Project description:Histone proteins have traditionally been thought to be restricted to eukaryotes and most archaea, with eukaryotic nucleosomal histones deriving from their archaeal ancestors. In contrast, bacteria lack histones as a rule. However, in recent years histone proteins have been identified in a few bacterial clades, in particular the phylum Bdellovibrionota, and these histones have been proposed to exhibit a range of divergent features compared to histones in archaea and eukaryotes. However, no experimental functional genomic studies of the properties of Bdellovibrionota chromatin have been carried out. In this work, we map the landscape of chromatin accessibility, active transcription and three-dimensional genome organization in a member of Bdellovibrionota (a Bacteriovorax strain). We find that Bacteriovorax chromatin is characterized by preferential accessibility around promoter regions, similar to what is observed in eukaryotes with compact genomes such as yeast, and also to some archaea. As in eukaryotes, chromatin accessibility positively correlates with gene expression. Mapping active transcription through single-strand DNA (ssDNA) profiling revealed that Bacteriovorax promoters exhibit very strong polymerase pausing, unlike in yeast, but similar to the state of mammalian and fly promoters. Finally, the Bacteriovorax genome exists in a three-dimensional (3D) conformation analogous to that of other bacteria without histones, organized by the parABS system and along the axis defined by replication origin and termination regions. These results provide a foundation for understanding the chromatin biology of the unique Bdellovibrionota bacteria and the deep evolution of chromatin organization across the tree of life.
Project description:Gene regulation is one of the most ubiquitous processes in biology. And yet, while the catalogue of 15 bacterial genomes continues to expand rapidly, we remain ignorant about how almost all of the genes in 16 these genomes are regulated. Characterizing the molecular mechanisms by which regulatory sequences 17 operate still requires focused efforts using low-throughput methods. Here we show how a combination of 18 massively parallel reporter assays, mass spectrometry, and information-theoretic modeling can be used 19 to dissect bacterial promoters in a systematic and scalable way. We demonstrate this method on both 20 well-studied and previously uncharacterized promoters in the enteric bacterium Escherichia coli. In all 21 cases we recover nucleotide-resolution models of promoter mechanism. For some promoters, including 22 previously unannotated ones, we can further extract quantitative biophysical models describing 23 input-output relationships. This method opens up the possibility of exhaustively dissecting the 24 mechanisms of promoter function in E. coli and a wide range of other bacteria.
Project description:Six bacterial genomes, Geobacter metallireducens GS-15, Chromohalobacter salexigens, Vibrio breoganii 1C-10, Bacillus cereus ATCC 10987, Campylobacter jejuni subsp. jejuni 81-176 and Campylobacter jejuni NCTC 11168, all of which had previously been sequenced using other platforms were re-sequenced using single-molecule, real-time (SMRT) sequencing specifically to analyze their methylomes. In every case a number of new N6-methyladenine (m6A) and N4-methylcytosine (m4C) methylation patterns were discovered and the DNA methyltransferases (MTases) responsible for those methylation patterns were assigned. In 15 cases it was possible to match MTase genes with MTase recognition sequences without further sub-cloning. Two Type I restriction systems required sub-cloning to differentiate their recognition sequences, while four MTases genes that were not expressed in the native organism were sub-cloned to test for viability and recognition sequences. No attempt was made to detect 5-methylcytosine (m5C) recognition motifs from the SMRT sequencing data because this modification produces weaker signals using current methods. However, all predicted m6A and m4C MTases were detected unambiguously. This study shows that the addition of SMRT sequencing to traditional sequencing approaches gives a wealth of useful functional information about a genome showing not only which MTase genes are active, but also revealing their recognition sequences. Examination of the methylomes of six different strains of bacteria using kinetic data from single-molecule, real-time (SMRT) sequencing on the PacBio RS.
Project description:We have designed and experimentally validated the BactoChip, a 60-mer oligonucleotide microarray for simultaneous detection and quantification of multiple bacterial species of clinical interest. The Bactochip microarray targets a novel set of high-resolution marker genes, those genes that most unequivocally characterized each bacterial species. The accuracy of the BactoChip microarray was evaluated using the labeled total DNA of single bacterial species at different concentrations (from 65ng to more than 250ng). The specificity of the developed array was further validated using mixed cultures containing up to 15 different bacterial species in even or staggered amount. We employed the Agilent 'Custom HD-CGH 8x15k Array" (catalogue number: G4427A) and the Agilent'Genomic DNA ULS labeling Kit" (catalogue number: 5190-0419). The microarray successfully distinguished among bacterial species from 21 different genera. The BactoChip additionally proved accurate in determining species-level relative abundances over a 10-fold dynamic range in complex bacterial communities. In combination with the continually increasing number of sequenced bacterial genomes, future iterations of the technology could enable to highly accurate clinically-oriented tools for rapid assessment of bacterial community composition and relative abundances.
Project description:Small non-coding RNAs (sRNAs) are widespread effectors of post-transcriptional gene regulation in bacteria. Currently extensive information exists on the sRNAs of Listeria monocytogenes (Lm) expressed during growth in extracellular environments. We used deep sequencing of cDNAs obtained from fractioned RNA (<500nt) isolated from extracellularly growing bacteria and from Lm-infected macrophages to catalog the sRNA repertoire during intracellular bacterial growth. Here we report on the discovery of 150 regulatory RNAs of which 71 have never been previously described. A total of 29 regulatory RNAs, including small non-coding antisense RNAs, are specifically expressed intracellularly. We validated highly expressed sRNAs by Northern blotting and demonstrated by the construction and characterization of isogenic mutants of rli31, rli33-1 and rli50 for intracellular expressed sRNA candidates, that their expression is required for efficient growth of bacteria in macrophages. All three mutants were attenuated when assessed for growth in mouse and insect models of infection. Comparative genomic analysis revealed the presence of lineage specific sRNAs and the absence of sRNA loci in genomes of naturally-occurring infection-attenuated bacteria, with additional loss in non-pathogenic listerial genomes. Our analyses reveal extensive sRNA expression as an important feature of bacterial regulation during intracellular growth.