Competitive advantages of T-even phage lysis inhibition in response to secondary infection

T-even bacteriophages are known to employ lysis inhibition (LIN), where the lysis of an infected host is delayed in response to secondary adsorptions. Upon the eventual burst of the host, significantly more phage progenies are released. Here, we analysed the competitive advantage of LIN using a mathematical model. In batch culture, LIN provides a bigger phage yield at the end of the growth where all the hosts are infected due to an exceeding number of phage particles and, in addition, gives a competitive advantage against LIN mutants with rapid lysis by letting them adsorb to already infected hosts in the LIN state. By simulating plaque formation in a spatially structured environment, we show that, while LIN phages will produce a smaller zone of clearance, the area over which the phages spread is actually comparable to those without LIN. The analysis suggests that LIN induced by secondary adsorption is favourable in terms of competition, both in spatially homogeneous and inhomogeneous environments.Author summary: T-even bacteriophages can delay the lysis of their hosts when they detect more phages are adsorbing to the hosts. This behaviour is called lysis inhibition. While the delay slows down the rate at which phage progeny comes out from an infected host, it allows the phage to increase the progeny production per host. Using a mathematical model, we provide a quantitative analysis of this strategy’s competitive advantages and disadvantages in different environments. The model predicts that phage adsorption to lysis-inhibited cells provides a significant competitive advantage to lysis-inhibiting phage against phages that quickly lyse the cells. We also find that secondary infection-triggered delay does not hinder the spreading of the phage in a lawn of uninfected cells, even though the apparent plaque size, i.e., a zone that appears clear because cells have been lysed, is small. The analysis suggests that lysis inhibition provides a robust competitive advantage for a virulent phage.