A cyanobacterial AbrB-like protein affects the apparent photosynthetic affinity for CO2 by modulating low-CO2-induced gene expression

In Synechocystis sp. strain PCC 6803, over 450 genes are upregulated following transfer of the cells from a high (1–5% CO₂ in air, HC) to a low level of CO₂ (as in air or lower, LC). This includes sbtA , ndhF3 and cmpA involved in inorganic carbon (Ci) uptake. Earlier studies implicated NdhR in the regulation of LC-induced genes but there are indications that additional components are involved. Following extraction of proteins from cells grown under HC and (NH4)₂SO₄ fractionation, we have identified LexA and two AbrB-like proteins, Sll0359 and Sll0822, which bind to a fragment of the sbtA promoter. Using extracts prepared from LC-grown cells, Sll0822 did not bind to the sbtA promoter despite its presence in the cells, suggesting that it may serve as a repressor of LC-induced genes. This is supported by the fact that sbtA , ndhF3 and cmpA normally expressed only under LC in the wild-type are transcribed under both HC and LC in a Δ sll0822 mutant. When grown under HC this mutant exhibits an elevated apparent photosynthetic affinity to Ci, typically observed in the wild-type only under LC. Clearly, expression of genes essential for Ci uptake was sufficient to raise the apparent photosynthetic affinity for external Ci.     

Blooming of cyanobacteria in turbulent water with steep light gradients: The effect of intermittent light and dark periods on the oxygen evolution capacity of Synechocystis sp. PCC 6803

Abstract: The influence of intermittent high-light dosage on Synechocystis sp. PCC 6803 with respect to oxygen evolution capacity, fluorescence yield and carotenoid pigment pattern was investigated, using high-light- and low-light-adapted cultures. The results showed that this cyanobacterium was able to survive high light stress for a full day if this stress was applied on and off with intermittently presented recovery periods in darkness. Enhanced respiratory activity in the high-light adapted cells was detected and this may be an important factor in preventing photodamage under high light stress. Cyanobacterial photosynthetic and respiratory electron transfer pathways are both present within the same membrane, and share common electron carriers. The role of respiratory activity in preventing overexcitation of photosystem 2 is discussed with regard to cyanobacterial ecology.     

The malic enzyme is required for optimal photoautotrophic growth of Synechocystis sp. strain PCC 6803 under continuous light but not under a diurnal light regimen

A mutation was recovered in the slr0721 gene, which encodes the decarboxylating NADP(+)-dependent malic enzyme in the cyanobacterium Synechocystis sp. strain PCC 6803, yielding the mutant 3WEZ. Under continuous light, 3WEZ exhibits poor photoautotrophic growth while growing photoheterotrophically on glucose at rates nearly indistinguishable from wild-type rates. Interestingly, under diurnal light conditions (12 h of light and 12 h of dark), normal photoautotrophic growth of the mutant is completely restored.     

Novel cyanobacterial biosensor for detection of herbicides

The aim of this work was to generate a cyanobacterial biosensor that could be used to detect herbicides and other environmental pollutants. A representative freshwater cyanobacterium, Synechocystis sp. strain PCC6803, was chromosomally marked with the luciferase gene luc (from the firefly Photinus pyralis) to create a novel bioluminescent cyanobacterial strain. Successful expression of the luc gene during growth of Synechocystis sp. strain PCC6803 cultures was characterized by measuring optical density and bioluminescence. Bioluminescence was optimized with regard to uptake of the luciferase substrate, luciferin, and the physiology of the cyanobacterium. Bioassays demonstrated that a novel luminescent cyanobacterial biosensor has been developed which responded to a range of compounds including different herbicide types and other toxins. This biosensor is expected to provide new opportunities for the rapid screening of environmental samples or for the investigation of potential environmental damage.     

Interaction of fructose with the glucose permease of the cyanobacterium Synechocystis sp. strain PCC 6803.

Fructose was bactericidal for the cyanobacterium Synechocystis sp. strain PCC 6803. Each of ten independently isolated fructose-resistant mutants had an alteration of the glucose transport system, measured as uptake of glucose or of 3-O-methyl-D-glucose. In the presence of the analog, the wild-type Synechocystis strain was protected against fructose. Two mutants altered in photoautotrophy were also isolated.     

利用同源重组构建蓝藻集胞藻6803ndhO基因突变株及其分子鉴定

蓝藻NADPH脱氢酶(NDH-1)是一种重要的光合膜蛋白复合体,参与CO2吸收、围绕光系统I的循环电子传递和细胞呼吸。迄今为止,人们在蓝藻细胞中已鉴定出15种NDH-1复合体亚基(NdhA-NdhO)。然而,人们对NdhO亚基的研究尚不够,至今未见有反向遗传学等方面的研究。在通过构建同源重组载体、自然转化和多次继代筛选后,对转化子进行了PCR和蛋白免疫印迹鉴定。结果表明,卡那霉素基因已成功地插入到ndhO基因的保守区域,并完全破坏了ndhO基因的蛋白表达,从而获得了ndhO基因缺失的突变株,为进一步研究NdhO亚基对NDH-1复合体的稳定性和生理功能等奠定了实验基础。     

Circadian expression of the dnaK gene in the cyanobacterium Synechocystis sp. strain PCC 6803.

The expression of the dnaK gene in the cyanobacterium Synechocystis sp. strain PCC 6803 was continuously monitored as bioluminescence by an automated monitoring system, using the bacterial luciferase genes (luxAB) of Vibrio harveyi as a reporter of promoter activity. A dnaK-reporting bioluminescent Synechocystis strain was constructed by fusing a promoterless segment of the luxAB gene set downstream of the promoter region of the Synechocystis dnaK gene and introduction of this gene fusion into a BglII site downstream of the ndhB gene in the Synechocystis chromosome. Bioluminescence from this strain was continuously monitored and oscillated with a period of about 22 h for at least 5 days in continuous light. The phase of the rhythm was reset by the timing of the 12-h dark period administered prior to the continuous light. The period of the rhythm was temperature compensated between 25 and 35 degrees C. Thus, the bioluminescence rhythm satisfied the three criteria of circadian rhythms. Furthermore, the abundance of dnaK mRNA also oscillated with a period of about 1 day for at least 2 days in continuous light conditions, indicating circadian control of dnaK gene expression in Synechocystis sp. strain PCC 6803.     

Identification of a gene required for cis-to-trans carotene isomerization in carotenogenesis of the cyanobacterium Synechocystis sp. PCC 6803.

A disruptive mutant of the sll0033 gene of the cyanobacterium Synechocystis sp. PCC 6803 produced primarily cis carotenes and small amounts of all-trans carotenes, but no xanthophylls, under dark conditions. Under light conditions, however, it produced normal carotenoids, that were the same as those produced by wild-type cells grown under both light and dark conditions. When the mutant cells cultured under dark conditions were irradiated, cis-isomers of carotenes were converted to all-trans lycopene. These findings demonstrate that this gene, designated crtH, is involved in the isomerization of cis-carotenes to all-trans forms in dark conditions, and that cis-carotenes were also converted to all-trans forms under light conditions by photoisomerization.