An annual survey of bacterial production, respiration and ectoenzyme activity in coastal NW Mediterranean waters: temperature and resource controls.

We simultaneously measured bacterial production (BP), bacterial respiration (BR), alkaline phosphatase activity (phos) and ectoaminopeptidase activity (prot) in relation to biogeochemical parameters, nutritive resources and in situ temperature over a 1-year survey at the long-term observatory the SOLEMIO station (Marseille bay, NW Mediterranean Sea). Despite its proximity to the coast, oligotrophic conditions prevailed at this station (yearly mean of Chl a = 0.43 µg dm(-3), NO3 = 0.55 µmol dm(-3) and PO4 = 0.04 µmol dm(-3)). Episodic meteorological events (dominant winds, inputs from the Rhone River) induced rapid oscillations (within 15 days) in temperature and sometimes salinity that resulted in rapid changes in phytoplankton succession and a high variability in C/P ratios within the particulate and dissolved organic matter. Throughout the year, BP ranged from 0.01 to 0.82 µg C dm-(3) h-(1) and bacterial growth efficiency varied from 1 to 39%, with higher values in summer. Enrichment experiments showed that BP was limited most of the year by phosphorus availability (except in winter). A significant positive correlation was found between in situ temperature, BP, BR and phos. Finally, we found that temperature and phosphate availability were the main factors driving heterotrophic bacterial activity and thus play a fundamental role in carbon fluxes within the marine ecosystem.

An allometric model for trees.

This paper presents a general mathematical model for the morphometric description of trees. This model is based on the introduction of fractal theory, and more particularly of the concept of self-similarity, into a statistical physics rationale. Fractal theory provides the necessary tools to describe the complexity of tree structure. Statistics, when applied to physics, makes it possible to explain the properties of complex objects starting from their components. The combination of both tools allowed us to develop a theoretical model that is the probability density function of the morphometric lengths of trees. An example of validation of this law is given here: the theoretical model of morphometric lengths is compared with experimental data of Cupressocyparis.

Production primaire dans les eaux de surface de la Mediterranee occidentale. Calcul de la production journaliere.

We have found a relationship between the net absorption of carbon at time t divided by the net absorption of carbon in 24 h (AN(t)/AN(24)) and the incubation duration after sunrise, in surface waters of the western Mediterranean sea. This ratio is quite similar whatever the sample location, the sample depth and the 24-h net-absorption level. Considering this result, we have established a correction factor which may be used to convert primary production rates obtained from incubation durations < or = 24 h to daily rates (24 h dawn-to-dawn).

[Frequency of enteropathogenic K99+ ST+ Escherichia coli and rotaviruses in neonatal diarrhea of calves. Survey of a veterinarian's clientele in Sarthe]. / Fréquence de Escherichia coli entéropathogène K99+ ST+ et du rotavirus dans les diarrhées néonatales des veaux. Enquête dans une clientèle vétérinaire de la Sarthe.

A clinical and microbiological study was carried out on 21 diarrhoeic calves less than 20 days old, belonging to 20 different farms in the French department of Sarthe. Each diarrhoeic calf was compared with a clinically healthy calf of the same age, from the same farm. Two visits were made : one during the acute phase of diarrhoea, the other 10 to 15 days later. Of the 21 diarrhoeic calves, nine died. On the first visit, rotavirus was found in faeces of 11 diarrhoeic calves and E. coli K99+ ST+ in faeces of three diarrhoeic calves, in two cases together with rotavirus. At the same time, rotavirus was found in the faeces of five control calves whereas E. coli K99+ ST+ was not present. On the second visit, rotavirus was detected in the faeces of one of the 12 surviving diarrhoeic calves and in the faeces of two control calves. No E. coli K99+ and ST+ was found in any of the two groups. Short duration antibiotic treatment (sulfonamide + colistin) carried out on the first visit did not result in increased resistance of E. coli to the ten antibiotics tested. On the contrary, cases of resistance to certain of these antibiotics were more frequent during the acute phase of illness (and before any treatment) than 10 to 15 days later. This fact was explained by the presence, in at least five cases, of multiresistant E. coli strains which disappeared with recovery.