Thermophilic cyanobacteria of the genus Synechococcus are major contributors to photosynthetic carbon fixation in the photic zone of microbial mats in Octopus Spring, Yellowstone National Park. Synechococcus OS-B was characterized with regard to the ability to acclimate to a range of different light irradiances; it grows well at 25 to 200 HL]), we noted several responses that had previously been associated with HL acclimation of cyanobacteria, including cell bleaching, reduced levels of phycobilisomes and chlorophyll, and elevated levels of a specific carotenoid. Synechococcus OS-B synthesizes the carotenoids zeaxanthin and ,-carotene and a novel myxol-anhydrohexoside. Interestingly, 77-K fluorescence emission spectra suggest that Synechococcus OS-B accumulates very small amounts of photosystem II relative to that of photosystem I. This ratio further decreased at higher growth irradiances, which may reflect potential photodamage following exposure to HL. We also noted that HL caused reduced levels of transcripts encoding phycobilisome components, particularly that for CpcH, a 20.5-kDa rod linker polypeptide. There was enhanced transcript abundance of genes encoding terminal oxidases, superoxide dismutase, tocopherol cyclase, and phytoene desaturase. Genes encoding the photosystem II D1:1 and D1:2 isoforms (psbAI and psbAII/psbAIII, respectively) were also regulated according to the light regimen. The results are discussed in the context of how Synechococcus OS-B may cope with high light irradiances in the high-temperature environment of the microbial mat.Laminated microbial mats are present in the channels emanating from Octopus Spring, an alkaline, siliceous hot spring in Yellowstone National Park (44). Several studies have focused on the community structure (15,32,35) and the physiological/ecological features (34, 44) of the microbial biota of the mat and have helped to elucidate fundamental principles of community ecology and microbial diversity in this environment (2,31,43,44). Recent metagenomic analyses of these consortia are also beginning to reveal ways in which individuals of this community contribute to overall population metabolism (3a). Microbial hot spring communities represent excellent model systems for exploring how environmental parameters, such as light levels, temperature, nutrient availability, and oxic/anoxic conditions, shape the structural and functional aspects of the community. The photic zone of the microbial mat present in Octopus Spring comprises the uppermost 1 to 2 mm. In this region, cyanobacteria, represented by the genus Synechococcus, evolve O 2 and fix inorganic carbon (2). During the day, O 2 levels may reach Ͼ600% air saturation in the photic zone as a consequence of high rates of O 2 evolution and diffusion barriers associated with the polysaccharide matrix of the mat (34). Conversely, as light levels decline in the evening, the O 2 concentration rapidly diminishes and the mat becomes anoxic (34).Recent observations based on denaturing gradient gel electrophoresis and 1...
We have carefully characterized and reexamined the motility and phototactic responses of Synechocystis sp. adenylyl cyclase (Cya1) and catabolite activator protein (SYCRP1) mutants to different light regimens, glucose, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and cyclic AMP. We find that contrary to earlier reports, cya1 and sycrp1 mutants are motile and phototactic but are impaired in one particular phase of phototaxis in comparison with wild-type Synechocystis sp.
bSynechococcus OS-B=, a thermophilic unicellular cyanobacterium, recently isolated from the microbial mats in Octopus Spring (Yellowstone National Park), induces a suite of genes, including phosphatases and transporters, in response to phosphorus (P) starvation. Here we describe two different approaches to examine the ability of Synechococcus OS-B= to synthesize and break down polyphosphate (poly P), a key storage compound in many prokaryotes. First, we developed a transformation protocol to create mutants in the polyphosphate kinase (ppk), the major enzyme responsible for the synthesis of poly P. The ppk mutant exhibited a pleiotropic phenotype with defects in poly P accumulation, aberrant levels of Pho regulon transcripts, growth defects, and changes in cell size and exopolysaccharide levels, among others. Second, we measured transcripts of ppk and ppx (encoding the polyphosphatase) directly from mat samples and found that the levels varied dramatically over a diel cycle. We also used Western blot analysis to quantify levels of PPK and PPX and found that these enzymes differentially accumulated during the diel cycle. Levels of polyphosphate kinase peaked at night, while polyphosphatase levels were highest during the early morning hours. We hypothesize that the opposing activities of these two enzymes allow cells to store and utilize poly P to optimize growth over a diel cycle.
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