Abstract: Viral Community Dynamics in Stream Bacterial Biofilms

Marine ecosystems have been a focal point for microbial ecology studies.  Over two decades of research in the global ocean has revealed important roles of viruses in marine ecosystems, from controlling host populations, to influencing how nutrients cycle within marine food webs, to influencing host evolution through gene transfer. In comparison, much less is known about the roles of viruses in freshwater systems. Streams are incredibly important to global ecology as a huge site of carbon cycling as well as a place where ecosystems are connected and integrated. And unlike the ocean, many freshwaters have complex connections with terrestrial watersheds, which can also influence virus dynamics in these systems.  Understanding the impacts of viruses in freshwater microbial communities is the next important challenge in this field of research.

This summer, I plan to focus on bacteria and viruses in biofilms in the Crim Dell Creek. Biofilms are groups of microorganisms that adhere together into films on rocks and other surfaces in water systems such as lotic systems. To look at this, I will deploy three known size stones at three locations along the Crim Dell Creek and I plan to collect them at different times and perform inductions on them and use epifluorescence microscopy to look at bacteria and virus counts. This will allow me to examine how biofilms develop over time and how viruses infect these bacterial biofilms, which is relatively unknown due to their protective cuticles. I hypothesize that viruses are maintained within biofilm communities not through lytic but via lysogenic replication, and may be released by induction using Mitomycin C.

Bacterial Biofilm on Stream Rock


  1. semodlin says:

    Hello Alex!
    This seems like a really fun project and I hope it goes well. I have one question regarding your research: Why do you hypothesize that viruses will have the lysogenic replication instead of lytic?
    I understand what both terms are, I just curious to see why a virus would wait instead of immediately breaking out of the infected bacteria.

    Sarah Modlin

  2. Thats a great question! Biofilms form over time, beginning with a few cells that form a colony. As the colony grows, dead cells and other biological material forms a strong cuticle to protect the bacteria in the biofilm. Once this cuticle exists, phage in the stream water cannot reach the bacteria and attach onto them to infect them through the lytic cycle. I have the hypothesis that the phage infect the bacteria through lysogenic replication to get around this problem. It is completely possible that I will find that phage simply can’t infect biofilms, but my project is seeking to answer how and if biofilms are significantly infected by viruses. I hope that answers your question!