Inflammatory, Metabolic and Endothelial Biomarkers Before and After Pregnancy Complications.

Women with gestational diabetes mellitus (GDM), hypertensive disorders of pregnancy (HDP), and preterm birth (PTB) have excess cardiovascular disease compared to those with uncomplicated births, perhaps related to pre-pregnancy inflammation, dysmetabolism or endothelial dysfunction. We included 1238 women in the Coronary Artery Risk Development in Young Adults Study (1985-2011) with 2215 births classified according to outcomes (term, uncomplicated births were the referent). Repeated measures ANOVA estimated pre-pregnancy, post-pregnancy and biomarker change according to pregnancy outcomes, adjusted for confounders. GDM and HDP groups had higher pre-pregnancy hsCRP (+0.37 [0.08, 0.65]; +0.29 [0.04, 0.55] log mg/L), leptin (+0.29 [0.09, 0.50]; +0.37 [0.17, 0.56] log ng/ml), and lower adiponectin (-0.25 [-0.36, -0.13); -0.11 [-0.22, -0.01] log ng/ml) than those with uncomplicated births and these profiles persisted in magnitude post-pregnancy. Controlling for BMI attenuated most profiles, except lower pre-pregnancy adiponectin remained associated with GDM. PTB without HDP or GDM was related to lower pre-pregnancy hsCRP and sICAM-1 (-0.31 [-0.56, -0.06] log mg/L; -0.05 [-0.09, - 0.01] log ng/ml) and a larger leptin increase from pre- to post-pregnancy, (+0.20 [0.02, 0.37] log ng/ml). Pre-pregnancy inflammation and metabolic dysfunction contributed to GDM and HDP, perhaps due to higher BMI. PTB may be related to adverse metabolic changes post-pregnancy, though the unexpected endothelial biomarker profile warrants further study.

Sleep Quality in Individuals with and without Persistent Postpartum Hypertension.

OBJECTIVE: This study aimed to compare sleep quality at 1 year postpartum following a hypertensive disorder of pregnancy (HDP) among individuals with persistent postpartum hypertension (HTN) compared with those with normal blood pressures (BPs). STUDY DESIGN: We combined data from the Heart Health 4 New Moms pilot randomized trial (n = 118) and the Pathways prospective cohort study (n = 36). Individuals with a singleton pregnancy complicated by gestational HTN or preeclampsia underwent a research study visit at a mean 48.7 ± 9.5 weeks postpartum with standardized BP measurement and assessment of subjective sleep quality with the Pittsburgh Sleep Quality Index (PSQI). Persistent postpartum HTN was defined as Stage 1 HTN or greater (mean systolic BP ≥ 130 mm Hg or mean diastolic BP ≥ 80 mm Hg over three measurements at rest) or requiring antihypertensive medication. Statistical analysis was performed using univariate and multivariable logistic regression analyses. RESULTS: Of 154 individuals with an HDP included in the analysis, 84 (55%) were normotensive at 1 year postpartum and 70 (45%) had persistent postpartum HTN. Individuals with persistent postpartum HTN were more likely to be older, self-identify as Black race, have higher prepregnancy and 1-year postpartum body mass index (BMI), be multiparous, and deliver at an earlier gestational age. The mean global PSQI score was 8.7 ± 3.7, with 81% reporting poor sleep (PSQI > 5), and scores were higher among individuals who were persistently hypertensive (9.6 ± 3.5) compared with those who were normotensive at 1 year postpartum (7.9 ± 3.6), p < 0.01. Findings were unchanged in a multivariable model adjusting for age, self-reported race, prepregnancy BMI, and parity. CONCLUSION: Following an HDP, individuals reported poor sleep quality at 1 year postpartum. Individuals with persistent postpartum HTN reported lower sleep quality, suggesting that sleep behavior may be a target for intervention to improve maternal cardiovascular health following an HDP. KEY POINTS: · After an HDP, poor sleep quality was common at 1 year postpartum.. · Those with persistent postpartum HTN reported worse sleep quality at 1 year postpartum.. · Sleep behavior may be a target for intervention to improve maternal cardiovascular health..

Blood Pressure Trajectories Through the First Year Postpartum in Overweight or Obese Individuals Following a Hypertensive Disorder of Pregnancy.

BACKGROUND: Hypertensive disorders of pregnancy are associated with cardiovascular disease; however, patterns of blood pressure (BP) recovery are understudied. We compared pregnancy and postpartum BP trajectories among individuals with hypertensive disorders of pregnancy who developed persistent hypertension at 1-year postpartum compared with individuals with normalization of BP. METHODS: We used data from a randomized clinical trial of individuals with overweight, obesity, and hypertensive disorders of pregnancy conducted in the first year after delivery. Pregnancy BPs were obtained during prenatal visits; postpartum BPs were prospectively obtained through home monitoring. Demographic characteristics and trajectories were compared by hypertensive status (systolic BP ≥130 mm Hg, diastolic BP ≥80 mm Hg, or use of antihypertensive medications) at 1 year. We used repeated BP measures to fit separate mixed-effects linear regression models for pregnancy and postpartum using restricted cubic splines. RESULTS: We included 129 individuals; 75 (58%) individuals progressed to hypertension by 1-year postpartum. Individuals with hypertension were older, delivered at earlier gestational ages, and had higher body mass index at 1-year postpartum compared with those with normalization. Individuals with hypertension had similar BP trajectories during pregnancy to those with BP normalization but a significantly different BP trajectory (P<0.01 for systolic and diastolic BPs) in the first year postpartum. These differences persisted in multivariable models after adjustment for early pregnancy body mass index, age, and severity of hypertensive disorder of pregnancy (P<0.01 for systolic and diastolic BPs). CONCLUSIONS: BP trajectories in the first year postpartum, but not during pregnancy, may provide important information for risk stratification after a hypertensive disorder of pregnancy. REGISTRATION: URL: https://clinicaltrials.gov; Unique identifier: NCT03749746.

Maternal Mental Health, COVID-19-Related Distress, and Disruptions in Lifestyle Behaviors Among Postpartum Mothers With a Previous Hypertensive Disorder of Pregnancy.

BACKGROUND: Many perinatal people experienced pandemic-related distress and changes in health behaviors at the onset of the COVID-19 pandemic, but less is known about how the pandemic continued to impact their health. OBJECTIVE: The authors of this study examined the influence of pandemic-related distress and maternal mental health on postpartum lifestyle behaviors of mothers with a previous hypertensive disorder of pregnancy. METHODS: Between September 2021 and March 2022, 82 postpartum (19.2 ± 5.5 months) mothers with a hypertensive disorder of pregnancy completed measures of pandemic-related distress and pandemic-related disruption in lifestyle behaviors from the Coronavirus Perinatal Experiences Impact Survey. A Patient Health Questionnaire-9 score ≥ 10 and a score ≥ 3 on the Breslau scale indicated significant depressive and posttraumatic stress disorder (PTSD) symptoms, respectively. RESULTS: Twenty-two (27.2%) and 30 (36.6%) participants had significant depressive or PTSD symptoms, respectively. In models adjusted for education, income, parity, delivery prepandemic or peripandemic, intervention group, and prepregnancy mental health history, both PTSD symptoms (B = 0.229, P = .029) and pandemic-related distress (B = 0.492, P < .001) associated with greater disruption in health behaviors. Depressive symptoms did not associate with greater disruption in health behaviors (B = 0.169, P = .135). CONCLUSION: Monitoring PTSD symptoms may be vital in supporting mothers with hypertensive disorders of pregnancy in making lifestyle changes to prevent cardiovascular disease.

Postpartum home blood pressure monitoring and lifestyle intervention in overweight and obese individuals the first year after gestational hypertension or pre-eclampsia: A pilot feasibility trial.

OBJECTIVE: To test the feasibility of a randomised trial of home blood pressure monitoring paired with a remote lifestyle intervention (Heart Health 4 New Moms) versus home blood pressure monitoring alone versus control in individuals with a hypertensive disorder of pregnancy in the first year postpartum. DESIGN: Single-blinded three-arm randomised clinical trial. SETTING: Two tertiary care hospitals and a community organisation. POPULATION: Postpartum overweight and obese individuals with a hypertensive disorder of pregnancy and without pre-pregnancy hypertension or diabetes. METHODS: We assessed the feasibility of recruitment and retention of 150 participants to study completion at 1-year postpartum with randomisation 1:1:1 into each arm. Secondary aims were to test effects of the interventions on weight, blood pressure and self-efficacy. RESULTS: Over 23 months, we enrolled 148 of 400 eligible, screened individuals (37%); 28% black or other race and mean pre-pregnancy body mass index (BMI) of 33.4 ± 6.7 kg/m2 . In total, 129 (87%) participants completed the 1-year postpartum study visit. Overall, 22% of participants developed stage 2 hypertension (≥140/90 mmHg or on anti-hypertensive medications) by 1 year postpartum. There were no differences in weight or self-efficacy across the study arms. CONCLUSION: In this pilot, randomised trial, we demonstrate feasibility of HBPM paired with a lifestyle intervention in the first year postpartum. We detected high rates of ongoing hypertension, emphasising the need for the development of effective interventions in this population.

Sustainable citric acid production from CO2 in an engineered cyanobacterium.

Citric acid is one of the most widely used organic acids in the world, with applications ranging from acidity regulation in food and beverages to metal chelation in hydrometallurgical processes. Most of its production is currently derived from fermentative processes, using plant-derived carbon feedstocks. While these are currently dominant, there is an increasing need to develop closed-loop production systems that reduce process carbon footprint. In this work, we demonstrate for the first time that an engineered marine cyanobacterium Synechococcus sp. PCC 7002 can be used as a sustainable chassis for the photosynthetic conversion of CO2 to citric acid. Decreased citric acid cycle flux, through the use of a theophylline-responsive riboswitch, was combined with improved flux through citrate synthase and enhanced citric acid excretion, resulting in a significant improvement to citric acid production. While allowing citrate production, this strategy induces a growth defect which can be overcome by glutamate supplementation or by fine-tuning aconitase levels, resulting in an increase in production relative to WT of over 100-fold. This work represents a first step toward sustainable production of a commodity organic acid from CO2.

Evidence for Electron Transfer from the Bidirectional Hydrogenase to the Photosynthetic Complex I (NDH-1) in the Cyanobacterium Synechocystis sp. PCC 6803.

The cyanobacterial bidirectional [NiFe]-hydrogenase is a pentameric enzyme. Apart from the small and large hydrogenase subunits (HoxYH) it contains a diaphorase module (HoxEFU) that interacts with NAD(P)+ and ferredoxin. HoxEFU shows strong similarity to the outermost subunits (NuoEFG) of canonical respiratory complexes I. Photosynthetic complex I (NDH-1) lacks these three subunits. This led to the idea that HoxEFU might interact with NDH-1 instead. HoxEFUYH utilizes excited electrons from PSI for photohydrogen production and it catalyzes the reverse reaction and feeds electrons into the photosynthetic electron transport. We analyzed hydrogenase activity, photohydrogen evolution and hydrogen uptake, the respiration and photosynthetic electron transport of ΔhoxEFUYH, and a knock-out strain with dysfunctional NDH-1 (ΔndhD1/ΔndhD2) of the cyanobacterium Synechocystis sp. PCC 6803. Photohydrogen production was prolonged in ΔndhD1/ΔndhD2 due to diminished hydrogen uptake. Electrons from hydrogen oxidation must follow a different route into the photosynthetic electron transport in this mutant compared to wild type cells. Furthermore, respiration was reduced in ΔhoxEFUYH and the ΔndhD1/ΔndhD2 localization of the hydrogenase to the membrane was impaired. These data indicate that electron transfer from the hydrogenase to the NDH-1 complex is either direct, by the binding of the hydrogenase to the complex, or indirect, via an additional mediator.

Engineering improved ethylene production: Leveraging systems biology and adaptive laboratory evolution.

Ethylene is a small hydrocarbon gas widely used in the chemical industry. Annual worldwide production currently exceeds 150 million tons, producing considerable amounts of CO2 contributing to climate change. The need for a sustainable alternative is therefore imperative. Ethylene is natively produced by several different microorganisms, including Pseudomonas syringae pv. phaseolicola via a process catalyzed by the ethylene-forming enzyme (EFE), subsequent heterologous expression of EFE has led to ethylene production in non-native bacterial hosts including Escherichia coli and cyanobacteria. However, solubility of EFE and substrate availability remain rate-limiting steps in biological ethylene production. We employed a combination of genome-scale metabolic modelling, continuous fermentation, and protein evolution to enable the accelerated development of a high efficiency ethylene producing E. coli strain, yielding a 49-fold increase in production, the most significant improvement reported to date. Furthermore, we have clearly demonstrated that this increased yield resulted from metabolic adaptations that were uniquely linked to EFE (wild type versus mutant). Our findings provide a novel solution to deregulate metabolic bottlenecks in key pathways, which can be readily applied to address other engineering challenges.

Degradability of Biodegradable Soil Moisture Sensor Components and Their Effect on Maize (Zea mays L.) Growth.

Inexpensive and no-maintenance biodegradable soil moisture sensors could improve existing knowledge on spatial and temporal variability of available soil water at field-scale. Such sensors can unlock the full potential of variable-rate irrigation (VRI) systems to optimize water applications in irrigated cropping systems. The objectives of this study were to assess (i) the degradation of soil moisture sensor component materials and (ii) the effects of material degradation on maize (Zea Mays L.) growth and development. This study was conducted in a greenhouse at Colorado State University, Colorado, USA, by planting maize seeds in pots filled with three growing media (field soil, silica sand, and Promix commercial potting media). The degradation rate of five candidate sensor materials (three blends of beeswax and soy wax, balsa wood, and PHBV (poly(3-hydroxybutyrate-co-3-hydroxyvalerate))) was assessed by harvesting sensor materials at four maize growth stages (30, 60, 90, and 120 days after transplanting). All materials under consideration showed stability in terms of mass and dimension except PHBV. PHBV was degraded entirely within 30 days in soil and Promix, and within 60 days in sand. Balsa wood did now show any significant reduction in mass and dimensions in all growth media. Similarly, there was no significant mass loss across wax blends (p = 0.05) at any growth stage, with a few exceptions. Among the wax blends, 3:1 (beeswax:soy wax) was the most stable blend in terms of mass and dimension with no surface cracks, making it a suitable encapsulant for soil sensor. All materials under consideration did not have any significant effect on maize growth (dry biomass, green biomass, and height) as compared to control plants. These results indicated that 3:1 beeswax:soy wax blend, PHBV, and balsa wood could be suitable candidates for various components of biodegradable soil moisture sensors.

Heat therapy reduces sympathetic activity and improves cardiovascular risk profile in women who are obese with polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS) affects up to 15% of women and is associated with increased risk of obesity and cardiovascular disease. Repeated passive heat exposure [termed "heat therapy" (HT)] is a lifestyle intervention with the potential to reduce cardiovascular risk in obesity and PCOS. Women with obesity (n = 18) with PCOS [age 27 ± 4 yr, body mass index (BMI) 41.3 ± 4.7 kg/m2] were matched for age and BMI, then assigned to HT (n = 9) or time control (CON; n = 9). HT subjects underwent 30 one-hour hot tub sessions over 8-10 wk, whereas CON subjects did not undergo HT. Muscle sympathetic nerve activity (MSNA), blood pressure, cholesterol, C-reactive protein, and markers of vascular function were assessed at the start (Pre) and end (Post) of 8-10 wk. These measures included carotid and femoral artery wall thickness and flow-mediated dilation (FMD), measured both before and after 20 min of ischemia-20 min of reperfusion (I/R) stress. HT subjects exhibited reduced MSNA burst frequency (Pre: 20 ± 8 bursts/min, Post: 13 ± 5 bursts/min, P = 0.012), systolic (Pre: 124 ± 5 mmHg, Post: 114 ± 6 mmHg; P < 0.001) and diastolic blood pressure (Pre: 77 ± 6 mmHg, Post: 68 ± 3 mmHg; P < 0.001), C-reactive protein (Pre: 19.4 ± 13.7 nmol/L, Post: 15.2 ± 12.3 nmol/L; P = 0.018), total cholesterol (Pre: 5.4 ± 1.1 mmol/L, Post: 5.0 ± 0.8 mmol/L; P = 0.028), carotid wall thickness (Pre: 0.054 ± 0.005 cm, Post: 0.044 ± 0.005 cm; P = 0.010), and femoral wall thickness (Pre: 0.056 ± 0.009 cm, Post: 0.042 ± 0.005 cm; P = 0.003). FMD significantly improved in HT subjects over time following I/R (Pre: 5.6 ± 2.5%, Post: 9.5 ± 1.7%; P < 0.001). No parameters changed over time in CON, and BMI did not change in either group. These findings indicate that HT reduces sympathetic nerve activity, provides protection from I/R stress, and substantially improves cardiovascular risk profiles in women who are obese with PCOS.

Nanorg Microbial Factories: Light-Driven Renewable Biochemical Synthesis Using Quantum Dot-Bacteria Nanobiohybrids.

Living cells do not interface naturally with nanoscale materials, although such artificial organisms can have unprecedented multifunctional properties, like wireless activation of enzyme function using electromagnetic stimuli. Realizing such interfacing in a nanobiohybrid organism (or nanorg) requires (1) chemical coupling via affinity binding and self-assembly, (2) the energetic coupling between optoelectronic states of artificial materials with the cellular process, and (3) the design of appropriate interfaces ensuring biocompatibility. Here we show that seven different core-shell quantum dots (QDs), with excitations ranging from ultraviolet to near-infrared energies, couple with targeted enzyme sites in bacteria. When illuminated by light, these QDs drive the renewable production of different biofuels and chemicals using carbon-dioxide (CO2), water, and nitrogen (from air) as substrates. These QDs use their zinc-rich shell facets for affinity attachment to the proteins. Cysteine zwitterion ligands enable uptake through the cell, facilitating cell survival. Together, these nanorgs catalyze light-induced air-water-CO2 reduction with a high turnover number (TON) of ∼106-108 (mols of product per mol of cells) to biofuels like isopropanol (IPA), 2,3-butanediol (BDO), C11-C15 methyl ketones (MKs), and hydrogen (H2); and chemicals such as formic acid (FA), ammonia (NH3), ethylene (C2H4), and degradable bioplastics polyhydroxybutyrate (PHB). Therefore, these resting cells function as nanomicrobial factories powered by light.

Sub-cellular location of FtsH proteases in the cyanobacterium Synechocystis sp. PCC 6803 suggests localised PSII repair zones in the thylakoid membranes.

In cyanobacteria and chloroplasts, exposure to HL damages the photosynthetic apparatus, especially the D1 subunit of Photosystem II. To avoid chronic photoinhibition, a PSII repair cycle operates to replace damaged PSII subunits with newly synthesised versions. To determine the sub-cellular location of this process, we examined the localisation of FtsH metalloproteases, some of which are directly involved in degrading damaged D1. We generated transformants of the cyanobacterium Synechocystis sp. PCC6803 expressing GFP-tagged versions of its four FtsH proteases. The ftsH2-gfp strain was functional for PSII repair under our conditions. Confocal microscopy shows that FtsH1 is mainly in the cytoplasmic membrane, while the remaining FtsH proteins are in patches either in the thylakoid or at the interface between the thylakoid and cytoplasmic membranes. HL exposure which increases the activity of the Photosystem II repair cycle led to no detectable changes in FtsH distribution, with the FtsH2 protease involved in D1 degradation retaining its patchy distribution in the thylakoid membrane. We discuss the possibility that the FtsH2-GFP patches represent Photosystem II 'repair zones' within the thylakoid membranes, and the possible advantages of such functionally specialised membrane zones. Anti-GFP affinity pull-downs provide the first indication of the composition of the putative repair zones.

Localisation and interactions of the Vipp1 protein in cyanobacteria.

The Vipp1 protein is essential in cyanobacteria and chloroplasts for the maintenance of photosynthetic function and thylakoid membrane architecture. To investigate its mode of action we generated strains of the cyanobacteria Synechocystis sp. PCC6803 and Synechococcus sp. PCC7942 in which Vipp1 was tagged with green fluorescent protein at the C-terminus and expressed from the native chromosomal locus. There was little perturbation of function. Live-cell fluorescence imaging shows dramatic relocalisation of Vipp1 under high light. Under low light, Vipp1 is predominantly dispersed in the cytoplasm with occasional concentrations at the outer periphery of the thylakoid membranes. High light induces Vipp1 coalescence into localised puncta within minutes, with net relocation of Vipp1 to the vicinity of the cytoplasmic membrane and the thylakoid membranes. Pull-downs and mass spectrometry identify an extensive collection of proteins that are directly or indirectly associated with Vipp1 only after high-light exposure. These include not only photosynthetic and stress-related proteins but also RNA-processing, translation and protein assembly factors. This suggests that the Vipp1 puncta could be involved in protein assembly. One possibility is that Vipp1 is involved in the formation of stress-induced localised protein assembly centres, enabling enhanced protein synthesis and delivery to membranes under stress conditions.

Solar powered biohydrogen production requires specific localization of the hydrogenase.

Cyanobacteria contain a bidirectional [NiFe] hydrogenase which transiently produces hydrogen upon exposure of anoxic cells to light, potentially acting as a "valve" releasing excess electrons from the electron transport chain. However, its interaction with the photosynthetic electron transport chain remains unclear. By GFP-tagging the HoxF diaphorase subunit we show that the hydrogenase is thylakoid associated, comprising a population dispersed uniformly through the thylakoids and a subpopulation localized to discrete puncta in the distal thylakoid. Thylakoid localisation of both the HoxH and HoxY hydrogenase subunits is confirmed by immunogold electron microscopy. The diaphorase HoxE subunit is essential for recruitment to the dispersed thylakoid population, potentially anchoring the hydrogenase to the membrane, but aggregation to puncta occurs through a distinct HoxE-independent mechanism. Membrane association does not require NDH-1. Localization is dynamic on a scale of minutes, with anoxia and high light inducing a significant redistribution between these populations in favour of puncta. Since HoxE is essential for access to its electron donor, electron supply to the hydrogenase depends on a physiologically controlled localization, potentially offering a new avenue to enhance photosynthetic hydrogen production by exploiting localization/aggregation signals.

2-epi-5-epi-Valiolone synthase activity is essential for maintaining phycobilisome composition in the cyanobacterium Anabaena variabilis ATCC 29413 when grown in the presence of a carbon source.

The cyclase 2-epi-5-epi-valiolone synthase (EVS) is reported to be a key enzyme for biosynthesis of the mycosporine-like amino acid shinorine in the cyanobacterium Anabaena variabilis ATCC 29413. Subsequently, we demonstrated that an in-frame complete deletion of the EVS gene had little effect on in vivo production of shinorine. Complete segregation of the EVS gene deletion mutant proved difficult and was achieved only when the mutant was grown in the dark and in a medium supplemented with fructose. The segregated mutant showed a striking colour change from native blue-green to pale yellow-green, corresponding to substantial loss of the photosynthetic pigment phycocyanin, as evinced by combinations of absorbance and emission spectra. Transcriptional analysis of the mutant grown in the presence of fructose under dark or light conditions revealed downregulation of the cpcA gene that encodes the alpha subunit of phycocyanin, whereas the gene encoding nblA, a protease chaperone essential for phycobilisome degradation, was not expressed. We propose that the substrate of EVS (sedoheptulose 7-phosphate) or possibly lack of its EVS-downstream products, represses transcription of cpcA to exert a hitherto unknown control over photosynthesis in this cyanobacterium. The significance of this finding is enhanced by phylogenetic analyses revealing horizontal gene transfer of the EVS gene of cyanobacteria to fungi and dinoflagellates. It is also conceivable that the EVS gene has been transferred from dinoflagellates, as evident in the host genome of symbiotic corals. A role of EVS in regulating sedoheptulose 7-phosphate concentrations in the photophysiology of coral symbiosis is yet to be determined.

Control of electron transport routes through redox-regulated redistribution of respiratory complexes.

In cyanobacteria, respiratory electron transport takes place in close proximity to photosynthetic electron transport, because the complexes required for both processes are located within the thylakoid membranes. The balance of electron transport routes is crucial for cell physiology, yet the factors that control the predominance of particular pathways are poorly understood. Here we use a combination of tagging with green fluorescent protein and confocal fluorescence microscopy in live cells of the cyanobacterium Synechococcus elongatus PCC 7942 to investigate the distribution on submicron scales of two key respiratory electron donors, type-I NAD(P)H dehydrogenase (NDH-1) and succinate dehydrogenase (SDH). When cells are grown under low light, both complexes are concentrated in discrete patches in the thylakoid membranes, about 100-300 nm in diameter and containing tens to hundreds of complexes. Exposure to moderate light leads to redistribution of both NDH-1 and SDH such that they become evenly distributed within the thylakoid membranes. The effects of electron transport inhibitors indicate that redistribution of respiratory complexes is triggered by changes in the redox state of an electron carrier close to plastoquinone. Redistribution does not depend on de novo protein synthesis, and it is accompanied by a major increase in the probability that respiratory electrons are transferred to photosystem I rather than to a terminal oxidase. These results indicate that the distribution of complexes on the scale of 100-300 nm controls the partitioning of reducing power and that redistribution of electron transport complexes on these scales is a physiological mechanism to regulate the pathways of electron flow.

Loss of the SPHF homologue Slr1768 leads to a catastrophic failure in the maintenance of thylakoid membranes in Synechocystis sp. PCC 6803.

BACKGROUND: In cyanobacteria the photosystems are localised to, and maintained in, specialist membranes called the thylakoids. The mechanism driving the biogenesis of the thylakoid membranes is still an open question, with only two potential biogenesis factors, Vipp1 and Alb3 currently identified. METHODOLOGY/PRINCIPAL FINDINGS: We generated a slr1768 knockout using the pGEM T-easy vector and REDIRECT. By comparing growth and pigment content (chlorophyll a fluoresence) of the Δslr1768 mutant with the wild-type, we found that Δslr1768 has a conditional phenotype; specifically under high light conditions (130 µmol m(-2) s(-1)) thylakoid biogenesis is disrupted leading to cell death on a scale of days. The thylakoids show considerable disruption, with loss of both structure and density, while chlorophyll a density decreases with the loss of thylakoids, although photosynthetic efficiency is unaffected. Under low light (30 µmol m(-2) s(-1)) the phenotype is significantly reduced, with a growth rate similar to the wild-type and only a low frequency of cells with evident thylakoid disruption. CONCLUSIONS/SIGNIFICANCE: This is the first example of a gene that affects the maintenance of the thylakoid membranes specifically under high light, and which displays a phenotype dependent on light intensity. Our results demonstrate that Slr1768 has a leading role in acclimatisation, linking light damage with maintenance of the thylakoids.

Evidence for the intense exchange of MazG in marine cyanophages by horizontal gene transfer.

BACKGROUND: S-PM2 is a phage capable of infecting strains of unicellular cyanobacteria belonging to the genus Synechococcus. S-PM2, like other myoviruses infecting marine cyanobacteria, encodes a number of bacterial-like genes. Amongst these genes is one encoding a MazG homologue that is hypothesized to be involved in the adaption of the infected host for production of progeny phage. METHODOLOGY/PRINCIPAL FINDINGS: This study focuses on establishing the occurrence of mazG homologues in other cyanophages isolated from different oceanic locations. Degenerate PCR primers were designed using the mazG gene of S-PM2. The mazG gene was found to be widely distributed and highly conserved among Synechococcus myoviruses and podoviruses from diverse oceanic provinces. CONCLUSIONS/SIGNIFICANCE: This study provides evidence of a globally connected cyanophage gene pool, the cyanophage mazG gene having a small effective population size indicative of rapid lateral gene transfer despite being present in a substantial fraction of cyanophage. The Prochlorococcus and Synechococcus phage mazG genes do not cluster with the host mazG gene, suggesting that their primary hosts are not the source of the mazG gene.

Genetic dissection of the light-inducible carQRS promoter region of Myxococcus xanthus.

In Myxococcus xanthus photoprotective carotenoids are produced in response to illumination due to regulated expression of carotenoid biosynthesis genes at two loci. Induction of the carotenogenesis regulon is dependent on expression of the carQRS operon. The first gene product of the operon, CarQ, is a sigma factor belonging to the ECF family and is responsible for light-dependent initiation of transcription at the carQRS promoter. We defined the minimal carQRS promoter as a 145-bp fragment of DNA upstream of the carQRS transcriptional start site, which includes the promoter for a divergent gene, gufA. In order to elucidate regions with the promoter required for activity, point mutations were introduced into the carQRS promoter between positions -151 and 6. While most sequence changes abolished carQRS promoter activity, two changes enhanced promoter activity and two changes caused the mutant promoter to become constitutive and independent of CarQ. The promoter-null point mutations and 6-bp deletion mutations implied that the carQRS promoter requires a functional gufA promoter for transcriptional activity and vice versa. By mapping the extent of the promoter region, identifying sequences important for promoter activity, and highlighting potential topological effects, we provide a foundation for further analysis of the carQRS promoter.