A new medium for the isolation of Pseudomonas cepacia from respiratory tract secretions of patients with cystic fibrosis (CF) is described. This medium consists of inorganic salts, 0.5% pyruvate, and 0.1% proteose peptone as nutritive components and 0.0001% crystal violet, 0.15% bile salts, 100 ,ug of ticarcillin per ml, and 300 U of polymyxin B per ml as selective agents. The medium, designated PC medium, supported superior growth of 38 of 50 stock isolates of P. cepacia after 48 h of incubation when compared with MacConkey agar (O of 50). The medium completely inhibited the growth of 112 of 124 stock isolates of organisms commonly found in respiratory secretions of CF patients. Cultures were made on PC medium with respiratory secretions of 169 CF patients. P. cepacia was recovered from 35 patients with isolates on PC medium but from only 21 patients with isolates on MacConkey agar. Of 221 other potentially pathogenic isolates found in these specimens, only six (two Pseudomonas aeruginosa isolates, two molds, one yeast, and one Serratia marcescens isolate) grew on PC medium. PC medium should facilitate the recovery of P. cepacia from CF patients.

An acid-fast, slow-growing scotochromogenic mycobacterium was isolated from a medium specific for hydrogen-utilizing chemolithotrophs. The organism grew well in pure culture in simple mineral salts media under an atmosphere of hydrogen, oxygen, and carbon dioxide. No growth occurred in the absence of the gas mixture unless organic substrates were added. Four tested strains of the tap-water scotochromogen, Mycobacterium gordonae, were also able to grow autotrophically, whereas none of eight tested strains of M, scrofulaceum grew using hydrogen. Twenty-one other mycobacterial strains were negative for autotrophic growth; a strain of M. xenopi grew very slowly. The isolated scotochromogen conformed to the properties of M. scrofuzaceum except for its ability to grow at 19 C and its autotrophic ability. This organism exhibited two major colony types. During autotrophic cultivation, a flat, rough colony form was dominant; heterotrophic cultivation caused a population shift t o a smooth, domed variety. The two colony forms exhibited qualitatively similar biochemical properties, and the unusual rough-t o-smooth transition seemed to correlate with the quantitatively enhanced heterotrophic growth capacities of the smooth strain. Rough-tosmooth variation was reversible, and predominantly smooth inocula gave rise to predominantly rough populations under conditions of chemoautotrophy. The ability to grow autotrophically may be a useful characteristic for distinguishing the saprophytic scotochromogens from the more pathogenic strains.A number of reports (2, 5, 10) indicate the ability of some members of the order ActinomycetaZes to grow autotrophically in mineral salts media under an atmosphere of hydrogen, oxygen, and carbon dioxide. Some early studies reporting autotrophic growth of mycobacteria attempted t o correlate this ability with hydrocarbon utilization, and the strains of mycobacteria were generally reported to be rapid-growing soil and water saprophytes (2, 10). One study listed a "tap water" type among some mycobacterial strains found t o grow autotrophically ( 10); other strains were identified as members of the genus Nocardia (5). However, we are not aware of any detailed investigation of autotrophic capacities among the slowgrowing mycobacteria. In addition, there have been no reports suggesting the importance of the chem olitho t rophic capacity for distinguishing the normally saprophytic tap-water scotochromogen Mycobacteriurn gordonae from the similar but more commonly pathogenic M. scrofulaceum and from other mycobacteria The chemolithotrophic capacity of M. gordonae and a new scotochromogenic isolate and ( 12). the results of some physiological studies with rough and smooth variants of the isolated mycobacterium are included in this report. MATERIALS AND METHODSBacterial strains. The mycobacterial strains employed in the present study and their sources are listed in Table 1 . Strains AU and 6Y are rough and smooth variants, respectively, of the mycobacterium originally isolated as a contaminant in an autot...

Auxotrophic mutants of Hydrogenomonas eutropha and H. facilis requiring utilizable amino acids were employed to demonstrate the simultaneous utilization of H2 and an organic substrate for growth. The ratio of the cell yields under dual substrate conditions compared to heterotrophic conditions indicated the relative contributions of the autotrophic and heterotrophic systems to the growth of the organism. Wildtype H. eutropha grown under simultaneous conditions exhibited a dicycic growth pattern, the first cycle representing either heterotrophic or simultaneous growth and the second cycle representing autotrophic growth. The duration of the changeover period was either very short with no plateau or long with a plateau up to 8 hr, depending upon the organic substrate. The growth rate under simultaneous conditions with some organic substrates was faster than either the autotrophic or heterotrophic rate, but was not the sum of the two rates. The data suggest that, in the presence of both organic and inorganic substrates, heterotrophic metabolism functions normally but autotrophic metabolism is partially repressed.