TITLE:

Phage capsid structure: Theory, phage lifestyle constraints, and environmental diagnostic

DATE:

Friday, May 5th, 2017

TIME:

3:30 PM

LOCATION:

Bioscience Center Gold Auditorium

SPEAKER:

Dr. Antoni Luque, Dept. Math and Stats, CSRC, and Viral Information Institute, SDSU

ABSTRACT:

Phages are viruses that infect bacteria and are the most abundant entity on the planet. About eighty percent of these viruses are made of a protein shell—the capsid—that stores the phage genome, adopts an icosahedral shape, and has a tail that inoculates the genome into the bacterial host. These phages have tuned this architecture to succeed in all sorts of environments from the cold waters of the arctic and the hot springs of Yellowstone to the mucosal surfaces of the human gut. We hypothesize that the malleable and rapidly evolving structure of tailed phages can be used as an early predictor of ecosystem changes due to environmental factors. To address this, we developed a mathematical model that predicts the structure of phages based on accessible environmental data such as phage genome size or capsid size. We validated the theory for 30 phages that are well-characterized structurally, and we applied the model to predict the structure associated to 500 phage genomes that have been annotated with the bioinformatic platform PhAnToMe. The structural analysis of these phages show that the lysogenic lifestyle—which allows phages to integrate in the bacterial host—imposes a strong constraint on the structure of the phage capsid. The lytic lifestyle—associated to the predatory life cycle of phages—promotes instead structural variability of the capsid. Despite the biological reason for this result remains unclear, the methodology provides a new approach to study the emergence of lysogeny, which has been linked to diseases and ecosystem degradation. To this end, we have analyzed phage samples from the Curonian Lagoon (near the Baltic sea), and we predict the emergence of lysogeny on the nearshore of Klaipeda. This methodology has a broad range of potential applications, for example, in the diagnosis of lysogenic variation within the human digestive tract and respiratory tract.

HOST:

Dr. Jose Castillo

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