Cavendish Laboratory, University of Cambridge, Cambridge, UK.
Department of Plant Sciences, University of Cambridge, Cambridge, UK.
ISME J. 2014 Jul;8(7):1418-27. doi: 10.1038/ismej.2014.9. Epub 2014 Feb 13.
The growth dynamics of populations of interacting species in the aquatic environment is of great importance, both for understanding natural ecosystems and in efforts to cultivate these organisms for industrial purposes. Here we consider a simple two-species system wherein the bacterium Mesorhizobium loti supplies vitamin B12 (cobalamin) to the freshwater green alga Lobomonas rostrata, which requires this organic micronutrient for growth. In return, the bacterium receives photosynthate from the alga. Mathematical models are developed that describe minimally the interdependence between the two organisms, and that fit the experimental observations of the consortium. These models enable us to distinguish between different mechanisms of nutrient exchange between the organisms, and provide strong evidence that, rather than undergoing simple lysis and release of nutrients into the medium, M. loti regulates the levels of cobalamin it produces, resulting in a true mutualism with L. rostrata. Over half of all microalgae are dependent on an exogenous source of cobalamin for growth, and this vitamin is synthesised only by bacteria; it is very likely that similar symbiotic interactions underpin algal productivity more generally.
水生环境中相互作用的物种群体的生长动态非常重要，这不仅有助于理解自然生态系统，还有助于为工业目的培养这些生物。在这里，我们考虑一个简单的两种物种系统，其中细菌 Mesorhizobium loti 为淡水绿藻 Lobomonas rostrata 提供维生素 B12（钴胺素），而绿藻生长需要这种有机微量营养素。作为回报，细菌从藻类中获得光合作用产物。我们开发了数学模型来描述这两种生物之间的相互依存关系，并拟合了联合体的实验观察结果。这些模型使我们能够区分生物体之间养分交换的不同机制，并提供有力的证据表明，M. loti 并非简单地裂解并将营养物质释放到培养基中，而是调节其产生的钴胺素水平，从而与 L. rostrata 形成真正的互利共生关系。超过一半的微藻依赖于外源钴胺素来生长，而这种维生素仅由细菌合成；很可能类似的共生相互作用更普遍地支撑着藻类的生产力。
