Rebecca Carlyon and Dr. Joel Griffitts, Microbiology and Molecular Biology
How does infection work? How do bacteria know where they are to function within a host? These processes are vital for understanding both disease-causing and beneficial bacteria. For example, infection in alfalfa by a bacterium called Sinorhizobium meliloti is advantageous for the legume. Rhizobia infects special plant organs called root nodules where they function to fix nitrogen—a vital mechanism for the plants’ survival. This is a crucial agricultural process, yet remains a under researched subject. An important aspect of infection is that in order for it to occur, there must exist communication between the bacteria and the plant.
In order to look for a type of communication process, Dr. Griffitts did preliminary tests involving transposons which disrupted regions of the genome of RM 1021, the wild type strain of S. meliloti. He studied the phenotype of nodules produced from different disrupted genes to note important genes for function. Two genes named feuP and feuQ are of particular interest. These regions of the DNA encode for two proteins which make a two component system. FeuQ is a sensor kinase which is responsible for sensing the environment for signals, and then forwarding it to FeuP, a response regulator which acts as a transcription factor. See the figure below.
My project involved finding the effect that FeuP has on symbiotic infection. I deleted the feuP gene through a plasmid mediated procedure and then I saw what effect this deletion would have on alfalfa infected with the mutant bacteria.
As we expected, RM 1021 wild type strain produced healthy nodules and a healthy plant, while the feuP mutant with the transposon allele (R3H1) and deletion allele (B119) produced sickly nodules and an unhealthy plant. The plants infected with the transposon allele and complementing feuP plasmid (B114) had normal functionality because the feuP gene was restored. The last group of plants (B120) confirmed that the deletion was indeed just involving the feuP gene, and not other areas of the gene, because the nodules were healthy.
This project was a great introduction to microbiology laboratory techniques. It asked a simple question regarding one gene’s effect on infection of S. meliloti. The results showed clearly that the FeuP protein is vital for the cells’ role in infection, but not for the cells livelihood. Further work will be done to determine other components of this pathway. It was an amazing experience and I am excited for my other projects that I am working on in this pathway.