Sucrose, sucrosyl oligosaccharides, and oxidative stress: scavenging and salvaging?

In nature, no single plant completes its life cycle withoutencountering environmental stress. When plant cells surpassstress threshold stimuli, chemically reactive oxygen species(ROS) are generated that can cause oxidative damage or act assignals. Plants have developed numerous ROS-scavenging systemsto minimize the cytotoxic effects of ROS. The role of sucrosyloligosaccharides (SOS), including fructans and the raffinosefamily oligosaccharides (RFOs), is well established during stressphysiology. They are believed to act as important membrane protectorsin planta. So far a putative role for sucrose and SOS duringoxidative stress has largely been neglected, as has the contributionof the vacuolar compartment. Recent studies suggest a link betweenSOS and oxidative defence and/or scavenging. SOS might be involvedin stabilizing membrane-associated peroxidases and NADPH oxidases,and SOS-derived radicals might fulfil an intermediate role inoxido-reduction reactions taking place in the vicinity of membranes.Here, these emerging features are discussed and perspectivesfor future research are provided. Key words: Fructan, oxidative stress, raffinose, ROS, sucrose, sucrosyl oligosaccharides Received 25 September 2008; Revised 20 October 2008 Accepted 23 October 2008     

Mycorrhizae of Entoloma saepium: parasitism or symbiosis?

The mycorrhizae of Entoloma saepium on Rosa sp. are comprehensively described and compared to other mycorrhizae of the genus Entoloma, as well as to similar unidentified mycorrhizae known from the literature. E. saepium appears to be more a parasite than a symbiont, as it invades and almost completely destroys the root meristem and young root cells.Considered as part IL of the series Studies on ectomycorrhizae; part XLVIII: Waller and Agerer (1993)     

Are bacteria the third partner of theAzolla-Anabaena symbiosis?

The development of the prokaryotic colony inAzolla filiculoides indicates thatAnabaena azollae is maintained through the life cycle of the fern and present in the leaves and megasporocarps. The same biological pattern is applied to the bacteria that are also present in these structures and seems to follow a development pattern identical to the cyanobacteria and probably can be considered the third partner of this symbiotic association.     

Microalgae–bacteria symbiosis in microalgal growth and biofuel production: a review

Photosynthetic microalgae can capture solar energy and convert it to bioenergy and biochemical products. In nature or industrial processes, microalgae live together with bacterial communities and may maintain symbiotic relationships. In general interactions, microalgae exude dissolved organic carbon that becomes available to bacteria. In return, the bacteria remineralize sulphur, nitrogen and phosphorous to support the further growth of microalgae. In specific interactions, heterotrophic bacteria supply B vitamins as organic cofactors or produce siderophores to bind iron, which could be utilized by microalgae, while the algae supply fixed carbon to the bacteria in return. In this review, we focus on mutualistic relationship between microalgae and bacteria, summarizing recent studies on the mechanisms involved in microalgae–bacteria symbiosis. Symbiotic bacteria on promoting microalgal growth are described and the relevance of microalgae–bacteria interactions for biofuel production processes is discussed. Symbiotic microalgae–bacteria consortia could be utilized to improve microalgal biomass production and to enrich the biomass with valuable chemical and energy compounds. The suitable control of such biological interactions between microalgae and bacteria will help to improve the microalgae-based biomass and biofuel production in the future.     

Methylglyoxal production in bacteria: suicide or survival?

Methylglyoxal is a toxic electrophile. In Escherichia coli cells, the principal route of methylglyoxal production is from dihydroxyacetone phosphate by the action of methylglyoxal synthase. The toxicity of methylglyoxal is believed to be due to its ability to interact with the nucleophilic centres of macromolecules such as DNA. Bacteria possess an array of detoxification pathways for methylglyoxal. In E. coli, glutathione-based detoxification is central to survival of exposure to methylglyoxal. The glutathione-dependent glyoxalase I-II pathway is the primary route of methylglyoxal detoxification, and the glutathione conjugates formed can activate the KefB and KefC potassium channels. The activation of these channels leads to a lowering of the intracellular pH of the bacterial cell, which protects against the toxic effects of electrophiles. In addition to the KefB and KefC systems, E. coli cells are equipped with a number of independent protective mechanisms whose purpose appears to be directed at ensuring the integrity of the DNA. A model of how these protective mechanisms function will be presented. The production of methylglyoxal by cells is a paradox that can be resolved by assigning an important role in adaptation to conditions of nutrient imbalance. Analysis of a methylglyoxal synthase-deficient mutant provides evidence that methylglyoxal production is required to allow growth under certain environmental conditions. The production of methylglyoxal may represent a high-risk strategy that facilitates adaptation, but which on failure leads to cell death. New strategies for antibacterial therapy may be based on undermining the detoxification and defence mechanisms coupled with deregulation of methylglyoxal synthesis. Received: 30 March 1998 / Accepted: 22 June 1998     

Can bacteria outcompete phytoplankton for phosphorus? a chemostat test

Although the bacterioplankton of lakes are usually considered primarily in terms of mineralization processes, recent studies suggest that they may also strongly compete for phosphorus with the phytoplankton. In the present study, we have tested in chemostat culture, and found support for the hypotheses that (1) a freshwater bacterium (Pseudomonas paucimobilis), whose carbon source is excretion from a phosphorus-limited alga (Synedra ulna var.danica), can outcompete that alga for phosphorus (P) under widely varied P supply rates; (2) exogenously-supplied organic carbon positively influences bacterial biomass and negatively influences algal biomass; (3) the ratio of bacterial to algal phosphorus uptake in short-term³²P orthophosphate uptake experiments is an accurate predictor of their relative long-term phosphorus assimilation (i.e., growth) in mixed culture.     

Bacterial virulence factors targeting Rho GTPases: parasitism or symbiosis?

In the past few years, an important question in microbiology has arisen from reports indicating that several pathogenic bacteria have evolved virulence factors directed towards a Ras subfamily of GTPases, namely the Rho GTPases. Progress made in studying both the virulence factors and the signaling pathways involving Rho GTPases has shed light on this crosstalk. One central question is raised by the findings that both activating and inactivating virulence factors that target Rho GTPases coexist in some pathogenic bacteria. Further studies on this peculiar aspect of the bacteria-host cell interactions, which leads to the outbreak of infectious diseases, might clarify whether this aspect of Rho GTPase activation or inactivation represents a finely adapted response of the pathogen for its own benefit or might lead to a reaction of the host against the bacteria.     

Cell proliferation and growth inZoothamnium niveum (Oligohymenophora, Peritrichida) — Thiotrophic bacteria symbiosis

Chemolithoautotrophic, sulphide-oxidizing (thiotrophic) symbioses represent spectacular adaptations to fluctuating environmental gradients and survival is often accomplished when growth is fuelled by sufficient nourishment through the symbionts leading to fast cell proliferation. Here we show 5′-bromo-2′ deoxyuridine (BrdU) pulse labelling of vegetative growingZoothamnium niveum, a colonial ciliate obligately associated with thiotrophic ectosymbionts, and demonstrate age related growth profiles in three heteromorphic host cell types. At the colony’s apex, a large top terminal zooid performed high proliferation activity, which decreased significantly with increasing colony age but was still present in old colonies indicating that this cell possesses lifelong cell division potential. In contrast, terminal branch zooids proliferated independent of colony age but appeared to be limited by their cell division capacity predetermined by branch size, thus leading to the strict, feather-shaped colony form. Appearance of labelled terminal branch zooids allowed us to distinguish a highly proliferating apical colony region from an almost inactive, senescent basal region. In macrozooids attached to the colony, extensive BrdU labelling suggests that DNA synthesis occurs in preparation for a new generation. As motile swarmers, the macrozooids seem to be arrested in the cell cycle and mitosis and cell division occur when the swarmer settles and transforms into a top terminal zooid buildingup a new colony.     

Toxin-antitoxin pairs in bacteria: killers or stress regulators?

Plasmid toxin-antitoxin systems, which kill daughter cells that fail to inherit the plasmid genome, have chromosomal homologs in eubacteria and archaea. In this issue of Cell, Pederson et al. show that the E. coli RelE toxin cleaves mRNA in the ribosomal A site, potentially allowing it to function as a stress regulator during amino acid starvation.     

Denitrification in pathogenic bacteria: for better or worst?

A large variety of physiological and taxonomic groups have the ability to use nitrogen oxides as alternative electron acceptors. Brucella spp. is an alpha-proteobacteriaceae that induces a persistent disease in some mammals. Recent work has revealed that a denitrifying gene cluster is important in the interaction of Brucella neotomoae with its host.     

Reactivity of carbon nanotubes: Free radical generation or scavenging activity?

Carbon nanotubes (CNTs) currently attract intense research efforts because of their unique properties which make them suitable for many industrial applications. When inhaled, CNTs constitute a possible hazard to human health. Several studies have shown that when instilled in the lung of experimental animals, CNTs induced an inflammatory and fibrotic response similar to that caused by other toxic particles which might be the result of oxidative stress caused by particle- and/or cell-derived free radicals. There is, however, no direct experimental evidence of a capacity of carbon nanotubes to generate directly free radicals. Here we report that multiwall carbon nanotubes (MWCNT) in aqueous suspension do not generate oxygen or carbon-centered free radicals in the presence of H2O2 or formate, respectively, as detected with the spin-trapping technique. Conversely, we observed that, when in contact with an external source of hydroxyl or superoxide radicals, MWCNT exhibit a remarkable radical scavenging capacity. It is therefore possible that the inflammatory reaction reported in vivo must be ascribed to MWCNT features other than particle-derived free radical generation.     

Spatial structure and β-diversity of phytoplankton in Tibetan Plateau lakes: nestedness or replacement?

Hydrobiologia - Spatial patterns and β-diversity of phytoplankton assemblages depend on the relative importance of species dispersal capacity and species-sorting. Variability in species...     

Antimicrobial peptides: pore formers or metabolic inhibitors in bacteria?

Antimicrobial peptides are an abundant and diverse group of molecules that are produced by many tissues and cell types in a variety of invertebrate, plant and animal species. Their amino acid composition, amphipathicity, cationic charge and size allow them to attach to and insert into membrane bilayers to form pores by 'barrel-stave', 'carpet' or 'toroidal-pore' mechanisms. Although these models are helpful for defining mechanisms of antimicrobial peptide activity, their relevance to how peptides damage and kill microorganisms still need to be clarified. Recently, there has been speculation that transmembrane pore formation is not the only mechanism of microbial killing. In fact several observations suggest that translocated peptides can alter cytoplasmic membrane septum formation, inhibit cell-wall synthesis, inhibit nucleic-acid synthesis, inhibit protein synthesis or inhibit enzymatic activity. In this review the different models of antimicrobial-peptide-induced pore formation and cell killing are presented.     

Environment or kin: whence do bees obtain acidophilic bacteria?

As honey bee populations decline, interest in pathogenic and mutualistic relationships between bees and microorganisms has increased. Honey bees and bumble bees appear to have a simple intestinal bacterial fauna that includes acidophilic bacteria. Here, we explore the hypothesis that sweat bees can acquire acidophilic bacteria from the environment. To quantify bacterial communities associated with two species of North American and one species of Neotropical sweat bees, we conducted 16S rDNA amplicon 454 pyrosequencing of bacteria associated with the bees, their brood cells and their nests. Lactobacillus spp. were the most abundant bacteria in many, but not all, of the samples. To determine whether bee-associated lactobacilli can also be found in the environment, we reconstructed the phylogenetic relationships of the genus Lactobacillus. Previously described groups that associate with Bombus and Apis appeared relatively specific to these genera. Close relatives of several bacteria that have been isolated from flowers, however, were isolated from bees. Additionally, all three sweat bee species associated with lactobacilli related to flower-associated lactobacilli. These data suggest that there may be at least two different means by which bees acquire putative probiotics. Some lactobacilli appear specific to corbiculate apids, possibly because they are largely maternally inherited (vertically transmitted). Other lactobacilli, however, may be regularly acquired from environmental sources such as flowers. Sweat bee-associated lactobacilli were found to be abundant in the pollen and frass inside the nests of halictids, suggesting that they could play a role in suppressing the growth of moulds and other spoilage organisms.     

Evolution and diversity in the legume-rhizobium symbiosis: chaos theory?

This paper examines the general biology of mycorrhizal associations alongside the wide range of alternative trophic adaptations which higher plants may employ when competing for limited resources of specific nutrients within an ecosystem. All examples described come from highly nutrient-impoverished heathlands or open woodlands of the kwongan of southwest Australia. An account is given of the general patterns of rooting morphology and their association with various mycorrhizal and non-mycorrhizal nutrient-acquiring strategies, including various forms of parasitism, epiparasitism, autotrophy with or without mycorrhizal association. Taxonomic affinities of each grouping are examined alongside growth and life form characteristics. A case study of patterns of utilization of a specific nutrient, nitrogen in a Banksia woodland ecosystem is presented to illustrate how a multifaceted approach can be used for studying species responses and interactions. The study categorizes species according to nitrate-utilizing ability and suggests how ¹⁵N natural abundance of soil and plant components and organic solutes of nitrogen is xylem might be utilized to separate species into different trophic categories. Response of the ecosystem to fire is examined in respect of the nutritional interrelationships of component species as the ecosystem changes from being nitrate dominant immediately after fire to increasingly ammonium-producing thereafter. The paper concludes by examining generally trophic relationships within whole ecosystems and outlines some of the challenges for future research in this connection.     

Endomycorrhizal and rhizobial symbiosis: How much do they share?

Abstract

Legume plants enter two important endosymbioses – with soil fungi, forming phosphorus acquiring arbuscular mycorrhiza (AM), and with nitrogen-fixing bacteria, leading to the formation of nitrogen-fixing root nodules. Both symbioses have been studied extensively because these symbioses have great potential for agricultural applications. Although 80% of all living land plants form AM, the nitrogen-fixing root nodule symbiosis with rhizobia is almost exclusively restricted to legumes. Despite varying degree of differences in the morphological responses induced by both endosymbionts in the host plants, significant similarities in the development of both fungal and bacterial symbioses have been reported. The signal perception and signal transduction cascades that initiate nodulation and mycorrhization in legumes partially overlap. Legume genes have been identified that are required for the establishment of both AM and root nodule symbiosis and are referred to as the common SYM genes. Genetic dissection of the common SYM signal transduction pathway required for bacterial and fungal root endosymbiosis has not only unraveled the players involved but also provided a first glimpse at conservation and specialization of signaling cascades essential for nodulation and mycorrhiza development. Based on the observation of common signaling cascades, it is tempting to speculate that the root nodule symbiosis, where fossil records date back to the late Cretaceaous, adopted and subsequently modified more ancient signal transduction pathways leading to AM formation, having already been in place 400 million years ago. This review discusses the common aspects of recognition of mycorrhizal fungi and Rhizobium by the host, and further signal transduction that leads to an effective symbiosis.