Complementation of a red-light-indifferent cyanobacterial mutant (original) (raw)
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Isolation and characterization of pigment mutants from a filamentous cyanobacterium
Folia Microbiologica, 1989
Five strains of a pigment mutant were isolated following UV irradiation and N-methyl-N'nitro-N-nitrosoguanidine (MNNG) mutagenesis from a non-nitrogen fixing mutant of the cyanobacterium Gloeotrichia ghosei. Two of them (B-1 and V-1) were isolated by UV mutagenesis and other three (B-3, B-7 and Br-6) by MNNG mutagenesis. Among the five strains, cultures of three strains (B-l, B-3 and B-7) were typically blue-green in colour. Culture of strain V-1 was found to be violet-pink and of Br-6 was brownish in colour. The parent strain of these mutants was dark-blue in colour. Blue-green mutants showed the predominance of phycocyanin (610 nm) whereas violet-pink and brown strains showed the predominance of phycoerythrin (550 nm) in the absorption spectra of water-soluble pigments. In contrast to these strains their parent strain showed both the absorption peaks (at 550 and 610 nm). Occurrence of stable pigment mutants of a filamentous cyanobacterium indicates that the synthesis of water-soluble pigments is genetically controlled in these mutant strains.
Proceedings of the National Academy of Sciences, 2013
Cyanobacteriochromes (CBCRs) are cyanobacterial members of the phytochrome superfamily of photosensors. Like phytochromes, CBCRs convert between two photostates by photoisomerization of a covalently bound linear tetrapyrrole (bilin) chromophore. Although phytochromes are red/far-red sensors, CBCRs exhibit diverse photocycles spanning the visible spectrum and the near-UV (330–680 nm). Two CBCR subfamilies detect near-UV to blue light (330–450 nm) via a “two-Cys photocycle” that couples bilin 15Z/15E photoisomerization with formation or elimination of a second bilin–cysteine adduct. On the other hand, mechanisms for tuning the absorption between the green and red regions of the spectrum have not been elucidated as of yet. CcaS and RcaE are members of a CBCR subfamily that regulates complementary chromatic acclimation, in which cyanobacteria optimize light-harvesting antennae in response to green or red ambient light. CcaS has been shown to undergo a green/red photocycle: reversible ph...
Annual Review of Microbiology, 2019
Chromatic acclimation (CA) encompasses a diverse set of molecular processes that involve the ability of cyanobacterial cells to sense ambient light colors and use this information to optimize photosynthetic light harvesting. The six known types of CA, which we propose naming CA1 through CA6, use a range of molecular mechanisms that likely evolved independently in distantly related lineages of the Cyanobacteria phylum. Together, these processes sense and respond to the majority of the photosynthetically relevant solar spectrum, suggesting that CA provides fitness advantages across a broad range of light color niches. The recent discoveries of several new CA types suggest that additional CA systems involving additional light colors and molecular mechanisms will be revealed in coming years. Here we provide a comprehensive overview of the currently known types of CA and summarize the molecular details that underpin CA regulation.
Scientific Reports, 2016
Cyanobacteria harbor unique photoreceptors, designated as cyanobacteriochromes (CBCRs). In this study, we attempted to engineer the chromatic acclimation sensor CcaS, a CBCR derived from the cyanobacterium Synechocystis sp. PCC 6803. The wild-type CcaS induces gene expression under green light illumination and represses it under red light illumination. We focused on the domain structure of CcaS, which consists of an N-terminal transmembrane helix; a GAF domain, which serves as the sensor domain; a linker region (L1); two PAS domains; a second linker region (L2); and a C-terminal histidine kinase (HK) domain. Truncated versions of the photoreceptor were constructed by removing the L1 linker region and the two PAS domains, and fusing the GAF and HK domains with a truncated linker region. Thus constructed "miniaturized CcaSs" were grouped into four distinct categories according to their responses toward green and red light illumination, with some showing improved gene regulation compared to the wild type. Remarkably, one of the miniaturized CcaSs induced gene expression under red light and repressed it under green light, a reversed response to the light signal compared to wild type CcaS. These characteristics of engineered photoreceptors were discussed by analyzing the CcaS structural model. Recent advances in our understanding of photosensing in biological systems have led to the use of photoreceptors as novel genetic tools that regulate gene expression in bioprocess models. Optogenetics, which uses various photoreceptors to directly control cell behaviors via light exposure, has recently attracted attention as a synthetic biology-based bioprocess design. Light-regulated microbial bioprocesses using photoreceptors have been reported, demonstrating that gene expression can be regulated without the addition of chemical inducers to the cultures 1-5. Among several organisms, cyanobacteria are the most attractive sources of photoreceptors. Most cyanobacteria are capable of modulating the biosynthesis of phycobilisome or inducing phototaxis in response to light conditions. These bacteria harbor unique photoreceptors known as cyanobacteriochromes (CBCRs). CBCRs are further categorized into several subclasses 6-14 based on their primary sequences, spectral properties, and chromophores, which can sense green/red light, red/green light, ultraviolet-A, blue/green light, and far red/green light. Some CBCRs belong to two-component regulatory systems, inducing phenotypic changes such as phototaxis and the expression of light harvesting proteins for photosynthesis 15-20. Among several CBCRs, we focused on the optogenetic application of the chromatic acclimation sensor CcaS from the unicellular cyanobacterium Synechocystis sp. PCC 6803. CcaS has a phycocyanobilin (PCB) chromophore and is part of a green/red light sensing two-component regulatory system. CcaS is a sensor histidine kinase (HK), and together with its cognate response regulator CcaR, chromatically regulates the expression of the phycobilisome linker gene cpcG2. CcaS regulates the phosphorylation of CcaR, which when phosphorylated, promotes
Biochemistry, 2014
Cyanobacteriochromes (CBCRs) form a large, spectrally diverse family of photoreceptors (linear tetrapyrrole covalently bound via a conserved cysteine) that perceive ultraviolet to red light. The underlying mechanisms are reasonably well understood with, in certain cases, reversible formation of an adduct between a second cysteine and the chromophore accounting, in part, for their spectral diversity. These CBCRs are denoted as dual-Cys CBCRs, and most such CBCRs had been shown to reversibly absorb blue and green light. Herein, we report the structural and mechanistic characterization of a new type of dual-Cys CBCR, AM1_1186, which exhibits reversible photoconversion between a red-absorbing dark state (λ max = 641 nm) and a blue-absorbing photoproduct (λ max = 416 nm). The wavelength separation of AM1_1186 photoconversion is the largest found to date for a CBCR. In addition to one well-conserved cysteine responsible for covalent incorporation of the chromophore into the apoprotein, AM1_1186 contains a second cysteine in a unique position of its photosensory domain, which would be more properly classified as a red/green CBCR according to its sequence. Carboxyamidomethylation and mutagenesis of the cysteines revealed that the second cysteine forms an adduct with the tetrapyrrole, the phycocyanobilin, that can be reversed under blue light. The proline immediately upstream of this cysteine appears to determine the rate at which the cysteinylation following photoexcitation of the dark state chromophore can occur. We propose a possible reaction scheme and color-tuning mechanism for AM1_1186 in terms of its structure and its place in a phylogenetic tree.