Musat Florin, Harder Jens, Widdel Friedrich
Max-Planck-Institut für Marine Mikrobiologie, Celsiusstrasse 1, D-28359 Bremen, Germany.
Environ Microbiol. 2006 Oct;8(10):1834-43. doi: 10.1111/j.1462-2920.2006.01069.x.
Aerobic microbial degradation of pollutant oil (petroleum) in aquatic environments is often severely limited by the availability of combined nitrogen. We therefore studied whether the microbial community enriched in marine sediment microcosms with an added oil layer and exposure to light harboured nitrogenase activity. The acetylene reduction (AR) assay indeed indicated active nitrogenase; however, similar activity was observed in oil-free control microcosms. In both microcosms, the AR rate was significantly reduced upon a dark shift, indicating that enriched cyanobacteria were the dominant diazotrophs. Analysis of structural dinitrogenase reductase genes (nifH) amplified from both microcosms indeed revealed NifH sequences related mostly to those of heterocystous cyanobacteria. NifH sequences typically affiliating with those of heterotrophic bacteria were more frequently retrieved from the oil-containing sediment. Expression analyses showed that mainly nifH genes similar to those of heterocystous cyanobacteria were expressed in the light. Upon a dark shift, nifH genes related to those of non-heterocystous cyanobacteria were expressed. Expression of nifH assignable to heterotrophs was apparently not significant. It is concluded that cyanobacteria are the main contributors of fixed nitrogen to oil-contaminated and pristine sediments if nitrogen is a limiting factor and if light is available. Hence, also the oil-degrading heterotrophic community may thus receive a significant part of combined nitrogen from cyanobacteria, even though oil vice versa apparently does not stimulate an additional nitrogen fixation in the enriched community.
在水生环境中，污染物油类（石油）的需氧微生物降解常常受到化合态氮可用性的严重限制。因此，我们研究了在添加油层并暴露于光照的海洋沉积物微观世界中富集的微生物群落是否具有固氮酶活性。乙炔还原（AR）测定确实表明存在活性固氮酶；然而，在无油对照微观世界中也观察到了类似的活性。在这两种微观世界中，黑暗转变后AR速率均显著降低，表明富集的蓝细菌是主要的固氮微生物。对从两种微观世界中扩增的结构二氮酶还原酶基因（nifH）的分析确实揭示了与异形胞蓝细菌的NifH序列大多相关的NifH序列。通常与异养细菌的NifH序列相关的序列更频繁地从含油沉积物中获得。表达分析表明，主要是与异形胞蓝细菌相似的nifH基因在光照下表达。黑暗转变后，与非异形胞蓝细菌相关的nifH基因表达。可归因于异养生物的nifH表达显然不显著。得出的结论是，如果氮是限制因素且有光照，蓝细菌是受油污染和原始沉积物中固定氮的主要贡献者。因此，即使油显然不会刺激富集群落中额外的固氮作用，降解油的异养群落也可能从蓝细菌中获得相当一部分化合态氮。
