Exploitation of N2-fixation capacity for enrichment of anoxygenic photosynthetic bacteria in ecological studies

Abstract A procedure is described for the selective enrichment of anoxygenic photosynthetic bacteria from diverse natural sources containing numerous types of microorganisms. The enrichment medium contains a mixture of organic acid carbon sources, and the conditions used favor the growth of organisms that can multiply relatively rapidly anaerobically with N₂ as the nitrogen source and light as the source of growth energy; the development of oxygenic cyanobacteria is effectively excluded.     

Photosynthetic Units of Phototrophic Organisms

Photoautotrophic organisms play a key role in the biosphere of the Earth, converting solar energy of the 350-1000 nm range into biochemically available form. In contemporary aquatic and terrestrial ecosystems, the dominating groups are the oxygen evolving cyanobacteria, algae, and higher plants. Anoxygenic phototrophic microorganisms occupy mainly ecological niches with extreme environmental conditions. Despite diverse evolution of all these taxonomic groups, their photosynthetic apparatus has a similar molecular design and identical principles of operation. This review covers recent data about features of the structural and functional organization of pigment-protein complexes of the basic types of photosynthetic units in prokaryotes and eukaryotes. A correspondence between the optical properties of various photosynthetic units and the natural light conditions is discussed.     

NADPH thioredoxin reductase C is localized in plastids of photosynthetic and nonphotosynthetic tissues and is involved in lateral root formation in Arabidopsis

Plastids are organelles present in photosynthetic and nonphotosynthetic plant tissues. While it is well known that thioredoxin-dependent redox regulation is essential for leaf chloroplast function, little is known of the redox regulation in plastids of nonphotosynthetic tissues, which cannot use light as a direct source of reducing power. Thus, the question remains whether redox regulation operates in nonphotosynthetic plastid function and how it is integrated with chloroplasts for plant growth. Here, we show that NADPH-thioredoxin reductase C (NTRC), previously reported as exclusive to green tissues, is also expressed in nonphotosynthetic tissues of Arabidopsis thaliana, where it is localized to plastids. Moreover, we show that NTRC is involved in maintaining the redox homeostasis of plastids also in nonphotosynthetic organs. To test the relationship between plastids of photosynthetic and nonphotosynthetic tissues, transgenic plants were obtained with redox homeostasis restituted exclusively in leaves or in roots, through the expression of NTRC under the control of organ-specific promoters in the ntrc mutant. Our results show that fully functional root amyloplasts are not sufficient for root, or leaf, growth, but fully functional chloroplasts are necessary and sufficient to support wild-type rates of root growth and lateral root formation.     

Dynamical localization of a thylakoid membrane binding protein is required for acquisition of photosynthetic competency

Vipp1 is highly conserved and essential for photosynthesis, but its function is unclear as it does not participate directly in light‐dependent reactions. We analyzed Vipp1 localization in live cyanobacterial cells and show that Vipp1 is highly dynamic, continuously exchanging between a diffuse fraction that is uniformly distributed throughout the cell and a punctate fraction that is concentrated at high curvature regions of the thylakoid located at the cell periphery. Experimentally perturbing the spatial distribution of Vipp1 by relocalizing it to the nucleoid causes a severe growth defect during the transition from non‐photosynthetic (dark) to photosynthetic (light) growth. However, the same perturbation of Vipp1 in dark alone or light alone growth conditions causes no growth or thylakoid morphology defects. We propose that the punctuated dynamics of Vipp1 at the cell periphery in regions of high thylakoid curvature enable acquisition of photosynthetic competency, perhaps by facilitating biogenesis of photosynthetic complexes involved in light‐dependent reactions of photosynthesis.     

The role of crown architecture, leaf phenology and photosynthetic activity in promoting complementary use of light among coexisting species in temperate forests

Mixed forests comprising multiple tree species with contrasting crown architectures, leaf phenologies, and photosynthetic activity, tend to have high ecosystem productivity. We propose that in such forests, differentiation among coexisting species in their spatial and temporal strategies for light interception, results in complementary use of light. Spatial differentiation among coexisting tree species occurs as a result of adaptation of crown architecture and shoot/leaf morphology to the spatially variable light conditions of the canopy, sub-canopy, and understory. Temporal differentiation occurs as a result of variation in leaf phenology and photosynthetic activity. The arrangement of leaves in both space and time is an important aspect of plant strategies for light interception and determines photosynthetic carbon gain of the plant canopy. For example, at the shoot level, morphological and phenological differentiation between long and short shoots reflects their respective shoot functions, indicating that spatial and temporal strategies for light interception are linked. Complementary use of light is a consequence of the spatiotemporal differentiation in light interception among coexisting species. Because coexisting species may show differentiation in strategies for resource acquisition (functional diversification) or convergence with respect to some limiting resource (functional convergence), the relative importance of various crown functions and their contribution to growth and survival of individuals need to be evaluated quantitatively and compared among coexisting species.     

光照混菌培养应用研究进展

光合细菌与其他微生物在光照条件下混合培养是近年来的研究热点。综述了光照混菌培养的特点和目前光照混菌培养在水体净化、生物制氢和高价值物质生产方面的应用,并对影响混合菌株生长代谢与繁殖的因素做了总结。分析表明菌株之间存在的相互协同共生作用能促进微生物的生长繁殖,使底物被充分利用,提高物质产率。光照混菌培养工艺简单、成本较低,在水体净化、生物制氢、高价值物质生产方面的应用具有相当好的效果。在影响因素中对混合培养影响最大的因素是菌株接种量、接种比和培养基pH。在总结光照混菌培养应用现存不足的基础上,对其发展前景作出展望。     

茄子嫁接苗与自根苗光合特性比较

对茄子嫁接苗与自根苗的光合生理特性进行了比较研究。结果表明,不同时期嫁接苗功能叶片的净光合速率（Pn）均显著高于自根苗;茄子嫁接苗与自根苗功能叶片的Pn日变化均呈“双峰”曲线,但嫁接苗的“午休”程度较自根苗轻;嫁接苗比自根苗有较低的光补偿点（LCP）和CO2补偿点（CCP）,较高的光饱和点（LSP）和CO2饱和点（CSP）;有较低的光合冷限温度和较高的光合热限温度,光合最适温度两者之间没有明显的差别;有较高的光饱和、CO2饱和及最适温度时的Pn;嫁接苗Pn高是因为嫁接苗胞间的光合反应的底物浓度大（Ci高）,表观量子效率（AQY）、羧化效率（CE）和光合能力（A350）高的缘故。     

Light inside sponges

Sponges are the most basal metazoan organisms. As sessile filter feeders in marine or freshwater habitats, they often live in close association with phototrophic microorganisms. Active photosynthesis by the associated microorganisms has been believed to be restricted to the outer tissue portion of the sponge hosts. However, phototrophic microorganisms have also been detected in deeper tissue regions. In many cases they are found around spicules, siliceous skelettal elements of demosponges and hexactinellids. The finding of phototrophic organisms seemingly assembled around spicules led to the hypothesis of a siliceous light transmission system in sponges. The principle ability to conduct light was already shown for sponge derived, explanted spicules. However it was not shown until now, that in deed sponges have a light transmission system, and can harbour photosynthetically active microorganisms in deeper tissue regions.Here we show for the first time, that, as hypothesized 13 year ago, sponge spicules in living specimens transmit light into deeper tissue regions. Our results demonstrate that in opposite to the actual opinion, photosynthetically active microorganisms can also live in deeper tissue regions, and not only directly beneath the surface, when a light transmission system (spicules) is present.Our results show the possibility of massive or globular sponges being supplied with photosynthetic products or pathways throughout their whole body, implying not only a more important role of these endobioses. Our findings also elucidate the in-situ function of a recently more and more interesting biomaterial, which is unique not only for its mechanical, electrical and optical properties. Biosilica is of special interest for the possibility to produce it enzymatically under environmental conditions.     

Thermal acclimation of photosynthesis: on the importance of adjusting our definitions and accounting for thermal acclimation of respiration

While interest in photosynthetic thermal acclimation has been stimulated by climate warming, comparing results across studies requires consistent terminology. We identify five types of photosynthetic adjustments in warming experiments: photosynthesis as measured at the high growth temperature, the growth temperature, and the thermal optimum; the photosynthetic thermal optimum; and leaf-level photosynthetic capacity. Adjustments of any one of these variables need not mean a concurrent adjustment in others, which may resolve apparently contradictory results in papers using different indicators of photosynthetic acclimation. We argue that photosynthetic thermal acclimation (i.e., that benefits a plant in its new growth environment) should include adjustments of both the photosynthetic thermal optimum (T _opt) and photosynthetic rates at the growth temperature (A _growth), a combination termed constructive adjustment. However, many species show reduced photosynthesis when grown at elevated temperatures, despite adjustment of some photosynthetic variables, a phenomenon we term detractive adjustment. An analysis of 70 studies on 103 species shows that adjustment of T _opt and A _growth are more common than adjustment of other photosynthetic variables, but only half of the data demonstrate constructive adjustment. No systematic differences in these patterns were found between different plant functional groups. We also discuss the importance of thermal acclimation of respiration for net photosynthesis measurements, as respiratory temperature acclimation can generate apparent acclimation of photosynthetic processes, even if photosynthesis is unaltered. We show that while dark respiration is often used to estimate light respiration, the ratio of light to dark respiration shifts in a non-predictable manner with a change in leaf temperature.     

Structure and function of developing barley plastids

Five different regions of the first foliage leaf of etiolated barley seedlings were studied with respect to leaf growth, plastid growth and replication, differentiation of etioplasts, and conversion of etioplasts into chloroplasts upon illumination. Ultrastructural changes of the plastids were correlated with chlorophyll synthesis and development of photosynthetic activity as measured by (14)CO(2) incorporation and O(2) evolution. The first foliage leaf has greater linear growth over a longer period of time in the dark than in the light. Only the bottom two regions (4 and 5) are still growing in the 5-day etiolated leaf. Region 4 grows by cell elongation, and region 5 grows by both cell division and elongation. Plastids in all five regions of the leaf are capable of enlarging when exposed to light. This is true both for the intact plant and for excised sections. Plastid replication occurs predominantly in the younger regions of the leaf (regions 3, 4, and 5). The amount of chlorophyll synthesized by different regions in the intact plant is significantly higher (3-40 times) than that made by excised sections. Ultrastructural changes occurring in each region when excised sections are illuminated were classified into five stages involving increased membrane synthesis and appression into grana, and these changes were correlated with the first appearance of photosynthetic activity. The earliest detectable photosynthetic activity occurs in region 1 after 2 hours of illumination when chloroplasts show only a few overlaps in the thylakoids. Plastids in younger regions of the leaf require up to 24 hours of light to form grana and develop photosynthetic activity. Plastids in each region of the leaf are in different stages of development when photosynthesis is initiated, indicating that development of photosynthetic activity is not strictly correlated with a certain stage of plastid development. Membrane appression is not indicative of photosynthetic activity since overlaps are formed in the dark, but it was always present when photosynthetic activity was detectable. Likewise, there does not appear to be any strict correlation between the presence of chlorophyll and membrane appression. These results show that the particular structural and functional correlations that can be made depend to a large degree on age of the tissue.     

Effect of Photosynthetic Bacteria and Compost on Degradation of Petroleum Products in Soil

Addition of diesel fuel and waste engine oil to soil was found to stimulate hydrocarbon-oxidizing microorganisms. Corynebacteria constitute a large group of hydrocarbon-oxidizing microorganisms. Addition of a liquid culture of photosynthetic bacteria to soil facilitates degradation of petroleum products and also stimulates growth of hydrocarbon-oxidizing microorganisms. Combined addition of photosynthetic bacteria and compost to soil polluted with petroleum products produces a greater increase in the number of hydrocarbon-oxidizing bacteria and substantially augments the rate of pollutant degradation.     

Genome-scale modeling of light-driven reductant partitioning and carbon fluxes in diazotrophic unicellular cyanobacterium Cyanothece sp. ATCC 51142

Genome-scale metabolic models have proven useful for answering fundamental questions about metabolic capabilities of a variety of microorganisms, as well as informing their metabolic engineering. However, only a few models are available for oxygenic photosynthetic microorganisms, particularly in cyanobacteria in which photosynthetic and respiratory electron transport chains (ETC) share components. We addressed the complexity of cyanobacterial ETC by developing a genome-scale model for the diazotrophic cyanobacterium, Cyanothece sp. ATCC 51142. The resulting metabolic reconstruction, iCce806, consists of 806 genes associated with 667 metabolic reactions and includes a detailed representation of the ETC and a biomass equation based on experimental measurements. Both computational and experimental approaches were used to investigate light-driven metabolism in Cyanothece sp. ATCC 51142, with a particular focus on reductant production and partitioning within the ETC. The simulation results suggest that growth and metabolic flux distributions are substantially impacted by the relative amounts of light going into the individual photosystems. When growth is limited by the flux through photosystem I, terminal respiratory oxidases are predicted to be an important mechanism for removing excess reductant. Similarly, under photosystem II flux limitation, excess electron carriers must be removed via cyclic electron transport. Furthermore, in silico calculations were in good quantitative agreement with the measured growth rates whereas predictions of reaction usage were qualitatively consistent with protein and mRNA expression data, which we used to further improve the resolution of intracellular flux values.     

Effect of photosynthetic bacteria and compost on degradation of petroleum products in soil

Addition of diesel fuel and waste engine oil to soil was found to cause biostimulation of hydrocarbon-oxidizing microorganisms. Corynebacteria constitute a large group of hydrocarbon-oxidizing microorganisms. Addition of a liquid culture of photosynthetic bacteria to soil not only facilitates degradation of petroleum products, but also stimulates growth of hydrocarbon-oxidizing microorganisms. Combined addition of photosynthetic bacteria and compost to soil polluted with petroleum products causes even a more significant increase in the count of hydrocarbon-oxidizing bacteria and substantially increases the rate of pollutant degradation.     

Light Intensity and Substrate Availability in Relation to Tracheid Development in Picea sitchensis

Assimilation and growth of Picea sitchensis seedlings maintainedat three light intensities were examined in relation to previously-reporteddata on tracheid development in this species. Increases in photosynthetic efficiency with decreased lightlevel failed to compensate completely for reduced total amountsof incident radiation as judged from assimilate distributionpattern and growth rate. Incorporation of assimilate into reservesand new growth declined with decreased light level, while theextent of turnover materials generally increased. Most treatment differences in relative dry weight distributionappeared to result from a combination of differences in growthrate and changes in growth pattern. The proportion of dry weightin branches and roots increased with increased light intensitywhile that in stems and the hypocotyl decreased At the two highest light levels tested, both absolute stem growthrate and total wall accumulation appeared to be independentof substrate availability. This situation contrasts with thatobserved in older material and it is suggested that the initialindependence reflects the temporary existence of a high ratioof functional foliage to stem and cambial material during thefirst year of growth. Since tracheid diameter showed a consistent, positive relationshipwith assimilate status, it is suggested that substrate levelcan exert an important modifying influence on cell expansion.     

微藻三酰甘油合成途径及其最新研究进展

三酰甘油(triacylglycerols,TAGs)是动物、植物、微生物和微藻细胞主要的储藏性脂类,它可应用于食品、轻工业和生物燃料等方面,是一种新型可再生能源——生物柴油生产的重要原料。与高等油料作物相比,微藻具有光合作用效率高、生长速度快、油脂产量高、不占用农业耕地和适应多种生长环境等优势,是一种潜在的新型生物柴油生产原料。然而,目前人们对有机体,尤其是微藻细胞内TAG合成与积累的分子机制及细胞的代谢调控机制还知之甚少。对TAG合成的一系列重要过程,包括脂肪酸的合成,TAG生物合成的主要途径和旁路途径,以及与TAG合成相关的关键酶和重要基因等进行了综述,特别对微藻细胞中与TAG合成相关的关键基因的最新研究进展进行了总结,旨在更好地了解油脂代谢的调控途径,为最大限度地供应生物柴油的生产原料提供理论基础。     

Photosynthetic plasticity of Phalaenopsis in response to different light environments

The ability of a plant to dynamically acclimate to different light environments is, in general, genetically determined. Phalaenopsis amabilis is a CAM orchid with heavy self-shading. The aim of this study was to find out how the photosynthetic capacity of its mature lower leaves acclimates to the low light environment, and whether it possessed a potential for reacclimation following transfer of lower leaves to higher irradiance. We found that the photosynthetic performance of the leaves of Phalaenopsis was flexibly and reversibly adjusted to growth irradiance, making it possible to improve the light environment of the plant by increasing light exposure of lower leaves and bring about a higher photosynthetic production. We have tested the effectiveness of a simple setup using mirrors to augment light from the side and thus enhanced the irradiance in the shaded area of the plant. Both photosynthesis and starch contents of leaves as well as the number of flowers per plant increased greatly.     

Review: the Antarctic Chlamydomonas raudensis: an emerging model for cold adaptation of photosynthesis

Permanently cold habitats dominate our planet and psychrophilic microorganisms thrive in cold environments. Environmental adaptations unique to psychrophilic microorganisms have been thoroughly described; however, the vast majority of studies to date have focused on cold-adapted bacteria. The combination of low temperatures in the presence of light is one of the most damaging environmental stresses for a photosynthetic organism: in order to survive, photopsychrophiles (i.e. photosynthetic organisms adapted to low temperatures) balance temperature-independent reactions of light energy capture/transduction with downstream temperature-dependent metabolic processes such as carbon fixation. Here, we review research on photopsychrophiles with a focus on an emerging model organism, Chlamydomonas raudensis UWO241 (UWO241). UWO241 is a psychrophilic green algal species and is a member of the photosynthetic microbial eukaryote community that provides the majority of fixed carbon for ice-covered lake ecosystems located in the McMurdo Dry Valleys, Antarctica. The water column exerts a range of environmental stressors on the phytoplankton community that inhabits this aquatic ecosystem, including low temperatures, extreme shade of an unusual spectral range (blue-green), high salinity, nutrient deprivation and extremes in seasonal photoperiod. More than two decades of work on UWO241 have produced one of our most comprehensive views of environmental adaptation in a cold-adapted, photosynthetic microbial eukaryote.     

玉米-花生间作对作物产量和光合作用光响应的影响

研究了玉米-花生间作对玉米、花生经济产量及功能叶片光合作用光响应的影响.结果表明：间作体系总体表现出明显的产量优势,2004和2005年分别为2 896和2 894 kg·hm^-2,土地利用率提高了14%～17%;玉米-花生间作提高了玉米功能叶片的光饱和点、光补偿点和强光时的光合速率,降低了花生功能叶片的光补偿点和光饱和点,但提高了花生表观量子效率和弱光时的光合速率.表明间作提高了玉米对强光和花生对弱光的利用能力,从而使间作体系表现出明显的产量优势.     

Inactivation of a predicted leader peptidase prevents photoautotrophic growth of Synechocystis sp. strain PCC 6803

To establish the role of the two putative type I leader peptidases (LepB1 and LepB2) encoded in the genome of the cyanobacterium Synechocystis sp. strain PCC 6803, we generated independent knockout mutants for both genes by introducing kanamycin resistance cassettes into the two open reading frames (sll0716 [lepB1] and slr1377 [lepB2], respectively). Although the insertion was successful in both instances, it was not possible to select homozygous mutant cells for lepB2, suggesting that the function of this gene is essential for cell viability. In contrast, LepB1 is apparently essential only for photoautotrophic growth, because homozygous lepB1::Km(r) cells could be propagated under heterotrophic conditions. They were even capable to some extent of photosynthetic oxygen evolution. However, the photosynthetic activity decreased gradually with extended incubation in the light and was particularly affected by high light intensities. Both features were indicative of photooxidative damage, which was probably caused by inefficient replacement of damaged components of the photosynthetic machinery due to the lack of a leader peptidase removing the signal peptides from photosynthetic precursor proteins. Indeed, processing of the PsbO precursor polypeptide to the corresponding mature protein was significantly affected in the mutant, and reduced amounts of other proteins that are synthesized as precursors with signal peptides accumulated in the cells. These results strongly suggest that LepB1 is important for removal of the signal peptides after membrane transport of the components of the photosynthetic machinery, which in turn is a prerequisite for the biogenesis of a functional photosynthetic electron transport chain.     

Effects of Red and Blue LED Light on the Growth and Photosynthesis of Barley (Hordeum vulgare L.) Seedlings

According to the action spectrum of photosynthesis, photosynthetic efficiency is highest for red light. However, long-term growth with only red light leads to unfavorable changes in plant morphology, decrease in photosynthetic capacity and plant productivity. Detailed mechanisms behind these changes are still poorly understood. We studied the effects of narrow-band red (RL) and blue (BL) LED lighting on the morphology and photosynthesis of barley (Hordeum vulgare L.) seedlings at 9 days old, when energy for plant growth comes mostly from the endosperm, and light has a mainly morphogenic effect on plant growth. Plants grown with white fluorescent lamps (WL) were used as a control. At this developmental stage, light spectrum had small but significant effects on most morphometric parameters, which may become more prominent as the plant grows. These effects were more pronounced in RL-grown plants and were similar to the ‘shade-avoidance response’, which is unusual as in nature it occurs when the fraction of red light in the spectrum is low. RL-grown plants also had impaired photosynthetic photochemical efficiency (as assessed by PAM-fluorometry and leaf absorption). BL-grown plants had a stronger similarity to control plants in their morphology and photosynthetic characteristics than RL-grown plants; however, they had higher NPQ and different NPQ induction kinetics than WL- and RL-grown plants. Our results suggest that photoregulation of plant morphology and photosynthesis evolutionarily adapted to natural light is miscoordinated in narrow-band LED light. We discuss possible reasons for this miscoordination and for the formation of observed phenotypes on the level of photoreceptors.