Article

Characterization of nifH gene expression, modification and rearrangement in Nodularia spumigena strain AV1

Department of Botany, Stockholm University, Stockholm, Sweden.
FEMS Microbiology Ecology (Impact Factor: 3.88). 05/2011; 77(2):449-59. DOI: 10.1111/j.1574-6941.2011.01127.x
Source: PubMed

ABSTRACT The annually reoccurring blooms that characterize the surface waters of the Baltic Sea are dominated by filamentous, heterocystous cyanobacteria such as Nodularia spumigena. In a previous study, we have demonstrated that N. spumigena strain AV1 differentiates heterocysts in the absence of detectable nitrogen fixation activity, an unusual physiological trait that is clearly distinct from other well-studied cyanobacteria. To further analyze the uncoupling between these two processes, we analyzed the gene expression and modification of the nitrogenase enzyme (the enzyme responsible for nitrogen fixation) in N. spumigena AV1, as well as in several other N. spumigena strains. Here, we demonstrate the occurrence of two nifH gene copies in N. spumigena strain AV1, only one of which is located in a complete nifHDK cluster and several NifH protein forms. Furthermore, we demonstrate the occurrence of a DNA rearrangement mechanism acting within the nifH gene copy located in the nifHDK cluster and present only in the strains exhibiting the previously reported uncoupling between heterocyst differentiation and nitrogen fixation processes. These data stress the existence of a distinct and complex regulatory circuit related to nitrogen fixation in this ecologically significant bloom-forming cyanobacterium.

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    • "During late stages in heterocyst differentiation, site-specific recombination between repeated sequences at the ends of the excision element causes deletion of the element leading to the transcription of nifH. Vintila et al. [55] have found that, unlike " model " cyanobacteria, the Baltic Sea N. spumigena contains an insertion element in the nifH of the nifHDK operon and an operating DNA rearrangement mechanism. They showed that this insertion element is present only in the tested Baltic Sea strains that exhibit " uncoupling " between N 2 -fixation and heterocyst differentiation, while it is absent in the tested non-Baltic Sea strains. "
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