Cyanobacteria are the bacterial ancestors of plant chloroplasts and perform oxygenic photosynthesis. Several strains grow in long filaments and differentiate into specialised cells, the heterocysts. These are the sites of nitrogen fixation and here nitrogen compounds are produced to supply the entire filament. Thereby, these bacteria are able to grow on any source of organic nutrition and to live on nothing but air and light. Cyanobacteria can be considered true multi-cellular organisms due to their division of labour between specialised cells with sophisticated cell-cell communication. Some strains form dormant spore-like akinetes to survive unfavourable conditions. Encountering beneficial conditions, they can germinate and differentiate into long filaments with heterocysts. Photosynthetically active cells are indicated by bright red autofluorescence.
In most bacteria, including B. subtilis, bacterial cell division is coordinated by assembly of FtsZ as the pace maker protein at the division site. For initiating cell division, FtsZ localizes at mid-cell, the prospective site of septum placement, and forms a ring-like structure, the so-called FtsZ-ring (or Z-ring). The Z-ring functions as a scaffold for proteins that synthesize the division septum (“divisome”). A novel class of antibiotic acyldepsipeptides (ADEPs) prevents cell division in many Gram-positive bacteria and induces strong filamentation of rod-shaped B. subtilis cells. ADEP treatment inhibits septum formation at the stage of Z-ring assembly by activating a bacterial peptidase (ClpP) for the untimely degradation of FtsZ proteins. Here, time-lapse fluorescence microscopy allows following the delocalization of mCherry-tagged FtsZ upon ADEP treatment as well as the starting filamentous growth of the bacteria in real-time. In addition to mCherry-FtsZ (red), further fluorescently-labelled proteins like GFP-tagged Noc protein (green), which binds to specific noc sites in the oriC proximal two-thirds of the B. subtilis chromosome, can be simultaneously imaged to e.g. visualize unaffected, ongoing chromosome segregation in relation to FtsZ displacement.