This weeks Monday seminar was by Prof Judy Armitage from Oxford (http://www.bioch.ox.ac.uk/aspsite/research/brochure/Armitage/) . Do go to her website as it will help you to see some of the pictures. She was interesting to us as a biologist (microbial physiologist) heading up a Systems Biology centre. Systems Biology is a trendy phrase but has almost as many meanings as there are centres. Systems Biology is really putting biology on a quantitative basis by developing mathematical models that accurately predict experiments. This can be at various scales, whole organisms, individual organs, whole cells or just a particular pathway. Prof Armitage has been studying the photosynthetic bacteria Rhodobacter sphaeroides for many years. It has now become more significant as Craig Ventner has found that a close relation is the most abundant organism in sea water and therefore central to photosynthesis in the sea.
However what Judy is currently studying is the chemotactic response where these bacteria swim towards their food source. In contrast to the well studied E.coli system where there is only one set of proteins, there are 4 operons in R.spheroides. Although in vitro the proteins were able to cross react and phosphorylate, they did not compensate for each other when deleted.
Her group showed by attaching fluorescent proteins (GFP/CFP) etc to the various components that unlike E.coli where the chemotactic proteins were all at the pole of the cell, there were two systems in R.spheroides, one at the pole but the other in the mid cell. One to sense the internal "happiness" of the cell- ie was it well fed and the other to go and find new food sources when it was not. She pointed out the importance of a number of their experimental details. Firstly they add the fluorescent protein in frame with the protein of interest in the genome so as to get natural abundance not overexpression. Secondly they only pay attention to those mutants where the pathway still functions as the fusions can sometimes disrupt the true localisation and give a false result, but when this happens the pathway does not work. The group has also done work on the flagellae that drive the bacteria and using a special fluorescent microscope were able to count the numbers of the subunits that drive the motor- 22 per complex.
Her take home message was that you cannot assume that all things work the same as E.coli!