Biosynthesis and control of beta-lactam antibiotics: the early steps in the "classical" tripeptide pathway

The interaction between growth and secondary metabolism develops from physiological responses of the producer organism to its environment. Nutrients are channelled into primary growth processes or into secondary processes such as antibiotic biosynthesis by a variety of metabolic controls, the nature of which has been extensively studied in organisms producing beta-lactam antibiotics via the tripeptide, delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine. In the following article we review the early stages of beta-lactam biosynthesis in fungi and actinomycetes, keeping in mind the regulation of primary pathways that provide the amino acid precursors of this group of antibiotics, as well as the regulation of the secondary pathway itself. Of special importance to organisms engaging in secondary metabolism are the control mechanisms that suppress the nonessential process during rapid growth but allow secondary metabolic genes to be expressed and resources to be diverted when environmental factors generate the appropriate biochemical signals.     

Sekundärstoffe – die Geheimwaffen der Pflanzen

Secondary metabolites Already 400 million years ago when land plants evolved, they probably produced secondary metabolites as means of defence against herbivores, microbes and competing plants. Secondary metabolites usually are bioactive agents, which can interfere with molecular targets in animals and microbes. Therefore, many plants and substances isolated from them can serve as valuable drugs in medicine and pharmacy. Some secondary metabolites also serve as signal compounds to attract pollinating animals and seed‐dispersing animals, but also for UV protection, as antioxidants or mobile nitrogen stores. Biology and evolution but also physiological and genetic bases of secondary metabolism are discussed in this overview.     

Critical analysis of protein signaling networks involved in the regulation of plant secondary metabolism: focus on anthocyanins

Anthocyanin biosynthesis in Arabidopsis is a convenient and relatively simple model for investigating the basic principles of secondary metabolism regulation. In recent years, many publications have described links between anthocyanin biosynthesis and general defense reactions in plants as well as photomorphogenesis and hormonal signaling. These relationships are complex, and they cannot be understood intuitively. Upon observing the lacuna in the Arabidopsis interactome (an interaction map of the factors involved in the regulation of Arabidopsis secondary metabolism is not available), we attempted to connect various cellular processes that affect anthocyanin biosynthesis. In this review, we revealed the main signaling protein modules that regulate anthocyanin biosynthesis. To our knowledge, this is the first reconstruction of a network of proteins involved in plant secondary metabolism.     

Secondary metabolism and pathophysiology

Mechanisms of regulation of biosynthesis of secondary metabolites in microorganisms under natural conditions differ from the regulation mechanisms resulting in an overproduction of these metabolites in industrial fermentations. The overproduction is attained by creating pathophysiological cultivation conditions and by using mutant strains which differ substantially from wild strains isolated from natural environment.     

Trichome regulator SlMIXTA‐like directly manipulates primary metabolism in tomato fruit

Trichomes are storage compartments for specialized metabolites in many plant species. In trichome, plant primary metabolism is significantly changed, providing substrates for downstream secondary metabolism. However, little is known of how plants coordinate trichome formation and primary metabolism regulation. In this report, tomato (Solanum lycopersicum) trichome regulator SlMIXTA‐like is indicated as a metabolic regulation gene by mGWAS analysis. Overexpression of SlMIXTA‐like in tomato fruit enhances trichome formation. In addition, SlMIXTA‐like can directly bind to the promoter region of gene encoding 3‐deoxy‐7‐phosphoheptulonate synthase (SlDAHPS) to activate its expression. Induction of SlDAHPS expression enhances shikimate pathway activities and provides substrates for downstream secondary metabolism. Our data provide direct evidence that trichome regulator can directly manipulate primary metabolism, in which way plants can coordinate metabolic regulation and the formation of storage compartments for specialized metabolites. The newly identified SlMIXTA‐like can be used for future metabolic engineering.     

链霉菌次级代谢调控相关的双组分系统研究进展

链霉菌具有强大的次级代谢能力, 能够产生众多具有生物活性的次级代谢产物, 如目前广泛应用的抗生素、抗肿瘤药物以及免疫抑制剂等。在链霉菌中, 次级代谢产物的生物合成受到包括途径特异性、多效性以及全局性调控基因在内的多层次严格调控。关键调控基因的缺失或过表达可以显著影响次级代谢产物的生物合成, 提示对于链霉菌次级代谢重要调控基因的功能及其作用机制的研究具有巨大的潜在应用价值。其中, 作为细菌信号传导系统的双组分系统(Two-component system, TCS)一直是大家研究的关注点。越来越多的研究表明TCS在链霉菌次级代谢过程中发挥着全局性的调控功能。本文重点介绍链霉菌模式菌株——天蓝色链霉菌中TCS(包括典型TCS)、孤立的组氨酸蛋白激酶(HK)以及应答调控蛋白(RR)参与次级代谢调控的研究进展。这些TCS的功能鉴定及机制解析为工业链霉菌的定向遗传改造以提高重要次级代谢产物的含量提供了理论依据。     

Quantitative <Superscript>1</Superscript>H NMR metabolomics reveals extensive metabolic reprogramming of primary and secondary metabolism in elicitor-treated opium poppy cell cultures

Background  

Opium poppy (Papaver somniferum) produces a diverse array of bioactive benzylisoquinoline alkaloids and has emerged as a model system to study plant alkaloid metabolism. The plant is cultivated as the only commercial source of the narcotic analgesics morphine and codeine, but also produces many other alkaloids including the antimicrobial agent sanguinarine. Modulations in plant secondary metabolism as a result of environmental perturbations are often associated with the altered regulation of other metabolic pathways. As a key component of our functional genomics platform for opium poppy we have used proton nuclear magnetic resonance (¹H NMR) metabolomics to investigate the interplay between primary and secondary metabolism in cultured opium poppy cells treated with a fungal elicitor.     

Coupling kinetic expressions and metabolic networks for predicting wine fermentations

Problematic fermentations are commonplace and cause wine industry producers substantial economic losses through wasted tank capacity and low value final products. Being able to predict such fermentations would enable enologists to take preventive actions. In this study we modeled sugar uptake kinetics and coupled them to a previously developed stoichiometric model, which describes the anaerobic metabolism of Saccharomyces cerevisiae. The resulting model was used to predict normal and slow fermentations under winemaking conditions. The effects of fermentation temperature and initial nitrogen concentration were modeled through an efficiency factor incorporated into the sugar uptake expressions. The model required few initial parameters to successfully reproduce glucose, fructose, and ethanol profiles of laboratory and industrial fermentations. Glycerol and biomass profiles were successfully predicted in nitrogen rich cultures. The time normal or slow wine fermentations needed to complete the process was predicted accurately, at different temperatures. Simulations with a model representing a genetically modified yeast fermentation, reproduced qualitatively well literature results regarding the formation of minor compounds involved in wine complexity and aroma. Therefore, the model also proves useful to explore the effects of genetic modifications on fermentation profiles.     

Renaissance der Oberflächenkultur: Produktion von Mutterkornalkaloiden und Sporenbildung

Industrially acceptable production of ergot alkaloids in surface culture under sterile conditions is described. After elucidation of the biochemical and morphological differentiation in the production microorganisms it is possible to elaborate a relatively simple cultivation method with good yields. Surface cultivation is especially advantageous for the production of spores in large quantities which are used as inoculum in industrial fermentations or as infection material (field production of ergot alkaloids, mycoinsecticides).     

植物次生代谢基因工程研究进展

随着对植物代谢网络日渐全面的认识,应用基因工程技术对植物次生代谢途径进行遗传改良已取得了可喜的进展.对次生代谢途径进行基因修饰的策略包括:导入单个、多个靶基因或一个完整的代谢途径,使宿主植物合成新的目标物质;通过反义RNA和RNA干涉等技术降低靶基因的表达水平,从而抑制竞争性代谢途径,改变代谢流和增加目标物质的含量;对控制多个生物合成基因的转录因子进行修饰,更有效地调控植物次生代谢以提高特定化合物的积累.作者结合对大豆种子异黄酮类代谢调控和基因工程改良的研究,着重介绍了花青素和黄酮类物质、生物碱、萜类化合物和安息香酸衍生物等次生代谢产物生物合成的基因工程研究进展.     

Biochemical characteristization of propionyl-coenzyme a carboxylase complex of <Emphasis Type="Italic">Streptomyces toxytricini</Emphasis>

Acyl-CoA carboxylases (ACC) are involved in important primary or secondary metabolic pathways such as fatty acid and/or polyketides synthesis. In the 62 kb fragment of pccB gene locus of Streptomyces toxytricini producing a pancreatic inhibitor lipstatin, 3 distinct subunit genes of presumable propionyl-CoA carboxylase (PCCase) complex, assumed to be one of ACC responsible for the secondary metabolism, were identified along with gene for a biotin protein ligase (Bpl). The subunits of PCCase complex were a subunit (AccA3), P subunit (PccB), and auxiliary ɛ subunit (PccE). In order to disclose the involvement of the PCCase complex in secondary metabolism, some biochemical characteristics of each subunit as well as their complex were examined. In the test of substrate specificity of the PCCase complex, it was confirmed that this complex showed much higher conversion of propionyl-CoA rather than acetyl-CoA. It implies the enzyme complex could play a main role in the production of methylmalonyl-CoA from propionyl-CoA, which is a precursor of secondary polyketide biosynthesis.     

Plant physiology meets phytopathology: plant primary metabolism and plant-pathogen interactions

Phytopathogen infection leads to changes in secondary metabolism based on the induction of defence programmes as well as to changes in primary metabolism which affect growth and development of the plant. Therefore, pathogen attack causes crop yield losses even in interactions which do not end up with disease or death of the plant. While the regulation of defence responses has been intensively studied for decades, less is known about the effects of pathogen infection on primary metabolism. Recently, interest in this research area has been growing, and aspects of photosynthesis, assimilate partitioning, and source-sink regulation in different types of plant-pathogen interactions have been investigated. Similarly, phytopathological studies take into consideration the physiological status of the infected tissues to elucidate the fine-tuned infection mechanisms. The aim of this review is to give a summary of recent advances in the mutual interrelation between primary metabolism and pathogen infection, as well as to indicate current developments in non-invasive techniques and important strategies of combining modern molecular and physiological techniques with phytopathology for future investigations.     

Controlled gas environments in industrial fermentations

The gas environment is of major importance in controlling aerobic fermentation processes for the manufacture of microbial products. Oxygen and carbon dioxide levels in gas-liquid equilibria affect productivity and energy consumption in such processes and appear to be implicated in the regulation of microbial metabolism. Gas-liquid transfer has been intensively studied by many investigators for Newtonian and non-Newtonian fluids, primarily in terms of oxygen-limitation in biomass and product formation. More recentreports show that microbial growth and product formation are affected by levels of oxygen and carbon dioxide in the gas environment, suggesting that microbial metabolism may be directed towards specific products by the control of such environments. High product concentrations may also be obtained by solid substrate fermentations with mycelial organisms cultured on semi-solid agricultural products at low moisture contents. Such methods are commonly used in the Orient for the manufacture of enzymes and traditional fermented foods and could probably be extended to other microbial products. This review covers fundamental aspects of engineering research in microbial processes that suggest applications for controlled gas environments in submerged culture and solid substrate fermentations of potential industrial interest.