Abstract
BackgroundIn the filamentous cyanobacterium Nostoc punctiforme ATCC 29133, removal of combined nitrogen induces the differentiation of heterocysts, a cell-type specialized in N2 fixation. The differentiation involves genomic, structural and metabolic adaptations. In cyanobacteria, changes in the availability of carbon and nitrogen have also been linked to redox regulated posttranslational modifications of protein bound thiol groups. We have here employed a thiol targeting strategy to relatively quantify the putative redox proteome in heterocysts as compared to N2-fixing filaments, 24 hours after combined nitrogen depletion. The aim of the study was to expand the coverage of the cell-type specific proteome and metabolic landscape of heterocysts.ResultsHere we report the first cell-type specific proteome of newly formed heterocysts, compared to N2-fixing filaments, using the cysteine-specific selective ICAT methodology. The data set defined a good quantitative accuracy of the ICAT reagent in complex protein samples. The relative abundance levels of 511 proteins were determined and 74% showed a cell-type specific differential abundance. The majority of the identified proteins have not previously been quantified at the cell-type specific level. We have in addition analyzed the cell-type specific differential abundance of a large section of proteins quantified in both newly formed and steady-state diazotrophic cultures in N. punctiforme. The results describe a wide distribution of members of the putative redox regulated Cys-proteome in the central metabolism of both vegetative cells and heterocysts of N. punctiforme.ConclusionsThe data set broadens our understanding of heterocysts and describes novel proteins involved in heterocyst physiology, including signaling and regulatory proteins as well as a large number of proteins with unknown function. Significant differences in cell-type specific abundance levels were present in the cell-type specific proteomes of newly formed diazotrophic filaments as compared to steady-state cultures. Therefore we conclude that by using our approach we are able to analyze a synchronized fraction of newly formed heterocysts, which enabled a better detection of proteins involved in the heterocyst specific physiology.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-1064) contains supplementary material, which is available to authorized users.
Highlights
In the filamentous cyanobacterium Nostoc punctiforme ATCC 29133, removal of combined nitrogen induces the differentiation of heterocysts, a cell-type specialized in N2 fixation
The strategy to compare the abundance of proteins in isolated heterocysts compared to in whole N2-fixing filaments has previously been applied in a few studies [7,18]
The theoretical PATRIC proteome is substantially larger than the standard theoretical RefSeq proteome and it should be pointed out that most of the low molecular weight proteins annotated in the theoretical N. punctiforme PATRIC proteome have to date not been detected in any proteomic analyses
Summary
In the filamentous cyanobacterium Nostoc punctiforme ATCC 29133, removal of combined nitrogen induces the differentiation of heterocysts, a cell-type specialized in N2 fixation. We have here employed a thiol targeting strategy to relatively quantify the putative redox proteome in heterocysts as compared to N2-fixing filaments, 24 hours after combined nitrogen depletion. The filamentous cyanobacterium Nostoc punctiforme ATCC 29133 ( on N. punctiforme) is a multicellular bacterium in which diverse cell-types can be formed by cell differentiation in response to various environmental stimuli [1,2]. In order to survive times of combined nitrogen limitation N. punctiforme differentiate a new cell-type; the heterocyst, which is specialized in the fixation of atmospheric nitrogen (N2) into ammonium [3]. The cell differentiation into a functional N2-fixing heterocyst takes about 24 hours and includes a significant reprogramming of the metabolism as well as morphological remodeling. In the heterocysts both energy and reducing equivalents are efficiently directed to the nitrogenase enzyme complex, which catalyzes the N2 fixation reaction [9]
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