Tackling resistance to food preservatives: Heterogeneity in fungal spore populations

多达三分之一的食物被真菌变质。这是全球粮食安全的一个主要问题。真菌使食物变质，使食物无法食用，并由于形成称为真菌毒素的物质而具有潜在的毒性。真菌孢子在环境中含量丰富，污染物种类繁多，能够在多种条件下生长发育。尽管有各种各样的策略来保存食品，但变质微生物进行了反击，一些微生物对特定的防腐剂产生了抵抗力。软饮料通常是酸性的，这些条件往往会抑制细菌等其他微生物。然而，许多种类的真菌(特别是霉菌)能够在酸性条件下生长并造成腐败。一种主要的防腐策略是在这些条件下加入像山梨酸这样的弱酸来抑制生长。在允许的水平下，山梨酸可以抑制大多数酵母和真菌，但一些仍然可以生长，一些可以将山梨酸降解成无毒的产品，改变味道。因此，软饮料生产过程中会出现长期的霉菌腐败现象。我们的工作表明，大多数腐败真菌产生一小部分对山梨酸具有高度抗性的孢子。其他真菌产生的孢子似乎对防腐剂更一致地敏感。正是这种能力产生了超抗的孢子子集，负责在较高山梨酸浓度下的真菌生长，这是该项目的重点。我们将把最新的基因技术应用于单孢子，以找出是什么定义了这些高度抵抗的孢子。然后，我们将利用这些信息开发新的方法来追踪实验室介质和饮料中的这些孢子。最后，我们将应用这些新工具来寻找能够抑制山梨酸抗性孢子的替代药物。这种方法可以为重新配制防腐剂提供解决方案，以更彻底地抑制腐烂霉菌，这是我们支持该项目的工业合作伙伴特别感兴趣的一个领域。虽然软饮料和山梨酸抗性为这项工作提供了范例，但所产生的知识将有助于制定更广泛地防止真菌食品变质的策略。

Up to one third of all foods is spoiled by fungi. This is a major concern for global food security. Spoilage of food by fungi renders the food inedible, and potentially toxic due to formation of substances termed mycotoxins. Fungal spores are abundant in the environment and prolific contaminants, being able to develop and grow in many conditions. Despite a variety of strategies to preserve foods, spoilage microorganisms fight back and some develop resistance to particular preservatives. Soft drinks are typically acidic and these conditions tend to inhibit other organisms like bacteria. However, many species of fungi (especially the moulds) are able to grow in acidic conditions and cause spoilage. A main preservative strategy is to include weak acids like sorbic acid to inhibit growth under these conditions. At permitted levels, sorbic acid inhibits most yeasts and fungi, but a number can still grow and some can degrade the sorbic acid to non-toxic products which alter flavour. Consequently, a chronic level of mould spoilage occurs in the manufacture of soft drinks. Our work has shown that most spoilage fungi produce a small subpopulation of spores that are highly resistant to sorbic acid. Spores produced by other fungi seem to be more uniformly sensitive to the preservative. It is this ability to produce a subset of spores that are hyper-resistant, responsible for fungal growth at higher sorbic acid concentrations, which is the focus of this project. We will apply the latest genetic technologies to single spores to find out what defines these hyper-resistant spores. We will then exploit that information to develop novel methods for tracking these spores in laboratory media and beverages. Finally, we will apply these new tools to find alternative agents that can inhibit the sorbic acid-resistant spores. This approach could offer solutions for reformulating preservatives to give more complete inhibition of spoilage moulds, an area of particular interest to our industrial partners supporting this project. While soft drinks and sorbic acid resistance provide the exemplar for this work, the knowledge generated will help develop strategies for preventing fungal food spoilage more broadly.