Auxin production and plant growth promotion by Microbacterium albopurpureum sp. nov. from the rhizoplane of leafless Chiloschista parishii Seidenf. orchid

Elena A Tsavkelova; Elena A Volynchikova; Natalia V Potekhina; Konstantin V Lavrov; Alexander N Avtukh

doi:10.3389/fpls.2024.1360828

Auxin production and plant growth promotion by Microbacterium albopurpureum sp. nov. from the rhizoplane of leafless Chiloschista parishii Seidenf. orchid

Front Plant Sci. 2024 Mar 15:15:1360828. doi: 10.3389/fpls.2024.1360828. eCollection 2024.

Authors

Elena A Tsavkelova^{1

2}, Elena A Volynchikova², Natalia V Potekhina², Konstantin V Lavrov³, Alexander N Avtukh⁴

Affiliations

¹ Department of Biology, Shenzhen Moscow State University and Beijing Institute of Technology (MSU-BIT) University, Shenzhen, Guangdong, China.
² Faculty of Biology, Lomonosov Moscow State University, Moscow, Russia.
³ Genomic Center of National Research Centre (NRC) "Kurchatov Institute", Moscow, Russia.
⁴ Skryabin Institute of Biochemistry and Physiology of Microorganisms, Pushchino Scientific Center for Biological Research, Russian Academy of Sciences, Pushchino, Russia.

Abstract

The strains of the genus Microbacterium, with more than 150 species, inhabit diverse environments; plant-associated bacteria reveal their plant growth-promoting activities due to a number of beneficial characteristics. Through the performance of diverse techniques and methods, including isolation of a novel Microbacterium strain from the aerial roots of leafless epiphytic orchid, Chiloschista parishii Seidenf., its morphological and biochemical characterization, chemotaxonomy, phylogenetic and genome analysis, as well as bioassays and estimation of its auxin production capacity, a novel strain of ET2^T is described. Despite that it shared 16S rRNA gene sequence similarity of 99.79% with Microbacterium kunmingense JXJ CY 27-2^T, so they formed a monophyletic group on phylogenetic trees, the two strains showed clear divergence of their genome sequences. The average nucleotide identity (ANI), average amino acid identity (AAI) and digital DNA-DNA hybridization (dDDH) values of ET2^T differed greatly from phylogenetically close JXJ CY 27-2^T. Based on the differences being below the threshold for species similarity, together with the unique chemotaxonomic characteristics, strain ET2^T represents a novel species of the genus Microbacterium. Several genes, putatively involved in auxin biosynthesis were predicted. This strain revealed obvious plant growth-promoting activities, including diazotrophy and biosynthesis of tryptophan-dependent auxins (indole-3-acetic and indole-3-pyruvic acids). Microbial auxins directly stimulated the rhizogenesis, so that the ET2^T-inoculated seeds of wheat, cucumber and garden cress showed evident promotion in their growth and development, both under optimal and under cold stress conditions. Based on phenotypic, chemotypic and genotypic evidences, the strain ET2^T belongs to the genus Microbacterium, order Micrococcales, class Actinomycetes, and it represents a novel species, for which the name Microbacterium albopurpureum sp. nov. is proposed, with strain ET2^T (VKPM Ac-2212, VKM Ас-2998) as the type strain.

Keywords: Actinobacteria; PGPB; indole-3-acetic and indole-3-pyruvic acids; microbial auxins; phytostimulation; plant-associated Microbacterium.

Grants and funding

The author(s) declare financial support was received partially for the research. This work was partially supported by the Ministry of Science and Higher Education of the Russian Federation (Grant agreement # 075-15-2021-1051). The study was carried out according to the scientific program of M.V. Lomonosov Moscow State University (# 121032300094–7).