- Volume 128, Issue 1, 1982

The interaction of tachhzauert of Toxoplasma gondii with plant protoplasts was compared with their interaction with their interaction with cultures of HeLa cells. Unlike the HeLa cells, the plant protoplasts were refractory to invwiest under all conditions tested. The lack of invasion was not an artefact of the protopiast isolation technique. This is the first description of a cell type refractory to Toxoplasme invasion; hence possible mechanisms for the specificity of parasite-host cell interaction can now be studied.

The resistance of Pseudomonas aeruginosa wild-type, uvr, pol and rec strains to ultraviolet (u.v.) light, X-rays and freezing and thawing was determined. An R plasmid, pPL1, which increased resistance of the wild-type, uvr, and pol but not rec strains to u.v. light, increased the resistance of only rec and pol mutants to X-rays and freezing and thawing. These findings reinforce the idea of DNA as a target in the organism for freeze-thaw stress and suggest that freeze-thaw-induced DNA damage might be similar to that produced by X-rays but different from that produced by u.v. light.

A set of four isogenic Escherichia coli strains has been constructed in which all possible combinations of NADH- and formate-dependent nitrite reductases are active or inactive. Each pathway can be inactivated genetically without a corresponding loss in the other activity: the two pathways are therefore biochemically independent. The generation of a membrane potential during nitrite reduction by formate has been demonstrated using an ion-selective electrode specific for a lipophilic cation. The observed energy conservation results, at least in part, from the ability of formate dehydrogenase in E. coli to pump protons.

Fatty acids of five strains of Leptotrichia buccalis were examined by gas-liquid chromatography. The strains showed identical patterns, characterized by the presence of n-hexadecanoate. octadecenoate and 3-hydroxytetradecanoate as major acids. The general acid pattern showed a distinct similarity to that of Fusobacterium species.