Nonclassical protein secretion by bacteria.

自由生活的微生物必须能够感知、理解、响应和利用它们的外部环境。微小的单细胞细菌通常对外界环境有非常灵活和多样的反应。有些是机会致病菌，因此当它们与宿主生物接触并感染宿主生物时，它们可以立即感知到。其他动物已经进化出利用最顽固的食物来源的方法。几丁质是地球上仅次于纤维素的第二丰富的天然聚合物。几丁质存在于昆虫和甲壳类动物的外骨骼以及真菌中，是一种n -乙酰氨基葡萄糖（GlcNAc）的线性链，完全不溶，非常坚韧和稳定。一些细菌已经知道如何利用甲壳素作为碳和氮的来源来生长。它们在细胞外分泌不同的几丁质酶，在细胞外协同作用，这些几丁质酶将几丁质分解成GlcNAc双糖。然后这些物质被吸收到细胞中，转化为葡萄糖、氨和乙酸。为了使这个系统起作用，几丁质酶必须首先在细胞内产生，然后在细胞外分泌。细菌如何做到这一点是本研究计划的主题。如果我们能找出他们是怎么做到的，也许我们能让他们做得更多。这将使我们能够将食物垃圾加工成生物燃料或其他化学物质。一些医学科学家还认为，分泌的几丁质酶可能有助于病原体感染宿主，因此，弄清楚如何阻止酶的分泌可能对社会也有价值。在提出这一建议的工作中，我们发现了一种叫做粘质沙雷氏菌的细菌分泌几丁质酶所必需的基因。这种细菌分布广泛，并得到了充分的研究，主要是因为它可能导致医疗保健获得性感染。几丁质酶分泌系统包括一组位于细胞包膜内的蛋白质，以及一种控制细胞壁通透性以允许几丁质酶流出的酶。这个研究项目将找出这个系统是如何工作的，因为目前还没有人知道。

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.