Cotner James B, Hall Edward K, Scott J Thad, Heldal Mikal
Department of Ecology, Evolution and Behavior, University of Minnesota St. Paul, MN, USA.
Front Microbiol. 2010 Dec 8;1:132. doi: 10.3389/fmicb.2010.00132. eCollection 2010.
Although aquatic bacteria are assumed to be nutrient-rich, they out-compete other foodweb osmotrophs for nitrogen (N) and phosphorus (P) an apparent contradiction to resource ratio theory. This paradox could be resolved if aquatic bacteria were demonstrated to be nutrient-poor relative other portions of the planktonic food web. In a survey of >120 lakes in the upper Midwest of the USA, the nutrient content of bacteria was lower than previously reported and very similar to the Redfield ratio, with a mean biomass composition of 102:12:1 (C:N:P). Individual freshwater bacterial isolates grown under P-limiting and P-replete conditions had even higher C:P and N:P ratios with a mean community biomass composition ratio of 875C:179N:1P suggesting that individual strains can be extremely nutrient-poor, especially with respect to P. Cell-specific measurements of individual cells from one lake confirmed that low P content could be observed at the community level in natural systems with a mean biomass composition of 259C:69N:1P. Variability in bacterial stoichiometry is typically not recognized in the literature as most studies assume constant and nutrient-rich bacterial biomass composition. We present evidence that bacteria can be extremely P-poor in individual systems and in culture, suggesting that bacteria in freshwater ecosystems can either play a role as regenerators or consumers of inorganic nutrients and that this role could switch depending on the relationship between bacterial biomass stoichiometry and resource stoichiometry. This ability to switch roles between nutrient retention and regeneration likely facilitates processing of terrestrial organic matter in lakes and rivers and has important implications for a wide range of bacterially mediated biogeochemical processes.
尽管水生细菌被认为富含营养，但它们在争夺氮（N）和磷（P）方面胜过其他食物网中的渗透营养生物，这显然与资源比率理论相矛盾。如果能证明与浮游食物网的其他部分相比，水生细菌营养匮乏，那么这个悖论就可以得到解决。在美国中西部上游对120多个湖泊的调查中，细菌的营养成分低于先前报道的水平，且与雷德菲尔德比率非常相似，平均生物量组成为102:12:1（碳：氮：磷）。在磷限制和磷充足条件下生长的单个淡水细菌分离株具有更高的碳磷比和氮磷比，平均群落生物量组成比为875碳：179氮：1磷，这表明单个菌株可能营养极度匮乏，尤其是在磷方面。对一个湖泊中单个细胞的细胞特异性测量证实，在自然系统的群落水平上可以观察到低磷含量，平均生物量组成为259碳：69氮：1磷。细菌化学计量的变异性在文献中通常未被认识到，因为大多数研究假设细菌生物量组成恒定且营养丰富。我们提供的证据表明，在单个系统和培养物中，细菌可能极度缺磷，这表明淡水生态系统中的细菌既可以作为无机养分的再生者，也可以作为消费者，并且这种角色可能会根据细菌生物量化学计量与资源化学计量之间的关系而转换。这种在养分保留和再生之间转换角色的能力可能有助于湖泊和河流中陆地有机物的处理，并且对广泛的细菌介导的生物地球化学过程具有重要意义。
