Banana (
Musa
spp.) is an important crop worldwide, but black Sigatoka disease caused by the fungus
Pseudocercospora fijiensis
threatens fruit production. In this work, we examined the potential of the endophytes of banana plants
Enterobacter cloacae
and
Klebsiella pneumoniae
, as antagonists of
P. fijiensis
and support plant growth in nutrient limited soils by N-transfer. The two bacterial isolates were identified by MALDI-TOF mass spectrometry and corroborated by 16S rRNA sequence analysis. Both bacteria were positive for beneficial traits such as N-fixation, indole acetic acid production, phosphate solubilization, negative for 1-aminocyclopropane 1-carboxylic acid deaminase and were antagonistic to
P. fijiensis
. To measure the effects on plant growth, the two plant bacteria and an
E. coli
strain (as non-endophyte), were inoculated weekly for 60 days as active cells (AC) and heat-killed cells (HKC) into plant microcosms without nutrients and compared to a water only treatment, and a mineral nutrients solution (MMN) treatment. Bacterial treatments increased growth parameters and prevented accelerated senescence, which was observed for water and mineral nutrients solution (MMN) treatments used as controls. Plants died after the first 20 days of being irrigated with water; irrigation with MMN enabled plants to develop some new leaves, but plants lost weight (−30%) during the same period. Plants treated with bacteria showed good growth, but
E. cloacae
AC treated plants had significantly greater biomass than the
E. cloacae
HKC. After 60 days, plants inoculated with
E. cloacae
AC showed intracellular bacteria within root cells, suggesting that a stable symbiosis was established. To evaluate the transference of organic N from bacteria into the plants, the 3 bacteria were grown with
15
NH
4
Cl or Na
15
NO
3
as the nitrogen source. The
15
N transferred from bacteria to plant tissues was measured by pheophytin isotopomer abundance. The relative abundance of the isotopomers
m/z
872.57, 873.57, 874.57, 875.57, 876.57 unequivocally demonstrated that plants acquired
15
N atoms directly from bacterial cells, using them as a source of N, to support plant growth in restricted nutrient soils.
E. cloacae
might be a new alternative to promote growth and health of banana crops.