Abstract：
Microbial communities occupy diverse niches in nature, and community members routinely exchange a variety of nutrients among themselves. While large-scale metagenomic and metabolomic studies shed some light on these exchanges, the contribution of individual species and the molecular details of specific interactions are difficult to track. In this study, we follow the exchange of vitamin B1 (thiamin) and its intermediates between microbes within synthetic cocultures of Escherichia coli and Vibrio anguillarum. Thiamin contains two moieties, 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) and 4-methyl-5-(2-hydroxyethyl)thiazole (THZ), which are synthesized by distinct pathways using enzymes ThiC and ThiG, respectively, and then coupled by ThiE to form thiamin. Even though E. coli ΔthiC, ΔthiE, and ΔthiG mutants are thiamin auxotrophs, we observed that cocultures of ΔthiC-ΔthiE and ΔthiC-ΔthiG mutants are able to grow in a thiamin-deficient medium, whereas the ΔthiE-ΔthiG coculture does not. Further, the exchange of thiamin and its intermediates in V. anguillarum cocultures and in mixed cocultures of V. anguillarum and E. coli revealed that there exist specific patterns for thiamin metabolism and exchange among these microbes. Our findings show that HMP is shared more frequently than THZ, concurrent with previous observations that free HMP and HMP auxotrophy is commonly found in various environments. Furthermore, we observe that the availability of exogenous thiamin in the media affects whether these strains interact with each other or grow independently. These findings collectively underscore the importance of the exchange of essential metabolites as a defining factor in building and modulating synthetic or natural microbial communities. IMPORTANCE Vitamin B1 (thiamin) is an essential nutrient for cellular metabolism. Microorganisms that are unable to synthesize thiamin either fully or in part exogenously obtain it from their environment or via exchanges with other microbial members in their community. In this study, we created synthetic microbial cocultures that rely on sharing thiamin and its biosynthesis intermediates and observed that some of them are preferentially exchanged. We also observed that the coculture composition is dictated by the production and/or availability of thiamin and its intermediates. Our studies with synthetic cocultures provide the molecular basis for understanding thiamin sharing among microorganisms and lay out broad guidelines for setting up synthetic microbial cocultures by using the exchange of an essential metabolite as their foundation.
摘要：
微生物群落在自然界中占据不同的生态位，社区成员经常在彼此之间交换各种营养素。虽然大规模的宏基因组和代谢组学研究为这些交流提供了一些启示，单个物种的贡献和特定相互作用的分子细节很难追踪。在这项研究中,我们跟踪维生素B1（硫胺素）及其中间体在大肠杆菌和弧菌的合成共培养物中的微生物之间的交换。硫胺素包含两个部分，4-氨基-5-羟甲基-2-甲基嘧啶（HMP）和4-甲基-5-（2-羟乙基）噻唑（THZ），使用酶ThiC和ThiG通过不同的途径合成，分别,然后与ThiE偶联形成硫胺素。即使大肠杆菌ΔthiC，ΔthiE,ΔthiG突变体是硫胺素营养缺陷型，我们观察到ΔthiC-ΔthiE和ΔthiC-ΔthiG突变体的共培养物能够在硫胺素缺乏的培养基中生长，而ΔthiE-ΔthiG共培养则没有。Further,硫胺素及其中间体在V.anguillarum共培养物以及V.anguillarum和E.coli的混合共培养物中的交换表明，这些微生物之间存在硫胺素代谢和交换的特定模式。我们的研究结果表明，HMP比THz共享更频繁，与以前的观察结果一样，游离HMP和HMP营养缺陷型普遍存在于各种环境中。此外，我们观察到，培养基中外源硫胺素的可用性影响这些菌株是否相互作用或独立生长。这些发现共同强调了必需代谢物交换作为建立和调节合成或天然微生物群落的决定性因素的重要性。重要性维生素B1（硫胺素）是细胞代谢的必需营养素。不能完全或部分合成硫胺素的微生物从其环境中或通过与其群落中的其他微生物成员交换而获得硫胺素。在这项研究中,我们创建了合成的微生物共培养物，它们依赖于共享硫胺素及其生物合成中间体，并观察到其中一些被优先交换。我们还观察到,共培养物组成由硫胺素及其中间体的生产和/或可用性决定。我们对合成共培养物的研究为了解硫胺素在微生物之间的共享提供了分子基础，并为通过交换必需代谢物作为基础来建立合成微生物共培养物奠定了广泛的指导原则。
