Role of Vitamin B12 in sustaining trophic interactions between human gut symbionts

该提案的目的是提供不同形式的维生素B12 （VitB12）的分子和生化细节，这些维生素B12可以被胃肠道内的肠道细菌合成或利用，并了解细菌如何能够参与这种营养供应和共享。为了人类健康的利益，开发针对肠道微生物的适应性营养方法需要这些基本知识。数以万亿计的细菌生活在我们的大肠（肠道微生物群）中，它们在保持身体健康方面起着至关重要的作用。复杂群落中的细菌共享资源，在这种生态系统中共同分布的关键分子之一是维生素b12，这种分子仅由相对较少的细菌产生，但被大多数细菌利用。细菌可以制造多达15种不同的类维生素b12分子，这些分子统称为钴酰胺。对于细菌来说，合成钴胺的成本很高，需要一个复杂的生化途径，大约需要30种酶来完成它们的生物生成，但一旦合成，它们就为宿主提供了显著的代谢优势。然而，目前尚不清楚这些维生素b12变体或类似物在肠道细菌菌株中有多大程度的活性。随着肠道微生物群现在与许多不同的健康状况有关，人们对开发营养策略的兴趣越来越大，这些营养策略旨在改变微生物的平衡，以改善健康。这可以通过膳食补充剂或“益生菌”方法来实现。生活在肠道内壁的细菌（黏液相关细菌），靠近我们的身体，特别容易影响或响应我们健康状况的变化。然而，人们通常不知道如何调节这些细菌。我们之前的研究表明，人类的罗伊氏乳杆菌菌株能够产生ViB12。在提出这一建议的工作中，我们证明了侏儒瘤菌（ruminocus gnavus），一种在人类黏液中定植的关键细菌，需要维生素b12才能生长，但在缺乏维生素b12的情况下，罗伊氏乳杆菌的存在也能够促进其生长。人们认为红毛鼠是人类健康的关键调节剂，因此学术界和临床医生对更好地了解这种生物的生物学和需求以及我们如何调节它以改善人类健康有着浓厚的兴趣。为了解决这种相互作用和维生素b12的需求，我们将确定维持R. gnavus生长所需的维生素b12形式的类型。我们将识别细菌中需要利用维生素b12的组成部分。通过使用厌氧发酵设施和模型来模拟人类结肠，我们将确定维生素b12产生菌（如罗伊氏乳杆菌和/或维生素b12类似物）调节维生素b12需用菌（如gnavus）的能力，并评估处理对肠道微生物群落的影响。然后，我们将通过使用含有人类肠道微生物群的小鼠模型研究体内类似效应来研究黏液相关菌株的调节。这也将告知“益生菌”方法（就地生产维生素b12）与补充特定维生素b12类似物的影响。总之，这一合作提议将为细菌如何通过分担代谢负担而进化出复杂的权衡这一基本问题提供长期寻求的信息。此外，该研究将获得和利用有关维生素b12如何导致操纵肠道微生物组成的新策略以造福人类健康的基础知识。

The aim of the proposal is to provide molecular and biochemical detail on the different forms of vitamin B12 (VitB12) that can be synthesised or utilised by gut bacteria in the gastrointestinal lining and understand how bacteria are able to participate in this nutrient provisioning and sharing. This fundamental knowledge is required to develop adapted nutritional approaches targeting gut microbes for the benefit of human health.Trillions of bacteria live in our large intestine (the gut microbiota) where they play a vital role in maintaining good health. Bacteria in complex communities share resource and one of the key molecules that is communally distributed in such ecosystems is VitB12, a molecule that is made by only relatively few bacteria but utilised by most. Bacteria can make a range of up to 15 different VitB12-like molecules that collectively are called cobamides. Cobamides are expensive for the bacteria to make, requiring a complex biochemical pathway of around 30 enzymes for their biogenesis, but once made they provide the host with significant metabolic advantages. However, it is not clear to what extent these VitB12 variants or analogues are active across gut bacterial strains. With the gut microbiota now being linked to so many different health conditions, there is a growing interest in developing nutritional strategies that look to alter the balance of microbes to improve health. This could be through dietary supplement or 'probiotic' approaches. Bacteria living in the gut lining (mucus-associated bacteria), close to our body, are particularly prone to affect or respond to changes in our health status. However, it is not usually known how to modulate these bacteria. We previously showed that human strains of Lactobacillus reuteri are able to produce ViB12. In the work leading to this proposal, we demonstrated that Ruminoccus gnavus, a keystone mucus colonising bacterium in humans, requires VitB12 to grow but that, in the absence of VitB12, the presence of L. reuteri is also able to promote its growth. R. gnavus has been implicated as a key modulator of human health and there is therefore strong interest from academics and clinicians in better understanding the biology and requirements of this organism and how we can modulate it to improve human health. To address this mutualism and VitB12 requirement, we will determine the type of VitB12 forms required to sustain the growth of R. gnavus. We will identify the component parts in the bacteria that are required for the bacteria to utilise VitB12. By using anaerobic fermentation facilities and models to mimic the human colon we will determine the ability of VitB12-producers such as L. reuteri and/or VitB12 analogues to modulate VitB12-requirers such as R. gnavus and assess the impact of the treatments on the gut microbial community. We will then investigate the modulation of mucus-associated strains by investigating similar effects in vivo using mouse models harbouring a human gut microbiota. This will also inform on the impact of a 'probiotic' approach (in situ-production of VitB12) versus supplementation with specific VitB12 analogues. Together, this collaborative proposal will provide long-sought information on the basic question of how bacteria have evolved their complex trade-offs by sharing metabolic burden. Furthermore, the research will gain and exploit fundamental knowledge on how VitB12 can lead to novel strategies for manipulating microbial composition in the gut for the benefit of human health.