Genomic and Physiological Investigation of Heavy Metal Resistance from Plant Endophytic Methylobacterium radiotolerans MAMP 4754, Isolated from Combretum erythrophyllum

Mampolelo M. Photolo, Lungile Sitole, Vuyo Mavumengwana and Matsobane G. Tlou
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Mampolelo M. Photolo: Department of Biochemistry, Faculty of Science, Auckland Park Campus, University of Johannesburg, Johannesburg 2092, South Africa
Lungile Sitole: Department of Biochemistry, Faculty of Science, Auckland Park Campus, University of Johannesburg, Johannesburg 2092, South Africa
Vuyo Mavumengwana: DST-NRF Centre of Excellence for Biomedical Tuberculosis Research, South African Medical Research Council Centre for Tuberculosis Research, Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Tygerberg Campus, Stellenbosch University, Cape Town 7505, South Africa
Matsobane G. Tlou: Department of Biochemistry, School of Physical and Chemical Sciences, Faculty of Natural and Agricultural Sciences, Mafikeng Campus, North-West University, Mafikeng 2790, South Africa

IJERPH, 2021, vol. 18, issue 3, 1-12

Abstract: Combretum erythrophyllum is an indigenous southern African tree species, a metal hyperaccumulator that has been used as a phytoextraction option for tailing dams in Johannesburg, South Africa. In hyperaccumulators, metal detoxification has also been linked or attributed to the activities of endophytes, and, in this regard, metal detoxification can be considered a form of endophytic behavior. Therefore, we report herein on the identification of proteins that confer heavy metal resistance, the in vitro characterization of heavy metal resistance, and the production of plant growth-promoting (PGP) volatiles by Methylobacterium radiotolerans MAMP 4754. Multigenome comparative analyses of M. radiotolerans MAMP 4754 against eight other endophytic strains led to the identification of zinc, copper, and nickel resistance proteins in the genome of this endophyte. The maximum tolerance concentration (MTC) of this strain towards these metals was also investigated. The metal-exposed cells were analyzed by transmission electron microscopy (TEM). The ethyl acetate and chloroform extracts (1:1 v / v ) of heavy metal untreated M. radiotolerans MAMP 4754 were also screened for the production of PGP compounds by Gas Chromatography–Mass Spectroscopy (GC/MS). The MTC was recorded at 15 mM, 4 mM, and 12 mM for zinc, copper, and nickel, respectively. The TEM analysis showed the accumulation of metals in the intracellular environment of M. radiotolerans MAMP 4754, while the GC/MS analysis revealed several plant growth-promoting compounds, including alcohols, phthalate esters, alkenes, ketones, sulfide derivatives, phenols, and thiazoles. Our findings suggest that the genetic makeup of M. radiotolerans MAMP 4754 encodes heavy metal resistant proteins that indicate hyperaccumulator-specific endophytic behavior and the potential for application in bioremediation. The production of plant growth-promoting volatiles in pure culture by M. raditotolerans MAMP 4754 is a characteristic feature for plant growth-promoting bacteria.

Keywords: Methylobacterium radiotolerans; endophyte; comparative genome analysis; maximum tolerance concentration; transmission electron microscopy (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2021
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