461 research outputs found
Identifying and tracking mobile elements in evolving compost communities yields insights into the nanobiome
Microbial evolution is driven by rapid changes in gene content mediated by horizontal gene transfer (HGT). While mobile genetic elements (MGEs) are important drivers of gene flux, the nanobiome-the zoo of Darwinian replicators that depend on microbial hosts-remains poorly characterised. New approaches are necessary to increase our understanding beyond MGEs shaping individual populations, towards their impacts on complex microbial communities. A bioinformatic pipeline (xenoseq) was developed to cross-compare metagenomic samples from microbial consortia evolving in parallel, aimed at identifying MGE dissemination, which was applied to compost communities which underwent periodic mixing of MGEs. We show that xenoseq can distinguish movement of MGEs from demographic changes in community composition that otherwise confounds identification, and furthermore demonstrate the discovery of various unexpected entities. Of particular interest was a nanobacterium of the candidate phylum radiation (CPR) which is closely related to a species identified in groundwater ecosystems (Candidatus Saccharibacterium), and appears to have a parasitic lifestyle. We also highlight another prolific mobile element, a 313 kb plasmid hosted by a Cellvibrio lineage. The host was predicted to be capable of nitrogen fixation, and acquisition of the plasmid coincides with increased ammonia production. Taken together, our data show that new experimental strategies combined with bioinformatic analyses of metagenomic data stand to provide insight into the nanobiome as a driver of microbial community evolution
Role of Operon aaoSo-mutT in Antioxidant Defense in Streptococcus oligofermentans
Previously, we have found that an insertional inactivation of aaoSo, a gene encoding L-amino acid oxidase (LAAO), causes marked repression of the growth of Streptococcus oligofermentans. Here, we found that aaoSo and mutT, a homolog of pyrophosphohydrolase gene of Escherichia coli, constituted an operon. Deletion of either gene did not impair the growth of S. oligofermentans, but double deletion of both aaoSo and mutT was lethal. Quantitative PCR showed that the transcript abundance of mutT was reduced for 13-fold in the aaoSo insertional mutant, indicating that gene polarity derived from the inactivation of aaoSo attenuated the expression of mutT. Enzymatic assays were conducted to determine the biochemical functions of LAAO and MutT of S. oligofermentans. The results indicated that LAAO functioned as an aminoacetone oxidase [47.75 nmol H2O2 (min·mg protein)–1]; and MutT showed the pyrophosphohydrolase activity, which removed mutagens such as 8-oxo-dGTP. Like paraquat, aaoSo mutations increased the expression of SOD, and addition of aminoacetone (final concentration, 5 mM) decreased the mutant’s growth by 11%, indicating that the aaoSo mutants are under ROS stress. HPLC did reveal elevated levels of cytoplasmic aminoacetone in both the deletion and insertional gene mutants of aaoSo. Electron spin resonance spectroscopy showed increased hydroxyl radicals in both types of aaoSo mutant. This demonstrated that inactivation of aaoSo caused the elevation of the prooxidant aminoacetone, resulting the cellular ROS stress. Our study indicates that the presence of both LAAO and MutT can prevent endogenous metabolites-generated ROS and mutagens. In this way, we were able to determine the role of the aaoSo-mutT operon in antioxidant defense in S. oligofermentans
BlackCAT: A catalogue of stellar-mass black holes in X-ray transients
During the last ~50 years, the population of black hole candidates in X-ray
binaries has increased considerably with 59 Galactic objects detected in
transient low-mass X-ray binaries, plus a few in persistent systems (including
~5 extragalactic binaries). We collect near-infrared, optical and X-ray
information spread over hundreds of references in order to study the population
of black holes in X-ray transients as a whole. We present the most updated
catalogue of black hole transients, which contains X-ray, optical and
near-infrared observations together with their astrometric and dynamical
properties. It provides new useful information in both statistical and
observational parameters providing a thorough and complete overview of the
black hole population in the Milky Way. Analysing the distances and spatial
distribution of the observed systems, we estimate a total population of ~1300
Galactic black hole transients. This means that we have already discovered less
than ~5% of the total Galactic distribution. The complete version of this
catalogue will be continuously updated online and in the Virtual Observatory,
including finding charts and data in other wavelengths.Comment: http://www.astro.puc.cl/BlackCAT - Accepted for publication in
Astronomy & Astrophysics. 20 pages, 8 figures, 5 Table
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