Cultivable bacteria from the rhizosphere of Indosasa acutiligulata: isolation, evaluation, and SynComs for promoting plant growth

Abstract:

Objective The rhizosphere of plants hosts a diverse array of microorganisms that play a crucial role in plant growth and health. This study identified functional bacteria in the rhizosphere soil of an economic bamboo species Indosasa acutiligulata and assessed the effects of synthetic microbial communities (SynComs) on bamboo growth. The results are expected to provide implications for enhancing forest quality and utilizing beneficial microorganisms in bamboo cultivation.Methods Rhizosphere soil samples of In. acutiligulata were collected from the Jiuyi Mountain National Nature Reserve. Bacteria were isolated by the dilution culture method, and a phylogenetic tree was established by the maximum-likelihood algorithm based on 16S rRNA gene sequences. Specific media and colorimetric assays were employed to study the functions of strains. The strains with plant growth-promoting effects and no antagonistic effects between each other were combined. The effects of SynComs on the growth of Phyllostachys edulis seedlings were examined by re-inoculation experiments.Results Seventy strains of rhizosphere bacteria were isolated, representing 35 genera belonging to 21 families of four phyla. The dominant phylum was Pseudomonadota and the predominant family was Burkholderiaceae. Functional analyses revealed that 30 strains produced indole-3-acetic acid (IAA), while 16 strains produced siderophores. Among those with dual functions, there were four strains capable of solubilizing inorganic phosphorus, four strains capable of mineralizing organic phosphorus, and three strains capable of solubilizing potassium. Strains TR5, TN6, and TN26 exhibited capabilities to produce IAA and siderophores, as well as solubilize inorganic phosphorus and mineralize organic phosphorus. They were identified as Burkholderia pyrrocinia, Burkholderia paludis, and Paraburkholderia kirstenboschensis, respectively, based on physiological and biochemical properties and 16S rRNA gene sequences alignments. Re-inoculation experiments demonstrated that the SynCom FH, comprising strains TR5, TN6, and TN26, significantly enhanced the root, leaf, and rhizoma growth of Ph. edulis seedlings.Conclusion The rhizosphere of In. acutiligulata harbors diverse functional microorganisms capable of producing IAA and siderophores, solubilizing phosphorus, and releasing potassium. The re-inoculation experiments confirmed that the SynCom FH promotes the growth of Ph. edulis seedlings.