Summary Magnetotactic bacteria (MTB) are a group of phylogenetically and physiologically diverse Gram‐negative bacteria that synthesize intracellular magnetic crystals named magnetosomes. MTB are affiliated with three classes of Proteobacteria phylum, Nitrospirae phylum, Omnitrophica phylum and probably with the candidate phylum Latescibacteria. The evolutionary origin and physiological diversity of MTB compared with other bacterial taxonomic groups remain to be illustrated. Here, we analysed the genome of the marine magneto‐ovoid strain MO‐1 and found that it is closely related to Magnetococcus marinus MC‐1. Detailed analyses of the ribosomal proteins and whole proteomes of 390 genomes reveal that, among the Proteobacteria analysed, only MO‐1 and MC‐1 have coding sequences (CDSs) with a similarly high proportion of origins from Alphaproteobacteria , Betaproteobacteria , Deltaproteobacteria and Gammaproteobacteria . Interestingly, a comparative metabolic network analysis with anoxic network enzymes from sequenced MTB and non‐MTB successfully allows the eventual prediction of an organism with a metabolic profile compatible for magnetosome production. Altogether, our genomic analysis reveals multiple origins of MO‐1 and M. marinus MC‐1 genomes and suggests a metabolism‐restriction model for explaining whether a bacterium could become an MTB upon acquisition of magnetosome encoding genes.
Motivation: Sequence similarity is a common technique to compare gene-products. However, many applications need to compare gene-products based on what they do, not how they are. Most gene-products are being annotated with terms describing their biological function. These terms are defined in biological ontologies. This makes it possible to implement similarity measures between gene-products based on their behavior. Results: We define FuSSiMeG, a functional similarity measure between gene-products that compares the semantic similarity between the terms in their annotations. Availability: Software available from http://xldb.fc. ul.pt/rebil/ssm/. Contact: fcouto@di.fc.ul.pt
The fungus Laccaria bicolor — seen in its above-ground fruiting body presence as the 'bicoloured deceiver' mushroom — lives symbiotically on the roots of trees. Its genome has now been sequenced, and the key features of the genome characterized by transcript profiling. The study throws light on the mechanism of mycorrhizal symbiosis, the union of roots and soil fungi that is of vital important to plant productivity. And it will be of keen interest to evolutionary and plant biologists for its revelations about plant–fungus interactions shaping genomes over time. The genome of the fungus Laccaria bicolor is described; it is of keen interest to evolutionary and plant biologists for its revelations about plant–fungus interactions shaping genomes over time. Mycorrhizal symbioses—the union of roots and soil fungi—are universal in terrestrial ecosystems and may have been fundamental to land colonization by plants1,2. Boreal, temperate and montane forests all depend on ectomycorrhizae1. Identification of the primary factors that regulate symbiotic development and metabolic activity will therefore open the door to understanding the role of ectomycorrhizae in plant development and physiology, allowing the full ecological significance of this symbiosis to be explored. Here we report the genome sequence of the ectomycorrhizal basidiomycete Laccaria bicolor (Fig. 1) and highlight gene sets involved in rhizosphere colonization and symbiosis. This 65-megabase genome assembly contains ∼20,000 predicted protein-encoding genes and a very large number of transposons and repeated sequences. We detected unexpected genomic features, most notably a battery of effector-type small secreted proteins (SSPs) with unknown function, several of which are only expressed in symbiotic tissues. The most highly expressed SSP accumulates in the proliferating hyphae colonizing the host root. The ectomycorrhizae-specific SSPs probably have a decisive role in the establishment of the symbiosis. The unexpected observation that the genome of L. bicolor lacks carbohydrate-active enzymes involved in degradation of plant cell walls, but maintains the ability to degrade non-plant cell wall polysaccharides, reveals the dual saprotrophic and biotrophic lifestyle of the mycorrhizal fungus that enables it to grow within both soil and living plant roots. The predicted gene inventory of the L. bicolor genome, therefore, points to previously unknown mechanisms of symbiosis operating in biotrophic mycorrhizal fungi. The availability of this genome provides an unparalleled opportunity to develop a deeper understanding of the processes by which symbionts interact with plants within their ecosystem to perform vital functions in the carbon and nitrogen cycles that are fundamental to sustainable plant productivity.
Given the large amount of data stored in biological databases, the management of uncertainty and incompleteness in them is a non-trivial problem. To cope with the large amount of sequences being produced, a significant number of genes and proteins have been functionally characterized by automated tools. However, these tools have also produced a significant number of misannotations that are now present in the databases. This paper proposes a new approach for validating the automated annotations, which uses the large amount of publicly available information to compare automated annotations with preexisting curated annotations. To test the proposed approach, we developed a novel unsupervised method for filtering misannotations provided by automated annotation systems. We evaluated our method using the automated annotations submitted to BioCreAtIvE, a joint evaluation of state-of-the-art text-mining systems in Biology. The method scored each of these annotations and those scored below a certain threshold were discarded. The results have shown a small trade-off in recall for a large improvement in precision. For example, we were able to discard 44.6%, 66.8% and 81% of the misannotations, maintaining 96.9%, 84.2%, and 47.8% of the correct annotations, respectively. Moreover, we were able to outperform each individual submission to BioCreAtIvE by proper adjustment of the threshold. These results show the effectiveness of our approach in assisting curators of large biological databases in the use of contemporary tools for automatic identification of annotations.
We propose to apply the correlation between structure and function of gene products to curate information automatically extracted from biological literature. This can be achieved by automatically validating extracted information that satisfies the correlation, since it has strong evidence of being correct. We applied a semantic similarity measure (SSM) to identify a correlation between the modular structures of glycoside hydrolases (GHs) and functional terms extracted from associated literature. The source of GHs was CAZy, a database of carbohydrate-active enzymes classified in various families by their modular structure. We retrieved literature associated with each GH. From this literature, we extracted Gene Ontology (GO) functional terms. We implemented a SSM on GO to measure the relatedness between the GO terms extracted. Finally, we identified the correlation by comparing the probability of extracting similar terms inside with outside a family.
The human gut is home to trillions of microbes, thousands of bacterial phylotypes, as well as hydrogen-consuming methanogenic archaea. Studies in gnotobiotic mice indicate that Methanobrevibacter smithii, the dominant archaeon in the human gut ecosystem, affects the specificity and efficiency of bacterial digestion of dietary polysaccharides, thereby influencing host calorie harvest and adiposity. Metagenomic studies of the gut microbial communities of genetically obese mice and their lean littermates have shown that the former contain an enhanced representation of genes involved in polysaccharide degradation, possess more archaea, and exhibit a greater capacity to promote adiposity when transplanted into germ-free recipients. These findings have led to the hypothesis that M. smithii may be a therapeutic target for reducing energy harvest in obese humans. To explore this possibility, we have sequenced its 1,853,160-bp genome and compared it to other human gut-associated M. smithii strains and other Archaea. We have also examined M. smithii's transcriptome and metabolome in gnotobiotic mice that do or do not harbor Bacteroides thetaiotaomicron, a prominent saccharolytic bacterial member of our gut microbiota. Our results indicate that M. smithii is well equipped to persist in the distal intestine through (i) production of surface glycans resembling those found in the gut mucosa, (ii) regulated expression of adhesin-like proteins, (iii) consumption of a variety of fermentation products produced by saccharolytic bacteria, and (iv) effective competition for nitrogenous nutrient pools. These findings provide a framework for designing strategies to change the representation and/or properties of M. smithii in the human gut microbiota.
Plant-parasitic nematodes are major agricultural pests worldwide and novel approaches to control them are sorely needed. We report the draft genome sequence of the root-knot nematode Meloidogyne incognita, a biotrophic parasite of many crops, including tomato, cotton and coffee. Most of the assembled sequence of this asexually reproducing nematode, totaling 86 Mb, exists in pairs of homologous but divergent segments. This suggests that ancient allelic regions in M. incognita are evolving toward effective haploidy, permitting new mechanisms of adaptation. The number and diversity of plant cell wall-degrading enzymes in M. incognita is unprecedented in any animal for which a genome sequence is available, and may derive from multiple horizontal gene transfers from bacterial sources. Our results provide insights into the adaptations required by metazoans to successfully parasitize immunocompetent plants, and open the way for discovering new antiparasitic strategies.
The distribution of cellulosomal cohesin domains among the sequences currently compiled in various sequence databases was investigated. Two cohesin domains were detected in two consecutive open reading frames (ORFs) of the recently sequenced genome of the archaeon Archaeoglobus fulgidus . Otherwise, no cohesin‐like sequence could be detected in organisms other than those of the Eubacteria. One of the A. fulgidus cohesin‐containing ORFs also harbored a dockerin domain, but the additional modular portions of both genes are undefined, both with respect to sequence homology and function. It is currently unclear what function(s) the putative cohesin and dockerin‐containing proteins play in the life cycle of this organism. In particular, since A. fulgidus contains no known glycosyl hydrolase gene, the presence of a cellulosome can be excluded. The results suggest that cohesin and dockerin signature sequences cannot be used alone for the definitive identification of cellulosomes in genomes.
Lateral gene transfer (LGT) between bacteria constitutes a strong force in prokaryote evolution, transforming the hierarchical tree of life into a network of relationships between species. In contrast, only a few cases of LGT from eukaryotes to prokaryotes have been reported so far. The distal animal intestine is predominantly a bacterial ecosystem, supplying the host with energy from dietary polysaccharides through carbohydrate-active enzymes absent from its genome. It has been suggested that LGT is particularly important for the human microbiota evolution. Here we show evidence for the first eukaryotic gene identified in multiple gut bacterial genomes. We found in the genome sequence of several gut bacteria, a typically eukaryotic glycoside-hydrolase necessary for starch breakdown in plants. The distribution of this gene is patchy in gut bacteria with presence otherwise detected only in a few environmental bacteria. We speculate that the transfer of this gene to gut bacteria occurred by a sequence of two key LGT events; first, an original eukaryotic gene was transferred probably from Archaeplastida to environmental bacteria specialized in plant polysaccharides degradation and second, the gene was transferred from the environmental bacteria to gut microbes.
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