The tradeoff between resistance to phages and nitrogen fixation in bloom-forming cyanobacteria
Speaker: Sarit Avrani (University of Haifa)
Venue: 7E02, Lecture Hall
Host: Karl Forchhammer
Abstract:
Cyanobacterial blooms negatively impact aquatic environments worldwide. Diazotrophic cyanobacteria, such as Cylindrospermopsis, can even form blooms under nitrogen starvation, due to their ability to fix atmospheric nitrogen (N2). Phages could potentially control cyanobacterial growth; however, cyanobacteria are able to adapt to the presence of phages quite rapidly by acquiring resistance to the phage, thus, the role of phages in bloom dynamics is -as yet- unclear. We examined the resistance to phages of two strains of diazotrophic cyanobacteria: the invasive bloom-forming C. raciborskii, and the model strain Nostoc PCC 7120. Our results demonstrate that this resistance, comes with reduced ability to induce heterocyst cells, in which N2 is fixed. This reduction causes reduced N2 fixation by the mutant strains, along with reduced growth or even death under nitrogen starvation. Such cost can prevent the survival of phage-resistant cyanobacteria under nitrogen starvation, and may suggest that spontaneous resistance to phages is a transient trait in diazotrophic bloom-forming cyanobacteria. Whole genome sequence analysis of the resistant strains reviles new genes essential for heterocyst development and function, which may enable us to use selection for resistance to phages as a tool for identifying new genes involved in nitrogen fixation.