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Chloroflexus: cellulose degradation at 70°C!

We have cultivated a thermophilic strain from the phylum chloroflexi from geothermal soils within the Taupo Volcanic Zone (TVZ)(1).

Figure: Scanning and transmission electron micrographs of geothermal soil isolates. Panel A: Chloroflexi isolate P352 filaments; Panel B: Chloroflexi isolate P352 spores. Scale bar = 1 µm.

Figure: Scanning and transmission electron micrographs of geothermal soil isolates. Panel A: Chloroflexi isolate P352 filaments; Panel B: Chloroflexi isolate P352 spores. Scale bar = 1 µm.

The phylum Chloroflexi is phenotypically, extremely diverse(2). There are twelve recognized genera in Chloroflexi if Thermomicrobia is included as a class of Chloroflexi(3,4) The phylum spans mesophiles to thermophiles, aerobes and anaerobes and Gram-positives and Gram-negatives. It encompasses full spectrum of metabolic types and abilities including phototrophs, chemotrophs, autotrophs and heterotrophs.

Our isolates were most similar (80-83% 16S rRNA sequence identity) to the recently described mesophilic soil bacteria Ktedonobacter (5): aerobic, moderately acidophilic, Gram-positive, filamentous cells producing branched mycelia and spore clusters. However, they had a much higher temperature limit (75°C) and utilised a wide range of substrates as energy sources, including complex nutrient media and complex polysaccharides such as gellan and carboxymethylcellulose, as well as the crystalline cellulose Avicel®. Their enrichment and isolation was probably facilitated by the fact that they were an abundant population in the sites combined with their ability to utilise a range of organic substrates.

We are continuing to investigate the cellulose degradation potential of these isolates for use in the production of bioethanol. We are also sequencing the genome of this species as part of our biofuels research programme.

References

  1. Stott, M.B., Crowe, M.A., Mountain, B.W., Smirnova, A.V., Alam, M., and Dunfield, P.F. (2008) Isolation of novel bacteria, including a candidate division, from geothermal soils in New Zealand. Environ. Microbiol. 10:2030-2041.
  2. Hanada, S., and Pierson, B.K. (2002) The family Chloroflexaceae. In The Prokaryotes: an Evolving Electronic Resource for the Microbiological Community 3rd edn (release 3.11, November 22 2002, Edited by M. Dworkin, S. Falkow, E. Rosenberg, K.-H. Schleifer & E. Stackebrandt. New York: Springer
  3. Hugenholtz. P, and Stackebrandt, E. (2004) Reclassification of Sphaerobacter thermophilus from the subclass Sphaerobacteridae in the phylum Actinobacteria to the class Thermomicrobia (emended description) in the phylum Chloroflexi (emended description) Int J Syst Evol Microbiol 54: 2049-2051.
  4. Janssen, P.H. (2006) Identifying the dominant soil bacterial taxa in libraries of 16S rRNA and 16S rRNA genes. Appl Environ Microbiol 72: 1719-1728.
  5. Cavaletti, L., Monciardini, P., Bamonte, R., Schumann, P., Ronde, M., Sosio, M., and Donadio, S. (2006) New lineage of filamentous, spore-forming, gram-positive bacteria from soil. Appl Environ Microbiol 72: 4360-4369.