PDF(Pubmed)
Abstract：
Leaf litter microbes collectively degrade plant polysaccharides, influencing land-atmosphere carbon exchange. An open question is how substrate complexity-defined as the structure of the saccharide and the amount of external processing by extracellular enzymes-influences species interactions. We tested the hypothesis that monosaccharides (i.e. xylose) promote negative interactions through resource competition, and polysaccharides (i.e. xylan) promote neutral or positive interactions through resource partitioning or synergism among extracellular enzymes. We assembled a three-species community of leaf litter-degrading bacteria isolated from a grassland site in Southern California. In the polysaccharide xylan, pairs of species stably coexisted and grew equally in coculture and in monoculture. Conversely, in the monosaccharide xylose, competitive exclusion and negative interactions prevailed. These pairwise dynamics remained consistent in a three-species community: all three species coexisted in xylan, while only two species coexisted in xylose, with one species capable of using peptone. A mathematical model showed that in xylose these dynamics could be explained by resource competition. Instead, the model could not predict the coexistence patterns in xylan, suggesting other interactions exist during biopolymer degradation. Overall, our study shows that substrate complexity influences species interactions and patterns of coexistence in a synthetic microbial community of leaf litter degraders.
摘要：
凋落叶微生物共同降解植物多糖，影响陆地-大气碳交换。一个悬而未决的问题是底物复杂性-定义为糖的结构和胞外酶的外部加工量-如何影响物种相互作用。我们检验了单糖(即，木糖)通过资源竞争促进负面互动，和多糖(即，木聚糖）通过资源分配或胞外酶之间的协同作用促进中性或积极的相互作用。我们从南加州的一个草地上分离出了三个物种的叶子凋落物降解细菌群落。在多糖木聚糖中，成对的物种在共培养和单一培养中稳定共存并平等生长。相反，在单糖木糖中，竞争排斥和消极互动盛行。这些成对动态在三个物种群落中保持一致：所有三个物种共存于木聚糖中，而木糖中只有两种共存,一种能够使用蛋白胨的物种。数学模型表明，在木糖中，这些动力学可以通过资源竞争来解释。相反，该模型无法预测木聚糖中的共存模式，表明在生物聚合物降解过程中存在其他相互作用。总的来说,我们的研究表明，底物的复杂性影响物种的相互作用和共存模式的合成微生物群落的叶凋落物降解。
