Exogenous quinones inhibit photosynthetic electron transfer in Chloroflexus aurantiacus by specific quenching of the excited bacteriochlorophyll c antenna.

In the photosynthetic green filamentous bacterium Chloroflexus aurantiacus, excitation energy is transferred from a large bacteriochlorophyll (BChl) c antenna via smaller BChl a antennas to the reaction center. The effects of substituted 1,4-naphthoquinones on BChl c and BChl a fluorescence and on flash-induced cytochrome c oxidation were studied in whole cells under aerobic conditions. BChl c fluorescence in a cell suspension with 5.4 microM BChl c was quenched to 50% by addition of 0.6 microM shikonin ((R)-2-(1-hydroxy-4-methyl-3-pentenyl)-5,8-dihydroxy-1, 4-naphthoquinone), 0.9 microM 5-hydroxy-1,4-naphthoquinone, or 4 microM 2-acetyl-3-methyl-1,4-naphthoquinone. Between 25 and 100 times higher quinone concentrations were needed to quench BChl a fluorescence to a similar extent. These quinones also efficiently inhibited flash-induced cytochrome c oxidation when BChl c was excited, but not when BChl a was excited. The quenching of BChl c fluorescence induced by these quinones correlated with the inhibition of flash-induced cytochrome c oxidation. We concluded that the quinones inhibited electron transfer in the reaction center by specifically quenching the excitation energy in the BChl c antenna. Our results provide a model system for studying the redox-dependent antenna quenching in green sulfur bacteria because the antennas in these bacteria inherently exhibit a sensitivity to O(2) similar to the quinone-supplemented cells of Cfx. aurantiacus.     

Genomic analysis reveals key aspects of prokaryotic symbiosis in the phototrophic consortium “Chlorochromatium aggregatum”

Background

‘Chlorochromatium aggregatum’ is a phototrophic consortium, a symbiosis that may represent the highest degree of mutual interdependence between two unrelated bacteria not associated with a eukaryotic host. ‘Chlorochromatium aggregatum’ is a motile, barrel-shaped aggregate formed from a single cell of ‘Candidatus Symbiobacter mobilis”, a polarly flagellated, non-pigmented, heterotrophic bacterium, which is surrounded by approximately 15 epibiont cells of Chlorobium chlorochromatii, a non-motile photolithoautotrophic green sulfur bacterium.

Results

We analyzed the complete genome sequences of both organisms to understand the basis for this symbiosis. Chl. chlorochromatii has acquired relatively few symbiosis-specific genes; most acquired genes are predicted to modify the cell wall or function in cell-cell adhesion. In striking contrast, ‘Ca. S. mobilis’ appears to have undergone massive gene loss, is probably no longer capable of independent growth, and thus may only reproduce when consortia divide. A detailed model for the energetic and metabolic bases of the dependency of ‘Ca. S. mobilis’ on Chl. chlorochromatii is described.

Conclusions

Genomic analyses suggest that three types of interactions lead to a highly sophisticated relationship between these two organisms. Firstly, extensive metabolic exchange, involving carbon, nitrogen, and sulfur sources as well as vitamins, occurs from the epibiont to the central bacterium. Secondly, ‘Ca. S. mobilis’ can sense and move towards light and sulfide, resources that only directly benefit the epibiont. Thirdly, electron cycling mechanisms, particularly those mediated by quinones and potentially involving shared protonmotive force, could provide an important basis for energy exchange in this and other symbiotic relationships.     

Mutational analysis of three <Emphasis Type="Italic">bchH</Emphasis> paralogs in (bacterio-)chlorophyll biosynthesis in <Emphasis Type="Italic">Chlorobaculum tepidum</Emphasis>

The first committed step in the biosynthesis of (bacterio-)chlorophyll is the insertion of Mg²⁺ into protoporphyrin IX by Mg-chelatase. In all known (B)Chl-synthesizing organisms, Mg-chelatase is encoded by three genes that are homologous to bchH, bchD, and bchI of Rhodobacter spp. The genomes of all sequenced strains of green sulfur bacteria (Chlorobi) encode multiple bchH paralogs, and in the genome of Chlorobaculum tepidum, there are three bchH paralogs, denoted CT1295 (bchT), CT1955 (bchS), and CT1957 (bchH). Cba. tepidum mutants lacking one or two of these paralogs were constructed and characterized. All of the mutants lacking only one of these BchH homologs, as well as bchS bchT and bchH bchT double mutants, which can only produce BchH or BchS, respectively, were viable. However, attempts to construct a bchH bchS double mutant, in which only BchT was functional, were consistently unsuccessful. This result suggested that BchT alone is unable to support the minimal (B)Chl synthesis requirements of cells required for viability. The pigment compositions of the various mutant strains varied significantly. The BChl c content of the bchS mutant was only ~10% of that of the wild type, and this mutant excreted large amounts of protoporphyrin IX into the growth medium. The observed differences in BChl c production of the mutant strains were consistent with the hypothesis that the three BchH homologs function in end product regulation and/or substrate channeling of intermediates in the BChl c biosynthetic pathway. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Dominance of a clonal green sulfur bacterial population in a stratified lake

For many years, the chemocline of the meromictic Lake Cadagno, Switzerland, was dominated by purple sulfur bacteria. However, following a major community shift in recent years, green sulfur bacteria (GSB) have come to dominate. We investigated this community by performing microbial diversity surveys using FISH cell counting and population multilocus sequence typing [clone library sequence analysis of the small subunit (SSU) rRNA locus and two loci involved in photosynthesis in GSB: fmoA and csmCA ]. All bacterial populations clearly stratified according to water column chemistry. The GSB population peaked in the chemocline ( c . 8 × 10⁶ GSB cells mL⁻¹) and constituted about 50% of all cells in the anoxic zones of the water column. At least 99.5% of these GSB cells had SSU rRNA, fmoA , and csmCA sequences essentially identical to that of the previously isolated and genome-sequenced GSB Chlorobium clathratiforme strain BU-1 (DSM 5477). This ribotype was not detected in Lake Cadagno before the bloom of GSB. These observations suggest that the C. clathratiforme population that has stabilized in Lake Cadagno is clonal. We speculate that such a clonal bloom could be caused by environmental disturbance, mutational adaptation, or invasion.     

aAd-p53基因靶向治疗癌性胸腹水的临床效果分析

目的:探讨aAd-p53注射液靶向灌注治疗癌性胸腹水的临床疗效和安全性。方法:选择2012年5月-2014年2月在我院接受治疗的癌性胸腹水患者80例,根据治疗方法的不同,将患者随机分为研究组和对照组,每组40例。研究组患者采用腔内灌注rAd-p53治疗,对照组患者采用表阿霉素灌注治疗,观察并比较两组患者的治疗总有效率、不良反应的发生率及KPS功能评分的变化情况。结果:所有患者均顺利完成灌注治疗,病情获得好转,生存质量得到改善。研究组和对照组的治疗总有效率分别为70%、67.5%,两组比较无显著性差异(P0.05)。两组治疗后KPS评分均显著高于治疗前,且研究组高于对照组,差异具有统计学意义(P0.05)。研究组和对照组不良反应的发生率分别为20%和25%,研究组低于对照组,但两组差异并无统计学意义(P0.05)。结论:rAd-p53注射液靶向灌注治疗是一种治疗癌性胸腹水安全有效的方法,值得临床推广。     

春尺蠖蛹雌雄外部形态特征快速鉴别分析

为依据春尺蠖Apocheima cinerarius Erschoff蛹的形态特征快速、无损、准确鉴别雌雄个体,对其头部、胸部、腹部和体色外部鉴别特征进行了分析,并通过解剖生殖系统验证准确性.结果表明:以春尺蠖蛹的胸部和腹部特征识别雌雄准确率明显高于头部和体色特征,识别率可达100％.首先,雌蛹第8腹节腹板前缘中部具有"Y"型沟,与第7腹节腹板后缘形成倒三角状,而雄蛹无此特征.其次,雌蛹生殖孔与产卵孔连接形成裂缝,两侧平坦无突起,而雄蛹第9腹节腹板中央有一纵裂缝的生殖孔,两侧各有半圆状瘤状突起.最后,雌蛹的胸部背板各节间相对长度均小于雄蛹,而雄蛹中胸背板最宽,其后缘明显向外凸起.因此,春尺蠖蛹胸部或腹部特征可用于快速、准确地鉴别雌雄性别.     

Enemy release or invasional meltdown? Deer preference for exotic and native trees on Isla Victoria,Argentina

Abstract How interactions between exotic species affect invasion impact is a fundamental issue on both theoretical and applied grounds. Exotics can facilitate establishment and invasion of other exotics (invasional meltdown) or they can restrict them by re‐establishing natural population control (as predicted by the enemy‐release hypothesis). We studied forest invasion on an Argentinean island where 43 species of Pinaceae, including 60% of the world's recorded invasive Pinaceae, were introduced c. 1920 but where few species are colonizing pristine areas. In this area two species of Palearctic deer, natural enemies of most Pinaceae, were introduced 80 years ago. Expecting deer to help to control the exotics, we conducted a cafeteria experiment to assess deer preferences among the two dominant native species (a conifer, Austrocedrus chilensis, and a broadleaf, Nothofagus dombeyi) and two widely introduced exotic tree species (Pseudotsuga menziesii and Pinus ponderosa). Deer browsed much more intensively on native species than on exotic conifers, in terms of number of individuals attacked and degree of browsing. Deer preference for natives could potentially facilitate invasion by exotic pines. However, we hypothesize that the low rates of invasion currently observed can result at least partly from high densities of exotic deer, which, despite their preference for natives, can prevent establishment of both native and exotic trees. Other factors, not mutually exclusive, could produce the observed pattern. Our results underscore the difficulty of predicting how one introduced species will effect impact of another one.     

Chlorobium Tepidum: Insights into the Structure,Physiology, and Metabolism of a Green Sulfur Bacterium Derived from the Complete Genome Sequence

Green sulfur bacteria are obligate, anaerobic photolithoautotrophs that synthesize unique bacteriochlorophylls (BChls) and a unique light-harvesting antenna structure, the chlorosome. One organism, Chlorobium tepidum, has emerged as a model for this group of bacteria primarily due to its relative ease of cultivation and natural transformability. This review focuses on insights into the physiology and biochemistry of the green sulfur bacteria that have been derived from the recently completed analysis of the 2.15-Mb genome of Chl. tepidum. About 40 mutants of Chl. tepidum have been generated within the last 3 years, most of which have been made based on analyses of the genome. This has allowed a nearly complete elucidation of the biosynthetic pathways for the carotenoids and BChls in Chl. tepidum, which include several novel enzymes specific for BChl c biosynthesis. Facilitating these analyses, both BChl c and carotenoid biosynthesis can be completely eliminated in Chl. tepidum. Based particularly on analyses of mutants lacking chlorosome proteins and BChl c, progress has also been made in understanding the structure and biogenesis of chlorosomes. In silico analyses of the presence and absence of genes encoding components involved in electron transfer reactions and carbon assimilation have additionally revealed some of the potential physiological capabilities, limitations, and peculiarities of Chl. tepidum. Surprisingly, some structural components and biosynthetic pathways associated with photosynthesis and energy metabolism in Chl. tepidum are more similar to those in cyanobacteria and plants than to those in other groups of photosynthetic bacteria.     

Molecular contacts for chlorosome envelope proteins revealed by cross-linking studies with chlorosomes from Chlorobium tepidum

Chlorosomes are unique light-harvesting antennae found in two phyla of green bacteria: Chlorobi and Chloroflexi. In the green sulfur bacterium Chlorobium tepidum, 10 proteins (CsmA, CsmB, CsmC, CsmD, CsmE, CsmF, CsmH, CsmI, CsmJ, and CsmX) exist in the chlorosome envelope. Chlorosomes from the wild type and mutants lacking a single chlorosome protein were cross-linked with the zero-length cross-linker 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) and analyzed by gel electrophoresis. Similar cross-linking products were observed when the time and temperature were varied or when EDC was replaced with glutaraldehyde. Specific interactions between chlorosome proteins in cross-linked products were identified by immunoblotting with polyclonal antibodies raised against recombinant chlorosome proteins. We confirmed these interactions by demonstrating that these products were missing in appropriate mutants. Confirming the location of CsmA in the paracrystalline baseplate, cross-linking showed that CsmA forms dimers, trimers, and homomultimers as large as dodecamers and that CsmA directly interacts with the Fenna-Matthews-Olson protein. Cross-linking further suggests that the precursor form of CsmA is inserted near the edges of the baseplate, where CsmA and pre-CsmA interact with CsmB and CsmF. Several chlorosome proteins, including CsmA, CsmC, CsmD, CsmH, CsmI, CsmJ, and CsmX, were shown to exist as homomultimers in the chlorosome envelope. On the basis of the structural information obtained from these cross-linking experiments, a model for the locations and interactions of the proteins of the chlorosome envelope is proposed.     

Prokaryotic photosynthesis and phototrophy illuminated

Genome sequencing projects are revealing new information about the distribution and evolution of photosynthesis and phototrophy. Although coverage of the five phyla containing photosynthetic prokaryotes (Chlorobi, Chloroflexi, Cyanobacteria, Proteobacteria and Firmicutes) is limited and uneven, genome sequences are (or soon will be) available for >100 strains from these phyla. Present knowledge of photosynthesis is almost exclusively based on data derived from cultivated species but metagenomic studies can reveal new organisms with novel combinations of photosynthetic and phototrophic components that have not yet been described. Metagenomics has already shown how the relatively simple phototrophy based upon rhodopsins has spread laterally throughout Archaea, Bacteria and eukaryotes. In this review, we present examples that reflect recent advances in phototroph biology as a result of insights from genome and metagenome sequencing.