Lysogeny
All phages can enter a lytic infection cycle, in which they take over their host’s machineries for multiple phage progeny production and eventually kill their host. Under specific conditions, some phages can enter a lysogenic infection cycle, in which their genomes are being incorporated into the genome of the host, where they remain dormant as a “prophage” until an environmental signal can lead to their excision and they enter a lytic cycle.
The ability to enter a lysogenic cycle can affect both population dynamics of the phage and the host (by postponing the host lysis for example) and their evolution. This is extremely relevant in cyanobacterial bloom-forming species, due to the extreme fluctuations in host abundance while coexisting with their phages.
We aim to identify the mechanisms and environmental factors that affect the “decision” whether to enter a lytic or lysogenic cycle and those affecting prophage excision in bloom-forming cyanobacteria. Moreover, we aim to uncover the genomic diversity of prophages found in cyanobacterial genomes.
TECHNIQUES & APPROACHES
Coevolution
One of the mechanisms that enable the long-term coexistence of cyanobacteria and their phages is coevolution. In that process, the cyanobacteria become resistant to their host by various defence mechanisms. The phage can then acquire mutations (“host-range mutations”) that enable the infection of the resistant host strains. This “arms race” affects phage and host population dynamics and diversity.
In our lab, we study the mutations and mechanisms that confer resistance to bloom-forming cyanobacteria and the host-range mutations in the phage. Additionally, we are interested in the pleiotropic effects of these mutations. For example, we discovered that when nitrogen fixing cyanobacteria become resistant to their phages, they lose their ability to fix nitrogen. This tradeoff may have a significant influence on these strains’ survival and bloom ability under nitrogen starvation conditions.
TECHNIQUES & APPROACHES
Sinkholes
The continuous desiccation of the Dead Sea is driving the formation of thousands of collapse sinkholes around its shoreline that form an emerging aquatic habitat, which is constantly changing. While the origin of the brine in many of these pools is the old Dead Sea brine, the salinity level in them varies greatly. This unique scenario can serve as a refugee for microbes that previously inhabited the Dead Sea, as well as to other organisms.
Moreover, this scenario can serve as an ideal setup for studying the fine-scale eco-evolutionary dynamics of microbial populations under a continuously changing environment.
We combine a geochemical approach with metagenomics analyses and classical microbiology to characterize, in-depth, the biotic and abiotic factors that drive changes in microbial communities in the Dead Sea sinkhole pools. We aim to uncover the composition and dynamics of these communities, including strain turnover and phage-host interactions.