Stoffels, L; (2015) Microalgae as a novel production platform for antibacterial proteins. Doctoral thesis , UCL (University College London).

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Abstract

Widespread antibiotic resistance among pathogenic bacteria and the low specificity of these drugs cause a pressing need for the development of novel antibiotics. Endolysins are proteins that are produced by bacteriophage infected cells and digest the bacterial cell wall for phage progeny release. These efficient enzymes are highly specific for the target bacteria without affecting other species. Development of resistance against endolysins is rare, because they evolved to target molecules that are essential for bacterial viability. Taken together, this makes them promising novel antibiotics. The development of recombinant endolysins as antibacterial agents requires an inexpensive and safe production platform. Microalgae emerged as an alternative expression platform in the last years. This study investigated therefore the production of endolysins in two distinct microalgal systems, the eukaryotic green microalga Chlamydomonas reinhardtii and the cyanobacterium Synechocystis sp. PCC 6803. C. reinhardtii is an attractive production platform for therapeutic proteins, due to the lack of endotoxins and infectious agents and its GRAS status (Generally Recognised as Safe). Synechocystis is a prokaryotic system and is natural transformable. Both offer established techniques for the expression of foreign genes and can be cultivated in full containment in simple photobioreactors. Transgenic lines of C. reinhardtii and Synechocystis expressing endolysins specific to the human pathogens Streptococcus pneumoniae and Staphylococcus aureus were created. The S. pneumoniae-specific endolysin Pal has been purified in an active form and its specificity and efficiency in killing the target bacterium demonstrated in vitro. Another endolysin specific to Propionibacterium acnes, a bacterium involved in the skin condition acne vulgaris, was synthesised in Synechocystis. The synthesis of the endolysins in the microalgae was analysed under the influence of different expression elements and at different growth stages, and the yields of recombinant protein were quantified to evaluate microalgae as a production platform for antibacterial and other protein therapeutics. ! !

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