Accurate read-based metagenome characterization using a hierarchical suite of unique signatures.

A major challenge in the field of shotgun metagenomics is the accurate identification of organisms present within a microbial community, based on classification of short sequence reads. Though existing microbial community profiling methods have attempted to rapidly classify the millions of reads output from modern sequencers, the combination of incomplete databases, similarity among otherwise divergent genomes, errors and biases in sequencing technologies, and the large volumes of sequencing data required for metagenome sequencing has led to unacceptably high false discovery rates (FDR). Here, we present the application of a novel, gene-independent and signature-based metagenomic taxonomic profiling method with significantly and consistently smaller FDR than any other available method. Our algorithm circumvents false positives using a series of non-redundant signature databases and examines Genomic Origins Through Taxonomic CHAllenge (GOTTCHA). GOTTCHA was tested and validated on 20 synthetic and mock datasets ranging in community composition and complexity, was applied successfully to data generated from spiked environmental and clinical samples, and robustly demonstrates superior performance compared with other available tools.

Draft genome sequence of the rubber tree Hevea brasiliensis.

BACKGROUND: Hevea brasiliensis, a member of the Euphorbiaceae family, is the major commercial source of natural rubber (NR). NR is a latex polymer with high elasticity, flexibility, and resilience that has played a critical role in the world economy since 1876. RESULTS: Here, we report the draft genome sequence of H. brasiliensis. The assembly spans ~1.1 Gb of the estimated 2.15 Gb haploid genome. Overall, ~78% of the genome was identified as repetitive DNA. Gene prediction shows 68,955 gene models, of which 12.7% are unique to Hevea. Most of the key genes associated with rubber biosynthesis, rubberwood formation, disease resistance, and allergenicity have been identified. CONCLUSIONS: The knowledge gained from this genome sequence will aid in the future development of high-yielding clones to keep up with the ever increasing need for natural rubber.

Globins synthesize the second messenger bis-(3'-5')-cyclic diguanosine monophosphate in bacteria.

Globin-coupled sensors are heme-binding signal transducers in Bacteria and Archaea in which an N-terminal globin controls the activity of a variable C-terminal domain. Here, we report that BpeGReg, a globin-coupled diguanylate cyclase from the whooping cough pathogen Bordetella pertussis, synthesizes the second messenger bis-(3'-5')-cyclic diguanosine monophosphate (c-di-GMP) upon oxygen binding. Expression of BpeGReg in Salmonella typhimurium enhances biofilm formation, while knockout of the BpeGReg gene of B. pertussis results in decreased biofilm formation. These results represent the first identification a signal ligand for any diguanylate cyclase and provide definitive experimental evidence that a globin-coupled sensor regulates c-di-GMP synthesis and biofilm formation. We propose that the synthesis of c-di-GMP by globin sensors is a widespread phenomenon in bacteria.

Cloning, expression, and purification of the N-terminal heme-binding domain of globin-coupled sensors.

Globin-coupled sensors (GCSs) are multidomain proteins, consisting of an N-terminal globin domain fused to a variety of C-terminal transmitter domains. Functional classification of GCSs is based on the transmitter domain(s) they possess, broadly falling under either aerotaxis or gene regulation. This chapter describes methods and strategies for cloning, expression, and purification of GCSs for spectroscopic analysis and determination of the minimum heme-binding domain, together with bioinformatic approaches for database searching and examination of domain architectures.

Globin-coupled sensors, protoglobins, and the last universal common ancestor.

The strategy for detecting oxygen, carbon monoxide, nitric oxide, and sulfides is predominantly through heme-based sensors utilizing either a globin domain or a PAS domain. Whereas PAS domains bind various cofactors, globins bind only heme. Globin-coupled sensors (GCSs) were first described as regulators of the aerotactic responses in Bacillus subtilis and Halobacterium salinarum. GCSs were also identified in diverse microorganisms that appear to have roles in regulating gene expression. Functional and evolutionary analyses of the GCSs, their protoglobin ancestor, and their relationship to the last universal common ancestor (LUCA) are discussed in the context of globin-based signal transduction.

Ancestral hemoglobins in Archaea.

Hemoglobins are ubiquitous in Eukarya and Bacteria but, until now, have not been found in Archaea. A phylogenetic analysis of the recently revealed microbial family of globin-coupled heme-based sensors suggests that these sensors descended from an ancient globin-only progenitor, or a protoglobin (Pgb). Here, we report the discovery and characterization of two Pgbs from the Archaea: ApPgb from the obligately aerobic hyperthermophile Aeropyrum pernix, and MaPgb from the strictly anaerobic methanogen Methanosarcina acetivorans. Both ApPgb and MaPgb bind molecular oxygen, nitric oxide, and carbon monoxide by means of a heme moiety that is coordinated to the protein through the F8 histidine (histidine 120). We postulate that these archaeal globins are the ancestors of contemporary hemoglobins.

The diversity of globin-coupled sensors.

The recently discovered globin-coupled sensors (GCSs) are heme-containing two-domain transducers distinct from the PAS domain superfamily. We have identified an additional 22 GCSs with varying multi-domain C-terminal transmitters through a search of the complete and incomplete microbial genome datasets. The GCS superfamily is composed of two major subfamilies: the aerotactic and gene regulators. We postulate the existence of protoglobin in Archaea as the predecessor to the chimeric GCS.