Thaxtomin, a next-generation weed killer ?
It is called “Streptomyces scabies”. This bacterium is feared by farmers because it causes common potato scab, a disease which despite being harmless causes distasteful lesions to appear on tuber crops. And yet this bacterium could become a micro-scale helper for these same farmers because the toxin it produces, thaxtomin, is a natural and biodegradable herbicide which is to date unfortunately too expensive to produce on a grand scale. Two researchers at the Center of Protein Engineering at the University of Liege, Sébastien Rigali and Samuel Jourdan, in collaboration with Dr. Isolde Francis and Professor Rosemary Loria of the University of Florida, have just discovered the molecular mechanism responsible for inducing the synthesis of this toxin. Their discovery forms the basis of a patent proposal whose objective is to make thaxtomin as a commercially viable natural herbicide.
The tip of the iceberg
It is no surprise that these Streptomyces should be in the sights of Sébastien Rigali and Samuel Jourdan, both of whom are researchers at the Center of Protein Engineering (C.I.P.) at ULg. “Our focus in the laboratory is to understand when, how and why these bacteria produce a molecule that has an antibiotic activity, the meaning of antibiotic being ‘against life’: against viruses, bacteria, plants, fungi, etc. The purpose of this is to find new antibiotics. We now know that the 10,000 molecules of Streptomyces that have been isolated to date are merely the tip of the iceberg! Genome mining has revealed the existence of numerous ‘cryptic’ antibiotics, that is to say, they are unknown because they are not produced under laboratory culture conditions. The genes coding for the proteins that synthesize these cryptic molecules are often ‘silent’, that is to say barely expressed or not at all. The key to unlocking the system must be found. These keys are the transcriptional regulators, proteins that are capable of repressing or activating the expression of genes”.
Scientists have been tirelessly attempting to identify the keys and locks involved in the expression of the genes involved in the production of antibiotics. Once the lock-and-key systems have been decoded, it becomes possible to identify the elicitors of the system, that is to say the triggering elements which, in their natural environment, cause the bacteria to produce these cryptic antibiotics. You might as well be looking for a needle in a haystack given the infinite number of lock-and-key combinations and elicitors that exist!
(1) Rigali S, Titgemeyer F, Barends S, Mulder S, Thomae AW, Hopwood DA, van Wezel GP. 2008. Feast or famine: the global regulator DasR links nutrient stress to antibiotic production by Streptomyces. EMBO reports 9:670-675.