High-cost production of bioplastics polyhydroxyalkanoates (PHA) is a major concern for their large scale application. In order to produce PHA economically, new technology must be developed to reduce costs on energy consumption, fresh water and substrate usages. It is also important to conduct the PHA production process in a continuous way rather than in a batch process.

Klebsiella oxytoca Rs-5 isolated with ACC (1-aminocyclopropane-1-carboxylate) deaminase activity as the sole nitrogen source could obviously promote cotton seedling growth under salt stress and produce phytohormone indole-3-acetic acid (IAA). The amount of IAA produced by the strain Rs-5 was measured, and the effect of IAA on cotton growth under salt stress was studied. Different treatments were set to treat cotton seeds with fermentation broth containing strain Rs-5 (FB), strain Rs-5, fermentation broth with bacteria removed (FB-NB), fermentation broth without bacteria or IAA (FB-NB-NI) and single IAA solutions (SI) according to the IAA concentration after strain Rs-5 culturing of 48, 72 and 120 h. The germination rate, dry weight, plant height, root length and malondialdehyde (MDA), proline and endogenous IAA content in roots were determined. The results showed that both IAA produced by strain Rs-5 and the strain were effective in promoting cotton growth under salt stress. The growth and ability to resist salt stress of cotton seedlings were increased with the enhancement of IAA concentration. The treatment of FB containing bacteria and IAA at 120 h obtained the best state of cotton growth, when the IAA content was the highest in the fermentation broth (42.14 μg·L–1). The germination rate, dry weight, plant height and root length were increased by 29.4%, 24.3%, 27.2% and 27.2% , respectively, compared to the saline control. The strain Rs-5 and/or IAA could obviously reduce the MDA and proline content and increase the endogenous IAA content in cotton seedlings. However, the efficacy of other components in the fermentation broth was inconspicuous.