Abstract
BackgroundSymbiotic Methylobacterium strains comprise a significant part of plant microbiomes. Their presence enhances plant productivity and stress resistance, prompting classification of these strains as plant growth-promoting bacteria (PGPB). Methylobacteria can synthesize unusually high levels of plant hormones, called cytokinins (CKs), including the most active form, trans-Zeatin (tZ).ResultsThis study provides a comprehensive inventory of 46 representatives of Methylobacterium genus with respect to phytohormone production in vitro, including 16 CK forms, abscisic acid (ABA) and indole-3-acetic acid (IAA). High performance-liquid chromatography—tandem mass spectrometry (HPLC–MS/MS) analyses revealed varying abilities of Methylobacterium strains to secrete phytohormones that ranged from 5.09 to 191.47 pmol mL−1 for total CKs, and 0.46 to 82.16 pmol mL−1 for tZ. Results indicate that reduced methanol availability, the sole carbon source for bacteria in the medium, stimulates CK secretion by Methylobacterium. Additionally, select strains were able to transform L-tryptophan into IAA while no ABA production was detected.ConclusionsTo better understand features of CKs in plants, this study uncovers CK profiles of Methylobacterium that are instrumental in microbe selection for effective biofertilizer formulations.
Highlights
Symbiotic Methylobacterium strains comprise a significant part of plant microbiomes
All bacterial isolates were cultured in a minimum medium supplemented with methanol as a sole carbon source (DSMZ-125)
Regarding the total CK levels secreted by bacteria, out of the 5 most productive strains, 3 were isolated from plant organs (M. oryzae LMG23582(T), M. phylosphaerae LMG24361(T), and M. oxalidis NBRC107715(T)), while the remaining two (M. radiotolerans LMG6379 and M. jeotgali LMG23639(T)), originated from the forest soil and the fermented food, respectively
Summary
Symbiotic Methylobacterium strains comprise a significant part of plant microbiomes. Their presence enhances plant productivity and stress resistance, prompting classification of these strains as plant growth-promoting bacteria (PGPB). Bacteria which colonize plants inhabiting the root zone (rhizospheric), leaf surfaces (epiphytic), and living within tissues (endophytic), are numerous and diverse [1]. These plant-associated microbes play critical roles in plant health, development, and [2,3,4,5,6,7]. Methylobacteria are ubiquitous in nature and non-pathogenic to humans or wildlife They are rodshaped, obligately aerobic microbes that can thrive in a wide range of environments including soil, air, water, and plants [8]. The distinct pink pigmentation of many Methylobacterium strains indicates the presence of specific carotenoids which may confer their tolerance to ultraviolet (UV) radiation [10,11,12] and provide a basis for further classifying individuals
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