Metabolic Flexibility as a Major Predictor of Spatial Distribution in Microbial Communities

A better understand the ecology of microbes and their role in the global ecosystem could be achieved if traditional ecological theories can be applied to microbes. In ecology organisms are defined as specialists or generalists according to the breadth of their niche. Spatial distribution is often used as a proxy measure of niche breadth; generalists have broad niches and a wide spatial distribution and specialists a narrow niche and spatial distribution. Previous studies suggest that microbial distribution patterns are contrary to this idea; a microbial generalist genus (Desulfobulbus) has a limited spatial distribution while a specialist genus (Methanosaeta) has a cosmopolitan distribution. Therefore, we hypothesise that this counter-intuitive distribution within generalist and specialist microbial genera is a common microbial characteristic. Using molecular fingerprinting the distribution of four microbial genera, two generalists, Desulfobulbus and the methanogenic archaea Methanosarcina, and two specialists, Methanosaeta and the sulfate-reducing bacteria Desulfobacter were analysed in sediment samples from along a UK estuary. Detected genotypes of both generalist genera showed a distinct spatial distribution, significantly correlated with geographic distance between sites. Genotypes of both specialist genera showed no significant differential spatial distribution. These data support the hypothesis that the spatial distribution of specialist and generalist microbes does not match that seen with specialist and generalist large organisms. It may be that generalist microbes, while having a wider potential niche, are constrained, possibly by intrageneric competition, to exploit only a small part of that potential niche while specialists, with far fewer constraints to their niche, are more capable of filling their potential niche more effectively, perhaps by avoiding intrageneric competition. We suggest that these counter-intuitive distribution patterns may be a common feature of microbes in general and represent a distinct microbial principle in ecology, which is a real challenge if we are to develop a truly inclusive ecology.若将传统生态学理论应用于微生物研究，则可更深入地解析微生物的生态特性及其在全球生态系统中的功能。在生态学领域，研究者依据生物的生态位宽度，将其划分为特化种（specialist）与广适种（generalist）。空间分布常被用作生态位宽度的替代衡量指标：广适种拥有较宽的生态位与更广的空间分布范围，而特化种的生态位与空间分布范围则相对狭窄。已有研究表明，微生物的分布模式与这一经典理论相悖——某广适微生物属脱硫叶菌属（Desulfobulbus）的空间分布范围有限，而某特化微生物属甲烷鬃毛菌属（Methanosaeta）却呈全球性分布。据此，我们提出假说：广适与特化微生物属间的这种反直觉分布模式，是微生物的普遍特征。本研究采用分子指纹技术，对英国某河口沿岸沉积物样本中的4个微生物属展开分布分析：其中2个为广适属，即脱硫叶菌属（Desulfobulbus）与产甲烷古菌甲烷八叠球菌属（Methanosarcina）；另外2个为特化属，即甲烷鬃毛菌属（Methanosaeta）与硫酸盐还原菌脱硫杆菌属（Desulfobacter）。两类广适属的检出基因型均呈现显著的空间分布差异，且与采样点间的地理距离呈显著相关；两类特化属的基因型则未表现出显著的空间分布差异。上述数据验证了本研究的假说：微生物广适种与特化种的空间分布模式，与大型生物中的广适种、特化种分布模式并不一致。这可能是因为：尽管广适微生物拥有更广阔的潜在生态位，但可能受属内竞争的限制，仅能利用其中极小一部分；而特化微生物的生态位约束极少，可通过规避属内竞争等方式更高效地占据其全部潜在生态位。我们认为，这类反直觉的分布模式可能是微生物的普遍共性，代表了生态学领域特有的微生物生态原则——若要构建真正具有普适性的生态学理论体系，这一原则将是一项亟需攻克的核心挑战。