Showing papers in "Fems Microbiology Letters in 1977"

The identification of mutants of Escherichia coli deficient in formate dehydrogenase and nitrate reductase activities using dye indicator plates

Abstract: The anaerobic, proton translocating, formatedependent nitrate reductase activity of Escherichia coli has been studied extensively, particularly with respect to the identification of the various redox components required, their functional organization in the cytoplasmic membrane, and the structural genes responsible for their synthesis [1,2]. The information so far available is summarized in Fig. 1 from which it is apparent that several outstanding problems remain. We have begun a detailed analysis of the molecular genetics of the system with particular emphasis on firstly the unambiguous characterizations of the products of the various structural genes so far described, and secondly the identification of the regulatory genes responsible for the control of structural gene expression. In this study it became apparent that many of the previously described methods for the identification and genetic characterization of relevant mutants were either time-consuming or imprecise. We describe here the application of two methods utilizing modified dye indicator plates which facilitate the rapid and unambiguous classification of mutants into those which: (i) specifically lack formate dehydrogenase activity; (ii) specifically lack D-lactate-dependent nitrate reductase activity; and (iii) pleiotropically lack both activities.

Ammonia assimilation in members of the Rhodospirillaceae

Abstract: The purple non-sulpliur bacteria (Rhodospirillaceae) are able to grow photolieterotrophically o n a number of inorganic sources of nitrogen including gaseous nitrogen, nitrate and ammonia. Evidence obtained in experiments with non-phototrophic bacteria [ 1 ] and with the phototrophic sulphur bacteria [2] (Chromatiaceae and Chlorobiaceae) suggests that during growth on low concentrations of anm~onia, the synthesis of glutamate (and hence ammonia assimilation) proceeds via glutamine synthetase (GS) (EC 6.3.1.2) and gh, tamate synthase (GOGAT) (EC 2.6.1.53), while at high ammonia concentrations, glutamate dehydrogenase (GDH) (EC 1.4.1.3) may be involved either instead of, or together with the GS/GOGAT system. Nagatani et al. [3] have shown GOGAT to be present in a number of nitrogen-fixing bacteria, and have demonstrated a requirement for the GS/GOGAT system in ammonia assimilation during nitrogen fixation in Klebsiella pneumoniae. Some nitrogen fixing clostridia lack GI)tl [4.5] and assimilate ammonia via a constitutive GS/GOGAT system. During growth on nitrate, annnonia assimilation in some Pseudomonas spp. [5--7] and in Klebsiella aerogenes [5] appears to proceed via the GS/GOGAT system, while in Rhizobium leguminosarum [8] growth in the presence of ltigh concentrations of nitrate results in a loss of both GS and GOGAT activity, while ammonia is assimilated via GDH. This paper describes variations in the activities of GS, GOGAT mad GDtt in extracts from cultures of purple non-sulphur bacteria that had been grown on different concentrations of nitrate in batch cultures, and when tixing nitrogen or growing on ammonia in continuous cultures. 2. Materials and methods