Scientists report first sequencing of environmen...( n said. The genome of Leptospiril...)

The genome of Leptospirillum group II is the first sequenced from the phylum Nitrospira, an important branch of the tree of life containing nitrate and nitrogen cycling bacteria, Banfield noted.

Once Banfield's group had the five new genomes, they compared the genes in each with a database of known genes to identify their functions. For the two microbes with the most complete draft genomes, they were able to reconstruct nearly the entire metabolic cycle.

Already they have determined how the microbes share tasks in the isolated microbial community of the mine. The Leptospirillum group II bacteria fix carbon and produce the biofilm that protects them and keeps them afloat, while a minor member of the community, Leptospirillum group III bacteria, fix both carbon and nitrogen. The iron is probably munched by the all of the biofilm members, including Ferroplasma microbes.

Interestingly, the Ferroplasma type II microbes in the biofilm apparently are a mix of many different strains, but the genome reconstruction shows that they all arose from three distinct ancestral strains. Random sex among the microbes for millions of years has combined and recombined the genomes of the three strains so that the population today consists of strains that mix and match genes from separate ancestors.

"This type of rampant exchange of genetic material has never been documented in Archaea or in natural samples before," Banfield said. "This recombination may be a strategy for maintaining optimization in the event of perturbations in the environment. The observation helps us understand the factors that shape evolution and drive development of new species."

Banfield said that the community genome technique worked in this situation because the dominant microbes were represented mostly by closely related strains. In more complex environments with more organisms, it may not be so easy.

"However, even in more complex environments it
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Contact: Robert Sanders
rls@pa.urel.berkeley.edu
510-643-6998
University of California - Berkeley
1-Feb-2004