No abstract

Sphingomonas sp. strain RB2256 was isolated from Resurrection Bay in Alaska and possibly represents the dominant bacterial species in some oligotrophic marine environments. Strain RB2256 has a high-affinity nutrient uptake system when growing under nutrient-limiting conditions, and growing cells are very small (<0.08 m 3). These characteristics indicate that RB2256 is highly evolved for withstanding nutrient limitations and grazing pressure by heterotrophic nanoflagellates. In this study, strain RB2256 was subjected to nutrient starvation and other stresses (high temperature, ethanol, and hydrogen peroxide). It was found that growing cells were remarkably resistant, being able to survive at a temperature of 56؇C, in 25 mM hydrogen peroxide, or in 20% ethanol. In addition, growing cells were generally as resistant as starved cells. The fact that vegetative cells of this strain are inherently resistant to such high levels of stress-inducing agents indicates that they possess stress resistance mechanisms which are different from those of other nondifferentiating bacteria. Only minor changes in cell volume (0.03 to 0.07 m 3) and maximum specific growth rate (0.13 to 0.16 h ؊1) were obtained for cells growing in media with different organic carbon concentrations (0.8 to 800 mg of C per liter). Furthermore, when glucose-limited, chemostat-grown cultures or multiple-nutrient-starved batch cultures were suddenly subjected to excess glucose, maximum growth rates were reached immediately. This immediate response to nutrient upshift suggests that the protein-synthesizing machinery is constitutively regulated. In total, these results are strong evidence that strain RB2256 possesses novel physiological and molecular strategies that allow it to predominant in natural seawater.

Three mutations impairing penicillin production in Aspergillus nidulans, npeB, npeC and npeD, have been located on linkage groups III, IV and II, respectively, and positioned relative to other loci on these chromosomes.

SUMMARYAs a preliminary to an investigation of the inheritance of penicillin productivity in Penicillium chrysogenum several strains were genetically labelled with nutritional deficiencies and mutant spore colours. Few auxotrophs of P. chrysogenum retained the potential for penicillin yield of their parents. An analysis suggests that when loss of penicillin production occurred in an auxotroph it was most likely due to pleiotropic effects of the single mutation to auxotrophy.

I N T R O D U C T I O NMutants blocked in the production of a metabolite can provide information on intermediate products in the biosynthetic pathway of that metabolite and the number of genetic loci involved. Lemke & Nash (I 972) have isolated mutant strains of Cephalosporium acremonium unable to yield P-lactam antibiotics and have reported on their ability to synthesize peptides implicated as intermediates in the elaboration of penicillin N and cephalosporin C.Bonner (1947) isolated 55 mutants of Penicillium notatum which produced less than 10 % of the normal amount of penicillin. Mixed cultures of all possible pairings of these mutants did not show normal penicillin production. Caglioti & Sermonti (1956) and Sermonti (1956) examined nine mutants of Penicillium chrysogenum with much reduced or no detectable penicillin activity. Heterozygous diploid strains were synthesized between different mutants and in only one case did complementation occur. These results indicated the existence of two loci affecting penicillin production.The work of Holt & Macdonald (I 968 a, b) and Macdonald, Holt & Ditchburn ( I 972) on Aspergillus nidulans established a useful system for the genetic study of penicillin production. In this mould, although penicillin yields are low (Holt & Macdonald, 1968a) the interpretation of crosses is easier than in P . chrysogenum. Work was therefore undertaken to produce mutants of A. nidulans impaired in penicillin biosynthesis for their use in complementation analyses. This communication reports the isolation of such mutants using a range of mutagens to avoid possible locus specificity. (biAI; w-OIO), ~3 0 (suAadEzo yA2 adEzo; acrAI; galAr; pyroA4; facA303; sB3; nicB8; riboBz), G~I (a; galAI; pyroAq; facA303; sB3; nicB8; riboBz), G H~ (biAI; fwAI), GHI I (yA2; pyroA4; cnxA5), G H I~ (biAI; niaD17), and ~~2 6 (biAI; methGI; w-005). Genetic symbols. For genes determining: inability to utilize a specific sugar as sole carbon source -galAI = galactose; nutritional requirements -adEzo = adenine, biAI = biotin, methGI = methionine, nicB8 = nicotinic acid, pyroA4 = pyridoxine, riboBz = riboflavin ; ability to suppress nutritional requirement -suAadEzo = suppressor of adEzo; inability to utilize specific nitrogen compounds as sole nitrogen source -cnxA5 = nitrate and hypoxanthine, niaD17 = nitrate; resistance -acrAI = acriflavine, fucA303 = Auoroacetate; METHODS Organisms. Mutants, derived from