Fluorescence Microscopy of Rice Root Colonization by Synechocystis sp. PCC 6803 (PCC-M)

<b>Co-Inoculation of Rice roots with cyanobacteria</b><b><br></b>Glass cultivation tubes (Photosystem Instruments, PSI) containing 100 mL BG11 liquid medium were inoculated with <i>Synechocystis</i> sp. PCC 6803 (PCC-M) to an optical density (OD₇₅₀) of 0.15. To investigate the relevance of type IV piliation on root colonization the non-piliated mutant Δ<i>hfq </i>was applied as a control. Roots of young rice seedlings (variety Kitaake; ~ 1 week after germination) were pulled through the outflow holes of the silicone plugs (PSI) and submerged into the inoculated BG11 medium. Co-cultivation took place at ~30 °C under constant illumination (~ 100 μmol photons m^-2 s^-1, Environmental Test Chamber, Sanyo).In oder to visualize root colonization, bright field and (cyanobacterial) Chlorophyll <i>a</i> autofluorescence were recorded after 2 weeks of co-cultivation. Three different magnifications (10x, 63x, 100x [w/ immersion oil]) were applied; bright field and fluorescence figures were merged using the ImageJ software. <br>Three major observations were made:<br>1. root colonization of roots by wild-type <i>Synechocystis </i>but not by the non-motile mutant Δ<i>hfq</i><i><br></i>2.<i> </i>wild-type <i>Synechocystis </i>appear to build biofilm-like assemblies surrounding the root surface<br><br>3. wild-type <i>Synechocystis</i> cells<i> congregate</i> inside of small but abundant cracks on the root surface <br>