Carbohydrate metabolism is essential for the colonization of Streptococcus thermophilus in the digestive tract of gnotobiotic rats

Streptococcus thermophilus is the archetype of lactose-adapted bacterium and so far, its sugar metabolism has been mainly investigated in vitro. The objective of this work was to study the impact of lactose and lactose permease on S. thermophilus physiology in the gastrointestinal tract (GIT) of gnotobiotic rats. We used rats mono-associated with LMD-9 strain and receiving 4.5% lactose. This model allowed the analysis of colonization curves of LMD-9, its metabolic profile, its production of lactate and its interaction with the colon epithelium. Lactose induced a rapid and high level of S. thermophilus in the GIT, where its activity led to 49 mM of intra-luminal L-lactate that was related to the induction of mono-carboxylic transporter mRNAs (SLC16A1 and SLC5A8) and p27(Kip1) cell cycle arrest protein in epithelial cells. In the presence of a continuous lactose supply, S. thermophilus recruited proteins involved in glycolysis and induced the metabolism of alternative sugars as sucrose, galactose, and glycogen. Moreover, inactivation of the lactose transporter, LacS, delayed S. thermophilus colonization. Our results show i/that lactose constitutes a limiting factor for colonization of S. thermophilus, ii/that activation of enzymes involved in carbohydrate metabolism constitutes the metabolic signature of S. thermophilus in the GIT, iii/that the production of lactate settles the dialogue with colon epithelium. We propose a metabolic model of management of carbohydrate resources by S. thermophilus in the GIT. Our results are in accord with the rationale that nutritional allegation via consumption of yogurt alleviates the symptoms of lactose intolerance.     

丛枝菌根真菌N代谢与C代谢研究进展

N元素是植物需求量最大的元素,丛枝菌根（arbuscular mycorrhizal,AM）真菌可以与大部分植物形成共生关系,通过根外菌丝促进植物对N元素的吸收。C元素也是AM真菌完成其生命过程的必备元素,AM真菌依赖宿主植物提供所必需的C源。近年来对AM真菌的N代谢途径的研究有了新的进展,AM真菌中与代谢途径相关酶的发现,相关基因的克隆,更进一步验证了N元素在AM真菌中的代谢途径。对C代谢及与N代谢的关系也有所涉及。综述近几年文献,总结了AM真菌的最新研究进展。     

Alternative lactose catabolic pathway in Lactococcus lactis IL1403

In this study, we present a glimpse of the diversity of Lactococcus lactis subsp. lactis IL1403 beta-galactosidase phenotype-negative mutants isolated by negative selection on solid media containing cellobiose or lactose and X-Gal (5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside), and we identify several genes essential for lactose assimilation. Among these are ccpA (encoding catabolite control protein A), bglS (encoding phospho-beta-glucosidase), and several genes from the Leloir pathway gene cluster encoding proteins presumably essential for lactose metabolism. The functions of these genes were demonstrated by their disruption and testing of the growth of resultant mutants in lactose-containing media. By examining the ccpA and bglS mutants for phospho-beta-galactosidase activity, we showed that expression of bglS is not under strong control of CcpA. Moreover, this analysis revealed that although BglS is homologous to a putative phospho-beta-glucosidase, it also exhibits phospho-beta-galactosidase activity and is the major enzyme in L. lactis IL1403 involved in lactose hydrolysis.     

丛枝菌根真菌与植物硫素营养研究进展

丛枝菌根真菌是土壤微生物群落的重要组成部分,是最常见的地下共生菌,对植物和土壤具有多种有益作用.本文阐述了近年来丛枝菌根真菌对植物吸收土壤硫素的最新进展,在目前耕地缺硫状况下,着重分析了丛枝菌根真菌改善植物硫素营养以及丛枝菌根真菌利用硫素的分子调控机制,总结了影响菌根硫代谢的因素,并指出该研究方向仍存在的一些问题以及未...     

重要食药用菌多糖降血糖分子机制研究进展

目前以糖尿病为代表的糖代谢紊乱疾病愈演愈烈,严重危害人体健康.食药用菌多糖因其具有良好的调节糖代谢作用而被关注,但其调节糖代谢的作用机制并未被很好地综述.本文从关键基因、蛋白、信号通路等方面综述了食药用菌活性多糖的降血糖机制,包括抑制蛋白酪氨酸磷酸酶1B(Protein Tyrosine Phosphatase-1B,...     

Differential analysis of protein expression of Bifidobacterium grown on different carbohydrates

We observed recently that colonic fermentation of lactose might be a major factor in the pathophysiology of lactose intolerance. Proteomic techniques could be helpful in interpreting the metabolic pathways of lactose fermentation. The objective of this study was to explore proteomic methodologies for studying bacterial lactose metabolism that can be used to detect and identify proteins associated with the onset of intolerance symptoms. Differential expression of cytoplasmic proteins of Bifidobacterium animalis, Bifidobacterium breve and Bifidobacterium longum grown on different carbohydrates (lactose, glucose, galactose) was analyzed with surface-enhanced laser desorption ionization-time of flight (SELDI-TOF) MS and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). After fractionation by SDS-PAGE, differentially-expressed proteins were identified with LC-MS/MS. The three strains grown on the same carbohydrate or the same strain grown on glucose or lactose showed differences in SELDI-TOF MS protein profiles. Differences in protein expression were observed in B. breve grown on glucose, galactose or lactose as analyzed with SDS-PAGE. With LC-MS/MS, proteins from Bifidobacterium were identified, which included enzymes for metabolism of lactose, glucose and galactose. In conclusion, the applied techniques can discern differences in protein expression of bacteria metabolizing different carbohydrates. These techniques are promising in studying metabolism of lactose and other substrates in a complex bacterial ecosystem such as the colonic microbiota.     

丛枝菌根真菌对植物次生代谢的影响

丛枝菌根(AM)是自然界中分布最为广泛、最为重要的一类菌根,许多研究已经观察到丛枝菌根真菌与植物次生代谢的相关性,丛枝菌根真菌能够直接或间接地影响植物的次生代谢过程。植物的次生代谢产物主要分为萜类物质、酚类物质和含氮化合物(主要是生物碱)三大类群,该文简要介绍了丛枝菌根真菌对这3类植物次生代谢产物的影响。丛枝菌根真菌与萜类物质代谢关系的研究比较细致和深入,有些工作已经从细胞及分子水平探讨其间的作用机制,如Blumenin、类胡萝卜素等。丛枝菌根真菌与酚类物质代谢关系的研究也比较深入,其中具有特殊功能的酚类物质——植保素、细胞壁酚酸、类黄酮/异类黄酮等倍受关注。目前有关丛枝菌根真菌与生物碱关系的研究相对较少,不过现有的研究表明,菌根的形成有助于生物碱积累。     

Secondary metabolism as an expression of microbial growth and development

A case is made out for regarding secondary metabolism as part of normal cell growth, related to its interactions with the environment. Secondary metabolism is widespread, especially in fungi and actinomycetes, and is not to be regarded as confined to the production of antibiotics and other special substances. It is part of the normal maturation process. Examples are given of the influence of secondary metabolism in ecological systems. It is also shown that cell productivity can be related to age structure. Secondary metabolism is thus linked with growth, although in many cases this may not be obvious in laboratory work. Initiation of production will arise from the system which regulates growth and differentiation. These processes are little understood at present, but it is clear that the factors involved differ in different instances and that they involve a very great variety of biochemical and physiological processes.     

LaeA在丝状真菌次级代谢、生长发育和其他重要生物过程中的作用

LaeA是在构巢曲霉中首次鉴定的一种全局调控因子,其同源蛋白在丝状真菌中广泛存在,具有高度的保守性。LaeA及其同源蛋白序列存在S-腺苷甲硫氨酸结合基序,是一种甲基转移酶,可能影响组蛋白修饰,导致染色体结构的改变,进而调控一系列基因的表达。大量研究表明,LaeA及其同源蛋白参与调控丝状真菌多种次级代谢产物的生物合成,影响丝状真菌的生长发育和形态分化,甚至在丝状真菌生产有机酸和一些工业酶的过程中也发挥着重要作用。本文综述了LaeA及其同源蛋白的作用机制,以及该蛋白在丝状真菌次级代谢、生长发育和其他重要生物过程中的作用,并对存在的问题及应用前景进行讨论与展望。     

化脓性链球菌碳水化合物代谢及毒力影响研究进展

化脓性链球菌(Streptococcus pyogenes)是一种引起人类多种疾病的革兰阳性病原菌,在宿主体内获取营养物质是其生存和繁殖进而损伤宿主的前提,其中碳水化合物是营养物质的主要成分.化脓性链球菌具有糖酵解、非完全糖酵解及磷酸烯醇丙酮酸依赖性磷酸转移酶系统(Phosphoenol pyruvate-depend...     

Genomic and proteomic analyses of the fungus Arthrobotrys oligospora provide insights into nematode-trap formation

Nematode-trapping fungi are "carnivorous" and attack their hosts using specialized trapping devices. The morphological development of these traps is the key indicator of their switch from saprophytic to predacious lifestyles. Here, the genome of the nematode-trapping fungus Arthrobotrys oligospora Fres. (ATCC24927) was reported. The genome contains 40.07 Mb assembled sequence with 11,479 predicted genes. Comparative analysis showed that A. oligospora shared many more genes with pathogenic fungi than with non-pathogenic fungi. Specifically, compared to several sequenced ascomycete fungi, the A. oligospora genome has a larger number of pathogenicity-related genes in the subtilisin, cellulase, cellobiohydrolase, and pectinesterase gene families. Searching against the pathogen-host interaction gene database identified 398 homologous genes involved in pathogenicity in other fungi. The analysis of repetitive sequences provided evidence for repeat-induced point mutations in A. oligospora. Proteomic and quantitative PCR (qPCR) analyses revealed that 90 genes were significantly up-regulated at the early stage of trap-formation by nematode extracts and most of these genes were involved in translation, amino acid metabolism, carbohydrate metabolism, cell wall and membrane biogenesis. Based on the combined genomic, proteomic and qPCR data, a model for the formation of nematode trapping device in this fungus was proposed. In this model, multiple fungal signal transduction pathways are activated by its nematode prey to further regulate downstream genes associated with diverse cellular processes such as energy metabolism, biosynthesis of the cell wall and adhesive proteins, cell division, glycerol accumulation and peroxisome biogenesis. This study will facilitate the identification of pathogenicity-related genes and provide a broad foundation for understanding the molecular and evolutionary mechanisms underlying fungi-nematodes interactions.     

Metabolite profiling of fungi and yeast: from phenotype to metabolome by MS and informatics

Filamentous fungi and yeast from the genera Saccharomyces, Penicillium, Aspergillus, and Fusarium are well known for their impact on our life as pathogens, involved in food spoilage by degradation or toxin contamination, and also for their wide use in biotechnology for the production of beverages, chemicals, pharmaceuticals, and enzymes. The genomes of these eukaryotic micro-organisms range from about 6000 genes in yeasts (S. cerevisiae) to more than 10,000 genes in filamentous fungi (Aspergillus sp.). Yeast and filamentous fungi are expected to share much of their primary metabolism; therefore much understanding of the central metabolism and regulation in less-studied filamentous fungi can be learned from comparative metabolite profiling and metabolomics of yeast and filamentous fungi. Filamentous fungi also have a very active and diverse secondary metabolism in which many of the additional genes present in fungi, compared with yeast, are likely to be involved. Although the 'blueprint' of a given organism is represented by the genome, its behaviour is expressed as its phenotype, i.e. growth characteristics, cell differentiation, response to the environment, the production of secondary metabolites and enzymes. Therefore the profile of (secondary) metabolites--fungal chemodiversity--is important for functional genomics and in the search for new compounds that may serve as biotechnology products. Fungal chemodiversity is, however, equally efficient for identification and classification of fungi, and hence a powerful tool in fungal taxonomy. In this paper, the use of metabolite profiling is discussed for the identification and classification of yeasts and filamentous fungi, functional analysis or discovery by integration of high performance analytical methodology, efficient data handling techniques and core concepts of species, and intelligent screening. One very efficient approach is direct infusion Mass Spectrometry (diMS) integrated with automated data handling, but a full metabolic picture requires the combination of several different analytical techniques.     

Forms of nitrogen uptake, translocation, and transfer via arbuscular mycorrhizal fungi: A review

Arbuscular mycorrhizal (AM) fungi are obligate symbionts that colonize the roots of more than 80% of land plants. Experiments on the relationship between the host plant and AM in soil or in sterile root-organ culture have provided clear evidence that the extraradical mycelia of AM fungi uptake various forms of nitrogen (N) and transport the assimilated N to the roots of the host plant. However, the uptake mechanisms of various forms of N and its translocation and transfer from the fungus to the host are virtually unknown. Therefore, there is a dearth of integrated models describing the movement of N through the AM fungal hyphae. Recent studies examined Ri T-DNA-transformed carrot roots colonized with AM fungi in ¹⁵N tracer experiments. In these experiments, the activities of key enzymes were determined, and expressions of genes related to N assimilation and translocation pathways were quantified. This review summarizes and discusses the results of recent research on the forms of N uptake, transport, degradation, and transfer to the roots of the host plant and the underlying mechanisms, as well as research on the forms of N and carbon used by germinating spores and their effects on amino acid metabolism. Finally, a pathway model summarizing the entire mechanism of N metabolism in AM fungi is outlined.     

城市菌根真菌多样性、变化机制及功能应用

菌根真菌能够与大多数陆生植物的根系形成菌根共生体,具有改善宿主植物矿质营养、增强抗逆性、改良土壤结构等重要生态功能。城市化过程中气候、土壤、植被、土地利用等因素的改变,对菌根真菌的多样性产生了直接或间接的影响。目前城市菌根真菌的研究多侧重对其空间分布及群落组成的简单描述,缺乏针对城市典型生态现象及生态问题系统性的探讨。分别从城市菌根真菌的多样性变化、影响机制及功能应用等3方面进行了综述,全面揭示城市菌根真菌的研究现状及研究的复杂性,发现当前研究存在多样性评估简单化、研究层次单一化、内在机制现象化及功能应用停滞化等问题,认为今后应建立更为系统、综合、标准的研究体系以深刻而准确地认识与理解城市化对菌根真菌多样性的影响,为城市微生物资源的保存及绿地系统维持提供理论依据。     

De novo transcriptome sequencing of marine-derived <Emphasis Type="Italic">Aspergillus glaucus</Emphasis> and comparative analysis of metabolic and developmental variations in response to salt stress

Aspergillus glaucus HB1-19 is a typical marine-derived fungus preferring the dependence on sea water for its growth, asexual development and polyketides biosynthesis. Therein, salt stress greatly functions even in superior to light illumination, which is also a critical regulation signal for fungi. Here, comparative RNA-seq analysis of this strain was performed under conditions of salt-stress + dark (group A), non salt-stress + dark (group B), salt-stress + light (group C). The RNA-seq generated a total of 19,024 unigenes with an average length of 1415 bp. Differentially expressed genes were very similar between group A and group C but greatly differed between group A and group B, proving that salt stress functioned superior to light illumination globally. Salt stress highly enhanced primary metabolism and activated Ras and MAPK signaling pathways. There seems no direct interaction between asexual development and polyketides biosynthesis. Salt stress inhibited terpenoids biosynthesis but showed little influences on polyketide pathway as well as other secondary metabolism pathways. These findings provide a better understanding of marine fungi adapting to marine environment. Also, it indicates that the so-called ‘salt stress-induced’ may truly be a ‘metal ions-induced’ for biosynthesis of secondary metabolites in marine fungi.