Estimation de la biomasse bactérienne dans les effluents urbains par mesure de l'activité exoprotéolytique potentielle

Des études récentes ont montré que, lors du rejet d'eaux usées dans une rivière, la quantité de biomasse bactérienne hétérotrophe amenée par les effluents influence considérablement la cinétique de biodégradation de la matière organique dans la rivière et donc les caractéristiques du déficit d'oxygène généralement observé dans le milieu naturel en aval du rejet. La mesure de la biomasse bactérienne contenue dans un rejet domestique est donc nécessaire afin de bien comprendre la cinétique de biodégradation. Cette biomasse peut être estimée en microscopie à épifluorescence après coloration des cellules bactériennes par un fluorochrome. Cette technique appliquée aux eaux usées est néanmoins difficile et fastidieuse. Dans cette étude, une méthode alternative à l'estimation de la biomasse bactérienne dans les eaux usées a été testée ; elle consiste à mesurer l'activité exoprotéolytique potentielle (AEP) des bactéries. Nous avons montré qu'il existait, dans les eaux usées, une corrélation significative entre l'AEP et la biomasse bactérienne estimée en microscopie à épifluorescence ce qui permet d'utiliser l'AEP pour estimer facilement et rapidement la biomasse bactérienne dans ce type d'échantillon. Comme exemple d'application, des mesures d'AEP nous ont permis d'étudier l'impact de divers types de traitement dans plusieurs stations d'épuration sur la biomasse bactérienne hétérotrophe des effluents urbains. Sur base de ces mesures, les charges spécifiques en biomasse bactérienne (charge par habitant et par jour) des eaux brutes et traitées ont pu être calculées.Recent studies have shown that when wastewaters are discharged into a river, heterotrophic bacterial biomass in the effluent exerts considerable influence on the biodegradation kinetics of organic matter and provokes the oxygen deficits often observed downstream from outfalls. Quantification of bacterial biomass in wastewaters is required for a good understanding the biodegradation kinetics. Bacterial biomass can be estimated by epifluorescence microscopy after staining cells with fluorochrome. Applying this technique to wastewater samples, however, is painstaking and difficult. In this study, an alternative method for estimating bacterial biomass in wastewaters was tested; it consists of measuring the potential exoproteolytic activity (PEA) of bacteria. Previous studies on other types of aquatic systems have shown that bacterial biomass can be estimated from PEA. After optimising the PEA procedure for use with wastewater, we found a significant correlation between PEA and the bacterial biomass estimated by epifluorescence microscopy. This opens the way for PEA measurements for rapid and easy estimates of bacterial biomass in wastewaters. As an example of the application of this technique, the impact of wastewater treatment on bacterial biomass in effluent was investigated at various treatment plants. On the basis of our procedure, specific loads of bacterial biomass (load per inhabitant and per day) were calculated for raw and treated wastewaters

Reparative myogenesis in long-term denervated skeletal muscles of adult rats results in a reduction of the satellite cell population

This study, conducted on 25-month denervated rat hindlimb muscles, was directed toward elucidating the basis for the poor regeneration that is observed in long-term denervated muscles. Despite a ∼97.6% loss in mean cross-sectional area of muscle fibers, the muscles retained their fascicular arrangement, with the fascicles containing ∼1.5 times more fibers than age-matched control muscles. At least three distinct types of muscle fibers were observed: degenerating, persisting (original), and newly formed (regenerated) fibers. A majority of newly formed fibers did not appear to undergo complete maturation, and morphologically they resembled myotubes. Sites of former motor end-plates remained identifiable in persisting muscle fibers. Nuclear death was seen in all types of muscle fibers, especially in degenerating fibers. Nevertheless, the severely atrophic skeletal muscles continued to express developmentally and functionally important proteins, such as MyoD, myogenin, adult and embryonic subunits of the nicotinic acetylcholine receptor, and neural-cell adhesion molecule. Despite the prolonged period of denervation, slow and fast types of myosin were found in surviving muscle fibers. The number of satellite cells was significantly reduced in long-term denervated muscles, as compared with age-matched control muscles. In 25-month denervated muscle, satellite cells were only attached to persisting muscle fibers, but were never seen on newly formed fibers. Our data suggest that the absence of satellite cells in a population of immature newly formed muscle fibers that has arisen as a result of continuous reparative myogenesis may be a crucial, although not necessarily the only, factor underlying the poor regenerative ability of long-term denervated muscle. Anat Rec 263:139–154, 2001. © 2001 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34290/1/1087_ftp.pd