A Novel Moderately Thermophilic Type Ib Methanotroph Isolated from an Alkaline Thermal Spring in the Ethiopian Rift Valley.

Antonio Garcia-Moyano,Amare Gessesse,Tajul Islam,J. Colin Murrell,Lise Øvreås

doi:10.3390/microorganisms8020250

Abstract

Aerobic moderately thermophilic and thermophilic methane-oxidizing bacteria make a substantial contribution in the control of global warming through biological reduction of methane emissions and have a unique capability of utilizing methane as their sole carbon and energy source. Here, we report a novel moderately thermophilic Methylococcus-like Type Ib methanotroph recovered from an alkaline thermal spring (55.4 °C and pH 8.82) in the Ethiopian Rift Valley. The isolate, designated LS7-MC, most probably represents a novel species of a new genus in the family Methylococcaceae of the class Gammaproteobacteria. The 16S rRNA gene phylogeny indicated that strain LS7-MC is distantly related to the closest described relative, Methylococcus capsulatus (92.7% sequence identity). Growth was observed at temperatures of 30–60 °C (optimal, 51–55 °C), and the cells possessed Type I intracellular membrane (ICM). The comparison of the pmoA gene sequences showed that the strain was most closely related to M. capsulatus (87.8%). Soluble methane monooxygenase (sMMO) was not detected, signifying the biological oxidation process from methane to methanol by the particulate methane monooxygenase (pMMO). The other functional genes mxaF, cbbL and nifH were detected by PCR. To our knowledge, the new strain is the first isolated moderately thermophilic methanotroph from an alkaline thermal spring of the family Methylococcaceae. Furthermore, LS7-MC represents a previously unrecognized biological methane sink in thermal habitats, expanding our knowledge of its ecological role in methane cycling and aerobic methanotrophy.

Highlights

Methane plays a key role in the global carbon cycle, being 34 times more powerful as a greenhouse gas than CO2, and is the most substantial contributor to climate effect [1]
Further analysis exhibited 91.2–92.4% sequence similarity to other strains (Supplementary Table S3). These results suggested that strain LS7-MC may represent a new member of the Type Ib methanotrophs rather than Type Ia (Methylomonadaceae) or Type Ic (Methylothermaceae) in the class Gammaproteobacteria
We have retrieved an obligate moderately thermophilic Type Ib methanotroph that belongs to the family Methylococcaceae of the class Gammaproteobacteria

Summary

Introduction

Methane plays a key role in the global carbon cycle, being 34 times more powerful as a greenhouse gas than CO2, and is the most substantial contributor to climate effect [1]. Anaerobic microbials (the presence of methanogenic archaea) in hyperthermal hot springs contribute formation and releasing of biogenic methane into the atmosphere [2,3,4]. In some parts of Ethiopia (the Great Rift Valley regions), natural methane is released through thermal springs nearby the Rift Valley lakes. Such lakes and thermally heated water sediments from hot springs may affect the community structure and diversity of microorganisms and may have a major influence in the global carbon cycle

Methods

Results

Conclusion