- Volume 124, Issue 1, 1981

Summary: The effects of tetracycline (hydrophilic) and minocycline (hydrophobic) on the synthesis of proteins in Escherichia coli were determined. The activity of minocycline against membrane-bound and free ribosomes could not be distinguished from that of tetracycline.

The efficiency of a variety of common mutagens in producing mutation in Rhizobium trifolii P3 was examined. Ethyl methanesulphonate, methyl methanesulphonate, decarbamoyl mitomycin C, nitrous acid and gamma radiation did not mutate R. trifolii P3. N-Methyl-N′-nitro-N-nitrosoguanidine (MNNG) and ultraviolet radiation were both mutagenic, the former being the more effective. Transposon mutagenesis with Tn5 yielded the same frequency and range of auxotrophs as did MNNG.

In an attempt to isolate a strain of Rhizobium trifolii which could be highly mutated by ultraviolet light (u.v.), a u.v.-sensitive mutant was isolated using a semi-selective procedure. The mutant was not only 85 times more sensitive than the wild-type to the lethal effects of u.v., but was mutated at u.v. doses which had little mutagenic effect on the wild-type. Its sensitivity to the mutagenic agents methyl methanesulphonate and gamma rays was unaltered, but its spontaneous mutation frequencies for two antibiotic resistances were increased. The mutation conferring u.v. sensitivity was mapped on the chromosome of Rhizobium leguminosarum 300 in a position between the markers ser-2 and ade-88. Unsuccessful attempts were made to transfer into the u.v.-sensitive mutant any one of a number of plasmids known to decrease the lethality of u.v. and enhance its mutagenicity.

Addition of glycine in low concentrations to modified Youman’s medium led to a slight increase in both the total lipid and phospholipid content of Mycobacterium smegmatis ATCC 607 without a concomitant alteration in either the ratio of the individual phospholipids or the amount and characteristics of growth. However, high concentrations of glycine led to a decrease in both the total lipid and phospholipid content, a change in the ratio of the individual phospholipids, a decrease in the amount of growth and a change in its characteristics. The association of a decrease in the amount of growth and a change in its characteristic with a decrease in the content of triacylated mannophosphoinositides points to the biological importance of these phosphoglycolipids.

Microtubules and microtubule-organizing centres of Dictyostelium discoideum were investigated using indirect immunofluorescence with antibodies against a microtubule-associated protein from a rabbit preimmune serum. The microtubule system showed a cell cycle dependent variation. The cytoplasmic microtubule network present in interphase disappeared in mitosis, in contrast to the astral fibres and central spindle fibres which remained evident. In both cell cycle stages microtubules radiated from microtubule-organizing centres which corresponded to the nucleus-associated organelles in interphase and the spindle pole bodies in mitosis.

An iron-oxidizing bacterium has been isolated from an ochre-polluted stream. Growth occurs optimally at pH 2·5 in a mineral medium containing 200 μg ferrous ions ml−1 but lacking organic carbon. Manganese salts are not oxidized. The organism grows as long unbranched filaments encrusted with iron particles and is morphologically and physiologically distinct from other well characterized iron-oxidizing bacteria.

Summary: A second-stage mutant of Escherichia coli K12 designated as strain 806 grew faster on d-lyxose than the mutant strain 805 previously described. Both mutants produced constitutively a novel enzyme, d-mannose isomerase, but strain 806 produced twice as much as strain 805. The enzyme could fortuitously convert d-lyxose to d-xylulose, which is a normal intermediate in the d-xylose catabolic pathway. The purified enzyme consisted of four subunits each with a molecular weight of about 40000. In 0·14 m-Na2SO4, the tetramer dissociated completely into dimers. While the tetramer K m values for d-mannose and d-lyxose were 80 mm and 300 mm, respectively, the dimer K m values for these two sugars were both 300 mm. The amino acid composition of the enzyme was also determined.

Summary: Restriction-proficient strains of Salmonella typhimurium are shown to be ineffective as recipients of normal RP4:: Mucts62 due to the operation of two restriction systems (hsdSA and hsdLT) on the Mu moiety of this plasmid. Strains mutant in both these hsd loci are excellent recipients.