The cyanobacterium Nostoc: Complex behavior, big genome
You are studying the cyanobacterium Nostoc, a remarkable creature capable of photosynthesis, nitrogen-fixation, and, perhaps most unusual of all for a bacterium, spatially patterned cell differentiation. In response to nitrogen-deprivation, specialized cells, called heterocysts, appear at semiregular intervals along a filament, pale white pearls (here stained blue) interspersed amongst green beads.

This complex behavior comes at a cost: lots of genes. At about 9.5 million bases, Nostoc punctiforme checks in the bacterium with the biggest genome sequenced to date. But is gene number the whole story behind the large genome? Eukaryotic genomes achieve their size not by an elevated number of genes but by huge intergenic regions, full of repeated sequences. What lies in the intergenic regions of Nostoc's huge genome?

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