Mutations in Methanobacterium formicicum conferring resistance to anti-80S ribosome-targeted antibiotics

Methanogens: biochemical background and biotechnological applications

Since fossil sources for fuel and platform chemicals will become limited in the near future, it is important to develop new concepts for energy supply and production of basic reagents for chemical industry. One alternative to crude oil and fossil natural gas could be the biological conversion of CO2 or small organic molecules to methane via methanogenic archaea. This process has been known from biogas plants, but recently, new insights into the methanogenic metabolism, technical optimizations and new technology combinations were gained, which would allow moving beyond the mere conversion of biomass. In biogas plants, steps have been undertaken to increase yield and purity of the biogas, such as addition of hydrogen or metal granulate. Furthermore, the integration of electrodes led to the development of microbial electrosynthesis (MES). The idea behind this technique is to use CO2 and electrical power to generate methane via the microbial metabolism. This review summarizes the biochemical and metabolic background of methanogenesis as well as the latest technical applications of methanogens. As a result, it shall give a sufficient overview over the topic to both, biologists and engineers handling biological or bioelectrochemical methanogenesis.

Gene structure, organization, and expression in archaebacteria

Major advances have recently been made in understanding the molecular biology of the archaebacteria. In this review, we compare the structure of protein and stable RNA-encoding genes cloned and sequenced from each of the major classes of archaebacteria: the methanogens, extreme halophiles, and acid thermophiles. Protein-encoding genes, including some encoding proteins directly involved in methanogenesis and photoautotrophy, are analyzed on the basis of gene organization and structure, transcriptional control signals, codon usage, and evolutionary conservation. Stable RNA-encoding genes are compared for gene organization and structure, transcriptional signals, and processing events involved in RNA maturation, including intron removal. Comparisons of archaebacterial structures and regulatory systems are made with their eubacterial and eukaryotic homologs.

Genetic transformation system in the archaebacterium Methanobacterium thermoautotrophicum Marburg

A wild-type strain of Methanobacterium thermoautotrophicum Marburg was transformed by DNA from strains resistant to 5-fluorouracil. Recipient cells were grown without selection on gellan gum (GELRITE) plates with DNA. Drug-resistant cells were recovered by replica plating the resulting colonies onto drug plates. Transformation required high-molecular-weight DNA with appropriate markers and was not observed on agar or in liquid media under a variety of conditions.

5-Fluorouracil-resistant strain of Methanobacterium thermoautotrophicum

Growth of Methanobacterium thermoautotrophicum Marburg is inhibited by the pyrimidine, 5-fluorouracil (FU). It was shown previously that methanogenesis is not inhibited to the same extent as growth. A spontaneously occurring FU-resistant strain (RTAE-1) was isolated from a culture of strain Marburg. The growth of both strains was inhibited by 5-fluorodeoxyuridine but not 5-fluorocytosine, and the wild type was more susceptible to inhibition by 5-azauracil and 6-azauracil than was strain RTAE-1. The cellular targets for the pyrimidine analogs are not known. When the accumulation of 14C-labeled uracil or FU by the two strains was compared, the wild type took up 15-fold more radiolabel per cell than did the FU-resistant strain. In the wild type, radiolabel from uracil was incorporated into the soluble pool, RNA, and DNA. The metabolism of uracil appeared to involve a uracil phosphoribosyltransferase activity. Strain Marburg extracts contained this enzyme, whereas FU-resistant strain RTAE-1 extracts had less than 1/10 as much activity. Although it is possible that a change in permeability to the compounds plays a role in the stable resistance of strain RTAE-1, the fact that it lacks the ability to metabolize pyrimidines to nucleotides is sufficient to account for its phenotype.

Genetic transformation in the methanogen Methanococcus voltae PS

Mutations causing requirements for histidine, purine, and vitamin B12 were obtained in strain PS of Methanococcus voltae (archaebacteria) upon irradiation with UV or gamma rays. The first two mutations were shown to revert at low frequencies and were used to demonstrate the occurrence of transformation with homologous, wild-type DNA. The transformation rates obtained for these presumably chromosomal markers were in the range of 2 to 100 transformants per microgram of DNA. Mutants resistant to 2-bromoethanesulfonate and to 5-methyl-DL-tryptophan were also isolated.