Mitomycin C eliminates cyanobacterial transcription without detectable lysogen induction in a -dominated bloom in Lake Erie.

Although evidence indicates that viruses are important in the ecology of spp., many questions remain. For example, how does exist at high, bloom-associated cell concentrations in the presence of viruses that infect it? The phenomenon of lysogeny and associated homoimmunity offer possible explanations to this question. Virtually nothing is known about lysogeny in , but a metatranscriptomic study suggests that widespread, transient lysogeny is active during blooms. These observations lead us to posit that lysogeny is important in modulating blooms. Using a classic mitomycin C-based induction study, we tested for lysogeny in a -dominated community in Lake Erie in 2019. Treated communities were incubated with 1 mg L mitomycin C for 48 h alongside unamended controls. We compared direct counts of virus-like-particles (VLPs) and examined community transcription for active infection by cyanophage. Mitomycin C treatment did not increase VLP count. Mitomycin C effectively eliminated transcription in the cyanobacterial community, while we detected no evidence of induction. Metatranscriptomic analysis demonstrated that the standard protocol of 1 mg L was highly-toxic to the cyanobacterial population, which likely inhibited induction of any prophage present. Follow-up lab studies indicated that 0.1 mg L may be more appropriate for use in freshwater cyanobacterial studies. These findings will guide future efforts to detect lysogeny in blooms.