This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lovett, P. S. Search for Related Content PubMed PubMed Citation Articles by Lovett, P. S.

Spontaneous Auxotrophic and Pigmented Mutants Occurring at High Frequency in Bacillus pumilus NRRL B-3275

¹ Department of Biological Sciences, University of Maryland Baltimore County, Catonsville, Maryland 21228

ABSTRACT

Broth cultures of Bacillus pumilus NRRL B-3275 (BpB1) grown at 25, 30, or 37 C contain 1 to 2% spontaneous auxotrophic mutants in both the exponential and stationary phases of growth. Of 70 such mutants isolated from cultures grown at 37 C, approximately two-thirds reverted at such a high frequency as to preclude their study. Of the remaining 22 mutants, 18 required a single amino acid, 1 required adenine, and 1 required uracil. Two of the auxotrophs each required two unrelated amino acids resulting from two independent mutations. All of the mutations reverted spontaneously. Enhanced reversion of approximately one-third of the mutations was obtained with nitrosoguanidine, ethyl methane sulfonate, or diethyl sulfate, or with more than one of these mutagens. The reversion of one mutation was enhanced by 2-aminopurine. The reversion of the remaining mutations was not enhanced by the above mutagens, nor by mutagens known to induce (and revert) frameshift mutations in other bacterial systems. Nine of 10 mutants examined did not show a selective growth advantage over the parents. All but three of the mutations could be linked by PBS1 transduction to one of the previously described auxotrophic markers in strain BpB1. No evidence was obtained for clustering of the mutations on the BpB1 genome. Six of the mutations conferred a requirement for serine. One linked by transduction to trp-2, three linked to argA1, and two (ser-2, -3) linked to argO1. Pigmented mutants (containing a carotenoid-like pigment), which occur spontaneously in BpB1 cultures at a frequency on the order of 1 to 5 mutants per 10⁴ cells, link by transduction to ser-2, -3. Spontaneous mutants of strain BpB1 resistant to rifampin, streptomycin, erythromycin, 5-fluorouracil, or 5-methyltryptophan occur at a frequency similar to that of strains of B. pumilus which do not exhibit a high rate of spontaneous mutation to auxotrophy. It is suggested that certain sites or regions of the BpB1 genome exhibit a high rate of spontaneous mutation.