Histochemical evidence for lipid A (endotoxin) in eukaryote chloroplasts

A Water Extract from Chlorella sorokiniana Cell Walls Stimulates Growth of Bone Marrow Cells and Splenocytes

A water extract derived from the isolated cell walls of Chlorella sorokiniana (C. sorokiniana, Chlorella water extract, CWE) was analyzed for the presence of lipopolysaccharide (LPS)-related material via the Limulus amebocyte lysate (LAL) assay and evaluated for its growth stimulation effect on the bone marrow cells and splenocytes in vitro cell cultures. The extract contained low levels of LPS-related material, and a mass spectrum suggested that the extract contained many components, including a low level of a lipid A precursor, a compound known as lipid X, which is known to elicit a positive response in the LAL assay. Treatment with the CWE dose- and time-dependently stimulated the growth of mouse bone marrow cells (BMCs) and splenocytes (SPLs). Treatment with the CWE also increased specific BMC subpopulations, including antigen-presenting cells (CD19⁺ B cells, 33D1⁺ dendritic cells and CD68⁺ macrophages), and CD4⁺ and CD8⁺ T cells, but decreased the number of LY6G⁺ granulocytes. Treatment with the CWE also increased cytokine mRNA associated with T cell activation, including TNFα, IFNγ, and granzyme B in human lymphoblasts. The present study indicates that the cell wall fraction of C.sorokiniana contains an LPS-like material and suggests a candidate source for the bioactivity that stimulates growth of both innate and adaptive immune cells.

Cell Wall Membrane Fraction of Chlorella sorokiniana Enhances Host Antitumor Immunity and Inhibits Colon Carcinoma Growth in Mice

A colon cancer growth inhibitor partially purified from the isolated cell wall membrane fraction of Chlorella sorokiniana, here referred to as Chlorella membrane factor (CMF), was evaluated for its antitumor and immunomodulatory effects in cell culture and in a colon carcinoma mouse model. The CMF treatment dose- and time-dependently inhibited colon carcinoma cell growth in 2-dimensional cultures. Treatment with CMF also significantly inhibited the growth of colon carcinoma spheroids in 3-dimensional cell culture in coculture with T lymphocytes. In a mouse CT26 colon carcinoma peritoneal dissemination model, intraperitoneal injection of CMF (10 or 30 mg dry weight/kg body weight, every other day) dose-dependently and significantly attenuated the growth of tumor nodules via induction of tumor cell apoptosis. Evaluation of immune cell populations in ascites showed that CMF treatment tended to increase T lymphocytes but lower granulocyte populations. The present study suggests that the cell wall membrane fraction of Chlorella sorokiniana contains a bioactive material that inhibits colon carcinoma growth via direct cell growth inhibition and stimulation of host antitumor immunity. Hence, it is suggested that the Chlorella cell wall membrane extract or a bioactive substance in the extract is an attractive complementary medicine for cancer therapy.

Exopolysaccharides extracted from Parachlorella kessleri inhibit colon carcinoma growth in mice via stimulation of host antitumor immune responses

The newly purified extracellular polysaccharides (exopolysaccharides) from Parachlorella kessleri (PCEPS) were evaluated on their antitumor and immunomodulatory effects in cell culture and mouse colon carcinoma peritoneal dissemination model. In two-dimensional cell culture, the PCEPS treatment inhibited cell growth of both murine and human colon carcinoma cells in a dose- and time-dependent manner. In contrast, the growth of mouse splenocytes (SPLs) and bone marrow cells (BMCs) were stimulated by the treatment with PCEPS. The treatment with PCEPS also increased specific subpopulations of the cells in BMCs: antigen presenting cells (CD19⁺ B cells, 33D1⁺ dendritic cells and CD68⁺ macrophage) and CD8⁺ cytotoxic T cells. In three-dimensional spheroid culture, spheroid growth of CT26 cells co-cultured with HL-60 human neutrophilic promyeloblasts and Jurkat cells (human lymphoblasts), but not THP-1 human monocyte/macrophage was significantly attenuated by PCEPS treatment. In a mouse CT26 colon carcinoma peritoneal dissemination model, intraperitoneal injection of PCEPS (10 mg/kg, twice per week) significantly attenuated the growth of CT26 colon carcinoma in syngeneic mice. The present study suggests that PCEPS inhibits colon carcinoma growth via direct cell growth inhibition and a stimulation of the host antitumor immune responses. Taken together, the current study suggests that exopolysaccharides derived from Parachlorella kessleri contain significant bioactive materials that inhibit colon carcinoma growth.

Invited review: Priming, induction and modulation of plant defence responses by bacterial lipopolysaccharides

Bacterial lipopolysaccharides (LPSs) have multiple roles in plant—microbe interactions. LPS contributes to the low permeability of the outer membrane, which acts as a barrier to protect bacteria from plant-derived antimicrobial substances. Conversely, perception of LPS by plant cells can lead to the triggering of defence responses or to the priming of the plant to respond more rapidly and/or to a greater degree to subsequent pathogen challenge. LPS from symbiotic bacteria can have quite different effects on plants to those of pathogens. Some details are emerging of the structures within LPS that are responsible for induction of these different plant responses. The lipid A moiety is not solely responsible for all of the effects of LPS in plants; core oligosaccharide and O-antigen components can elicit specific responses. Here, we review the effects of LPS in induction of defence-related responses in plants, the structures within LPS responsible for eliciting these effects and discuss the possible nature of the (as yet unidentified) LPS receptors in plants.

Capture of lipopolysaccharide (endotoxin) by the blood clot: a comparative study

In vertebrates and arthropods, blood clotting involves the establishment of a plug of aggregated thrombocytes (the cellular clot) and an extracellular fibrillar clot formed by the polymerization of the structural protein of the clot, which is fibrin in mammals, plasma lipoprotein in crustaceans, and coagulin in the horseshoe crab, Limulus polyphemus. Both elements of the clot function to staunch bleeding. Additionally, the extracellular clot functions as an agent of the innate immune system by providing a passive anti-microbial barrier and microbial entrapment device, which functions directly at the site of wounds to the integument. Here we show that, in addition to these passive functions in immunity, the plasma lipoprotein clot of lobster, the coagulin clot of Limulus, and both the platelet thrombus and the fibrin clot of mammals (human, mouse) operate to capture lipopolysaccharide (LPS, endotoxin). The lipid A core of LPS is the principal agent of gram-negative septicemia, which is responsible for more than 100,000 human deaths annually in the United States and is similarly toxic to arthropods. Quantification using the Limulus Amebocyte Lysate (LAL) test shows that clots capture significant quantities of LPS and fluorescent-labeled LPS can be seen by microscopy to decorate the clot fibrils. Thrombi generated in the living mouse accumulate LPS in vivo. It is suggested that capture of LPS released from gram-negative bacteria entrapped by the blood clot operates to protect against the disease that might be caused by its systemic dispersal.

Green algal infection of American horseshoe crab (Limulus polyphemus) exoskeletal structures

Degenerative lesions in the dorsum of the horseshoe crab (Limulus polyphemus) exoskeleton, eyes, arthrodial membrane, and base of the telson were documented in a population of wild caught laboratory animals. The disease can lead to loss of tissue structure and function, deformed shells, abnormal molting, loss of ocular structures, erosion of interskeletal membranes, and cardiac hemorrhage. Microscopy, histopathology, and in vitro culture confirmed the causative agent to be a green algae of the family Ulvaceae. Further research may explain how green algae overcome horseshoe crab innate immunity leading to external and internal damage.

Metabolomics as a Hypothesis-Generating Functional Genomics Tool for the Annotation of Arabidopsis thaliana Genes of "Unknown Function"

Metabolomics is the methodology that identifies and measures global pools of small molecules (of less than about 1,000 Da) of a biological sample, which are collectively called the metabolome. Metabolomics can therefore reveal the metabolic outcome of a genetic or environmental perturbation of a metabolic regulatory network, and thus provide insights into the structure and regulation of that network. Because of the chemical complexity of the metabolome and limitations associated with individual analytical platforms for determining the metabolome, it is currently difficult to capture the complete metabolome of an organism or tissue, which is in contrast to genomics and transcriptomics. This paper describes the analysis of Arabidopsis metabolomics data sets acquired by a consortium that includes five analytical laboratories, bioinformaticists, and biostatisticians, which aims to develop and validate metabolomics as a hypothesis-generating functional genomics tool. The consortium is determining the metabolomes of Arabidopsis T-DNA mutant stocks, grown in standardized controlled environment optimized to minimize environmental impacts on the metabolomes. Metabolomics data were generated with seven analytical platforms, and the combined data is being provided to the research community to formulate initial hypotheses about genes of unknown function (GUFs). A public database (www.PlantMetabolomics.org) has been developed to provide the scientific community with access to the data along with tools to allow for its interactive analysis. Exemplary datasets are discussed to validate the approach, which illustrate how initial hypotheses can be generated from the consortium-produced metabolomics data, integrated with prior knowledge to provide a testable hypothesis concerning the functionality of GUFs.

Multiple lines of evidence localize signaling, morphology, and lipid biosynthesis machinery to the mitochondrial outer membrane of Arabidopsis

The composition of the mitochondrial outer membrane is notoriously difficult to deduce by orthology to other organisms, and biochemical enrichments are inevitably contaminated with the closely associated inner mitochondrial membrane and endoplasmic reticulum. In order to identify novel proteins of the outer mitochondrial membrane in Arabidopsis (Arabidopsis thaliana), we integrated a quantitative mass spectrometry analysis of highly enriched and prefractionated samples with a number of confirmatory biochemical and cell biology approaches. This approach identified 42 proteins, 27 of which were novel, more than doubling the number of confirmed outer membrane proteins in plant mitochondria and suggesting novel functions for the plant outer mitochondrial membrane. The novel components identified included proteins that affected mitochondrial morphology and/or segregation, a protein that suggests the presence of bacterial type lipid A in the outer membrane, highly stress-inducible proteins, as well as proteins necessary for embryo development and several of unknown function. Additionally, proteins previously inferred via orthology to be present in other compartments, such as an NADH:cytochrome B5 reductase required for hydroxyl fatty acid accumulation in developing seeds, were shown to be located in the outer membrane. These results also revealed novel proteins, which may have evolved to fulfill plant-specific requirements of the mitochondrial outer membrane, and provide a basis for the future functional characterization of these proteins in the context of mitochondrial intracellular interaction.

Pathway for lipid A biosynthesis in Arabidopsis thaliana resembling that of Escherichia coli

The lipid A moiety of Escherichia coli lipopolysaccharide is a hexa-acylated disaccharide of glucosamine that makes up the outer monolayer of the outer membrane. Arabidopsis thaliana contains nuclear genes encoding orthologs of key enzymes of bacterial lipid A biosynthesis, including LpxA, LpxC, LpxD, LpxB, LpxK and KdtA. Although structurally related lipid A molecules are found in most other gram-negative bacteria, lipid A and its precursors have not been directly detected in plants previously. However, homozygous insertional knockout mutations or RNAi knock-down constructs of Arabidopsis lpx and kdtA mutants revealed accumulation (or disappearance) of the expected monosaccharide or disaccharide lipid A precursors by mass spectrometry of total lipids extracted from 10-day old seedlings of these mutants. In addition, fluorescence microscopy of lpx-gfp fusions in transgenic Arabidopsis plants suggests that the Lpx and KdtA proteins are expressed and targeted to mitochondria. Although the structure of the lipid A end product generated by plants is still unknown, our work demonstrates that plants synthesize lipid A precursors using the same enzymatic pathway present in E. coli.

Evolution of the Kdo2-lipid A biosynthesis in bacteria

Background

Lipid A is the highly immunoreactive endotoxic center of lipopolysaccharide (LPS). It anchors the LPS into the outer membrane of most Gram-negative bacteria. Lipid A can be recognized by animal cells, triggers defense-related responses, and causes Gram-negative sepsis. The biosynthesis of Kdo₂-lipid A, the LPS substructure, involves with nine enzymatic steps.

Results

In order to elucidate the evolutionary pathway of Kdo₂-lipid A biosynthesis, we examined the distribution of genes encoding the nine enzymes across bacteria. We found that not all Gram-negative bacteria have all nine enzymes. Some Gram-negative bacteria have no genes encoding these enzymes and others have genes only for the first four enzymes (LpxA, LpxC, LpxD, and LpxB). Among the nine enzymes, five appeared to have arisen from three independent gene duplication events. Two of such events happened within the Proteobacteria lineage, followed by functional specialization of the duplicated genes and pathway optimization in these bacteria.

Conclusions

The nine-enzyme pathway, which was established based on the studies mainly in Escherichia coli K12, appears to be the most derived and optimized form. It is found only in E. coli and related Proteobacteria. Simpler and probably less efficient pathways are found in other bacterial groups, with Kdo₂-lipid A variants as the likely end products. The Kdo₂-lipid A biosynthetic pathway exemplifies extremely plastic evolution of bacterial genomes, especially those of Proteobacteria, and how these mainly pathogenic bacteria have adapted to their environment.

The properties of the outer membrane localized Lipid A transporter LptD

Gram-negative bacteria are surrounded by a cell wall including the outer membrane. The outer membrane is composed of two distinct monolayers where the outer layer contains lipopolysaccharides (LPS) with the non-phospholipid Lipid A as the core. The synthesis of Lipid A is initiated in the cytosol and thereby the molecule has to be transported across the inner and outer membranes. The β-barrel lipopolysaccharide-assembly protein D (LptD) was discovered to be involved in the transfer of Lipid A into the outer membrane of gram-negative bacteria. At present the molecular procedure of lipid transfer across the outer membrane remains unknown. Here we approached the functionality of the transfer system by an electrophysiological analysis of the outer membrane protein from Escherichia coli named ecLptD. In vitro the protein shows cation selectivity and has an estimated pore diameter of about 1.8 nm. Addition of Lipid A induces a transition of the open state to a sub-conductance state with two independent off-rates, which might suggest that LptD is able to bind and transport the molecule in vitro. To generalize our findings with respect to the Lipid A transport system of other gram-negative bacteria we have explored the existence of the proteins involved in this pathway by bioinformatic means. We were able to identify the membrane-inserted components of the Lipid A transport system in all gram-negative bacteria, whereas the periplasmic components appear to be species-specific. The LptD proteins of different bacteria are characterized by their periplasmic N-terminal domain and a C-terminal barrel region. The latter shows distinct sequence properties, particularly in LptD proteins of cyanobacteria, and this specific domain can be found in plant proteins as well. By electrophysiological experiments on LptD from Anabaena sp. PCC 7120 we are able to confirm the functional relation of anaLptD to Lipid A transport.

Characterization of a putative 3-deoxy-D-manno-2-octulosonic acid (Kdo) transferase gene from Arabidopsis thaliana

The structures of the pectic polysaccharide rhamnogalacturonan II (RG-II) pectin constituent are remarkably evolutionary conserved in all plant species. At least 12 different glycosyl residues are present in RG-II. Among them is the seldom eight-carbon sugar 3-deoxy-d-manno-octulosonic acid (Kdo) whose biosynthetic pathway has been shown to be conserved between plants and Gram-negative bacteria. Kdo is formed in the cytosol by the condensation of phosphoenol pyruvate with d-arabinose-5-P and then activated by coupling to cytidine monophosphate (CMP) prior to its incorporation in the Golgi apparatus by a Kdo transferase (KDTA) into the nascent polysaccharide RG-II. To gain new insight into RG-II biosynthesis and function, we isolated and characterized null mutants for the unique putative KDTA (AtKDTA) encoded in the Arabidopsis genome. We provide evidence that, in contrast to mutants affecting the RG-II biosynthesis, the extinction of the AtKDTA gene expression does not result in any developmental phenotype in the AtkdtA plants. Furthermore, the structure of RG-II from the null mutants was not altered and contained wild-type amount of Rha-alpha(1-5)Kdo side chain. The cellular localization of AtKDTA was investigated by using laser scanning confocal imaging of the protein fused to green fluorescent protein. In agreement with its cellular prediction, the fusion protein was demonstrated to be targeted to the mitochondria. These data, together with data deduced from sequence analyses of higher plant genomes, suggest that AtKDTA encodes a putative KDTA involved in the synthesis of a mitochondrial not yet identified lipid A-like molecule rather than in the synthesis of the cell wall RG-II.

The occupant as a source of house dust bacteria

BACKGROUND

Markers for microbial groups are commonly measured in house dust samples to assess indoor exposure to microbes in studies on asthma and allergy. However, little is known about the sources of different microbes. A better understanding of the nature and origin of microbes present in the immediate environment of human beings is crucial if one wants to elucidate protective as well as adverse effects on human health.

OBJECTIVE

To determine the extent to which the bacterial composition of mattress and floor dust reflects the presence of the human body in relation to other environmental sources.

METHODS

House dust and skin surface swab samples of occupants in 4 homes were collected and analyzed for their bacterial content, using a culture-independent methodology. Bacterial sequences analyzed from the different house dusts and skin surface swabs represented random samples of bacteria present in a given sample. Highly similar sequences were grouped to assess biodiversity and to draw conclusions about the sources of bacteria.

RESULTS

The bacterial flora in the house dust samples was found to be highly diverse and dominated by gram-positive bacteria. To a considerable extent, the presence of different bacterial groups was attributed to human sources. In the individuals' mattress dust samples, 69% to 88% of the bacterial sequences analyzed were associated with human origins. The respective percentages for the individual floor dusts ranged from 45% to 55%.

CONCLUSION

Our study indicates that human-derived bacteria account for a large part of the mainly gram-positive bacterial content in house dust.

SOLID2: an antibody array-based life-detector instrument in a Mars Drilling Simulation Experiment (MARTE)

A field prototype of an antibody array-based life-detector instrument, Signs Of LIfe Detector (SOLID2), has been tested in a Mars drilling mission simulation called MARTE (Mars Astrobiology Research and Technology Experiment). As one of the analytical instruments on the MARTE robotic drilling rig, SOLID2 performed automatic sample processing and analysis of ground core samples (0.5 g) with protein microarrays that contained 157 different antibodies. Core samples from different depths (down to 5.5 m) were analyzed, and positive reactions were obtained in antibodies raised against the Gram-negative bacterium Leptospirillum ferrooxidans, a species of the genus Acidithiobacillus (both common microorganisms in the Río Tinto area), and extracts from biofilms and other natural samples from the Río Tinto area. These positive reactions were absent when the samples were previously subjected to a high-temperature treatment, which indicates the biological origin and structural dependency of the antibody-antigen reactions. We conclude that an antibody array-based life-detector instrument like SOLID2 can detect complex biological material, and it should be considered as a potential analytical instrument for future planetary missions that search for life.

Finding novel metabolic genes through plant-prokaryote phylogenomics

Plants and prokaryotes share thousands of genes. Those with known functions mostly encode enzymes of primary metabolism or other key biochemical components, and the same is almost surely true of those whose function is still obscure. The availability of hundreds of sequenced genomes and of rich postgenomic resources now makes possible the use of comparative genomics ('phylogenomics') of plants and prokaryotes to infer, and then verify, functions for such unknown genes. In this type of analysis, plant and prokaryote data each inform the search for function, and do so synergistically. This breaks with the past pattern of gene discovery, in which the information flow was most often unidirectional from prokaryotes to plants.

Lipid A modification systems in gram-negative bacteria

The lipid A moiety of lipopolysaccharide forms the outer monolayer of the outer membrane of most gram-negative bacteria. Escherichia coli lipid A is synthesized on the cytoplasmic surface of the inner membrane by a conserved pathway of nine constitutive enzymes. Following attachment of the core oligosaccharide, nascent core-lipid A is flipped to the outer surface of the inner membrane by the ABC transporter MsbA, where the O-antigen polymer is attached. Diverse covalent modifications of the lipid A moiety may occur during its transit from the outer surface of the inner membrane to the outer membrane. Lipid A modification enzymes are reporters for lipopolysaccharide trafficking within the bacterial envelope. Modification systems are variable and often regulated by environmental conditions. Although not required for growth, the modification enzymes modulate virulence of some gram-negative pathogens. Heterologous expression of lipid A modification enzymes may enable the development of new vaccines.