4. Discussion
The three Bacillus sp. and the Enterobacter sp. bacterial strains
here selected were able to produce IAA and to phosphate solubilise
(particularly B. megaterium and Enterobacter sp.) under non-stress
and stress conditions in vitro. Minaxi (2011) also reported multiple
plant promoting traits in a Bacillus sp. isolated from semiarid crops.
Bacillus was the most abundant genus in the rhizosphere of
autochthonous drought-adapted target plants, probably because
the ability of these bacteria to form spores allows a better survival
under stress conditions (Marulanda et al., 2006). Nevertheless,
Enterobacter sp. resulted in the most tolerant bacteria able to
survive under 40% of PEG in the growing medium. Indeed, under
the greatest osmotic stress assayed (40% PEG), shows a high level of
proline and PHB but the lowest antioxidants activities (CAT and
APX) for osmotic cellular adaptation, as previously found
(Marulanda et al., 2009). Such bacterial activities may represent
an important protection against water limitation. Nevertheless,the
MDA production, as indicator of stress oxidation, resulted in a
higher level than expected. These intrinsic metabolic bacterial
characteristics in the axenic culture under non-stress and stress
conditions support the fitness of these bacteria to facilitate