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Pasteurella haemolyticaFnrP is homologous to Fnr, the global transcriptional regulator of anaerobic respiration in Escherichia coli. To investigate the role of O2in the expression of P. haemolyticaleukotoxin, we tested a lktC::lacZfusion constructed in E. colifor a FnrP‐mediated regulatory effect under aerobic and anaerobic growth conditions. Both E. coliFnr and FnrP suppressed leukotoxin transcription under aerobic conditions. Under anaerobic conditions, Fnr suppressed transcription, while FnrP increased transcription. These results were confirmed using FnrP*, a mutant form of FnrP that activates anaerobically inducible genes under aerobic conditions. In mobility shift assays, partially purified FnrP bound to a potential regulatory site in a P. haemolytica lktCpromoter fragment.

Staphylococcus aureusenterotoxin D is one of the serotypes most commonly associated with food poisoning. Further characterization of the enterotoxin D‐encoding plasmid revealed the presence of an open reading frame which encodes a previously unidentified enterotoxin, designated staphylococcal enterotoxin J (SEJ). SEJ is a protein of 269 amino acid residues which has substantial sequence similarity to the staphylococcal A, E, D family of enterotoxins. The enterotoxin D and J open reading frames are transcribed in opposite directions and are separated by an 895 nucleotide intergenic region which contains a perfect inverted repeat, with each arm of the repeat having a length of 21 nucleotides. Chloramphenicol acetyl transferase (cat) transcriptional fusions were used to quantify expression from the enterotoxin gene promoters. Both enterotoxin genes are expressed in S. aureus. However, only sedis regulated by the agrvirulence gene signal transduction pathway. Western blot analyses utilizing anti‐enterotoxin antisera have confirmed the results obtained with the catreporter system. PCR amplification studies suggest that the sejdeterminant may be present on all sed‐encoding plasmids.

The growth of Staphylococcus aureusMF 31 was suppressed when grown in association with Streptococcus diacetilactisand other lactic streptococci. The data indicated that the initial proportion of staphylococci present in the medium was of less importance than the depletion of vital nutrients. Investigation revealed that factors present in Yeast Nitrogen Base medium could reverse the inhibition which was due to antagonism. The major factor found was nicotinamide, and further study revealed that the biological availability of this compound was influenced by the pH of the medium. The addition of nicotinamide to depleted media with careful control of the pH resulted in increased growth of S. aureusin the test system. Further data indicated that additional factors may affect the degree of growth by S. aureusin depleted media.

Iandolo, JohnJ. (University of Illinois, Urbana), and Z. John Ordal. Repair of thermal injury of Staphylococcus aureus. J. Bacteriol. 91:134–142. 1966.—Exposure of Staphylococcus aureusMF 31 to sublethal temperatures produced a temporary change in the salt tolerance and growth of the organism. After sublethal heat treatment at 55 C for 15 min, more than 99% of the viable population was unable to reproduce on media containing 7.5% NaCl. The data presented demonstrate that thermal injury, in part, occurred owing to changes in the cell membrane, which allowed soluble cellular components to leak into the heating menstruum. When the cells were placed in a limiting medium, complete recovery did not occur, regardless of the incubation time. The temperature and the pH which produced the optimal rate of recovery were similar to those described previously for the multiplication of uninjured cells. However, the rate of recovery as well as the unchanging total count during recovery indicated that cell multiplication was not a factor during the recovery process. The nutrient requirements for the complete recovery of injured cells consisted of a solution containing an energy source, such as glucose, a mixture of amino acids, and phosphate. The use of the metabolic inhibitors, penicillin, cycloserine, 2,4-dinitrophenol, and chloramphenicol, did not inhibit recovery. Actinomycin D, however, completely suppressed recovery. This result implied that ribonucleic acid synthesis was particularly involved; this inference was substantiated by radio tracer experiments. The rate at which label was incorporated in the nucleic acid fraction paralleled that of recovery and the return of salt tolerance.

Thermally shocked cells of Staphylococcus aureusrapidly synthesized ribonucleic acid (RNA) during the early stages of recovery. During this period, protein synthesis was not observed and occurred only after RNA had reached a maximum level. Even in the absence of coordinated protein synthesis, a large portion of the RNA appeared in newly synthesized ribosomes. Although the 30Ssubunit was specifically destroyed by the heating process, both ribosomal particles were reassembled during recovery. The addition of chloramphenicol did not inhibit the formation of the ribosomal subunits, nor was the presence of immature chloramphenicol particles detected. Extended recovery with highly prelabeled cells showed that the original ribosomal proteins present before heating are conserved and recycled. Furthermore, the data indicate that the 50Ssubunit is turned over and used as a source of protein for new ribosome assembly. Kinetic studies of the assembly process by pulse labeling have not revealed the presence of the normally reported precursor particles. Rather, the data suggest that assembly may occur, in this system, in a manner similar to that reported for in vitro assembly of Escherichia colisubunits.