Table 1.
Comparison of the major characteristics of the acid-tolerant moderately thermophilic strains BFH1 and BFH2 with themotolerant, thermophilic, and acid-tolerant methane oxidizing bacteria of the families Methylococcaceae and Methylothermaceae.
| Characteristic | Strains BFH1 and BFH2 | 1Methylocaldum spp. | 2Methylothermus thermalis | 3Methylococcus capsulatus | 4Methylomagnum ishizawai | 5Acid-tolerant strain M200 |
|---|---|---|---|---|---|---|
| Cell morphology | Coccoids | Rods-pleomorphic | Coccoids | Coccoids | Rods | Cocci |
| Acidophilic condition | Acid-tolerant | Neutrophilic | Neutrophilic | Neutrophilic | Neutrophilic | Acid-tolerant |
| ICM arrangement | Type I | Type I | Type I | Type I | Type I | Type I |
| Motility | - | - | - | - | - | + |
| Cyst formation | - | + | - | - | + | - |
| Pigmentation | White | Brown/cream | White | Yellow | White | Pink |
| Methane oxidation | pMMO | pMMO | pMMO | pMMO/sMMO | pMMO | pMMO/PxmA |
| mmoX | - | +a | - | + | + | - |
| mxaF | + | + | + | + | nr | nr |
| cbbL | + | + | + | + | nr | nr |
| N2-fixation | + | + | - | + | - | + |
| Temperature (optimal) °C | 30-60 (51-55) | 20-61 (42-55) | 37-67 (57-59) | 20-47 (42-45) | 20-37 (31-33) | 4-30 |
| Growth of pH (optimal) | 4.2-7.5 (5.5-6.0)b | 6.0-8.5 (7.0-7.2) | 6.5-7.5 (6.8)c | 5.5-7.5 (6.5) | 5.5-9.0 (6.8-7.4) | 4.1-7.0 (5.5) |
| Growth on methanol (0.1%) | + | - | + | + | - | + |
| Vitamin required | - | - | - | - | - | - |
| G+C content (mol%) | 62.7 | 58.5 | 62.5 | 62.5 | 64.1 | 52.2d |
| Isolation source (pH) | Tropical topsoil (pH 5.0) | Manure, silage (pH 6.0) | Hot spring (pH 6.0) | Hot spring (pH 6.0) | Rhizosphere soil (pH 6.8) | Sphagnum mosses (pH 3.8–4.3) |
Reference for strains: 1Bodrossy et al., 1997 and Eshinimaev et al., 2004; 2Tsubota et al., 2005; 3Bowman et al., 1993; 4Khalifa et al., 2015; 5Kip et al., 2011. +, positive results; –, negative results; nr, not reported; ICM, intracytoplasmic membrane. aOnly Methylocaldum marinum strain S8T (Takeuchi et al., 2013) possessed mmoX (encodes soluble methane monooxygenase). bGrowth on LMA with methane or methanol of strain BFH2 was observed at pH range 4.5-7.5. cMethylothermus subterraneus strain HTM55T grew at pH 5.2–7.5 (Hirayama et al., 2011). d16S rRNA, pmoA, and pxmA genes sequences were used for computing measurement of DNA G+C content (mol%).
Significance of bold values: to compare pH growth among methane oxidizers.