Indole Acetic Acid Production and Growth-Promoting Activity of Methylobacterium extorquens MP₁ and Methylobacterium zatmanii MS₄ in Tomato

ABSTRACT

Pink-pigmented facultative methylotrophs (PPFMs) are prevalent aerobic bacteria colonizing the phyllosphere of various plant species. PPFMs have the ability to utilize plant-derived methanol as an energy substrate when plants are being colonized under stress. The study was undertaken to explore the metabolic potential of methylotrophs isolated from diverse sources and their role in growth and development of Tomato (Solanum lycopersicum L.) plants, because it is easily grown under laboratory conditions. PPFMs were isolated from the phyllosphere of Peach (Prunus persica L.) and Strawberry (Fragaria ananassa L.) by the leaf imprint method. The bacterial isolates MP₁ and MS₄ are rod shaped as confirmed by scanning electron microscopy (SEM) analysis. Methylotrophy of the isolates was authenticated by polymerase chain reaction (PCR) amplification of the highly conserved mxaF gene. The 16S rRNA gene sequences demonstrated that the isolates MP₁ and MS₄ were Methylobacterium extorquens and Methylobacterium zatmanii, respectively. High-performance thin-layer chromatographic analysis indicated production of indole acetic acid (IAA) by M. extorquens MP₁ and M. zatmanii MS₄. The amount of IAA produced was 10.353 and 8.473 μg·mL⁻¹ for M. extorquens MP₁ and M. zatmanii MS₄, respectively. Tomato seed were treated with M. extorquens and M. zatmanii and had seed vigor indices (SVIs) of 1383.33 ± 90.26 and 1240.79 ± 244.09, respectively, compared to untreated control seed, which had an SVI of 1031.68 ± 83.96. Foliar application of M. extorquens MP₁ and M. zatmanii MS₄ augmented its impact on plant growth promotion in tomato compared to the control. The increased production of IAA and subsequent enhancement in growth-promoting traits indicates that methylotrophs from diverse plant species can be used to improve early plant development in tomato under controlled conditions.

KEYWORDS:

• Solanum lycopersicum
• mxaF
• methylotrophs
• phyllosphere
• seed vigor index

Acknowledgment

The authors thank the Central Instrumentation Facilities, Pondicherry University, for providing facilities for HPTLC analysis.