Klebsiella sp. S6; a halotolerant rhizosphere bacterium of Phragmites communis L. with potential plant-growth promotion of pepper

Phragmites communis L. is a halophytic plant that can withstand harsh environmental conditions such as salinity. In the present study, we isolated a bacterium associated with the rhizosphere of Phragmites communis L. Based on morphological and biochemical as well as MALDI-TOF and 16S rRNA sequencing results, the strain S6 was identified as Klebsiella aerogenes with a score of 2.34 for MALDI-TOF and a similarity of 99.86% with type strain Klebsiella aerogenes KCTC 2190T. Furthermore, we demonstrated that strain S6 tolerated up to 2.5 M of NaCl and exhibited resistance to only three antibiotics that are frequently used for Enterobacteriaceae. Plant growth-promoting (PGP) results showed that the strain S6 had multiple traits, it was able to fix atmospheric nitrogen, solubilized inorganic phosphate (Ca3(PO4)2 and potassium in addition to the production of siderophores, ammonia, cellulase, protease and amylase. Indole acetic acid (IAA) production was also detected, and the strain S6 showed a positive ACC deaminase activity. Moreover, when the strain S6 was used as an inoculum for pepper seeds, increases in different parameters including shoot and root lengths and fresh and dry weights were shown under normal and saline conditions. We reported in this study, that the inoculation of pepper (Capsicum annuum L.) seeds with the Klebsiella sp. strain S6 was efficient for pepper growth in normal and salt stress conditions. The results of this study thus indicate that natural plants from saline habitats present a good source for isolating beneficial PGPR to grow crops like pepper under saline conditions.