In co-culture with non-parenchymal liver epithelial cells, rat hepatocytes show a marked increase in albumin and total protein synthesis when compared with cells maintained as pure populations in which an early decline in albumin secretion takes place. Analysis of the relative amounts of different mRNA sequences, determined by hybridization, indicated that the increase in protein synthesis resulted essentially from an increased level of the corresponding mRNAs. In addition, when cell-cell contacts were established between the two cell types several days after the seeding of hepatocytes, the stimulation of albumin secretion was similarly observed with a significant increase of the corresponding mRNA on days 10-14 of culture. Transcriptional assays, in which isolated nuclei were used for the study of RNA synthesis, showed that liverspecific gene transcription was significantly increased and maintained for at least 2 weeks. These results demonstrate for the first time long-term stabilization and reversibility of various specific mRNAs at high levels by adult hepatocytes in primary culture. They suggest that establishment of cellcell contacts between hepatocytes and liver epithelial cells are essential for the maintenance of a high rate of transcription of the liver-specific genes.

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Dairy propionic acid bacteria, particularly the species Propionibacterium freudenreichii, play a major role in the ripening of Swiss type cheese. Isometric and filamentous bacteriophages infecting P. freudenreichii have previously been isolated from cheese. In order to determine the origin of these bacteriophages, lysogeny of P. freudenreichii was determined by isometric bacteriophage type analysis. The genomic DNA of 76 strains were hybridized with the DNA of nine bacteriophages isolated from Swiss type cheeses, and the DNA of 25 strains exhibited strong hybridization. Three of these strains released bacteriophage particules following UV irradiation (254 nm) or treatment with low concentrations of mitomycin C. A prophage-cured derivative of P. freudenreichii was readily isolated and subsequently relysogenized. Lysogeny was therefore formally demonstrated in P. freudenreichii.Based on habitat, the genus Propionibacterium can be divided into two groups: cutaneous and dairy (or classic) propionic acid bacteria (dairy PAB). Dairy PAB are gram-positive, non-spore-forming, catalase-positive, nonmotile, facultatively anaerobic organisms (18). They are used in the manufacture of Swiss type cheeses to ensure eye formation and the development of a typical flavor (19).Like members of many other bacterial genera, dairy PAB are infected by viruses (14). Two types of bacteriophages which can infect dairy PAB have been isolated in Swiss type cheeses. One type belongs to group B1 of Bradley's classification, and the other is, to our knowledge, the first infective filamentous virus found in gram-positive bacteria (16). The existence of bacteriophage DNA able to replicate and express itself in the genus Propionibacterium enabled us to determine the efficiency of electrotransfection for developing a cloning vector (13).The isometric type of bacteriophages that infect dairy PAB have frequently been shown to be present in Swiss type cheeses; the levels of contamination range from 14 to 7 ϫ 10 5 PFU/g of cheese, depending on the cheese and the indicator strain used for detection. These bacteriophages are produced during multiplication of dairy PAB during cheese ripening and may multiply on either endogenous or starter strains (15). In order to understand and control the multiplication of bacteriophages during cheese production, it is important to determine their source in the manufacturing plant. We have shown that raw milk can be a source of free bacteriophages (15), although lysogenic strains may also produce them.Lysogeny is widespread in nature, but in the context of the genus Propionibacterium, only lysogeny of Propionibacterium acnes has been studied previously (33,35).The purpose of this work was to demonstrate lysogeny of dairy PAB. Studies of putative lysogeny are hindered by problems with finding the lysogen and sensitive strains. It is also difficult to determine the optimum amount of mutagenic agent and the optimum bacterial growth stage for massive prophage induction. There is some homology between the virulent and temp...

Two types of bacteriophage (phage) infecting dairy propionibacteria (PAB) were isolated from Swiss-type cheeses. One belongs to Bradley' s classification group BI and the other is, to our knowledge, the first infective filamentous virus described in Gram positive bacteria. Both types of phages were present in several different Swiss-type cheeses. A possible source has been shown to be raw milk where they are found in small quantities. The BI type phage can be harboured by PAB in the prophage state. DNA hybridization experiments showed that ail PAB BI phages are closely related, although they were isolated from different cheeses and probably have a common origin. As sensitive strains can constitute the predominant PAB flora at the end of cheese ripening, it seems obvious that phage did not disturb the development of this flora and consequently did not have an unfavourable effect on the organoleptic properties of Swiss-type cheeses. This information conceming phages allowed us to develop an efficient cloning system for Propionibacteriumfreudenreichii. © InralElsevier, Paris. bacteriophage 1PropionibacteriumfreudenreichiiRésumé -Des bactériophages de bactéries propioniques laitières. Deux types de bactériophages (phages) infectant des bactéries propioniques laitières (BPL) ont été isolés à partir de fromages à pâte pressée cuite. L'un appartient au groupe Bide la classification décrite par Bradley alors que l'autre est à notre connaissance le premier virus filamenteux infectieux décrit à ce jour chez une bactérie à Gram positif. Les deux types de phages ont été identifiés dans plusieurs fromages à pâte pressée cuite différents. Leur origine pourrait être le lait cru où de faibles quantités de phage ont été détectées. Les phages du groupe BI peuvent être portés par les BPL à l'état de prophage. L'hybridation de l'ADN montre que tous les phages de BPL du groupe BI sont étroitement liés, bien qu'ils aient été isolés de fromages différents. Ils ont donc probablement une origine commune. La flore propionique dominante à la fin de l'affinage des fromages peut être constituée d'une souche de BPL sen-Oral communication at the 2nd Symposium on Propionibacteria,

Adult chicken hepatocytes were obtained by an adaptation of the two step in situ collagenase perfusion. Usually 0.5 to 1 x 10(9) cells were obtained, with 75 to 95% viability. Hepatocytes attached within 2 h when plated on plastic cell culture dishes and spread in 4 h, surviving for several months in a specific serum-free medium. These cells retained a typical parenchymal cell morphology and the ability to produce a specific protein (albumin) throughout the culture period. We hereby provide a suitable model for studying hepatic metabolism in birds.

Hepatocytes isolated from 9-week-old chickens were cultured in a serum-free, hormonally defined medium. Relative amounts of mRNAs coding for lipogenic enzymes (acetyl-CoA carboxylase, fatty acid synthase, delta 9 desaturase, malic enzyme) and apoproteins (apoprotein A1 and apoprotein B) were determined until the 12th day. beta-actin and albumin mRNA, as well as albumin secretion, were also assessed. Cellular metabolic activity appeared to be very low for the first days of culture, but increased after the 7th day. All the mRNAs studied, except for that of malic enzyme, were present from this time throughout the culture lifespan. The biological significance of the observed results and the relevance of this chicken hepatocyte culture system for long-term metabolic and genetic studies are discussed.