Intracellular events are responsible for the differential expression of fibronectin on the fibroblast surface during chick embryo development

We previously showed that differences in the adhesive behaviour of fibroblasts obtained from 8-day-old (8-day CEF) and 16-day-old chick embryos (16-day CEF) were not due to alterations of cell surface fibronectin receptors. Herein we show that fibronectin (FN) was expressed more rapidly on the 8-day CEF surface (30 min) than on the 16-day CEF surface (60 min). In order to elucidate the mechanism responsible for these differences in the expression of cell surface FN we investigated the biosynthesis and the post-translational modifications of FN in 8- and 16-day CEF. Pulse-chase experiments revealed that FN was processed more slowly to an endo-beta-N-acetylglucosaminidase H (endo H)-resistant form in 16-day CEF than in 8-day CEF, whereas the kinetic of FN biosynthesis was similar in both cell populations. This difference was not related to a differential retention of FN in endoplasmic reticulum (ER) as determined after saponin-permeabilization. These results suggested that the rate-limiting step in the transport of FN to the cell surface in 16-day cells occurred between the ER and the medial part of the Golgi apparatus. It seems that the delay in the processing of endo H-resistant N-glycans was sufficient to account for differences between 8- and 16-day CEF in the rate of surface expression of FN and CEF adhesion to a plastic substratum.     

Extrapolation of urn models via poissonization: accurate measurements of the microbial unknown

The availability of high-throughput parallel methods for sequencing microbial communities is increasing our knowledge of the microbial world at an unprecedented rate. Though most attention has focused on determining lower-bounds on the α-diversity i.e. the total number of different species present in the environment, tight bounds on this quantity may be highly uncertain because a small fraction of the environment could be composed of a vast number of different species. To better assess what remains unknown, we propose instead to predict the fraction of the environment that belongs to unsampled classes. Modeling samples as draws with replacement of colored balls from an urn with an unknown composition, and under the sole assumption that there are still undiscovered species, we show that conditionally unbiased predictors and exact prediction intervals (of constant length in logarithmic scale) are possible for the fraction of the environment that belongs to unsampled classes. Our predictions are based on a poissonization argument, which we have implemented in what we call the Embedding algorithm. In fixed i.e. non-randomized sample sizes, the algorithm leads to very accurate predictions on a sub-sample of the original sample. We quantify the effect of fixed sample sizes on our prediction intervals and test our methods and others found in the literature against simulated environments, which we devise taking into account datasets from a human-gut and -hand microbiota. Our methodology applies to any dataset that can be conceptualized as a sample with replacement from an urn. In particular, it could be applied, for example, to quantify the proportion of all the unseen solutions to a binding site problem in a random RNA pool, or to reassess the surveillance of a certain terrorist group, predicting the conditional probability that it deploys a new tactic in a next attack.     

Development of the cellulolytic microflora in the rumen of lambs transferred into sterile isolators a few days after birth

Seven lambs, separated from their dam 24 h after birth, were kept in a conventional environment until transferred to sterile isolators between 1 and 9 days of age: two on day 1 (IA and IB), two on day 4 (IVA and IVB), one on day 8 (VIIIA), and two on day 9 (IXA and IXB). The lambs were reared in these isolators until 120 days of age. Lambs IA, IB, IXA, and IXB were free of cellulolytic bacteria when they were placed in the isolators. They were then inoculated with Bacteroides succinogenes S85 which became established in the four lambs. Until the age of 2 months, the population of this strain fluctuated and then stabilized at a high level (10(8)-10(9) cells/mL). Cellulolytic bacteria were present in the rumen of lambs IVA, IVB, and VIIIA when they were transferred to the isolators. In IVA, and IVB, the cellulolytic population slowly increased with the animal age. In contrast, in VIIIA, the cellulolytic bacteria disappeared within a few days. Bacteroides succinogenes S85 inoculated thereafter became established rapidly and reached a level comparable to that observed in lambs IA and IB. The total number of viable rumen bacteria in the isolated lambs was similar to that observed in conventionally raised animals, but differences were observed in the selective enumeration of bacteria utilizing specific energy sources.     

Quantitative Determination of H2-Utilizing Acetogenic and Sulfate-Reducing Bacteria and Methanogenic Archaea from Digestive Tract of Different Mammals

Total number of bacteria, cellulolytic bacteria, and H₂-utilizing microbial populations (methanogenic archaea, acetogenic and sulfate-reducing bacteria) were enumerated in fresh rumen samples from sheep, cattle, buffaloes, deer, llamas, and caecal samples from horses. Methanogens and sulfate reducers were found in all samples, whereas acetogens were not detected in some samples of each animal. Archaea methanogens were the largest H₂-utilizing populations in all animals, and a correlation was observed between the numbers of methanogens and those of cellulolytic microorganisms. Higher counts of acetogens were found in horses and llamas (1 × 10⁴ and 4 × 10⁴ cells ml⁻¹ respectively).     

Fibronectin biosynthesis: influence on fibroblast adhesion during chick embryo development

Eight d (8d) and 16d (16d) chick embryo fibroblasts (CEF) exhibited marked differences in their adhesive capacity on plastic support, but not on fibronectin substratum. This suggests differences in fibronectin (FN) expression and/or FN receptor expression. Both 8d and 16d CEF expressed an identical number of membrane receptors for FN with similar affinity. In contrast, the newly synthesized FN appeared de novo in 30 min in 8d CEF versus 60 min in 16d CEF. This difference is not due to a modification of the polypeptide chain biosynthetic rate. The FN synthesized in 8d CEF became insensitive to endo beta-N-acetyl-glucosaminidase H (endo H) treatment after 20 min, whereas it remained sensitive to endo H until 60 min in 16d CEF. Post-translational modifications of N-linked mannose-rich chains to complex type chain may account for the difference in the expression of cell surface FN and thus for the difference in cell adhesion capacity to plastic.     

Establishment,counts, and identification of the fibrolytic microflora in the digestive tract of rabbit. Influence of feed cellulose content

Dam-mediated adenine methylation at GATC sites can interfere with gene expression. By use oflacZ fusion technology, the efficiency oftrpR andtrpS promoters (which contain a GATC site) and oftrp (the target of TrpR repressor) was analyzed indam ⁺ anddam ^– backgrounds. In exponentially growing cells, thedam mutation leads to an increased activity oftrpR promoter but does not affecttrpS ortrp promoters. The Dam-mediated induction oftrpR was, however, found to be repressed bytrpR-mediated autoregulation. In contrast,trp-lacZ directed-galactosidase activity was increased at least sixfold indam ^– cells in late logarithmic growth phase. Indam ⁺ cells, expression oftrp-lacZ was similarly late-growth-phase induced, albeit to a reduced extent. Hence, we propose that enhancement of growth phase-dependent gene induction constitutes a previously unidentified trait ofdam mutation. This finding is discussed in the context of the pleiotropic phenotype ofdam mutation.     

Degradation of maize stem by two rumen fungal species, Piromyces communis and Caecomyces communis, in pure cultures or in association with cellulolytic bacteria.

Two species of rumen fungi, Piromyces (Piromonas) communis FL and Caecomyces (Sphaeromonas) communis FG10, were cultured alone or in association with the cellulolytic bacteria Ruminococcus flavefaciens or Fibrobacter succinogenes on maize stem. A kinetic study of the degradation of the substrate was then made. After 48 h of culture, all non-lignified tissues observed by scanning electron microscopy disappeared with P communis and degradation was as complete as that observed in the rumen. In contrast, C communis degraded little of the plant cell walls. The ability of P communis to more rapidly degrade maize stem was probably due to the presence of filamentous rhizoids. The extent of dry matter loss after 8 days of incubation was practically the same in all the monocultures and in the 4 cocultures. However, the rate of degradation was faster in the bacterial than in the fungal monocultures and the co-cultures. No metabolic interaction was observed.     

Effect of Methanobrevibacter sp MF1 inoculation on glycoside hydrolase and polysaccharide depolymerase activities, wheat straw degradation and volatile fatty acid concentrations in the rumen of gnotobiotically-reared lambs

Four naturally born lambs were placed in sterile isolators 24 h after birth before the natural establishment of cellulolytic microorganisms and archaea methanogens. At the age of 6 weeks they were inoculated with pure cultures of the strains FD1 and 007 of Ruminococcus flavefaciens and at the age of 4 months with a pure culture of Methanobrevibacter sp. MF1. Following the establishment of MF1, the population of R. flavefaciens slightly increased in the rumen of the four lambs, there was also an increase in straw degradation, in the activity of some glycoside and polysaccharide hydrolases of the adherent microbial populations and in the concentration of acetate in ruminal contents.     

Elastic properties of viruses

Viruses are compact biological nanoparticles whose elastic and dynamical properties are hardly known. Inelastic (Brillouin) light scattering was used to characterize these properties, from microcrystals of the Satellite Tobacco Mosaic Virus, a nearly spherical plant virus of 17-nm diameter. Longitudinal sound velocities in wet and dry Satellite Tobacco Mosaic Virus crystals were determined and compared to that of the well-known protein crystal, lysozyme. Localized vibrational modes of the viral particles (i.e., particle modes) were sought in the relevant frequency ranges, as derived assuming the viruses as full free nanospheres. Despite very favorable conditions, regarding virus concentration and expected low damping in dry microcrystals, no firm evidence of virus particle modes could be detected.