DNA targeting and interference by a bacterial Argonaute nuclease.

Members of the conserved Argonaute protein family use small RNA guides to locate their mRNA targets and regulate gene expression and suppress mobile genetic elements in eukaryotes1,2. Argonautes are also present in many bacterial and archaeal species3-5. Unlike eukaryotic proteins, several prokaryotic Argonaute proteins use small DNA guides to cleave DNA, a process known as DNA interference6-10. However, the natural functions and targets of DNA interference are poorly understood, and the mechanisms of DNA guide generation and target discrimination remain unknown. Here we analyse the activity of a bacterial Argonaute nuclease from Clostridium butyricum (CbAgo) in vivo. We show that CbAgo targets multicopy genetic elements and suppresses the propagation of plasmids and infection by phages. CbAgo induces DNA interference between homologous sequences and triggers DNA degradation at double-strand breaks in the target DNA. The loading of CbAgo with locus-specific small DNA guides depends on both its intrinsic endonuclease activity and the cellular double-strand break repair machinery. A similar interaction was reported for the acquisition of new spacers during CRISPR adaptation, and prokaryotic genomes that encode Ago nucleases are enriched in CRISPR-Cas systems. These results identify molecular mechanisms that generate guides for DNA interference and suggest that the recognition of foreign nucleic acids by prokaryotic defence systems involves common principles.

Antibacterial and Anti-Biofilm Properties of Diopside Powder Loaded with Lysostaphin.

BACKGROUND: Diopside-based ceramic is a perspective biocompatible material with numerous potential applications in the field of bone prosthetics. Implantable devices and materials are often prone to colonization and biofilm formation by pathogens such as Staphylococcus aureus, which in the case of bone grafting leads to osteomyelitis, an infectious bone and bone marrow injury. To lower the risk of bacterial colonization, implanted materials can be impregnated with antimicrobials. In this work, we loaded the antibacterial enzyme lysostaphin on diopside powder and studied the antibacterial and antibiofilm properties of such material to probe the utility of this approach for diopside-based prosthetic materials. METHODS: Diopside powder was synthesized by the solid-state method, lysostaphin was loaded on diopside by adsorption, the release of lysostaphin from diopside was monitored by ELISA, and antibacterial and anti-biofilm activity was assessed by standard microbiological procedures. RESULTS AND CONCLUSIONS: Lysostaphin released from diopside powder showed high antibacterial activity against planktonic bacteria and effectively destroyed 24-h staphylococcal biofilms. Diopside-based materials possess a potential for the development of antibacterial bone grafting materials.

The Abundance and Taxonomic Diversity of Filterable Forms of Bacteria during Succession in the Soils of Antarctica (Bunger Hills).

Previous studies have shown that a significant part of the bacterial communities of Antarctic soils is represented by cells passing through filters with pore sizes of 0.2 µm. These results raised new research questions about the composition and diversity of the filterable forms of bacteria (FFB) in Antarctic soils and their role in the adaptation of bacteria to the extreme living conditions. To answer such questions, we analyzed the succession of bacterial communities during incubation of Antarctic soil samples from the Bunger Hills at increased humidity and positive temperatures (5 °C and 20 °C). We determined the total number of viable cells by fluorescence microscopy in all samples and assessed the taxonomic diversity of bacteria by next-generation sequencing of the 16S rRNA gene region. Our results have shown that at those checkpoints where the total number of cells reached the maximum, the FFB fraction reached its minimum, and vice versa. We did not observe significant changes in taxonomic diversity in the soil bacterial communities during succession. During our study, we found that the soil bacterial communities as a whole and the FFB fraction consist of almost the same phylogenetic groups. We suppose rapid transition of the cells of the active part of the bacterial population to small dormant forms is one of the survival strategies in extreme conditions and contributes to the stable functioning of microbial communities in Antarctic soils.