Stuff I worked on:

The maintenance of sex in bacteria is ensured by its potential to reload genes

with Imre Derényi and Tibor Vellai

Why sex is maintained in nature is a fundamental question in evolutionary biology. Natural genetic transformation (NGT) is a sexual process by which bacteria actively take up exogenous DNA and use it to replace homologous chromosomal sequences. As it has been demonstrated, the role of NGT in repairing deleterious mutations under constant selection is insufficient for its survival, and the lack of other viable explanations have left no alternative except that DNA uptake provides nucleotides for food. Here we develop a novel simulation approach for the long-term dynamics of genome organization (involving the loss and acquisition of genes) in a bacterial species consisting of a large number of spatially distinct populations subject to independently fluctuating ecological conditions. Our results show that in the presence of weak inter-population migration NGT is able to subsist as a mechanism to reload locally lost, intermittently selected genes from the collective gene pool of the species through DNA uptake from migrants. Reloading genes and combining them with those in locally adapted genomes allow individual cells to re-adapt faster to environmental changes. The machinery of transformation survives under a wide range of model parameters readily encompassing real-world biological conditions. These findings imply that the primary role of NGT is not to serve the cell with food, but to provide homologous sequences for restoring genes that have disappeared from or become degraded in the local population.


Szollosi GJ, Derenyi I, Vellai T (2006) The Maintenance of Sex in Bacteria is Ensured by its Potential to Reload Genes Genetics; arxiv;


Phase transition in the collective migration of tissue cells: experiment and model

with Bálint Szabó and Tamás Vicsek

We have recorded the swarming-like collective migration of a large number of keratocytes (tissue cells obtained from the scales of goldfish) using long-term videomicroscopy. By increasing the overall density of the migrating cells, we have been able to demonstrate experimentally a kinetic phase transition from a disordered into an ordered state. Near the critical density a complex picture emerges with interacting clusters of cells moving in groups. Motivated by these experiments we have constructed a flocking model that exhibits a continuous transition to the ordered phase, while assuming only short-range interactions and no explicit information about the knowledge of the directions of motion of neighbors. Placing cells in microfabricated arenas we found spectacular whirling behavior which we could also reproduce in simulations.


Szabó B, Szöllősi GJ, Gönci B, Jurányi Zs, Selmeczi D, Vicsek,T
(2006) Phase Transition in the Collective Migration of Tissue Cells: Experiment and Model. Phys Rev E; arxiv;

videos; (misc. old attempts that look nice 1 2 3 )