Klebsiella aerogenes V9A possesses at least three galactoside permeases, the lactose permease (LacP), the melibiose permease (MelP) and a third permease (GPIII), and also a galactose permease. It is shown that the first three of these permeases all accumulate both lactose and melibiose efficiently, while the galactose permease takes up neither sugar. Lactose only induces LacP and melibiose only induces MelP. d-fucose, isopropyl-β-d-thiogalactoside (IPTG) and methyl-β-d-thiogalactoside (TMG) all induce GPIII, but galactose does not. GPIII takes up both lactose and melibiose but cannot accumulate lactose in the presence of IPTG. Thus substantial differences are found between the galactoside permeases of Klebsiella and Escherichia coli.

A defined medium for Physarum polycephalum plasmodia has been devised containing glutamic acid, glycine, methionine, biotin, thiamine, glucose, salts and haematin, which supports good growth on agar plates of many different strains. Tests on this medium have revealed a requirement for valine in some plasmodia formed by homothallic progeny (mthapt-l+) from the cross a (mt1apt-l+) × APT1 (mthapt-l−). The valine requirement was also inherited among heterothallic progeny of this cross and its segregation was followed in several heterothallic crosses. To explain the results it is proposed that valine synthesis requires the presence of dominant alleles at either of two unlinked loci and that only plasmodia homozygous for recessive alleles at both loci are valine dependent. In some crosses studied only one pair of alleles is segregating and valine requirement thus provides a useful genetic marker, and the first reported nutritional marker in P. polycephalum. The value of crosses with apt− mutants for both the detection and analysis of plasmodial markers is demonstrated and discussed.

Lifetime reproductive performance was studied in 50 sib-pairs of female mice, one member of each pair chromosomally XX and the other XO. Twenty-five pairs were irradiated with 25 rad X-rays at 10 days of age and 25 were unirradiated. In both the irradiated and control series the XO mice had a significantly shorter reproductive life than the XX ones, but unirradiated XO bred longer than irradiated XX. The median age of unirradiated XO at birth of last litter was 280 days and they had 6·5 ± 0·80 litters, whereas for XX the figures were 420days and 12·6 ± 0·74. The mean litter-size of XO mice was only about 55% and their lifetime productivity 34% of that of their XX sibs. Similarly, the lifetime productivity of irradiated XX females was only 31% of that of unirradiated XX. Histological studies showed that in the unirradiated XO mice reproduction ended through shortage of oocytes, and the resulting secondary ovarian changes were similar to those in irradiated mice. Thus, the differences between human and mouse XO types are to some extent reconciled. Both become sterile through death of oocytes, in humans before puberty and in mice after. This difference may be connected with different times from oogenesis to puberty in the two species.

A temperate phage, M6, has been isolated from a lysogenic strain of Pseudomonas maltophilia. An extended range mutant, M6a, plates on P. aeruginosa and is capable of general transduction in this species. This phage may be of value for comparing the genetic maps of different species of Pseudomonas.

Proposals are made for symbols consisting of a primary gene symbol of lower case italic letters referring to the mutant phenotype (three letters for new symbols, old symbols unchanged), an italic capital locus specific letter (or a hyphen in mutants not yet tested for allelism) and an italic mutant number. Optional superscripts are recommended to convey additional information. Further proposals relate to symbols for chromosome aberrations and to strain numbers.

The origin of a number of R-factors used for genetic studies in Pseudomonas aeruginosa is described.

An enhancement of cross-over frequencies previously reported by Newcombe & Threlkeld (1972) is shown to be due to two regions located on linkage group I, a few cross-over units to the right of the centromere. The distal region appears to be shorter than the proximal region, but equally effective in enhancing cross-over frequencies. The longer proximal region is readily divisable by cross-overs and probably spans several crossover units.

The properties of two transfer-deficient Flac mutants (in Escherichia coli K12) carrying mutations in the cistron traL are described. The traL product is needed for conjugational DNA transfer and for pilus formation, but not for surface exclusion; it is not plasmid-specific. traL maps between traA and traE; one of the traL mutations is apparently polar on traA. The properties of Tra+ revertants of this mutation suggest that the traL product is directly required for F-specific phage infection.

Measurement of ColEl transfer by ColV2, in E. coli K12, showed that ColV2 specifies a surface exclusion system. This system is different from those specified by Flac, and by ColVBtrp and Rl-19. Like these other two systems, the ColV2 surface exclusion system is subject to inhibition by the appropriate transfer inhibitor, and is not expressed in stationary phase cells.