Scanning electron and light microscopic study of microbial succession on bethlehem st. Nectaire cheese

St. Nectaire cheese is a semisoft cheese of French origin that, along with Brie and Camembert cheeses, belongs to the class of surface mold-ripened cheese. The surface microorganisms that develop on the cheese rind during ripening impart a distinctive aroma and flavor to this class of cheese. We have documented the sequential appearance of microorganisms on the cheese rind and in the curd over a 60-day ripening period. Scanning electron microscopy was used to visualize the development of surface fungi and bacteria. Light microscopy of stained paraffin sections was used to study cross sections through the rind. We also monitored the development of bacterial and yeast populations in and the pH of the curd and rind. The earliest stage of ripening (0 to 2 days) is dominated by the lactic acid bacterium Streptococcus cremoris and multilateral budding yeasts, primarily Debaryomyces and Torulopsis species. Geotrichum candidum follows closely, and then zygomycetes of the genus Mucor develop at day 4 of ripening. At day 20, the deuteromycete Trichothecium roseum appears. From day 20 until the end of the ripening process, coryneforms of the genera Brevibacterium and Arthrobacter can be seen near the surface of the cheese rind among fungal hyphae and yeast cells.     

Enzymes of ammonia assimilation in hyphae and vesicles of Frankia sp. strain CpI1.

Frankia spp. are filamentous actinomycetes that fix N2 in culture and in actinorhizal root nodules. In combined nitrogen-depleted aerobic environments, nitrogenase is restricted to thick-walled spherical structures, Frankia vesicles, that are formed on short stalks along the vegetative hyphae. The activities of the NH4(+)-assimilating enzymes (glutamine synthetase [GS], glutamate synthase, glutamate dehydrogenase, and alanine dehydrogenase) were determined in cells grown on NH4+ and N2 and in vesicles and hyphae from N2-fixing cultures separated on sucrose gradients. The two frankial GSs, GSI and GSII, were present in vesicles at levels similar to those detected in vegetative hyphae from N2-fixing cultures as shown by enzyme assay and two-dimensional polyacrylamide gel electrophoresis. Glutamate synthase, glutamate dehydrogenase, and alanine dehydrogenase activities were restricted to the vegetative hyphae. Vesicles apparently lack a complete pathway for assimilating ammonia beyond the glutamine stage.     

An antibody to a synthetic peptide that recognises SV40 small-t antigen.

A peptide Tyr.Arg.Asp.Leu.Lys.Leu corresponding to the carboxy-terminal six amino acids of small-t antigen predicted from the DNA sequence of SV40 was synthesised, coupled to bovine serum albumin and to ovalbumin and used to raise antibody in rabbits. The sera obtained immunoprecipitated [125I]peptide. It also recognised SV40 small-t that was synthesised in vitro from SV40 mRNA or extracted from SV40 infected monkey cells. The immunoprecipitation of small-t was inhibited by added peptide. To demonstrate that the determinant was present at the carboxy-terminal end of the molecule, truncated versions of small-t coded for by 0.54-0.59 deletion mutants were tested. dl 890 small-t, which contains an in-phase deletion removing nine amino acids but leaving the carboxy-terminal sequences intact, was recognised by the antipeptide serum. By contrast dl 885 small-t, which has an out-of-phase deletion leading to an altered carboxy terminus coded in an alternative reading frame, was not recognised. The data confirm the location and specificity of the determinant recognised on small-t by the antipeptide serum.     

An improved technique for the culture of jerusalem artichoke (Helianthus tuberosus L.) explants for use in the study of xylem differentiation

An improved technique is described for the culture of explants from Helianthus tuberosus L. (Jerusalem artichoke). No xylem is formed when tuber discs are pre-cultured on a medium containing ßNAA, allowing uninfected discs to be selected for investigation of xylogenesis. Subsequent growth on a medium containing 0.45M 2,4-D and 9.3M kinetin stimulates a high proportion (up to 36%) of the cells to differentiate into xylem elements within a relatively short time (between 1 and 3 d after transfer).     

Regulation of membrane peptides by the Pseudomonas plasmid alk regulon.

Pseudomonas putida strains carrying the plasmid alk genes will grow on n-alkanes. Induced alk+ strains contain membrane activities for alkane hydroxylation and dehydrogenation of aliphatic primary alcohols. P. putida cytoplasmic and outer membranes can be separated by sucrose gradient centrifugation after disruption of cells by either mild detergent lysis or passage through a French press. Both the membrane component of alkane hydroxylase and membrane alcohol dehydrogenase fractionated with the cytoplasmic membrane. Induction of the alk regulon resulted in the appearance of at least three new plasmid-determined cytoplasmic membrane peptides of about 59,000 (59K), 47,000 (47K), and 40,000 (40K) daltons as well as the disappearance of a pair of chromosomally encoded outer membrane peptides of about 43,000 daltons. The 40K peptide is the membrane component of alkane hydroxylase and the product of the plasmid alkB gene because the alkB1029 mutation altered the properties of alkane hydroxylase in whole cells, reduced its thermal stability in cell extracts, and led to increased electrophoretic mobility of the inducible 40K peptide. These results are consistent with a model for vectorial oxidation of n-alkanes in the cytoplasmic membrane of P. putida.     

The low availability of dietary choline for the nutrition of the sheep.

1. Choline, which is present in the diet of the sheep either in the non-esterified form or combined in phospholipids, is rapidly degraded in the rumen. The ultimate product formed from the N-methyl groups is methane. 2. Analysis of the non-esterified choline and the phosphatidylcholine in ruminal and abomasal digesta indicate that the phospholipid is the main vehicle for the passage of choline to the lower digestive tract. 3. The concentration of phosphatidylcholine in abomasal digesta is lower than that of ruminal digesta, which is in line with a selective retention of protozoa in the rumen as observed by others. 4. On defaunation of the rumen to remove ciliated protozoa the concentration of phosphatidylcholine in ruminal digesta falls markedly and becomes lower than that in abomasal digesta. 5. Calculation shows that the adult sheep obtains at most only about 20--25 mg of effective choline per day from its diet (0.002--0.0025% of dietary total dry-weight intake). This is some fifty times less than the minimum required to avoid pathological lesions and death in other species investigated (0.1%+ of dietary dry-weight intake). 6. Sheep liver can synthesize choline from [14C]ethanolamine both in vitro and in vivo, but the synthesis of choline per kg body weight is many times less than it is in the rat. 7. The intact sheep oxidizes an injected dose of [1,2-14C]choline to CO2 at a rate that is several times less than that observed for the rat. This could help to explain the apparent minimal requirement of sheep for dietary choline.     

Saccharomyces cerevisiae DNA-dependent RNA polymerase III: a zinc metalloenzyme.

Yeast nuclear RNA polymerase III was purified by batch adsorption to phosphocellulose, followed by ion-exchange chromatography on DEAE-Sephadex and affinity chromatography on DNA-Sepharose. Polyacrylamide gel electrophoresis of the purified enzyme showed a single protein band which contained polymerase activity. The molecular weight estimated by sedimentation velocity centrifugation in a glycerol gradient was 380 000. Enzyme activity was inhibited 50% at 0.1 mM 1,10-phenanthroline and 100% of 1.0 mM, but was restored when 1,10-phenanthroline was removed by dialysis. Enzyme activity was not inhibited by 7,8-benzoquinoline, a nonchelating structural analogue of 1,10-phenanthroline. These results strongly suggest that inhibition of enzyme activity occurs by the formation of a reversible enzyme-zinc-phenanthroline ternary complex. The zinc content, measured by atomic absorption spectroscopy, was 2 g-atoms per mol of enzyme. Zinc was not removed from the enzyme by gel filtration on Sephadex G-25, by passage through Chelex-100 resin, or by dialysis against buffer containing 1,10-phenanthroline. Enzyme-bound zinc was removed by dialysis after denaturation of the enzyme with heat and sodium dodecyl sulfate. Enzyme-bound zinc did not exchange with free zinc. These results establish yeast nuclear RNA polymerase III as a zinc metalloenzyme.     

Occurrence of a regulatory deficiency in purine biosynthesis among purA mutants of Salmonella typhimurium

Summary A defect in the repression of the de novo purine biosynthetic enzymes was detected among purA mutants of Salmonella typhimurium. We suggest that the defect is caused by an altered purine regulation gene (purR) which affects the response level of at least five of the de novo enzymes to repression by excess adenine. Thus the unlinked genes controlling these enzymes constitute a regulation controlled wholly or in part by a purR gene product. The regulation of the guanine operon is regulated by some other mechanism independent of purR.