Complete Genome Sequence of Methylococcus capsulatus MIR, a Methanotroph Capable of Growth on Methanol

Methyloraptor flagellatus gen. nov., sp. nov., novel Ancalomicrobiaceae-affiliated facultatively methylotrophic bacteria that feed on methanotrophs of the genus Methylococcus

A morphologically conspicuous microbial association was detected in a bioreactor running in a continuous mode with methanotrophic bacteria of the genus Methylococcus and natural gas as a growth substrate. The association consisted of spherical Methylococcus cells colonized by elongated rods, which produced rosette-like aggregates and inhibited the cultivation process. An isolate of these bacteria, strain S20T, was obtained and identified as belonging to the alphaproteobacterial family Ancalomicrobiaceae but displaying only a distant relationship (93.9-95.1 % 16S rRNA gene sequence similarity) to characterized members of this family. Strain S20T was represented by aerobic, motile, facultatively methylotrophic bacteria, which grew between 10 and 45 °C (optimum 30-35 °C) in a pH range of 4.5-8.5 (optimum pH 6.0). These bacteria were capable of attaching to Methylococcus cells and breaking the integrity of methanotroph cell walls, presumably to feed on methanol. The same interaction was observed with Methylomonas species. The finished genome sequence of strain S20T consisted of a 5.0 Mb chromosome and one plasmid, 0.26 Mb in size; the DNA G + C content was 68.4 %. The genome encoded 3 rRNA operons and ∼ 4400 proteins including MxaFI- and XoxF-like methanol dehydrogenases, all enzymes of the serine pathway as well as a complete chemotaxis pathway, a unipolar polysaccharide adhesin, and a wide range of peptidases. The genome sequence displayed 67.20-69.56 % average amino acid identity to those of earlier described Ancalomicrobiaceae species. We propose to classify these bacteria as representing a novel genus and species, Methyloraptor flagellatus gen. nov., sp. nov., with the type strain S20T (=KCTC 8649T = VKM B-3853T).

Impacts of O2:CH4 ratios and CH4 concentrations on the denitrification and CH4 oxidations of a novel AME-AD system

Aerobic methane (CH4) oxidation coupled to denitrification (AME-D) is a promising process for the denitrification of low C/N wastewater. Compared with anaerobic denitrifying bacteria, aerobic denitrifying bacteria may enable AME-D have high denitrification ability under aerobic conditions. This study constructed a novel aerobic methane oxidation coupled to aerobic denitrification (AME-AD) system using the typical aerobic denitrifying bacteria Paracoccus pantotrophus ATCC35512 and the typical aerobic methane oxidizing bacteria Methylosinus trichosporium OB3b. The denitrification and CH4 oxidations of AME-AD with different O2:CH4 ratios (0:1, 0.25:1, 0.5:1, 0.75:1, 1:1 and 1.25:1) and CH4 concentrations (0, 14000, 28000, 42000, 56000 and 70000 mg m-3) were investigated in batch experiments. Higher O2:CH4 ratios can significantly improve the denitrification and CH4 oxidations of the AME-AD (P < 0.05). The treatment with an O2:CH4 ratio of 1.25:1 had the highest denitrification rate (0.036 mg h-1) and highest CH4 oxidation rate (0.20 mg h-1). The CH4 concentration in the headspace was positively correlated with the AME-AD denitrification rate. The calculated CH4/NO3-(mol/mol) in most treatments ranged from 5.76 to 6.84. In addition, excessively high O2 and CH4 concentrations can lead to increased nitrous oxide (N2O) production in AME-AD. The N2O production rate was up to 1.00 μg h-1 when the O2:CH4 was 1.25:1. These results can provide data support for the application of AME-AD for low-C/N wastewater treatment and greenhouse gas emission reduction.

Complete genome sequences of Methylococcus capsulatus (Norfolk) and Methylocaldum szegediense (Norfolk) isolated from a landfill methane biofilter

Here we report the complete genome sequence of two moderately thermophilic methanotrophs isolated from a landfill methane biofilter, Methylococcus capsulatus (Norfolk) and Methylocaldum szegediense (Norfolk).

Methylococcus mesophilus sp. nov., the first non-thermotolerant methanotroph of the genus Methylococcus, from a rice field

Strain 16-5T, a mesophilic methanotroph of the genus Methylococcus, was isolated from rice field soil sampled in Chungcheong Province, Republic of Korea. Strain 16-5T had both particulate and soluble methane monooxygenases and could only grow on methane and methanol as electron donors. Strain 16-5 T cells are Gram-negative, white to light tan in color, non-motile, non-flagellated, diplococcoid to cocci, and have the typical type I intracytoplasmic membrane system. Strain 16-5T grew at 18-38 °C (optimum, 27 °C) and at pH 5.0-8.0 (optimum, pH 6.5-7.0). C16 : 1 ω7c (38.8%), C16 : 1  ω5c (18.8%), C16 : 1  ω6c (16.8%) and C16 : 0 (16.9%) were the major fatty acids, and phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol and an unidentified phospholipid were the major polar lipids. The main respiratory quinone was methylene-ubiquinone-8. Strain 16-5T displayed the highest 16S rRNA gene sequence similarities to other taxonomically recognized members of the genus Methylococcus, i.e. Methylococcus capsulatus TexasT (98.62%) and Methylococcus geothermalis IM1T (98.49 %), which were its closest relatives. It did, however, differ from all other taxonomically described Methylococcus species due to some phenotypic differences, most notably its inability to grow at temperatures above 38 °C, where other Methylococcus species thrive. Its 4.34 Mbp-sized genome has a DNA G+C content of 62.47 mol%, and multiple genome-based properties such as average nucleotide identity and digital DNA-DNA hybridization value distanced it from its closest relatives. Based on the data presented above, this strain represents the first non-thermotolerant species of the genus Methylococcus. The name Methylococcus mesophilus sp. nov. is proposed, and 16-5T (=JCM 35359T=KCTC 82050T) is the type strain.