Isolation and Classification of Methanogens and Investigation of Their Osmolyte Glycine Betaine Transport Systems

• Main Authors: Sheng-Chung Chen, 陳聖中
• Other Authors: Mei-Chin Lai
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/73634126626150853286

博士 === 國立中興大學 === 生命科學系 === 93 === Strictly anaerobic methanogenic archaea are ubiquitous. Dr. Lai’s lab has isolated over twenty methanogens from Taiwan. Among them, strain N2F9704T was isolated from the seawater fish pond and strain P2F9704aT isolated from the estuarine near Wong-gong, Taiwan. Both strains are mesophilic, irregular cocci. Cells could metabolize formate and H2/CO2 as carbon source to obtain the energy through methanogenesis. Trace amounts of tungstate not only promoted growth of strain N2F9704T but also extended the range of growth conditions. However the trace element of tungstate only lightly stimulated the growth of strain P2F9704aT. Analyses of 16S rDNA sequences revealed that strain N2F9704T and strain P2F9704aT are members of genera Methanofollis and Methanocalculus respectively, and are named as Methanofollis aquaemaris N2F9704T and Methanocalculus taiwanensis P2F9704aT. Additionally, strain N2F9704T was infected with a novel coccus-shaped, enveloped virus MMV with a diameter of 200 nm. Both strains were the first published new methanogenic species from Taiwan. In addition to characterization of methanogens from Taiwan, the investigation of the osmoregulation of the betaine synthesizing halophilic methanogen, Methanohalophilus portucalensis FDF1, and the comparisons of osmoregulatory mechanisms between bacteria and archaea are our subject. Firstly, searching the bacterial osmoprotectants transporters through 25 archaeal genomes showed it may be the effect of the lateral gene transfer that archaea contain several homologues genes of bacterial osmoregulatory transporters, including proU, opuD and proP. Based on these informations, an ABC type transporter for betaine, the Bta (betaine transporter in Archaea) system, was identified in M. portucalensis FDF1. The gene structure of the bta gene was similar to proU of Escherichia coli. Transcriptional inducer tests revealed that betaine, choline and its de novo synthesized intermediates, glycine, sarcosine and dimethylglycine, could immediately increase the transcriptional level of the bta gene under the hyperosmotic stress. But proline and carnitine, the osmolytes occurred in bacteria, couldn’t increase the bta expression. Upon the heat shock, the transcription of the bta gene was also activated immediately in the presence of external glycine betaine. Moreover, the upstream sequences of the bta gene have conserved sequences similar to other archaeal heat shock responsed genes, like dnaK and grpE. It suggests that in addition to play a role in osmotic stress, bta also responds to the heat stress. This ABC type glycine betaine transporter Bta system is first dicovered in the betaine-synthesizing organisms.