raw data from 822 (224 women and 598 men) Caucasian healthy subjects with age ranging from 19 to 50 years leads to a multiple correlation coefficient equal to 0.75 between vital capacity and age, height and weight. In spite of this highly significant correlation coefficient, the predicting value of the regression equation is very poor: on the one hand, residual fluctuation is very important, on the other hand, because of the small intraindividual variability, "normal for the group' does not necessarily mean "normal for the individual'.