Project description:Low-GC Actinobacteria are among the most abundant and widespread microbes in freshwaters and have largely resisted all cultivation efforts. Consequently, their phages have remained totally unknown. In this work, we have used deep metagenomic sequencing to assemble eight complete genomes of the first tailed phages that infect freshwater Actinobacteria. Their genomes encode the actinobacterial-specific transcription factor whiB, frequently found in mycobacteriophages and also in phages infecting marine pelagic Actinobacteria. Its presence suggests a common and widespread strategy of modulation of host transcriptional machinery upon infection via this transcriptional switch. We present evidence that some whiB-carrying phages infect the acI lineage of Actinobacteria. At least one of them encodes the ADP-ribosylating component of the widespread bacterial AB toxins family (for example, clostridial toxin). We posit that the presence of this toxin reflects a 'trojan horse' strategy, providing protection at the population level to the abundant host microbes against eukaryotic predators.
Project description:Genomic material isolated from purified phage YerA41 lysate was shown to contain RNA. YerA41 phage lysate was RNase treated to remove phage-external RNA and total RNA was then isolated from the phage preparate using Qiagen Rneasy mini kit. The isolated RNA was sequenced to elucidate its origin. The results suggested that the RNA originated from intact ribosomes of the host bacterium that contaminated the phage lysate.
Project description:To better understand host/phage interactions and the genetic bases of phage resistance in a model system relevant to potential phage therapy, we isolated several spontaneous mutants of the USA300 S. aureus clinical isolate NRS384 that were resistant to phage K. Six of these had a single missense mutation in the host rpoC gene, which encodes the RNA polymerase beta prime subunit. To examine the hypothesis that the mutations in the host RNA polymerase affect the transcription of phage genes, we performed RNA-seq analysis on total RNA samples collected from NRS384 wild-type (WT) and rpoC G17D mutant cultures infected with phage K, at different time points after infection. Infection of the WT host led to a steady increase of phage transcription relative to the host. Our analysis allowed us to define different early, middle, and late phage genes based on their temporal expression patterns and group them into transcriptional units. Predicted promoter sequences defined by conserved -35, -10, and in some cases extended -10 elements were found upstream of early and middle genes. However, sequences upstream of late genes did not contain clear, complete, canonical promoter sequences, suggesting that factors in addition to host RNA polymerase are required for their regulated expression. Infection of the rpoC G17D mutant host led to a transcriptional pattern that was similar to the WT at early time points. However, beginning at 20 minutes after infection, transcription of late genes (such as phage structural genes and host lysis genes) was severely reduced. Our data indicate that the rpoCG17D mutation prevents the expression of phage late genes, resulting in a failed infection cycle for phage K. In addition to illuminating the global transcriptional landscape of phage K throughout the infection cycle, these studies can inform our investigations into the bases of phage K’s control of its transcriptional program as well as mechanisms of phage resistance.