Rapid adaptation to acute environmental change demands co-evolution of indigenous viral populations and their hosts.
Horizontal gene transfer (HGT) is a highly efficient adaptive mechanism, but a difficult phenomena to dectect. The
mosaic nature of bacteriophage genomes resulting from HGT has generally been explored using phylogenetic analysis of
coding regions. Focusing on the proteome certainly provides one window into the origin and evolution of genome
information storage. However, the original fitness function for a nucleotide polymer would arise from a more primal
survival imperative predating the appearance of a coding function. Multivariate analysis of a genome information storage
metric (lossless compression), nucleotide distributions, and distributions of the three major physiochemical
characteristics of the polymer (triple:double bonding [G+C], purine:pyrimidine [G+A], and keto:amine [G+T] fractions)
produces a metric to detect and characterize mosaicism in both coding and non-coding regions of a genome. We discuss
possibilities and limitations of using these techniques to investigate HGT and the origins and evolution of genome
complexity. Analysis of available virus (n= 2374) and bacteriophage genomes (n=417) indicates these probes can
perform whole-genome taxonomy tasks or sliding window searches for evidence of HGT in a single genome. HGT
responses may serve as a canary or bell-weather for global environmental change. We discuss one area of application of
considerable interest to our institute: the response of cyanophage and their cyanobacteria hosts to variations in ultraviolet
solar flux in geographically isolated Antarctic lakes.
Soap Lake is a hypersaline, alkaline lake in Central Washington State (USA). For the past five years the lake has been
the site of an NSF Microbial Observatory project devoted to identifying critical geochemical and microbial
characteristics of the monimolimnion sediment and water column, and has demonstrated rich multispecies communities
occupy all areas of the lake. Soap Lake and similar soda lakes are subject to repeated transient periods of extreme
evaporation characterized by significant repetitive alterations in salinity, pH, and total water volume, yet maintain high
genetic and metabolic diversity. It has been argued that this repetitive cycle for salinity, alkalinity, and sulfur
concentration has been a major driver for prokaryote evolution and diversity. The rapidity of wet-dry cycling places
special demands on genome evolution, requirements that are beyond the relatively conservative eukaryotic evolutionary
strategy of serial alteration of existing gene sequences in a relatively stable genome. Although HGT is most likely
responsible for adding a significant amount of noise to the genetic record, analysis of HGT activity can also provide us
with a much-needed probe for exploration of prokaryotic genome evolution and the origin of diversity. Packaging of
genetic information within the protective protein capsid of a bacteriophage would seem preferable to exposing naked
DNA to the highly alkaline conditions in the lake. In this study, we present preliminary data demonstrating the presence
of a diverse group of phage integrases in Soap Lake. Integrase is the viral enzyme responsible for the insertion of phage
DNA into the bacterial host's chromosome. The presence of the integrase sequence in bacterial chromosomes is evidence
of lysogeny, and the diversity of integrase sequences reported here suggests a wide variety of temperate phage exist in
this system, and are especially active in transition zones.
Soap Lake is a haloalkaline lake located in central Washington. This lake is a remnant of the Missoula flood events that
created the landscape of western Montana, the southeastern portion of Washington state, and much of Oregon. It is
15,000 - 20,000 years old, and has maintained a stable meromixis for the last 10,000 years. This carbonate lake is
characterized by a brackish mixolimnion, and a monimolimnion with a salinity of ~14%. The pH of both layers of the
lake is approximately 10. Both layers also have a high concentration of dissolved sulfate, with the mineral mirabilite
(Na2SO4•10H2O) found in the monimolimnion sediments. Sulfide concentrations in the monimolimnion exceed 100 mM.
As part of the mission of the NSF Soap Lake Microbial Observatory, microorganisms involved in the sulfur cycle in this
lake were studied in terms of their diversity and function. High rates of sulfate reduction were measured in both layers of
the lake, with new species of sulfate-reducing bacteria seen in both areas. A particularly novel psychrophilic sulfur
oxidizer was isolated from the monimolimnion. This organism has the ability to induce the formation of mirabilite,
which was assumed to be an abiotically deposited evaporite mineral. This is the first evidence for a biogenic origin of
this mineral. This leads to the possibility that related sulfate minerals, such as those reported on the Mars surface, may
have a biogenic origin.
Conference Committee Involvement (4)
Instruments, Methods, and Missions for Astrobiology XI
12 August 2008 | San Diego, California, United States
Instruments, Methods, and Missions for Astrobiology X
28 August 2007 | San Diego, California, United States
Instruments, Methods, and Missions for Astrobiology IX
14 August 2006 | San Diego, California, United States
Instruments, Methods, and Missions for Astrobiology IX
31 July 2005 | San Diego, California, United States
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