Search

One of the two dominant phylotypes of Crenarchaeota that colonizes the roots of tomato plants grown in soil from a Wisconsin field is selectively enriched in mixed cultures amended with root extract. Results indicate that the diversity of crenarchaeal soil assemblage is influenced by the rhizosphere and that mesophilic soil crenarchaeotes are associated with plant roots that show the growth of nonthermophilic crenarchaeotes in culture.

The ruminal cellulolytic bacteria Ruminococcus flavefaciens and Fibrobacter succinogens coexist in substrate-excess culture with almost equal population size. However, R. flavefaciens outcompetes the other strain for cellobiose in the substrate-limited condition, regardless of whether they are coinoculated or a steady-state culture of F. succinogens is challenged by R. flavefaciens. R. albus outcompetes F. succinogens and R. flavefaciens in substrate-excess and -limited conditions respectively. This is due to the selection in the chemostat of a population of R. albus with a higher affinity for cellobiose.

Fibrobacter succinogenes contains cellobiose and cellodextrin phosphorylases which can both breakdown and form cellodextrins. The cellodextrins moves out of the F. succinogenes cells and is used by the cells of F. succinogens which are not attached to the cellulose and by the non-cellulose using bacteria like Streptococcus bovis. If the concentration of cellulose is less, most of the F. succinogenes cells are not attached to the cellulose and thus cellulse digestion depends on the cellulose concentration and not on the cellodextrin efflux.

The relation of plant metabolites that inhibit the fermentation of plant structural polysaccharides to the variable digestibility of cicer milkvetch by ruminal microorganisms is discussed. Water extracted and unextracted cicer milkvetch neutral detergent fiber were fermented in vitro. Cellulose fermentation was inhibited by mixed ruminal microflora and ruminal cellulolyticbacteria. It was found that the presence of a water-soluble agent causes the inhibition of cicer milkvetch ruminal digestion.

Variable-pressure scanning electron microscopy (VP-SEM) and chemical analysis were employed to characterize the glycocalyx of the ruminal bacterium Ruminococcus albus strain 7. The results have shown that the energy demand for synthesis of the nonprotein fraction of extracellular polymeric substances (EPS) by this organism has represented only a small fraction of the anabolic ATP expenditure of the bacterium.

Expression of 17 genes associated with cellulose degradation, intracellular phosphorolysis, primary catabolism and catabolic regulation in Clostridium thermocellum ATCC 27405 grown at different rates was quantified to determine relative expression. It suggest that at least some cellulosomal components are transcriptionally regulated but differences in expression with growth rate or among substrates do not directly account for observed changes in fermentation end product distribution.

Traditional cloning and gene-walking PCR techniques reveal an opera reading frame (albB) encoding a protein with a predicted molecular mass of 32,168 Da. A blast search reveals two homologs of AlbB from the unfinished genome of R. albus 8 and moderate similarity to LlpA, a 30-kDa bacteriocin from pseudomonas sp. strain BW11M1.