Streptomyces bacteria: Antibiotic production in the wheat endosphere

链霉菌：小麦内圈的抗生素生产

• 批准号: BB/T015446/1
• 负责人: Matthew Hutchings
• 金额: $ 64.04万
• 依托单位: John Innes Centre
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FT015446%2F1
• 关键词: Streptomyces; bacteria; Antibiotic; production; wheat

Plants use photosynthesis to fix carbon dioxide from the air into glucose which they use as food. However, up to 40% of the carbon they fix is released into the soil from their roots and this appears to be a mechanism to attract beneficial bacteria from the surrounding soil. The bacteria use the root exudates as food and this helps the plants assemble a healthy microbiome. Some of these microbes protect the plants against disease and others help them get important nutrients from the soil. The root microbiome is therefore essential for plant health, but crop breeding over hundreds of years has selected traits such as bigger plants with more grain while perhaps neglecting the (unknown) effects on the microbiome. There is now growing interest in manipulating the microbiomes of crop plants such as wheat to make them more resistant to disease and to abiotic stresses like drought and salinity. Wheat is a staple crop for about 4 billion people and one of the most important crops in the world so increasing yields is essential if we are to support a growing world population. Our project focuses on a genus of soil bacteria called Streptomyces. The ~600 known species of Streptomyces make numerous secondary metabolites, and these account for half of all the known antibiotics. They are easy to isolate from soil but also form stable interactions with plant roots and can colonise the rhizosphere and endosphere of a wide range of different plants. We have found they are abundant inside wheat roots and that some strains can protect wheat against fungal diseases such as Take-all which can cause devastating crop losses. For one of these strains we have identified the molecules and genes responsible for this antifungal activity and shown it is increased two-fold when we add indole 3 acetic acid, a plant hormone present in wheat root exudates, to the growth medium. In this proposal we aim to look in more detail at the colonisation of wheat roots by soil dwelling, antibiotic-producing Streptomyces bacteria. We will sequence the genomes of 10 strains we have isolated from wheat plants which inhibit the take-all fungus on agar plates, identify the antifungals made by these strains and determine if they can protect wheat plants against take-all disease. We will also try to discover which molecules in wheat root exudates can feed these bacteria and switch on their production of secondary metabolites. Since Streptomyces bacteria form spores which can be dried and stored for long periods, we are interested in developing wheat seed coatings containing these spores so the bacteria grow into the roots of germinating wheat plants and protect them against disease. We will also test the role of the type VII secretion system in root colonisation by these strains since we have preliminary evidence that this system helps them outcompete other bacteria for wheat root colonisation. Our ultimate aim is to develop streptomycetes as seed coatings to protect wheat plants against fungal disease and to discover molecules from wheat root exudates that we can use to switch on secondary metabolite production in vitro because we know that 90% of the secondary metabolites they encode are not made under laboratory conditions. This could help us discover new and useful molecules from these bacteria.

植物利用光合作用将空气中的二氧化碳转化为葡萄糖作为食物。然而，它们固定的碳中有40%是从根部释放到土壤中的，这似乎是一种从周围土壤中吸引有益细菌的机制。细菌利用根部分泌物作为食物，这有助于植物聚集一个健康的微生物群。其中一些微生物保护植物免受疾病侵害，另一些微生物帮助植物从土壤中获得重要的营养。因此，根部微生物群对植物健康至关重要，但数百年来的作物育种选择了诸如更大的植物和更多的谷物等性状，而可能忽略了对微生物群的（未知）影响。现在，人们对控制小麦等农作物的微生物群越来越感兴趣，以使它们更能抵抗疾病和干旱、盐度等非生物压力。小麦是约40亿人的主要作物，也是世界上最重要的作物之一，因此，如果我们要养活不断增长的世界人口，提高产量至关重要。我们的项目关注的是一种叫做链霉菌的土壤细菌。已知的约600种链霉菌产生大量的次生代谢物，这些代谢物占所有已知抗生素的一半。它们很容易从土壤中分离出来，但也能与植物根系形成稳定的相互作用，并能在各种不同植物的根际和内圈定殖。我们发现它们在小麦根系中大量存在，一些菌株可以保护小麦免受真菌病的侵害，比如全身性真菌病，这种疾病会导致毁灭性的作物损失。对于其中一个菌株，我们已经确定了负责这种抗真菌活性的分子和基因，并表明当我们在生长培养基中添加吲哚乙酸（一种存在于小麦根分泌物中的植物激素）时，它的抗真菌活性增加了两倍。在这个建议中，我们的目标是更详细地研究土壤中居住的小麦根的定植，产生抗生素的链霉菌。我们将对从小麦植株中分离出来的10株在琼脂板上抑制全蚀菌的菌株进行基因组测序，鉴定这些菌株产生的抗真菌物质，并确定它们是否能保护小麦植株免受全蚀菌病的侵害。我们还将尝试发现小麦根系分泌物中的哪些分子可以为这些细菌提供食物，并开启它们次生代谢物的生产。由于链霉菌形成的孢子可以长时间干燥和储存，我们对开发含有这些孢子的小麦种子包衣很感兴趣，这样细菌就能生长到发芽的小麦植物的根部，保护它们免受疾病的侵害。我们还将测试VII型分泌系统在这些菌株的根定植中的作用，因为我们有初步证据表明该系统有助于它们在小麦根定植方面胜过其他细菌。我们的最终目标是开发链霉菌作为种子保护膜，保护小麦植物免受真菌疾病的侵害，并从小麦根系分泌物中发现分子，我们可以利用这些分子在体外启动次生代谢物的生产，因为我们知道它们编码的90%的次生代谢物不是在实验室条件下产生的。这可以帮助我们从这些细菌中发现新的有用的分子。