Project description:The social life of archaea is poorly understood. In particular, even though competition and conflict are common themes in microbial communities, there is scant evidence documenting antagonistic interactions between archaea and their abundant prokaryotic brethren: bacteria. Do archaea specifically target bacteria for destruction? If so, what molecular weaponry do they use? Here, we present an approach to infer antagonistic interactions between archaea and bacteria from genome sequence. We show that a large and diverse set of archaea encode peptidoglycan hydrolases, enzymes that recognize and cleave a structure – peptidoglycan – that is a ubiquitous component of bacterial cell walls but absent from archaea. We predict the bacterial targets of archaeal peptidoglycan hydrolases using a structural homology approach and demonstrate that the predicted target bacteria tend to inhabit a similar niche to the archaeal producer, indicative of ecologically relevant interactions. Using a heterologous expression system, we demonstrate that two peptidoglycan hydrolases from the halophilic archaeaon Halogranum salarium B-1 kill the halophilic bacterium Halalkalibacterium halodurans, a predicted target, and do so in a manner consistent with peptidoglycan hydrolase activity. Our results suggest that, even though the tools and rules of engagement remain largely unknown, archaeal-bacterial conflicts are likely common, and we present a roadmap for the discovery of additional antagonistic interactions between these two domains of life. Our work has implications for understanding mixed microbial communities that include archaea and suggests that archaea might represent a large untapped reservoir of novel antibacterials.
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:Eukaryotic genomes typically consist of multiple (linear) chromosomes that are replicated from multiple origins. Several hypothetical scenarios have been proposed to account for the evolution of multi-origin/multi-chromosome genomes, which are encountered in modern eukaryotes and archaea. Here we report an example of the generation of a new chromosome in the halophilic archaeon Haloferax volcanii through one of these scenarios: acquisition of new replication origins and splitting of an ancestral chromosome into two replication-competent chromosomes. The multi-origin main chromosome has split into two genome elements via homologous recombination. The newly generated elements possess all the features of bona fide chromosomes. To our knowledge, the spontaneous generation of a new chromosome in prokaryotes without horizontal gene transfer has not been reported previously.
Project description:Chromosome segregation is a vital process for all organisms. The mechanisms underpinning chromosomal partitioning in the archaeal domain remain elusive. Our group has identified the first chromosome segregation system in thermophilic archaea. Sulfolobus solfataricus partition system consists of SegA, an orthologue of bacterial Walker-type ParA proteins; SegB, an archaea-specific DNA binding protein and a cis-acting DNA region. ChIP-seq experiments disclosed multiple SegB binding sites scattered over the chromosome and revealed a novel DNA binding motif.
Project description:Single cell genomes and metagenomic pan genomes of oral bacteria from candidate division TM7 (Saccharibacteria) Genome sequencing and assembly