In total, 140 halotolerant bacterial strains were isolated
from both the soil of barren fields and the rhizosphere of
six naturally growing halophytic plants in the vicinity of
the Yellow Sea, near the city of Incheon in the Republic of
Korea. All of these strains were characterized for multiple
plant growth promoting traits, such as the production of
indole acetic acid (IAA), nitrogen fixation, phosphorus (P)
and zinc (Zn) solubilization, thiosulfate (S2O3) oxidation,
the production of ammonia (NH3), and the production
of extracellular hydrolytic enzymes such as protease,
chitinase, pectinase, cellulase, and lipase under in vitro
conditions. From the original 140 strains tested, on the
basis of the latter tests for plant growth promotional
activity, 36 were selected for further examination. These
36 halotolerant bacterial strains were then tested for 1-
aminocyclopropane-1-carboxylic acid (ACC) deaminase
activity. Twenty-five of these were found to be positive,
and to be exhibiting significantly varying levels of activity.
16S rRNA gene sequencing analyses of the 36 halotolerant
strains showed that they belong to 10 different bacterial
genera: Bacillus, Brevibacterium, Planococcus, Zhihengliuella,
Halomonas, Exiguobacterium, Oceanimonas, Corynebacterium,
Arthrobacter, and Micrococcus. Inoculation of the 14
halotolerant bacterial strains to ameliorate salt stress
(150 mM NaCl) in canola plants produced an increase in
root length of between 5.2% and 47.8%, and dry weight
of between 16.2% and 43%, in comparison with the
uninoculated positive controls. In particular, three of the
bacteria, Brevibacterium epidermidis RS15, Micrococcus
yunnanensis RS222, and Bacillus aryabhattai RS341, all
showed more than 40% increase in root elongation and
dry weight when compared with uninoculated saltstressed
canola seedlings. These results indicate that
certain halotolerant bacteria, isolated from coastal soils,
have a real potential to enhance plant growth under saline
stress, through the reduction of ethylene production via
ACC deaminase activity.

Keywords: ACC-deaminase, Plant growth-promoting rhizobacteria, Halophilic bacteria, Root elongation, Canola, Salt stress