Fig 2. Work flow for analyses of cyanobacteria and their associated heterotrophic bacteria.

A: Card-FISH image of a Nodularia sp. filament with two associated Alphaproteobacteria taken with a laser microdissectional microscope. The marking arrow can be seen at the right side. B: Scanning electron microscope image of the same spot for confirmation of associated bacteria (middle-right side of the filament) and identification of Nodularia sp. The tip of the marking arrow can be seen at the right side of the image. C: accumulated NanoSIMS images of the same spot with blue (low) to red (high) ¹⁵N signal (as example). The circled areas display the regions of interest, where ¹³C/¹²C and ¹⁵N/¹⁴N ratios were calculated. Control (filter without cyanobacteria or heterotrophic bacteria) regions can be seen at the top-right and down-left, Nodularia sp. regions are displayed in the bluish part, and the associated Alphaproteobacteria by the smaller regions in the reddish part of the image.