Control of and synthesis in Lactobacillus acidophilus Role of RNA and free amino acids.

In Lactobacillus acidophilus, the DNA synthesis in cells incubated in the absence of essential amino acids reaches levels corresponding to the initiation of further replication cycles than just to completing the cycles already running. This "relaxation of DNA synthesis" is stimulated by the presence of inhibitors of protein synthesis and by the presence of deoxyadenylate. These enhancements of DNA replication are cancelled by actinomycin D. In the presence of inhibitors of protein synthesis, the relaxtion of DNA synthesis is further stimulated by free amino acids. The effect of free amino acids, unlike in the former cases, is not inhibited by actinomycin D. It proposed that the chromosome replication in Lactobacillus acidophilus is regulated similarly as in some plasmids, i.e. independently of the synthesis of protein, depending on the synthesis of RNA and, in addition, on the presence of free amino acids.

Mutagenic activities of simple nitrofuran derivatives. I. Comparison of related compounds in the phage inductest, chloroplast-bleaching and bacterial-repair and mutagenicity tests.

Several simple furan and nitrofuran compounds were tested for mutagenicity and related biological activities, in the Ames test, the bacterial repair test, the prophage-induction test and the chloroplast-bleaching test. Only those compounds having the nitro-group were found to be active in the test. If the nitro-group was in the beta instead of the alpha position, the mutagenic activity was much reduced (0.3 revertants per nanomole, the other simple nitrofurans producing 5-15 reversions per nanomole, as did 5-nitrofuran and 5,2-dinitrofuran). The vinyl-group-containing compound, 5-nitro-2-furylacrylic acid, was by one decadic order more effective both in the Ames test and in the prophage-induction test. In the repair tests all nitrofurans displayed a much higher dependence on the recA-repair system than on the uvrA system. For 2 compounds, the dinitrofuran and, especially, the 5-nitrofuraldehyde, the urA cells were even less sensitive than the wild-type cells.

SOS induction of the gene sulA is partly inhibited in Escherichia coli K12 cells overproducing the RecA protein.

A study was made of the SOS induction of the gene sulA of Escherichia coli K12 in relation to the gene dosage of the gene recA. In experiments the sulA::lacZ fusion strain PQ37 and derivatives of PQ37 with the multi-copy plasmids pDR1453 or pBR322 were used. The SOS response was induced with nitrofurantoin, SOS induction of the gene sulA was determined on the basis of the amount of beta-galactosidase synthesized, i.e. by the SOS chromotest (Quillardet et al., 1982a). It was found in this work that cells with the plasmid pDR1453, which contain the gene recA of E. coli K12 (Sancar and Rupp, 1979), have a decreased SOS induction of the gene sulA. Cells with the plasmid pBR322 do not exhibit this decrease. Inactivation of the gene recA in the plasmid pDR1453 with preservation of the functional gene recA in the chromosome leads to a restoration of 'standard' SOS induction of the gene sulA. The results show that the amount of the gene product of the gene recA affects the SOS induction of the gene sulA.

Investigation of the SOS response of Escherichia coli after gamma-irradiation by means of the SOS chromotest.

The kinetics of SOS system induction in Escherichia coli PQ37 cells by gamma-irradiation has been studied by the SOS chromotest technique. It was shown that the synthesis of constitutive alkaline phosphatase is not immediately stopped in cells that suffered lethal damages from gamma-irradiation. The production of DNA damages inducing the SOS system was 0.021/Gy per genome. The SOS system was switched off approximately 200 min after gamma-irradiation. A correction is proposed to the calculation of the SOS system induction factor.

The promoters and bidirectional transcription in the immC region of P 22 and L phages.

It is proposed that the transcription of the c-2 repressor gene initiates at two promoters, pre and prm, similarly to the transcription of the c-I gene of lambda phage. In the P22 phage, these promoters are defined by mutations of c54 and K5.

Growth of Lactobacillus acidophilus in the absence of folic acid.

Soska, Jirí (Kansas State University, Manhattan). Growth of Lactobacillus acidophilus in the absence of folic acid. J. Bacteriol. 91:1840-1847. 1966.-A chemically defined medium, containing no folic acid, was used for the cultivation of Lactobacillus acidophilus R-26. In such a medium, the organism required thymine in addition to a deoxyriboside, purines, pyrimidines, and most amino acids. If thymine was present in this medium, an unlimited exponential growth was possible. The influence of the components of this medium on the growth is described. The concentration and type of adenine compounds in this medium were most important. Adenine and adenosine inhibited utilization of thymine, but not of thymidine, whereas adenylic acid inhibited recovery from amino acid starvation. In the absence of thymine or deoxyribosides, cells continued to grow in length, and after 3 hr a slow decline in viable count ensued.