Abstract:
Virus-microbe interactions in the ocean are commonly described by “boom and bust” dynamics, whereby a numerically
dominant microorganism is lysed and replaced by a virus-resistant one. Here, we isolated a microalga strain and
its infective dsDNA virus whose dynamics are characterized instead by parallel growth of both the microalga and
the virus. Experimental evolution of clonal lines revealed that this viral production originates from the lysis of a
minority of virus-susceptible cells, which are regenerated from resistant cells. Whole-genome sequencing demonstrated
that this resistant-susceptible switch involved a large deletion on one chromosome. Mathematical modeling
explained how the switch maintains stable microalga-virus population dynamics consistent with their observed
growth pattern. Comparative genomics confirmed an ancient origin of this “accordion” chromosome despite a
lack of sequence conservation. Together, our results show how dynamic genomic rearrangements may account
for a previously overlooked coexistence mechanism in microalgae-virus interactions.
