Environments frequently change to become more stressful over time - seasonally, between glacial and interglacial geological periods, or due to climate change. We expect that the rate of environmental change will affect both how and how easily populations adapt to stressful environments. Theoretical work predicts that populations experiencing gradual environmental change will adapt more readily than populations experiencing sudden environmental change, but experimental studies in microbes have not always confirmed this prediction.

We previously evolved the bacteriophage ɸ6 Cystovirus for the ability to withstand high-temperature heat shocks (thermostability). In different treatments, the heat shock temperature increased at a different rate (gradually, moderately, or suddenly). We found that at the end of the evolution experiment, populations exposed to high-temperature heat shocks had fixed not only mutations that increased their thermostability, but also mutations that decreased thermostability and increased growth rates.

We are currently sequencing our ɸ6 populations at earlier time points in their evolution in order answer questions such as:

• How does the rate of environmental change affect the fixation rates and diversity of mutations in these populations? (Mutational dynamics)
• How does the rate of environmental change affect the kinds of mutations that fix in these populations? (Genotype x Environment interactions)
• Does the rate of environmental change limit available mutations based on their effects on traits other than thermostability? (Pleiotropic interactions)

One of the biggest issues in modern medicine is the rise of antibiotic-resistant pathogenic bacteria that no longer respond to drug treatment. A potential solution is to use bacteriophages that can kill these antibiotic-resistant bacteria, a strategy known as phage therapy. However, phages tend only to infect specific bacterial hosts, making it vital to characterize the host range (number and kinds of bacteria the phage can infect) and infection dynamics (timing of the infection cycle and the number of new phages produced in an infection) of putative therapeutic phages. In collaboration with Dr. Wendy Lee's lab at SJSU, we are determining the basic life history traits of a novel bacteriophage, called "Halophage," isolated from sewage from the Santa Clara Valley Waste Treatment Facility. Using our baseline of the phage's behavior, we will be able to address questions such as:

• What genetic changes allow Halophage to infect a new bacterial host?
• What adaptive strategies does Halophage use to optimize its infection on current and novel hosts?