Root colonization of encapsulated Klebsiella oxytoca Rs-5 on cotton plants and its promoting growth performance under salinity stress

• Encapsulated bacteria are better than free bacteria in cell colonization.
• Encapsulated Rs-5 is effective in relieving salt stress for cotton growth.
• Encapsulated Rs-5 has positive effect as a controlled-release biofertilizer.

In order to enhance the root colonization of Klebsiella oxytoca Rs-5 isolated from salinized soil and promote cotton seedling growth under salinity stress, preparation of microcapsules containing K. oxytoca Rs-5 was performed. We investigated the effects of encapsulated and free K. oxytoca Rs-5 on cotton seedlings in terms of relieving salt stress and promoting growth and the colonization of bacterial cells in pot experiments. The results show that encapsulated bacterial treatment is better than free bacterial treatment in improving the cell colonization characteristics. The extent of cell colonization under the encapsulated bacterial (NSC, SC) treatments after 14, 21 and 28 days were about 10, 50 and 100 times that in the free bacteria (NSF, SF) treatments, respectively. In addition, treating cotton with bacterial agents alleviated the salt stress and promoted cotton seedling growth. The germination rates of cottonseeds treated with free bacteria (SF) increased by 15.40% compared with the control treatment (S), whereas those treated with encapsulation bacteria (SC) increased by 8.34%. The physiological parameters (chlorophyll a, soluble sugar, malondialdehyde, and proline) of cotton under the encapsulated bacterial treatments were better than that of cotton under unencapsulated bacterial treatments. The microencapsulated bacteria also effectively reduced the superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activity of the cotton seedlings. Hence, the results demonstrate that encapsulated K. oxytoca Rs-5 has more potential positive effects on cotton seedlings than free cell under salt stress.