Investigating the developmental roles for the functional amyloid system of Streptomyces venezuelae

Abstract

Amyloid proteins are found in all domains of life, and have a number of defining characteristics, including considerable β-sheet secondary structure and the ability to self-assemble into large, insoluble fibers. These insoluble aggregates are often deleterious to the cell, evidenced by amyloid proteins being involved in Alzheimer’s, Parkinson’s, and Huntington’s disease. Remarkably however, some organisms have found ways to circumvent the toxicity of amyloid proteins, and instead co-opt them as beneficial aspects of their development and survival. An example of this can be seen in the bacteria genus Streptomyces. Streptomyces bacteria have a complex, multicellular life cycle that involves progressing through a number of distinct developmental stages. The reproductive phase of the life cycle requires the activity of amyloid-forming proteins known as chaplins - hydrophobic proteins that polymerize on the cell surface, ultimately promoting reproductive development. Due to limitations in other model Streptomyces, key questions regarding the function of chaplins have not yet been addressed. The emerging model species Streptomyces venezuelae is unique given its rapid growth, its ability to develop in liquid, and its potential to adopt two distinct life cycle programs. This work sought to characterize how chaplins influence these processes. We created a number of chaplin mutants, and determined that chaplins contribute to these process in mostly redundant ways, but when deleted in bulk cause significant phenotypic changes. We have also shown that the requirement of chaplins in development goes beyond what was previously understood - as their loss affects development in all classical life cycle stages, and further impacts alternative life cycle programs. To understanding how chaplins are regulated in S. venezuelae, mutagenesis screens were conducted to identify mutants with altered chaplin regulation. These yielded promising candidates for further investigation. Collectively, this work has advanced our understanding of chaplin proteins, specifically how they are regulated, and how they affect various modes of Streptomyces growth and development.