Phototaxis in the Cyanobacterium Synechocystis sp. PCC 6803: Role of Different Photoreceptors

Abstract

The second cyanobacterial phytochrome Cph2 from Synechocystis sp. PCC 6803 was suggested as a part of a light-stimulated signal transduction chain inhibiting movement toward blue light. Cph2 has the two bilin binding sites, cysteine-129 and cysteine-1022, that might be involved in sensing of red/far-red and blue light, respectively. Here, we present data on wavelength dependence of the phototaxis inhibition under blue light, indicating that Cph2 itself is the photoreceptor for this blue light response. We found that inhibition of blue-light phototaxis in wild-type cells occurred below the transition point of about 470 nm. Substitution of cysteine-1022 with valine led to photomovement of the cells toward blue light (cph2(-) mutant phenotype). Analysis of mutants lacking cysteine-129 in the N-terminal chromophore binding domain indicated that this domain is also important for Cph2 function or folding of the protein. Furthermore, putative blue-light and phytochrome-like photoreceptors encoded by the Synechocystis sp. PCC 6803 genome were inactivated in wild-type and cph2 knockout mutant background. Our results suggest that none of these potential photoreceptors interfere with Cph2 function, although inactivation of taxD1 as well as slr1694 encoding a BLUF protein led to cells that reversed the direction of movement under blue light illumination in mutant strains of cph2.

Discovering Functional Novelty in Metagenomes: Examples from Light-Mediated Processes

“…BLUF domain proteins are part of the larger family of blue-light photosensors that use flavin chromophores, which together with the phytochromes, rhodopsins, and UV receptors make up the four major classes of bacterial light-sensing proteins (14). Proteins containing a BLUF domain have been shown to function as sensors upstream of phototaxis (24), nucleotide metabolism (35), and repression of anoxygenic photosynthesis (28). The domain is extremely well conserved among the Proteobacteria and Cyanobacteria, absent from the Archaea, and absent from eukaryotes except for the protist Euglena gracilis.…”

The competence gene, comF, from Synechocystis sp. strain PCC 6803 is involved in natural transformation, phototactic motility and piliation

“…strain PCC 6803 has led to the establishment of protocols that have been used in studies of photosynthesis and phototaxis (Bhaya et al, 2001;Fiedler et al, 2005;Hubschmann et al, 2005;Williams, 1988). Initial reports of the natural transformability of this strain also characterized the physiological factors that affected its transformation efficiency, including phase of growth and DNA concentration (Barten & Lill, 1995;Grigorieva & Shestakov, 1982).…”

“…strain PCC 6803 (Yoshihara et al, 2001). A functional Tfp apparatus is also critical for phototaxis, while the regulatory signals and pathways underlying the cells' response to light are rapidly being unravelled (Bhaya, 2004;Bhaya et al, 2001;Fiedler et al, 2005;Yoshihara et al, 2000;Yoshimura et al, 2002). It is apparent that transformability and phototaxis in Synechocystis sp.…”

Structure of the Cyanobacterial Phytochrome 2 Photosensor Implies a Tryptophan Switch for Phytochrome Signaling

“…c-di-GMP is known to be a universal regulator for pili-based motility in eubacteria (18) with domains of the GGDEF and EAL type being responsible for its synthesis and degradation (19). SynCph2 inhibits phototaxis, when cyanobacterial cells are exposed to blue but not to white or red light (20,21). Accordingly, the complex architecture of SynCph2 (Fig.…”