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The Microguards: Overview

Nowadays, there are numerous industrial processes that use microorganisms such as Escherichia coli and Saccharomyces cerevisiae to produce compounds of interest, like insulin, ethanol and various enzymes. The success of these processes depends on the absence of contamination by other microorganisms in the culture medium. The presence of contaminants in a fermentation process reduces its efficiency due to competition between the contaminant and the fermentative organism, causing losses of 5 to 10% of the gross production. To try to solve this problem, the aim of our project is to engineer strains of E. coli and S. cerevisiae that are able to recognize and destroy contaminants during industrial processes.

The Yeastguard

Industrial ethanol production occurs in open vats with over 500,000 L. This process is mostly hindered by lactobacilli contamination, which produces lactic acid as their main metabolic product. Once contaminated, the whole vat must be discarded and cleaned, thus generating losses ranking in the millions of dollars.

We want our engineered yeast to be able to detect and control the proliferation of lactobacilli by introduction of a simple genetic device. The device must be able to recognize the presence of lactate in the medium during fermentation. In order to allow the entrance of lactate in the cell, we will construct a gene coding for a lactate transporter under the control of a constitutive promoter. Once in the cell, this metabolite will induce the transcription of the gene coding for killer enzyme, lysozyme, which is the most widely used antibiotic for lactobacilli decontamination.

The greatest challenge of this project consists of characterizing a lactate-inducible promoter that is not subjected to glucose catabolic repression, since the device must be activated during the process of sugar fermentation of the diauxic shift of S. cerevisiae.