Nonclassical protein secretion by bacteria.

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Free-living microbes must be able to sense, make sense of, respond to, and exploit their outside environment. Microscopic, single-celled bacteria often have very nimble and varied responses to the outside environment. Some are opportunistic pathogens, so they can immediately sense when they have come into contact with a host organism and should infect it. Others have evolved ways to utilise even the most recalcitrant food sources that may be present. Chitin is, after cellulose, the second-most abundant natural polymer on Earth. Present in insect and crustacean exoskeletons, as well as in fungi, chitin is a linear chain of N-Acetyl Glucosamine (GlcNAc) and is completely insoluble and incredibly tough and stable.Some bacteria have figured out how to use chitin is a carbon and nitrogen source for growth. They secrete different chitinase enzymes all the way out of the cell and, working together outside, these chitinases breakdown the chitin into GlcNAc disaccharides. These are then taken up into the cell and converted to glucose, ammonia and acetic acid. For this system to work, the chitinases must be first made inside the cell and then secreted outside. How bacteria do this is the subject of this research proposal. If we can find out how they do it, maybe we can make them do it more. This will enable us to process food waste into biofuels or other chemicals. Some medical scientists also think that secreted chitinases may help pathogens infect their hosts, so figuring out how to stop enzyme secretion happening may also be of value to society.In work leading to this proposal we have found the genes essential for chitinase secretion in a bacterium called Serratia marcescens. This bacterium is widespread and well studied, mostly because it can be responsible for heathcare-acquired infections. The chitinase secretion system involves a set of proteins that reside in the cell envelope, surrounding the cell, and an enzyme that controls the permeability of the cell wall to allow the chitinases out. This research project will find out how the system works because nobody knows at the moment.