Krause Sascha M B, Johnson Timothy, Samadhi Karunaratne Yasodara, Fu Yanfen, Beck David A C, Chistoserdova Ludmila, Lidstrom Mary E
Department of Chemical Engineering, University of Washington, Seattle, WA 98195.
Department of Microbiology, University of Washington, WA 98195.
Proc Natl Acad Sci U S A. 2017 Jan 10;114(2):358-363. doi: 10.1073/pnas.1619871114. Epub 2016 Dec 27.
The utilization of methane, a potent greenhouse gas, is an important component of local and global carbon cycles that is characterized by tight linkages between methane-utilizing (methanotrophic) and nonmethanotrophic bacteria. It has been suggested that the methanotroph sustains these nonmethanotrophs by cross-feeding, because subsequent products of the methane oxidation pathway, such as methanol, represent alternative carbon sources. We established cocultures in a microcosm model system to determine the mechanism and substrate that underlay the observed cross-feeding in the environment. Lanthanum, a rare earth element, was applied because of its increasing importance in methylotrophy. We used co-occurring strains isolated from Lake Washington sediment that are involved in methane utilization: a methanotroph and two nonmethanotrophic methylotrophs. Gene-expression profiles and mutant analyses suggest that methanol is the dominant carbon and energy source the methanotroph provides to support growth of the nonmethanotrophs. However, in the presence of the nonmethanotroph, gene expression of the dominant methanol dehydrogenase (MDH) shifts from the lanthanide-dependent MDH (XoxF)-type, to the calcium-dependent MDH (MxaF)-type. Correspondingly, methanol is released into the medium only when the methanotroph expresses the MxaF-type MDH. These results suggest a cross-feeding mechanism in which the nonmethanotrophic partner induces a change in expression of methanotroph MDHs, resulting in release of methanol for its growth. This partner-induced change in gene expression that benefits the partner is a paradigm for microbial interactions that cannot be observed in studies of pure cultures, underscoring the importance of synthetic microbial community approaches to understand environmental microbiomes.
甲烷作为一种强效温室气体，其利用是局部和全球碳循环的重要组成部分，其特点是利用甲烷的（甲烷营养型）细菌和非甲烷营养型细菌之间存在紧密联系。有人提出，甲烷营养菌通过交叉喂养来维持这些非甲烷营养菌，因为甲烷氧化途径的后续产物，如甲醇，可作为替代碳源。我们在微观模型系统中建立了共培养体系，以确定环境中观察到的交叉喂养背后的机制和底物。由于镧在甲基营养中日益重要，因此使用了镧这种稀土元素。我们使用了从华盛顿湖沉积物中分离出的共同存在的菌株，这些菌株参与甲烷利用：一种甲烷营养菌和两种非甲烷营养型甲基营养菌。基因表达谱和突变分析表明，甲醇是甲烷营养菌提供的主要碳源和能源，以支持非甲烷营养菌的生长。然而，在非甲烷营养菌存在的情况下，主要甲醇脱氢酶（MDH）的基因表达从镧依赖性MDH（XoxF）型转变为钙依赖性MDH（MxaF）型。相应地，只有当甲烷营养菌表达MxaF型MDH时，甲醇才会释放到培养基中。这些结果表明了一种交叉喂养机制，即非甲烷营养型伙伴诱导甲烷营养菌MDH表达发生变化，从而释放甲醇以供其生长。这种伙伴诱导的有利于伙伴的基因表达变化是纯培养研究中无法观察到的微生物相互作用模式，强调了合成微生物群落方法对于理解环境微生物群的重要性。
