Detection of microbes in the subsurface

The search for evidence of microbial life in the deep subsurface of Earth has implications for the Mars Rover Sampling Return Missions program. If suitably protected environments can be found on Mars then the instrumentation to detect biomarkers could be used to examine the molecular details. Finding a lipid in Martian soil would represent possibly the simplest test for extant or extinct life. A device that could do a rapid extraction possibly using the supercritical fluid technology under development now with a detection of the carbon content would clearly indicate a sample to be returned

Adhesion of conidia and germlings of the plant pathogenic fungus Bipolaris sorokiniana to solid surfaces

Soon after coming in contact with its host, the plant pathogenic fungus Bipolaris sorokiniana produces an extracellular material that appears to be important for adhering conidia and germlings to the host surface. To further understand this step of the infection, the adhesion of B. sorokiniana to artificial solid surfaces was examined. On a hydrophobic (polystyrene) surface adhesion occurred in two stages, the first by conidia and the second by germlings. Conidial adhesion occurred shortly (0-1 h) after hydration. The conidia were easily detached by increasing the shear force and including detergents in the washing buffer. As conidia were hydrophobic, these observations indicate that conidial adhesion to polystyrene is due to weak, hydrophobic interaction. The second stage of adhesion was accompanied by conidial germination and occurred 1-2 h after hydration and contact with the surface. Concomitant with the delayed adhesion, the fungus produced an extracellular matrix (ECM). The adhesion of germlings was firm and surface-unspecific since they adhered to both hydrophobic and hydrophilic (glass) surfaces, Except for strong bases, hydrochloric acid and broad-specificity proteases (including Pronase E), none of the hydrolytic enzymes, electrolyte solutions, ionic and hydrophobic detergents and organic solvents removed germlings from the solid surfaces. The adhesion of germlings incubated in the presence of the protein glycosylation inhibitor tunicamycin or the lectins Con A (Concanavalin A) and GNA (from Galanthus nivalis) was significantly reduced, which indicates the involvement of surface glycoproteins in this process. The surface proteins of germlings were labelled with I-125, extracted and analysed by two-dimensional gel electrophoresis. This revealed about 40 surface proteins over a wide pH range (4-10) with molecular masses between 10 and 100 kDa

Low genetic diversity among isolates of the nematode-trapping fungus Duddingtonia flagrans: evidence for recent worldwide dispersion from a single common ancestor

The genetic variation of Duddingtonia flagrans, which has become a promising biocontrol agent of animal parasitic nematodes, was investigated in a worldwide collection of 22 isolates. We analysed the sequence variation in four nuclear genes, tubA (beta-tubulin), CMD1 (calmodulin), EF1alpha (translation elongation factor 1alpha), and PII (extracellular serine protease). 1428 aligned base pairs (bp) were analysed from the four genes, including 709 bp of introns. In addition, the variations in three anonymous genomic regions comprising 1155 bp were examined. Three single nucleotide polymorphisms (SNPs) were detected in the seven loci, none of them in the protein encoding genes. The genetic variation was significantly higher in the nematode-trapping fungus Arthrobotrys oligospora, the closest evolutionary relative to D. flagrans. Analysis of 12 isolates of A. oligospora revealed 30 SNPs in tub A, CMD1, EF1alpha and PII. The genetic variation in the isolates of D. flagrans was further examined using AFLP analysis. Five primer combinations were used to detect 159 bands, of which 94 (59.1%) were polymorphic. A neighbour-joining tree based on the AFLP data showed no clear association between genotype and geographical origin. Furthermore, the AFLP data suggest that D. flagrans is mainly clonal and no recombination could be detected, not even within the same country. The low genetic variation in D. flagrans suggests that this fungus has recently diverged from a single progenitor. Based on estimations of mutation rates, it was calculated that this most recent common ancestor lived about 16000-23000 years ago

PHOREST: a web-based tool for comparative analyses of expressed sequence tag data

Comparative analysis of expressed sequence tags is becoming an important tool in molecular ecology for comparing gene expression in organisms grown in certain environments. Additionally, expressed sequence tag database information can be used for the construction of DNA microarrays and for the detection of single nucleotide polymorphisms. For such applications, we present PHOREST, a web-based tool for managing, analysing and comparing various collections of expressed sequence tags. It is written in PHP (PHP: Hypertext Preprocessor) and runs on UNIX, Microsoft Windows and Macintosh (Mac OS X) platforms

Genomic Mechanisms Accounting for the Adaptation to Parasitism in Nematode-Trapping Fungi

Orbiliomycetes is one of the earliest diverging branches of the filamentous ascomycetes. The class contains nematode-trapping fungi that form unique infection structures, called traps, to capture and kill free-living nematodes. The traps have evolved differently along several lineages and include adhesive traps (knobs, nets or branches) and constricting rings. We show, by genome sequencing of the knob-forming species Monacrosporium haptotylum and comparison with the net-forming species Arthrobotrys oligospora, that two genomic mechanisms are likely to have been important for the adaptation to parasitism in these fungi. Firstly, the expansion of protein domain families and the large number of species-specific genes indicated that gene duplication followed by functional diversification had a major role in the evolution of the nematode-trapping fungi. Gene expression indicated that many of these genes are important for pathogenicity. Secondly, gene expression of orthologs between the two fungi during infection indicated that differential regulation was an important mechanism for the evolution of parasitism in nematode-trapping fungi. Many of the highly expressed and highly upregulated M. haptotylum transcripts during the early stages of nematode infection were species-specific and encoded small secreted proteins (SSPs) that were affected by repeat-induced point mutations (RIP). An active RIP mechanism was revealed by lack of repeats, dinucleotide bias in repeats and genes, low proportion of recent gene duplicates, and reduction of recent gene family expansions. The high expression and rapid divergence of SSPs indicate a striking similarity in the infection mechanisms of nematode-trapping fungi and plant and insect pathogens from the crown groups of the filamentous ascomycetes (Pezizomycotina). The patterns of gene family expansions in the nematode-trapping fungi were more similar to plant pathogens than to insect and animal pathogens. The observation of RIP activity in the Orbiliomycetes suggested that this mechanism was present early in the evolution of the filamentous ascomycetes

Divergence in gene expression related to variation in host specificity of an ectomycorrhizal fungus

Ectomycorrhizae are formed by mutualistic interactions between fungi and the roots of woody plants. During symbiosis the two organisms exchange carbon and nutrients in a specific tissue that is formed at the contact between a compatible fungus and plant. There is considerable variation in the degree of host specificity among species and strains of ectomycorrhizal fungi. In this study, we have for the first time shown that this variation is associated with quantitative differences in gene expression, and with divergence in nucleotide sequences of symbiosis-regulated genes. Gene expression and sequence evolution were compared in different strains of the ectomycorrhizal fungus Paxillus involutus; the strains included Nau, which is not compatible with birch and poplar, and the two compatible strains Maj and ATCC200175. On a genomic level, Nau and Maj were very similar. The sequence identity was 98.9% in the 16 loci analysed, and only three out of 1075 genes analysed by microarray-based hybridizations had signals indicating differences in gene copy numbers. In contrast, 66 out of the 1075 genes were differentially expressed in Maj compared to Nau after contact with birch roots. Thirty-seven of these symbiosis-regulated genes were also differentially expressed in the ATCC strain. Comparative analysis of DNA sequences of the symbiosis-regulated genes in different strains showed that two of them have evolved at an enhanced rate in Nau. The sequence divergence can be explained by a decreased selection pressure, which in turn is determined by lower functional constraints on these proteins in Nau as compared to the compatible strains

Phylogenetic Analysis Suggests That Habitat Filtering Is Structuring Marine Bacterial Communities Across the Globe

The phylogenetic structure and community composition were analysed in an existing data set of marine bacterioplankton communities to elucidate the evolutionary and ecological processes dictating the assembly. The communities were sampled from coastal waters at nine locations distributed worldwide and were examined through the use of comprehensive clone libraries of 16S ribosomal RNA genes. The analyses show that the local communities are phylogenetically different from each other and that a majority of them are phylogenetically clustered, i.e. the species (operational taxonomic units) were more related to each other than expected by chance. Accordingly, the local communities were assembled non-randomly from the global pool of available bacterioplankton. Further, the phylogenetic structures of the communities were related to the water temperature at the locations. In agreement with similar studies, including both macroorganisms and bacteria, these results suggest that marine bacterial communities are structured by “habitat filtering”, i.e. through non-random colonization and invasion determined by environmental characteristics. Different bacterial types seem to have different ecological niches that dictate their survival in different habitats. Other eco-evolutionary processes that may contribute to the observed phylogenetic patterns are discussed. The results also imply a mapping between phenotype and phylogenetic relatedness which facilitates the use of community phylogenetic structure analysis to infer ecological and evolutionary assembly processes

Lipid Biomarkers

Abstract is not availabl