The dimorphic yeast Candida albicans, as a member of the fungi imperfecti, has been assumed to be in the haploid, or imperfect, state. The deoxyribonucleic acid content of this species has been measured by flow microfluorometry, a technique capable of analyzing single cells. These results were compared with flow microfluorometric deoxyribonucleic acid determinations on a series of strains of Saccharomyces cerevisiae of known ploidy (haploid, diploid, triploid, and tetraploid). These ploidy levels were readily distinguished by the flow microfluorometry procedure. By this criterion, C. albicans was found to contain a diploid amount of deoxyribonucleic acid. Ultraviolet radiation survival and chemical mutagenesis experiments support the conclusion that both clinically isolated and laboratory strains of C. albicans are diploid.

Heating Staphylococcus aureus MF31 at 55 C for 15 min renders the organisms unable to reproduce on agar containing 7.5% NaCl (1). The heated organisms exhibited an extended lag period during which the organisms regained their ability to grow on the 7.5% NaCl-agar. Inhibitor and antibiotic data indicated that protein synthesis is not involved in this recovery process but nucleic acid synthesis is suggested (3). The data presented here further substantiate the noninvolvement of protein synthesis during recovery and further demonstrate the site of the thermally induced nucleic acid lesion. Methylated albumin kieselguhr column analysis showed the lesion site to be the ribosomal ribonucleic acid (rRNA). The rRNA is resynthesized during the extended lag period. Sucrose gradient analysis demonstrated that a ribosomal peak was undetectable subsequent to the thermal treatment, but this peak was regenerated during the recovery period. An extended lag phase is a culture response to thermal injury (4, 5). This extended lag phase can perhaps be more accurately described as a recovery period. Harris (2) explains this as "the period of 'getting back' organisms from their sublethal environment." This is commonly ac

Oligonucleotide cataloguing has been used to characterize a number of 5S RNA species from various Procaryotes. Such catalogs can be used to establish certain and detailed phylogenetic relationships among organisms. Confining attention at present to four Families of Procaryotes, theEnterobacteriaceae, theBacillaceae, theAchromobacteraceae, and thePseudomonadaceae, we have shown that the conventionally accepted classification of these organisms which places the first three in the orderEubacteriales, and the last in the orderPseudomonadales, is not phylogenetically valid.

The nature and properties of the 20 S ribonucleic acid which accumulates only during the sporulation of Saccharomyces cerevisiae were examined. The 20 S ribonucleic acid (RNA) has a base composition considerably different from ribosomal RNA species and is virtually unmethylated. The 20 S RNA did, however, exhibit approximately 70% homology with 18 S RNA by RNA-deoxyribonucleic acid filter hybridization competitions. The 20 S RNA showed a hybridization saturation plateau level 30 to 40% higher than 18 S , consistent with measurements of the size difference in polyacrylamide gels. Pulse-chase experiments in the presence and absence of cycloheximide indicate that the 20 S RNA has a presumptive relationship to the 20 S ribosomal RNA precursor normally observed only in short pulse-labeling in vegetative cells.

Homogeneous cell populations of increasing cell volume have been isolated from exponential and stationary cultures of Candida albicans by centrifugation on a sucrose gradient. Observations of the yeast-mycelial transition using these populations showed the following. (i) No fraction from early logarithmic phase cells was able to undergo morphological transition. (ii) The time of initiation of germ tube production was correlated with cell size in stationary-phase cultures. (iii) The rate of appearance of germ tubes was nearly identical in all fractions measured. (iv) Addition of N-acetyl-D-glucosamine to homogeneous cell populations decreased the time of initial appearance of germ tubes but did not affect the rate of appearance after initiation.Candida albicans is a dimorphic fungus which can undergo transition from yeastlike growth to mycelial growth. This transition takes place in a variety of media: serum (11), complex medium (5), minimal medium (6, 7), and N-acetyl-D-glucosamine in imadazole-Mn2+ buffer (9). The synchrony or asynchrony with which cultures undergo this transition may depend both on the state of the cell at the beginning of induction of the yeast-mycelial transition and the homogeneity of the population. In the experiments reported here we have utilized zonal rotor fractionation of cell cultures to examine the effect of these two factors on yeastmycelial transition in C. albicans.Synchronous cultures ofSaccharomyces cerevisiae show a linear increase in cell size throughout the yeast cell cycle. Fractions of exponential cultures grown on minimal medium and separated by zonal rotor centrifugation also show a similar linear increase. Since cells are separated according to size and thus stage during cell cycle after zonal centrifugation, analysis of fractions from the zonal rotor should represent the properties of the cell cycle. This technique has proved successful in elucidating vegetative cell cycle events (8,10). Relationships between cell cycle stage and ability to complete meiosis and sporulation have also been determined (4). The zonal rotor has been used to fractionate logarithmically growing and stationary-phase cultures of C. albicans. The relationship between cell cycle stage and tran-I Present address: Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Mass. 02154.sition, as well as population homogeneity and synchrony, have been observed, respectively. The homogeneous fractions of cultures obtained by this method were examined for initial appearance, rate of appearance, and extent of germ tube formation. Three types of cultures were separated by zonal rotor fractionation: exponentially growing cultures on minimal medium and stationary-phase cultures grown on minimal and rich media. In addition, the effect of N-acetyl-t-glucosamine on various fractions obtained from a stationary-phase culture was observed.