Hao Chang

Hunting down the histidine utilization (hut) operon that regulates histidine/urocanate utilization in Pseudomonads.

Histidine of being a common amino acid, its degradation pathway is regulated by the hut operon. Humans can metabolite histidine completely in the liver but partially on the skin where urocanate (the first intermediate in histidine degradation pathway) is accumulated. Urocanate absorbs UV light, so the accumulated urocanate on the skin is a protection humans used to against UV light. Many bacteria that colonize the human skin can utilize urocanate as the energy source as it is widely spread.

The ability of bacteria utilizing histidine or urocanate in the environment is poorly understood, under the co-supervisions of Dr. Xue-xian Zhang and Prof Paul Rainey and as a part of Microbiology training, I am extending this Microbiological question to a population level. Because the energy source in the environment is limited and the competitions between each bacterial species are high, bacteria will only turn on a gene for a purpose. I am examining this by using 2 environmental isolated plant-associated bacteria Pseudomonads. By borrowing tools such as PCR, functional complementation and molecular cloning from Genetics and Microbiology, my current results show that some particular Pseudomonads are only able to utilization either histidine or urocanate alone as the sole source of carbon and nitrogen, and by introducing transporter proteins of histidine and urocanate, most of them restored growth. This suggests that the presence of histidine and urocanate on the plant surfaces. The further investigation may be carried on the plant surfaces for the cue of urocanate, a possible explanation may lead to plants also accumulate urocanate on the surface as the defense mechanism for UV light.

The other part of my Master's project includes the multilocus sequence typing (MLST) of the 2 Pseudomonads populations that I am working on, this involves massive PCR and sequencing works, here I am trying to build up a phylogenetic tree based on their housekeeping gene similarities.