Competition-Integration of Blue and Orange Stimuli in Halobacterium salinarum Cannot Occur Solely in SRI Photoreceptor

Abstract

Experiments on the integration of blue and orange stimuli in Halobacterium salinarum were performed by using different combinations of blue and orange steps. The results show that the prevalence of the blue stimulus over the orange one depends on both the blue and the orange light intensities. A quantitative analysis of the current hypotheses on the phototransduction of orange and UV-blue light stimuli is presented, showing that the balancing between the two antagonistic stimuli should depend only on the intensity of the blue stimulus and not on that of the orange one, provided that the combination of the two stimuli occurs linearly at the photoreceptor stage. We conclude that blue and orange stimuli elicit distinct intracellular signals whose integration occurs downstream of the photoreceptor.

Chemotaxis-guided Movements in Bacteria

“…are attracted by substances exuded by plant roots during nodulation (Ames et al, 1980;Parke et al, 1985;Armitage et al, 1988;Pandya et al, 1999), Halobacterium sp. use phototaxis that is triggered by light of the wavelengths required for photosynthesis (Schimz and Hildebrand, 1979;Sundberg et al, 1990;Krohs, 1994;Cercignani et al, 2000), and motile E. coli and Salmonella cells move toward optimal nutrients such as sugars, amino acids, and oxygen (Stock and Surette, 1996). In addition to responses to environmental signals, motility and chemotaxis have been found to be involved in virulence of many pathogenic bacteria (Freter, 1981;Ottemann and Miller, 1997;Lux et al, 2000;Josenhans and Suerbaum, 2002).…”

Color-specific Conditioning Effects Due to Both Orange and Blue Stimuli Are Observed in a Halobacterium salinarum Strain Devoid of Putative Methylatable Sites on HtrI¶

“…The program detects cell positions in each frame and traces the cell trajectories, identifying the frames where reversals occur. The experimental set up and technique has been detailed recently (10).…”