Nucleolar size polymorphisms in commercial layer chickens; determination of incidence, inheritance, and nucleolar sizes.

In the chicken, one chromosome pair encodes the ribosomal (r)RNA genes and two nucleoli are formed in interphase cells. The nucleolus is the site of rRNA synthesis and ribosome biogenesis. Nucleolar size polymorphisms have been detected in research strains of chickens and found to represent heterozygosity for rRNA gene copy number. The objectives of the present study were to determine whether nucleolar size polymorphisms exist in commercial chicken flocks and whether such polymorphisms are under genetic control. The occurrence of nucleolar size polymorphisms was studied in three lines of commercial layer chickens (designated A, B, and C). Nucleolar size polymorphisms were found in all three lines. However, the lines differed in the proportion of individuals exhibiting the polymorphic phenotype of two unequal-sized nucleoli (2P). The 2P phenotype, determined in successive years, was found in 10 to 14% of Line A birds, 18 to 23% of Line B birds, and 41 to 63% of Line C birds. The inheritance pattern of the nucleolar size polymorphism and nucleoli sizes were studied in Line C birds. The 2P phenotype was found to be inherited in Mendelian fashion. The large nucleolus was 1.7x and 1.6x that of the smaller nucleolus in 2P males and females, respectively, and was larger than the nucleoli of 2E birds (2E = nonpolymorphic phenotype of two equal-sized nucleoli). Total nucleolar size was greater in cells of 2P birds than in cells of 2E birds. These data suggest that the genetic basis for the large nucleolus in Line C 2P cells is a "larger than normal" rDNA cluster.

Plasmids and phages in Bifidobacterium longum.

Fourteen strains of Bifidobacterium longum were tested for phage production with UV and mitomycin C as inducing agents. Only four strains released phage-like particles; of these four strains, two harbour plasmids, while two are apparently plasmid free. The induced phages have heads of dimensions ranging from 49 to 56 nm and tails from 76 to 268 nm long. No correlation is evident between any of the large variety of plasmids of B. longum and induced phages.

Antibiotic Resistances of Yogurt Starter Cultures Streptococcus thermophilus and Lactobacillus bulgaricus.

Twenty-nine strains of Lactobacillus bulgaricus and 15 strains of Streptococcus thermophilus were tested for resistance to 35 antimicrobial agents by using commercially available sensitivity disks. Approximately 35% of the isolates had uncharacteristic resistance patterns.

Plasmids, Lactic Acid Production, and N-Acetyl-d-Glucosamine Fermentation in Lactobacillus helveticus subsp. jugurti.

Two lactobacillus strains, Lactobacillus helveticus subsp. jugurti S13-8 and L. helveticus subsp. jugurti S36-2, were examined for the presence of plasmids. Plasmids of 16.45, 13.03, and 11.83 kilobases (kb) were found in the first, low lactic acid-producing strain; their function is not presently known. A single plasmid species of 13.17 kb was found in the second, high lactic acid-producing strain. This plasmid was found to be associated with lactic acid production and N-acetyl-d-glucosamine fermentation.