The promotion of sugarcane growth by the endophytic Pantoea agglomerans strain 33.1 was studied under gnotobiotic and
greenhouse conditions. The green fluorescent protein (GFP)-tagged strain P. agglomerans 33.1::pNKGFP was monitored in vitro
in sugarcane plants by microscopy, reisolation, and quantitative PCR (qPCR). Using qPCR and reisolation 4 and 15 days after
inoculation, we observed that GFP-tagged strains reached similar density levels both in the rhizosphere and inside the roots and
aerial plant tissues. Microscopic analysis was performed at 5, 10, and 18 days after inoculation. Under greenhouse conditions, P.
agglomerans 33.1-inoculated sugarcane plants presented more dry mass 30 days after inoculation. Cross-colonization was confirmed
by reisolation of the GFP-tagged strain. These data demonstrate that 33.1::pNKGFP is a superior colonizer of sugarcane
due to its ability to colonize a number of different plant parts. The growth promotion observed in colonized plants may be related
to the ability of P. agglomerans 33.1 to synthesize indoleacetic acid and solubilize phosphate. Additionally, this strain may
trigger chitinase and cellulase production by plant roots, suggesting the induction of a plant defense system. However, levels of
indigenous bacterial colonization did not vary between inoculated and noninoculated sugarcane plants under greenhouse conditions,
suggesting that the presence of P. agglomerans 33.1 has no effect on these communities. In this study, different techniques
were used to monitor 33.1::pNKGFP during sugarcane cross-colonization, and our results suggested that this plant growth promoter
could be used with other crops. The interaction between sugarcane and P. agglomerans 33.1 has important benefits that
promote the plant’s growth and fitness.