Complementation Between Different Mutations in the ilvA Gene of Escherichia coli K-12

An ilvA mutation carried by a ?80i(lambda)dilv transducing phage complemented some ilvA mutations and did not complement others. Complementation was accompanied by appearance of threonine deaminase activity in vivo. These results divided the ilvA mutations into two sets which formerly appeared to define two cistrons.     

Cerebrospinal fluid T cell receptor gamma/delta+ lymphocyte subsets in patient with AIDS-dementia complex.

A subset of peripheral T cells, whose physiological function is little known, expresses a distinct CD3-associated receptor composed of gamma and delta chains. We used two monoclonal antibodies to characterize the TcR gamma/delta lymphocytes (TcR delta 1+) and their fraction (TcS delta 1+) in peripheral blood and cerebrospinal fluid of patients affected by AIDS dementia complex (ADC). Thirty patients with ADC and a control group of twenty individuals with other non-inflammatory neurological diseases (OND) were recruited. Our results demonstrate that the TcR gamma/delta cells were also present in cerebrospinal fluid of ADC patients, but we did not find any statistical difference between the two groups.     

Key role of bacterial NH(4)(+) metabolism in Rhizobium-plant symbiosis.

Symbiotic nitrogen fixation is carried out in specialized organs, the nodules, whose formation is induced on leguminous host plants by bacteria belonging to the family Rhizobiaceae: Nodule development is a complex multistep process, which requires continued interaction between the two partners and thus the exchange of different signals and metabolites. NH(4)(+) is not only the primary product but also the main regulator of the symbiosis: either as ammonium and after conversion into organic compounds, it regulates most stages of the interaction, from the production of nodule inducers to the growth, function, and maintenance of nodules. This review examines the adaptation of bacterial NH(4)(+) metabolism to the variable environment generated by the plant, which actively controls and restricts bacterial growth by affecting oxygen and nutrient availability, thereby allowing a proficient interaction and at the same time preventing parasitic invasion. We describe the regulatory circuitry responsible for the downregulation of bacterial genes involved in NH(4)(+) assimilation occurring early during nodule invasion. This is a key and necessary step for the differentiation of N(2)-fixing bacteroids (the endocellular symbiotic form of rhizobia) and for the development of efficient nodules.     

Comparative study of the symbiotic plasmid DNA in free living bacteria and bacteroids of Rhizobium leguminosarum

Plasmids pIM13, pT127 and pBC16 delta 1, introduced by transformation into Clostridium acetobutylicum N1-4081, were shown to replicate in, and to confer antibiotic resistance upon this new host. Recombinant plasmids were constructed by inserting erythromycin-resistant plasmid pIM13 into the unique ClaI site of pBR322 or by ligating a tetracycline-resistant determinant of plasmid pT127 to HindIII-linearized pIM13. The hybrid plasmids replicated and expressed erythromycin resistance in C. acetobutylicum strain N1-4081 and in Escherichia coli or Bacillus subtilis, indicating that they might be useful as shuttle vectors for transferring genes between these strains. The efficiency and stability of different replicons in C. acetobutylicum were compared.