Two wild-type substrains of a motile cyanobacterium Synechocystis sp. PCC 6803 show positive phototaxis toward a light source (PCC-P) and negative phototaxis away from light (PCC-N). In this study, we found that a novel two-component system of photoresponse is involved in the phototactic regulation. Inactivation of slr1212 (pixA), which encodes a photoreceptor histidine kinase, reverted the positive phototaxis of PCC-P to negative phototaxis, and inactivation of the downstream slr1213 (nixB) and slr1214 (nixC), which encode AraC-like transcription factor-type and PatA-type response regulators, respectively, reverted the negative phototaxis of PCC-N to positive phototaxis. Opposite effects of pixA and nixBC disruption implies an unexpected signal transduction pathway in the switching of positive and negative phototaxis. The blue/green-type cyanobacteriochrome GAF domain of PixA was expressed in Synechocystis and phycocyanobilin-producing Escherichia coli. The holoprotein covalently bound a chromophore phycoviolobilin and showed reversible photoconversion between the violet- (Pv, λ(peak) = 396 nm) and green-absorbing (Pg, λ(peak) = 533 nm) forms, although the protein from E. coli partially bound a precursor phycocyanobilin. These results were discussed with regard to an idea that PixA serves as a violet light receptor for switching of positive and negative phototaxis by transcriptional and functional regulation.

Synechocystis: sp. PCC 6803 is a unicellular motile cyanobacterium, which shows positive or negative phototaxis on agar plates under lateral illumination. By gene disruption in a substrain showing of positive phototaxis, it was demonstrated that mutants defective in sll0038, sll0039, sll0041, sll0042 or sll0043 lost positive phototaxis but showed negative phototaxis away from the light source. Mutants of sll0040, which is located within the cluster of these genes, retained the capacity of positive phototaxis but to a lesser extent than the parent cells. These genes are homologous to che genes, which are involved in flagellar switching for bacterial chemotaxis. Interestingly, sll0041 (designated pisJ1) is predicted to have a chromophore-binding motif of phytochrome-like proteins and a signaling motif of chemoreceptors for bacterial chemotaxis. It is strongly suggested that the positive phototactic response was mediated by a phytochrome-like photoreceptor and CheA/CheY-type signal transduction system.

Positive orientation is a new construct posed at the core of positive evaluations about oneself, life, and the future. Previous findings attested to its associations with health, well-being, and achievement. In the present study, the authors traced standard measures of self-esteem, life satisfaction, and dispositional optimism to a common factor attesting to a similar factorial structure in Japan, Germany, and Italy. Partial invariance at both metric and scalar levels further corroborates generality of positive orientation across these 3 countries

ABSTRACrThe activities of several enzymes of the citric acid and poly-4e-hydroxybutyrate cycles were measured in Rhizobiumjapeoicwm 3IIB-143 bacteroids which had been isolated from soybean nodules by sucrose gradient centrifupaton. Duing the period of developing nitrogenase activity, the specfic activity of fumuase, hydroxybutyrate dehydrogenase, ,-ketothiohlse, and pyruvate dehydrogenase complex incesed whereas acetoacetate-succinyl-CoA transferase and isocitrate dehydrogenase decreased (2,8,9,15,17,21,25,28,29).The carbon metabolism of developing and senescing nodules and the metabolism of bacteroids have been reviewed recently (5,19,27 PHB has been measured in many rhizobia species (7,12,14 The purpose of this investigation was, first, to establish that PDC, selected enzymes from the citric acid cycle, (IDH, MDH, and FMR) and of the PHB cycle (KT, HBD, and AST) were present during the period of nitrogen fixation and PHB accumulation in R. japonicum; second, to follow their activity as a function ofage; and third, to relate temporal changes in activities to those of nitrogenase and PHB accumulation through the use of dispersion diagrams.