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

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.

Airborne Prokaryotic, Fungal and Eukaryotic Communities of an Urban Environment in the UK

“…Considering these weather conditions, the air particles originating from anthropogenic activities (with high metal concentrations) seemed to persist for a long time during this sampling period. The higher relative abundance of the OTU belonging to Methylobacterium in November 2019 samples could also be linked with higher heavy metal concentrations as many of the species belonging to Methylobacterium are known to be heavy metal resistant [50,51].…”

Diversity of cultivated methylotrophs from the extremely oligotrophic system in the Cuatro Cienegas Basin, Mexico: An unexplored ecological guild

“…4,53 Not surprising, the dominant specie in both environments was strongly related to the cosmopolitan M. radiotolerans, that has been found in all types of environments, including some extreme sites with high UV and gamma radiation 54,55 as well others with high concentrations of heavy metals. 56,57 Furthermore, M. radiotolerans is a plant-growth promoting bacteria with the ability to fix nitrogen, and with antimicrobial and antioxidant properties. 11,58 Within the CCB methylotrophic bacteria falling outside the Methylobacterium group, members of Methylorubrum (α-proteobacteria) and Methylophilus (β-proteobacteria) were confirmed.…”

Trends in Harnessing Plant Endophytic Microbiome for Heavy Metal Mitigation in Plants: A Perspective

“…Photolo et al [ 69 ] performed genome sequencing of an endophyte, Methylobacterium radiotolerans MAMP 4754, associated with Combretum erythrophyllum (a hyperaccumulator plant), and identified the genes involved in the tolerance of Ni, Cu and Zn metals. Future implications of these studies include the inclusion of information on the metal-tolerant microbiome and the genes in producing initiatives aimed at creating heavy metal-tolerant crops in the future [ 80 ].…”