Pinto Catarina, Melo-Miranda Rita, Gordo Isabel, Sousa Ana
CEDOC, Chronic Diseases Research Centre, NOVA Medical School, Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisbon, Portugal.
Department of Medical Sciences, Institute of Biomedicine (iBiMED), University of Aveiro, Aveiro, Portugal.
Front Microbiol. 2021 Jul 21;12:709259. doi: 10.3389/fmicb.2021.709259. eCollection 2021.
The operon is one of the best known gene regulatory circuits and constitutes a landmark example of how bacteria tune their metabolism to nutritional conditions. It is nearly ubiquitous in strains justifying the use of its phenotype, the ability to consume lactose, for species identification. Lactose is the primary sugar found in milk, which is abundant in mammals during the first weeks of life. However, lactose is virtually non-existent after the weaning period, with humans being an exception as many consume dairy products throughout their lives. The absence of lactose during adulthood in most mammals and the rarity of lactose in the environment, means that the selective pressure for maintaining the operon could be weak for long periods of time. Despite the ability to metabolize lactose being a hallmark of 's success when colonizing its primary habitat, the mammalian intestine, the selective value of this trait remains unknown in this ecosystem during adulthood. Here we determine the competitive advantage conferred by the operon to a commensal strain of when colonizing the mouse gut. We find that its benefit, which can be as high as 11%, is contingent on the presence of lactose in the diet and on the presence of other microbiota members in the gut, but the operon is never deleterious. These results help explaining the pervasiveness of the operon in , but also its polymorphism, as -negative strains albeit rare can naturally occur in the gut.
操纵子是最为人熟知的基因调控回路之一，是细菌如何根据营养条件调节其新陈代谢的一个标志性例子。它在菌株中几乎无处不在，这使得利用其表型（即消耗乳糖的能力）来进行物种鉴定成为可能。乳糖是牛奶中的主要糖类，在哺乳动物出生后的头几周，牛奶中乳糖含量丰富。然而，断奶期后乳糖几乎不存在，人类是个例外，因为许多人一生都食用乳制品。在大多数哺乳动物成年期乳糖不存在以及环境中乳糖稀少，这意味着维持操纵子的选择压力可能在很长一段时间内都很弱。尽管代谢乳糖的能力是[具体细菌名称]在其主要栖息地——哺乳动物肠道定殖成功的一个标志，但在成年期这个生态系统中，这一特性的选择价值仍不为人知。在这里，我们确定了操纵子在定殖小鼠肠道时赋予[具体细菌名称]共生菌株的竞争优势。我们发现，其益处（可高达11%）取决于饮食中乳糖的存在以及肠道中其他微生物群成员的存在，但操纵子从未有害。这些结果有助于解释操纵子在[具体细菌名称]中的普遍性，也有助于解释其多态性，因为[具体细菌名称]阴性菌株虽然罕见，但可自然出现在肠道中。
