Cockroaches are among the most common and obnoxious household pests, they harbor in damp and unsanitary places such as sewers, garbage disposals, kitchens, and bathroom, feed on human’s and pet’s food. Besides its importance as a sign of poor sanitation, cockroaches have been implicated in the transmission of several pathogenic organisms such as E.coli and Salmonella enteritidis which can cause diarrhea, pneumonia and so on. Also, expose to cockroach feces and body parts of dead roaches over time can trigger allergies and asthma. So it’s not safe to ignore these pests.
People rack their brains about cockroach control. Currently, there are two mainstream ways to control the population of cockroaches, physical and chemical methods. However, a chemical method like foggers, boric acid, and gel bait may cause environmental toxicity and the development of resistance in cockroaches. A physical method such as “cockroach house”, only trap few cockroaches. Neither chemical nor physical method can’t achieve the goal of environment-friendly and efficient control.
This year’s SZU China team want to tackle the cockroach control issue by using synthetic biology. We choose a kind of entomogenous fungi, Metarhizium anisopliae , as biological chassis. It is considered a safe and prospective choice for causing disease in insects only. But its lethality is still needed to be improved, which limits it's widespread used. We construct a system to enhance its virulence. Our system contains three parts: HsbA, BbChit, and MCL1. These three genes work sequentially during infecting cockroach, promote adhesion, penetration, and immune-avoidance respectively.
It encodes hydrophobic surface binding protein A, located on the surface of fungus. This protein works like “glue” by forming a hydrophobic bond between spores and the waxy epicuticle of their host.
It encodes chitinase, which can hydrolyze chitin. Chitosan is the major part of the insect body wall, chitinase can hydrolyze this to penetrate.
It encodes a collagen-like protein, which can combine with β-glucan.β-glucan is distributed on the cell wall surface of fungus and is the recognization site for insect hemocytes to combine and clear invader. MCL1 acts like putting an “invisible cloak” on the fungus. so that fungus can evade being recognized by the host immune system.
Then, we design a trap box named GreenGround to bring our idea into real world. We mix spores,banana powder and oil together to form emulsifiable powder,which is applied to non-woven fabrics for use. (Click, and check more details about our box)
We built a safety mechanism for our system. It consists of a tryptophan attenuator and a MazF venom protein. In the cultivating and cockroaches environment, the Tryptophan attenuator makes a difference that stops the translation before MazF, and then the fungi can keep alive. If the fungi abscise the environment we mention above, the Tryptophan attenuator would not work and the MazF expresses to make them die quickly. (Click and check ‘How to ensure safety’ for more details)
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