Biofilm development and toxic compound resistance

PhD ceremony: Mr. A.H. Zaidi, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen

Title: Biofilm development and toxic compound resistance

Promotor(s): prof. A.J.M. Driessen

Faculty: Mathematics and Natural Sciences

The study of Arsalan Haseeb Zaidi highlighted the repertoire of defence mechanisms used by Lactococcus lactis to overcome the adverse effects of toxic compounds it may encounter in its environment.

Gram-positive bacteria fulfil a vital role in food and health. How they interface and colonize the mammalian gastrointestinal milieu has been a subject of intense study. Active efflux is a mechanism by which cells excrete diverse toxic compounds. This process, also known as multidrug resistance (MDR), has been studied extensively in L. lactis over the past several years. LmrCD, an ATP binding cassette (ABC) transporter is the main determinant for both acquired and adaptive resistance to bile acids. In its absence, cells re-adapt to a bile acid challenge, but at the expense of fitness. Adapted cells exhibit an increased flocculation and physicochemical changes of their cell envelope. In the absence of bile acids, they show a reduced ability to adhere to hydrophobic surfaces. The presence of bile acids not only promotes adheres but also markedly stimulates the development of a biofilm. The enhanced biofilm formation does not result in an increased bile acid resistance of the cholate adapted cells. In an analogous manner cells lacking LmrCD readily develop resistance to non-surfactant chemicals such as rhodamine 6G. This resistance appears to be partly due to the expression of a previously uncharacterized transporter. Unlike the cholate resistance, this resistance does not result morphological changes, and changes in surface adherence or biofilm formation.