A B S T R A C T Products secreted by Streptococcus intermedius were studied for their effects on the immune response. Three different preparations of crude extracellular products from S. intermedius (CEP-Si) were found to have powerful suppressor activity in vitro as shown by inhibition of human lymphocyte proliferation (uptake of [3H]thymidine) and protein synthesis in response to a wide variety of stimulants, including mitogens and antigens, and suppression of plaque formation by human cells in response to sheep erythrocytes. CEP-Si was noncytotoxic, because cells incubated with high concentrations of CEP-Si and subsequently washed were viable and recovered their ability to respond to mitogens, and because leukocyte migration was not inhibited by CEP-Si, nor was the release of leukocyte migration inhibitory factor from sensitized lymphocytes. The possibility of antigen or mitogen competition was excluded. The effects of CEP-Si in vitro were time dependent and did not require the presence of monocytes. Cells pretreated with CEP-Si and then washed suppressed plaque formation by fresh autologous cells in highly stimulated cultures. CEP-Si injected into C57BL/6 mice also strongly suppressed their immune response to sheep erythrocytes, and the in vivo suppression was correlated with the effects of CEP-Si in vitro.

Dcparozcni of .o\icrobiology, lfo(tYn Stotic ULnivcr.sitY School of' .1Icdicice, D)ctroit, Mlicligan 48207 Recci\ed clor publication 4 I-ebruar_\ 1967 Pyocin, a bacteriocin obtained from l1sates of ultraviolet-induced cultures of Pseuldcolionaces aceruiiginosa was clhLrLacterized in vitro and in vivo aLfter I,000-fold purification by chemical, column, and differential centrifugation procedures. Electron micrographs of negatively stained pyocin p)repalrations contaLined rod-shaped particles whichi resembled the contrcactile tcalil protein of the T-even phages of Escherichia coli. Although two septLrate anid distinct pyocin fractions were eluted from diethylamninoethyl cellulose (p1H 7.5) during the puriticatioll procedure, the pLar

A number of mutants of Bacillus subtilis producing high levels of extracellular protease have been isolated. Analysis of culture supernatants of these mutants has shown that the total amount of proteolytic activity is elevated from 16to 37-fold over the wild strain. The elevated activity was due to a simultaneous increase in both the neutral and alkaline protease. All of the mutants genetically analyzed were found linked to the argC4 marker by PBS-1 transduction analysis.

The bacteriocin from Pseudomonas aeruginosa, pyocin, consists of a contractile sheath and inner core reminiscent of T-even coliphage tails. Contraction of the outer sheath was found to be promoted by 0.5 M magnesium chloride, 1 % Formalin, low pH, sonic treatment, and freezing or thawing or both. The contraction caused by 0.5 M magnesium chloride, however, was found to be reversible and occurred upon reduction of the salt concentration from 0.5 to 0.02 M. In addition, direct assay showed that pyocin activity was nearly proportional to the percentage of only uncontracted forms. Initial studies suggested that the adsorption of purified pyocin onto cell wall fragments from the sensitive indicator strain of P. aeruginosa occurs with the relaxed particle only and not with the contracted form. However, after adsorption, contraction occurred. Various morphological structures, such as tail fibers and base-platelike appendages, were also observed. Upon contraction, six tail fibers were observed on many particles, four of which appeared to originate from the sheath and two from the inner core. Polysheaths and polycores several hundred nanometers in length were also occasionally observed.