A mutant bacteriophage evolved to infect resistant bacteria gained a broader host range

Summary Bacteriophages (phages) are the most abundant entities in nature, yet little is known about their capacity to acquire new hosts and invade new niches. By exploiting the Gram positive soil bacterium Bacillus subtilis (B. subtilis) and its lytic phage SPO1 as a model, we followed the co-evolution of bacteria and phages. After infection, phage resistant bacteria were readily isolated. These bacteria were defective in production of glycosylated wall teichoic acid (TA) polymers, served as SPO1 receptor. Subsequently, a SPO1 mutant phage that could infect the resistant bacteria evolved. The emerging phage contained mutations in two genes, encoding the baseplate and fibers required for host attachment. Remarkably, the mutant phage gained the capacity to infect non-host Bacillus species that are not infected by the wild type phage. We provide evidence that the evolved phage lost its dependency on the species specific glycosylation pattern of TA polymers. Instead, the mutant phage gained the capacity to directly adhere to the TA backbone, conserved among different species, thereby crossing the species barrier.