Department of Marine Microbiology, Royal Netherlands Institute of Sea Research (NIOZ), PO Box 140, 4400 AC Yerseke, The Netherlands.
Arch Microbiol. 2012 Jun;194(6):483-91. doi: 10.1007/s00203-011-0787-5. Epub 2012 Jan 8.
Microbial mats are often found in intertidal areas experiencing a large range of salinities. This study investigated the effect of changing salinities on nitrogenase activity and on the composition of the active diazotrophic community (nifH transcript libraries) of three types of microbial mats situated along a littoral gradient. All three mat types exhibited highest nitrogenase activity at salinities close to ambient seawater or lower. The response to lower or higher salinity was strongest in mats higher up in the littoral zone. Changes in nitrogenase activity as the result of exposure to different salinities were accompanied by changes in the active diazotrophic community. The two stations higher up in the littoral zone showed nifH expression by Cyanobacteria (Oscillatoriales and Chroococcales) and Proteobacteria (Gammaproteobacteria and Deltaproteobacteria). At these stations, a decrease in the relative contribution of Cyanobacteria to the nifH transcript libraries was observed at increasing salinity coinciding with a decrease in nitrogenase activity. The station at the low water mark showed low cyanobacterial contribution to nifH transcript libraries at all salinities but an increase in deltaproteobacterial nifH transcripts under hypersaline conditions. In conclusion, increased salinities caused decreased nitrogenase activity and were accompanied by a lower proportion of cyanobacterial nifH transcripts.
微生物席通常存在于经历大范围盐度变化的潮间带区域。本研究调查了盐度变化对三种滨岸梯度微生物席的固氮酶活性和活性固氮微生物群落（nifH 转录文库）组成的影响。所有三种类型的微生物席在接近环境海水或更低的盐度下表现出最高的固氮酶活性。在滨岸带较高处的微生物席对低盐度或高盐度的反应最强。由于暴露于不同盐度而导致的固氮酶活性变化伴随着活性固氮微生物群落的变化。滨岸带较高的两个站位显示出蓝细菌（Oscillatoriales 和 Chroococcales）和变形菌（γ-变形菌纲和δ-变形菌纲）的 nifH 表达。在这些站位，随着盐度的增加，nifH 转录文库中蓝细菌的相对丰度减少，与固氮酶活性的下降一致。低水位标志处的站位在所有盐度下 nifH 转录文库中蓝细菌的贡献都较低，但在高盐条件下，δ-变形菌纲的 nifH 转录物增加。总之，盐度升高导致固氮酶活性降低，并伴随着蓝细菌 nifH 转录物比例降低。
