Cellulose biosynthesis and function in bacteria.

The current model of cellulose biogenesis in plants, as well as bacteria, holds that the membranous cellulose synthase complex polymerizes glucose moieties from UDP-Glc into beta-1,4-glucan chains which give rise to rigid crystalline fibrils upon extrusion at the outer surface of the cell. The distinct arrangement and degree of association of the polymerizing enzyme units presumably govern extracellular chain assembly in addition to the pattern and width of cellulose fibril deposition. Most evident for Acetobacter xylinum, polymerization and assembly appear to be tightly coupled. To date, only bacteria have been effectively studied at the biochemical and genetic levels. In A. xylinum, the cellulose synthase, composed of at least two structurally similar but functionally distinct subunits, is subject to a multicomponent regulatory system. Regulation is based on the novel nucleotide cyclic diguanylic acid, a positive allosteric effector, and the regulatory enzymes maintaining its intracellular turnover: diguanylate cyclase and Ca2(+)-sensitive bis-(3',5')-cyclic diguanylic acid (c-di-GMP) phosphodiesterase. Four genes have been isolated from A. xylinum which constitute the operon for cellulose synthesis. The second gene encodes the catalytic subunit of cellulose synthase; the functions of the other three gene products are still unknown. Exclusively an extracellular product, bacterial cellulose appears to fulfill diverse biological roles within the natural habitat, conferring mechanical, chemical, and physiological protection in A. xylinum and Sarcina ventriculi or facilitating cell adhesion during symbiotic or infectious interactions in Rhizobium and Agrobacterium species. A. xylinum is proving to be most amenable for industrial purposes, allowing the unique features of bacterial cellulose to be exploited for novel product applications.     

Phosphatidylcholine biosynthesis and function in bacteria

Phosphatidylcholine (PC) is the major membrane-forming phospholipid in eukaryotes and is estimated to be present in about 15% of the domain Bacteria. Usually, PC can be synthesized in bacteria by either of two pathways, the phospholipid N-methylation (Pmt) pathway or the phosphatidylcholine synthase (Pcs) pathway. The three subsequent enzymatic methylations of phosphatidylethanolamine are performed by a single phospholipid N-methyltransferase in some bacteria whereas other bacteria possess multiple phospholipid N-methyltransferases each one performing one or several distinct methylation steps. Phosphatidylcholine synthase condenses choline directly with CDP-diacylglycerol to form CMP and PC. Like in eukaryotes, bacterial PC also functions as a biosynthetic intermediate during the formation of other biomolecules such as choline, diacylglycerol, or diacylglycerol-based phosphorus-free membrane lipids. Bacterial PC may serve as a specific recognition molecule but it affects the physicochemical properties of bacterial membranes as well. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.     

Capnocytophaga: New genus of gram-negative gliding bacteria I. General characteristics,taxonomic considerations and significance

The characteristics of gliding bacteria isolated from both healthy and diseased sites in the oral cavity are, summarized and the taxonomic position of the bacteria discussed. Uniform attributes of the fusiform isolates include gliding motility, strictly fermentative metabolism dependent on the presence of CO₂ (or HCO ₃ ^- ), under either anaerobic or aerobic conditions, presence of benzidine-reactive components, and the production of acetic and succinic acids as the major or sole, acidic, metabolic and products. Given the guanine and cytosine content of DNA, their gliding motility, and the ability of many strains to attack polysaccharide a relationship to the cytophagas is suggested. This relationship, along with the CO₂-dependent growth is recognized by the generic name Capnocytophaga given them. Many of the isolates are grouped into three species C. ochracea, C. Sputigena, and C. gingivalis, separated on the basis of morphological and physiological traits.     

Molecular basis for biosynthesis and accumulation of polyhydroxyalkanoic acids in bacteria.

The current knowledge on the structure and on the organization of polyhydroxyalkanoic acid (PHA)-biosynthetic genes from a wide range of different bacteria, which rely on different pathways for biosynthesis of this storage polyesters, is provided. Molecular data will be shown for genes of Alcaligenes eutrophus, purple non-sulfur bacteria, such as Rhodospirillum rubrum, purple sulfur bacteria, such as Chromatium vinosum, pseudomonads belonging to rRNA homology group I, such as Pseudomonas aeruginosa, Methylobacterium extorquens, and for the Gram-positive bacterium Rhodococcus ruber. Three different types of PHA synthases can be distinguished with respect to their substrate specificity and structure. Strategies for the cloning of PHA synthase structural genes will be outlined which are based on the knowledge of conserved regions of PHA synthase structural genes and of the PHA-biosynthetic routes in bacteria as well as on the heterologous expression of these genes and on the availability of mutants impaired in the accumulation of PHA. In addition, a terminology for the designation of PHAs and of proteins and genes relevant for the metabolism of PHA is suggested.     

Merosity in flowers: Definition,origin, and taxonomic significance

The term merosity stands for the number of parts within whorls of floral organs, leaves, or stems. Trimery is considered to be a basic condition that arose through the cyclisation of a spiral flower. Pentamery is mostly derived from trimery by the repetitive fusion of two different whorls. Dimery is either directly derived from trimery, or through pentamery as an intermediate stage. Tetramery is linked with pentamery and should not be confused with dimery. Possible causes for a change in merosity are the reduction of the number of carpels and zygomorphy in flowers. Derivations of different merosities have important consequences for the arrangement of the androecium (the insertion of stamen whorls, their identifications, and their number). It is concluded that two main groups can be identified within the angiosperms: magnolialean and monocotyledonean taxa are mostly trimerous or dimerous; non-magnolialean dicots are mostly pentamerous or tetramerous.     

Tetrahydrofolate-dependent biosynthesis of ribothymidine in transfer ribonucleic acids of Gram-positive bacteria.

Trimethoprim, an inhibitor that prevents tetrahydrofolate-dependent transmethylation reactions inbacteria, was used in a comparative study to discriminate between two possible biosynthetic pathways, either the S-adenosylmethionine or the tetrahydrofolate-dependent formation of ribothymidine (rT) in transfer ribonucleic acids (tRNA's) of several strains of gram-positive and gram-negative microorganisms. rT-deficient tRNA's accumulate in trimethoprim-treated gram-positive Streptococcus faecium, Staphylococcus aureus, Corynebacterium bovis, Arthrobacter albidus, and all examined Bacillaceae, except Bacillus stearothermophilus. The rT-deficient rT-deficient tRNA's accept the methyl moiety from S-adenosylmethionine in vitro, with extracts from Escherichia coli (wild type) as a source of methylating enzymes; 90% of the incorporated methyl groups are present in rT. Trimethoprim does not inhibit the biosynthesis of rT in tRNA of gram-negative Enterobacteriaceae, Rhizobium lupini, and Pseudomonadaceae, suggesting that the rT-specific tRNA methyltransferases of these gram-negative strains use S-adenosylmethionine as coenzyme.     

Sterol molecule: structure, biosynthesis, and function.

This review briefly summarizes key researches on the structure of the sterol molecule from its very beginnings to the definitive elucidation in 1932. Cholesterol biosynthesis treated in somewhat greater detail covers the period from the 1930s to the 1960s. As a historic contribution, it presents researches previously published in numerous books, reviews, and original papers. The selection of topics, dictated by limits of time and space, is necessarily arbitrary and a personal choice. Readers of this journal will be familiar with the relevant chemical structures. Structural formulas are therefore omitted.     

Occurrence of nonmevalonate and mevalonate pathways for isoprenoid biosynthesis in bacteria of different taxonomic groups

The effect of fosmidomycin and mevinoline, inhibitors of the nonmevalonate and the mevalonate pathways of isoprenoid biosynthesis, respectively, on the growth of 34 anaerobic and 10 aerobic prokaryotic strains was studied. Fosmidomycin at the concentrations used was shown to inhibit the growth of 9 (of 10) representatives of the family Microbacteriaceae, 4 (of 5) strains of Thermoanaerobacter, and 11 (of 12) strains of Clostridium, whereas mevinoline inhibited the growth of lactobacilli (Carnobacterium), methanogenic and sulfate-reducing bacteria insensitive to fosmidomycin. During the late growth phase, four strains of actinobacteria (of nine) accumulated the compound, which, upon oxidation, generates a long-lived free radical; three strains synthesized 2-C-methyl-D-erythritol-2,4-cyclopyrophosphate (MEC). It was concluded that the difference in the sensitivity of the organisms to fosmidomycin and mevinoline might serve as a test to differentiate several representatives of the family Microbacteriaceae. The use of mevinoline for inhibiting methanogens in ecological investigations seems to be promising.__________Translated from Mikrobiologiya, Vol. 74, No. 2, 2005, pp. 185–190.Original Russian Text Copyright © 2005 by Trutko, Dorofeeva, Shcherbakova, Chuvilskaya, Laurinavichus, Binyukov, Ostrovskii, Hintz, Wiesner, Jomaa, Akimenko.     

Occurrence and taxonomic significance of oxo-fatty acids in lipopolysaccharides from members of Mesorhizobium

Lipopolysaccharides (LPSs) isolated from seven strains of Mesorhizobium were studied for the presence of fatty acids with particular attention for 27-oxooctacosanoic acid and 4-oxo fatty acids. The LPSs from all analysed strains contained various amounts of 27-oxo-28:0 and all of them, with the exception of Mesorhizobium tianshanense, contained also 4-oxo fatty acids (4-oxo-20:0, 4-oxo-i-21:0, 4-oxo-22:0). The group of amide-linked fatty acids consisted of a wide range of 3-hydroxylated and 4-oxo fatty acids whereas all the nonpolar as well as the (omega-1) hydroxylated long-chain acids and the 27-oxo-28:0 fatty acids were ester-linked. The characteristic spectrum of 3-hydroxy fatty acids and presence of 27-OH-28:0 as well as 27-oxo-28:0 acid in LPSs of Mesorhizobium showed that these strains were closely related. Therefore the lipid A fatty acid pattern could be a useful chemotaxonomic marker which helps to isolate the Mesorhizobium group from rhizobium bacteria during the classification process.     

Molecular basis for biosynthesis and accumulation of polyhydroxyalkanoic acids in bacteria

Abstract The current knowledge on the structure and on the organization of polyhydroxyalkanoic acid (PHA)-biosynthetic genes from a wide range of different bacteria, which rely on different pathways for biosynthesis of this storage polyesters, is provided. Molecular data will be shown for genes of Alcaligenes eutrophus , purple non-sulfur bacteria, such as Rhodospirillum rubrum , purple sulfur bacteria, such as Chromatium vinosum , pseudomonads belonging to rRNA homology group I, such as Pseudomonas aeruginosa, Methylobacterium extorquens , and for the Gram-positive bacterium Rhodococcus ruber . Three different types of PHA synthases can be distinguished with respect to their substrate specificity and structure. Strategies for the cloning of PHA synthase structural genes will be outlined which are based on the knowledge of conserved regions of PHA synthase structural genes and of the PHA-biosynthetic routes in bacteria as well as on the heterologous expression of these genes and on the availability of mutants impaired in the accumulation of PHA. In addition, a terminology for the designation of PHAs and of proteins and genes relevant for the metabolism of PHA is suggested.     

Trichothecene biosynthesis in Fusarium species: chemistry, genetics, and significance.

Several species of the genus Fusarium and related fungi produce trichothecenes which are sesquiterpenoid epoxides that act as potent inhibitors of eukaryotic protein synthesis. Interest in the trichothecenes is due primarily to their widespread contamination of agricultural commodities and their adverse effects on human and animal health. In this review, we describe the trichothecene biosynthetic pathway in Fusarium species and discuss genetic evidence that several trichothecene biosynthetic genes are organized in a gene cluster. Trichothecenes are highly toxic to a wide range of eukaryotes, but their specific function, if any, in the survival of the fungi that produce them is not obvious. Trichothecene gene disruption experiments indicate that production of trichothecenes can enhance the severity of disease caused by Fusarium species on some plant hosts. Understanding the regulation and function of trichothecene biosynthesis may aid in development of new strategies for controlling their production in food and feed products.     

O-acetylated peptidoglycan: its occurrence, pathobiological significance, and biosynthesis.

Bacterial cell walls and their structural units, particularly peptidoglycan, induce a vast variety of biological effects in host organisms. The pathobiological effects of peptidoglycan are greatly enhanced by various modifications and substitutions to its basic composition and structure. One such modification is the presence of acetyl moieties at the C-6 hydroxyl group of N-acetylmuramyl residues, and to date, 11 species of eubacteria, including some important human pathogens, such as Neisseria gonorrhoeae, Proteus mirabilis, and Staphylococcus aureus, are known to possess O-acetylated peptidoglycan. This review addresses the influence of O-acetylation of peptidoglycan on its resistance to degradation both in vitro and in vivo, the clinical importance of the modification, and the currently held views on the pathway for its biosynthesis.     

植物雄蕊合生的多样性、适应意义及分类学意义初探

定义并总结了雄蕊合生现象,对雄蕊合生的类型、适应意义、进化及分类学意义进行了初步的讨论和总结.本文定义"雄蕊合生"为,花内雄蕊与雄蕊之间部分或整体的结合生长,既包括愈合与黏合,也包括结合紧密的贴生和靠生.根据雄蕊合生部位的不同,将雄蕊合牛分为"花丝合生"、"花药合生"和"花丝花药均合生"等三大类.每一类中还存在着合生程度不同的子类型.雄蕊合生的结构还可能进一步与柱头或花柱合生在一起,形成"合蕊柱"一类的复杂结构.雄蕊合生在裸子植物较进化的科如百岁兰科和买麻藤科中就出现了,在种子植物中集中分布在近50个科内,且从系统关系来看,雄蕊合生各个类型可能发生过多次进化上的反复.在被子植物中,花丝合生类型更多地与较早进化的类群联系在一起,且多出现在离瓣花中;花药合生及花丝花药均合生则较晚进化,多与有着明显花冠筒的合瓣花伴随出现.这暗示着,雄蕊的合牛结构有可能与花部其他特征一起影响了植物的繁殖过程,具有一定的适应意义.目前,还没有实验研究针对雄蕊合生各个类型开展实验以揭示其发育机制和适应意义.理论上,花丝合乍能增强雄蕊的强度,有时候还形成了围绕子房与花柱的杯状、管状或环状结构,能对子房和花柱有着保护作用且承受传粉者在花内移动的压力:花丝合生还可将雄蕊固定在一个较为稳定的位置,使得花药接触传粉者身体的部位相对固定,减少了花粉浪费.花药合生能将花内花药都集中到同一个位置,花粉接触传粉者身体的同一部位,从而降低花粉损耗和提高异交授粉的准确性.花丝花药均合生可以同时具有以上两种合生方式的适应意义,而且还极大改变了雄蕊的结构与空间位置,改变了花药与柱头之间的空间位置(雌雄异位),对花内自交可能性和雌雄功能干扰有着潜在的影响.雄蕊合生各个类型的适应意义及其对访花者类型与行为和植物繁殖策略的影响,还需要开展实验进行针对性的研究.由于雄蕊形态与结构较为稳定,雄蕊合生的不同方式以及合生程度可以作为科与种的分类参考.     

Trichomes and stomata,and their taxonomic significance in theUrticales

Structure and ontogeny of stomata and trichomes have been studied in 23 species and 3 varieties of theUrticales. Stomata are anomocytic, more rarely paracytic; anisocytic and sometimes helicocytic and transitorial types are found inUrticaceae andDorstenia, rarely inArtocarpus. The ontogeny of anomocytic and actinocytic stomata is perigenous, of paracytic either mesogenous or perigenous, of anisocytic either mesogenous or mesoperigenous, and of helicocytic and transitional types mesogenous. Among trichomes eglandular unicellular (wide spread), bicellular or uniseriate filiform (Cannabis); glandular capitate with uni- or bicellular (Moraceae, Ulmaceae, Cannabaceae), uniseriate filiform (Ulmaceae) or multiseriate stalk (Cannabis); sunken glands (Artocarpus); uniseriate glandular with uniseriate stalk (Celtis), and stinging emergences (Urticaceae) have been observed. It is concluded that theUrticales represent a natural order with four families:Ulmaceae, Moraceae, Urticaceae andCannabaceae which are distinct but interrelated with each other.     

Partially hydrated pollen: taxonomic distribution, ecological and evolutionary significance

 The problem of the water content of pollen is reconsidered, especially the distinction between “partially hydrated pollen” (PH pollen), pollen with a water content greater than 30%, and “partially dehydrated pollen” (PD pollen), which has a water content of less than 30%. Both types have been found even in systematically contiguous groups or the same genus. Partially hydrated pollen, encountered in at least 40 families of angiosperms, has the advantage of germinating quickly, normally in a few minutes to less than an hour. Dispersal of highly hydrated pollen also occurs in orchids but for a different reason, i.e. to enable packaging of massulae. The disadvantage of pollen dispersed with a high water content is that water is readily lost and the pollen may desiccate and die unless it has biochemical or anatomical devices to retain water or phenological strategies, such as flowering when temperatures are not too high and when relative humidity is high. Most pollen of Gymnosperms and Angiosperms studied has, however, been found partially dehydrated. Received March 8, 2002; accepted April 8, 2002 Published online: November 14, 2002 Addresses of the authors: G.G. Franchi (e-mail: franchi@unisi.it), Department of Pharmacology, Università di Siena, Via delle Scotte 6, I-53100 Siena, Italy; M. Nepi (e-mail: nepim@unisi.it) and E. Pacini (e-mail: pacini@unisi.it), Department of Environmental Sciences, Università di Siena, Via P.A. Mattioli 4, I-53100 Siena, Italy; A. Dafni (e-mail: adafni@research.haifa.ac.il), Laboratory of Pollination Ecology, Institute of Evolution, University of Haifa, 31905 Israel.     

Polyisoprenoids: structure, biosynthesis and function

The polyisoprenoid alcohols and their derivatives are highlighted here. These linear polymers of isoprenoid residues are widespread in nature from bacteria to human cells. This review presents their structures, distribution and biogenesis. Attention will be focused on the biosynthesis of polyisoprenoid alcohols in plants in the context of two coexisting isoprenoid pathways, mevalonate and the recently described methylerythritol phosphate pathway. Structural aspects including modeling of the polyisoprenoid conformation will be presented and finally the postulated biological role of polyisoprenoid alcohols will be discussed including polyisoprenylation of proteins.     

Mycosporine-like amino acids (MAAs): chemical structure, biosynthesis and significance as UV-absorbing/screening compounds

Continuous depletion of the stratospheric ozone layer has resulted in an increase in ultraviolet-B (UV-B; 280-315 nm) radiation on the earth's surface which inhibits photochemical and photobiological processes. However, certain photosynthetic organisms have evolved mechanisms to counteract the toxicity of ultraviolet or high photosynthetically active radiation by synthesizing the UV-absorbing/screening compounds, such as mycosporine-like amino acids (MAAs) and scytonemin besides the repair of UV-induced damage of DNA and accumulation of carotenoids and detoxifying enzymes or radical quenchers and antioxidants. Chemical structure of various MAAs, their possible biochemical routes of synthesis and role as photoprotective compounds in various organisms are discussed.