Physics of viruses

Course description

This interdisciplinary seminar addressed advanced bachelor and master students from physics and biology. It is jointly organized by Ulrich Schwarz and Falko Ziebert (ITP) and Frederik Graw (BioQuant). Due to the corona crisis, it will be conducted as virtual block seminar. We will discuss the distribution of talks and dates for your meetings in a first introductory meeting on Wednesday April 14 2021 at 4 pm.

Scientific scope

Viruses have always fascinated physicists and the history of virology is full of important contributions by physicists. For example, Francis Crick (a theoretical physicist) together with Jim Watson first suggested that virus capsids must be made from only one or a few identical proteins (Nature paper 1956), a prediction that later was verified e.g. by Aaaron Klug (also a physicist) using electron microscopy and X-ray diffraction (Nobel prize 1982). Today structure determination by physical methods is daily routine when investigating the molecular structure of viruses. Interestingly, X-ray diffraction today is less important than it used to be, being more and more replaced by cryo electron microscopy (Nobel Prize Chemistry 2017).

Another important physical aspect is quantification of virus dynamics, which often is easier than for other more complex biological systems. The most impressive historical evidence in this direction is the work of Max Delbrück, by training a theoretical physicist, who was inspired by the work of Erwin Schrödinger and around 1940 started the famous phage group at Cold Spring Harbor Laboratory in the USA, together with the geneticist Salvador Luria. Their quantitative experiments on bacteriophages (viruses attacking bacteria) lead to an understanding of the decisive steps in virus replication and later earned them the Nobel prize. Today we have a fairly good understanding of the different steps in the life of many viruses inside their host cells, including uptake, transport, replication, assembly and exit. For all of these steps mathematical models exist that capture their essential physical aspects. What is much less understood, however, is how viruses spread between host cells, because this depends on many extracellular factors.

Spreading of viruses becomes more amendable to mathematical analysis if we consider it on the population level, where many details average out. This is evidenced by the huge success of the SIR-model (kinetic model with classes Susceptible, Infectious and Recovered). First analyzed by Kermack and McKendrick in 1927, the SIR-model and related kinetic models describe the typical time course of an infection (initially exponential growth, then peak and finally decline). The SIR-model has been extended and modified in many ways, including seasonal forcing, stochastic effects, age structure, the role of space and the spread on networks. In the current corona crisis, it has been used many times to predict the future course of the pandemics and the effect of possible control strategies (in particular social distancing).

Because viruses are essentially genomes wrapped by some protective coat, they are ideal systems to study genetics, in particular the dynamics of mutuations. Historically, the study of viruses was essential to decipher the genetic code and the difference between DNA and RNA. Today we need to understand their mutation dynamics to predict their evolution and to develop vaccines, in particular against new variants which invariably emerge if many people are being infected.

In this seminar, we will discuss the current state of the art regarding our quantitative understanding of viruses. This includes all the aspects described above, including their structure and assembly, uptake and exit processes, spreading in the extracellular environment, spreading on the population level and their evolutionary dynamics.

Given the current situation, we will of course also discuss SARS-CoV-2, which shares some similarities with Ebola and Influenza viruses, which are also enveloped RNA-viruses. Other viruses discussed in this seminar will be HIV and adenoviruses. All of these viruses are under current investigation at Heidelberg. In general, however, this seminar is concerned with the generic physical aspects of viruses and less with one specific virus like SARS-CoV-2.

Administration

To participate, you had to register through the physics database. Our meetings will be conducted on zoom. Please install the zoom app ahead of the meeting (free version sufficient). During our first meeting on Wednesday April 14 2021 at 4 pm, participants can choose their topic from a prepared list with literature. Typically two participants together will give a 30 min talk and answer questions during a 15 min discussion.

For physics bachelor students, participation and talk give two credit points. This will be counted as obligatory seminar for bachelor students (PSEM) and a mark will be reported for your transcript. For physics master students, you can get six credit points and a mark for an obligatory master seminar (MVSem), but for this you also have to hand in a 15-20 pages written paper on your subject after the seminar is finished (typically within 1-2 months). Everybody is welcome to ask questions to the organizers when preparing the presentation, possibly during one-on-one virtual meetings.