Rice endophyte Pantoea agglomerans YS19 forms multicellular symplasmata via cell aggregation

Pantoea agglomerans is characterized by the formation of multicellular symplasmata. One unanswered question regarding this bacterium is how these structures are formed. In this study, the rice diazotrophic endophyte P. agglomerans YS19 was selected for exploration of this theme. YS19 was labeled with green fluorescent protein and the resulting recombinant YS19::gfp was observed to grow only slightly more slowly (a decrease of 5.5%) than the wild-type strain, and to show high GFP label stability (label loss rate 8.9218 × 10^-6 per generation, nearly reaching the generally accepted spontaneous mutation rate for most bacteria). YS19::gfp resembled the wild-type YS19 in symplasmata formation and growth profiles. Based on associated cultivation of both strains by mixing their individually cultivated single cells, symplasmata were formed and composed of both YS19::gfp and YS19, suggesting that YS19 formed symplasmata via aggregation, not proliferation, of the original single cells.