I stepped out of my comfort zone a bit this morning and went to a session on Mars (okay, there weren’t any biology talks). This is far outside of my expertise, so if I say something outrageously wrong, feel free to set me straight in the comments (actually, you can always do that). I’ve never really given up on the idea of life on Mars. I remember the Viking missions and the ambiguous* results of their biological experiments, and I’m still surprised that none of the subsequent robotic missions have followed them up. I think there are better candidates further out in the Solar System, but Mars is a lot easier to get to.
Kevin Zahnle summarized the history of the search for methane on Mars. Methane is expected to break down quickly in the Martian atmosphere, so its presence in appreciable amounts would be strongly suggestive of a biological source. Martian methane has been announced several times, beginning in 1969, only to be retracted upon more sober reflection, further analysis, or additional data. The consensus now (from what I could gather from Dr. Zahnle’s talk) is that if methane does exist on Mars, it must be in fairly low concentrations, probably less than one part per billion. Even that level would be difficult to explain through known (non-biological) mechanisms, so settling this question would seem to be a high priority. The subsequent speaker, Paul Mahaffy, considers Martian methane confirmed, but cautions that the available data do not distinguish between biological and non-biological sources.
Caroline Freissinet reported on the search for organic molecules by the SAM (Sample Analysis at Mars) suite of instruments on the Curiosity rover. Chlorohydrocarbons detected in a soil sample by the gas chromatograph suggest the presence of more complex organic molecules. Dr. Freissinet identified several of these molecules and concluded that Martian surface conditions allow for their preservation just below the surface.
In an afternoon session, Carol Stoker introduced the Mars Icebreaker Life Mission, a proposal to follow up on the Viking missions with a lander capable of detecting signs of microbial life. With a proposed launch date only five years from now, Icebreaker would be the first mission since the 1970’s to look for life on Mars. Icebreaker would land in the same polar region as the Phoenix Lander, an area that Dr. Stoker argues is habitable. Phoenix confirmed the presence of water ice in this region, making it analogous to Earth’s permafrost regions, in which microbial life persists in thin films of liquid water coating grains of sand and rock. Mars is too cold now for liquid water to exist in these conditions, but higher temperatures recur on a 125,000-year cycle, at which time habitable conditions would exist. Some terrestrial microbes can survive millions of years, so Dr. Stoker argues that dormant cells from the last warming period could persist in a frozen state until the present.
In the afternoon, I was accompanied by a high school student as part of the SAGANet.org Mentor Program. We attended the afternoon lightning talks, an hour of 5-minute talks on a variety of subjects, and portions of two other sessions.
Of particular interest to me were a couple of talks by University of Montana colleagues in the session “Exploring the effects of stress on microbial mutation rates and survival strategies.” Scott Miller described his work with Emiko Sano and Amy Gallagher on recA paralogs in the cyanobacterium Acaryochloris. Acaryochloris is unusual among bacteria in having multiple copies of recA, a gene with multiple functions including roles in homologous recombination, DNA polymerization, and regulation of gene expression. Some isolates of Acaryochloris contain as many as seven copies of regA, where nearly all other bacteria have only one copy. The reasons for this are unclear, and Dr. Miller’s lab is working to understand them. Molecular sequence data suggest that the functions of the various recA copies have diverged in some cases, a possible example of subfunctionalization, in which different copies of a generalist gene independently lose some of their functions, effectively specializing on one function each. Dr. Miller suggested that both adaptive and non-adaptive processes may be involved, a theme that may sound familiar if you read yesterday’s post.
Evgueny Kroll showed some of his work on genome evolution in the yeast Saccharomyces cerevisiae. The structure of S. cerevisiae genomes turns out to by highly variable, and Dr. Kroll’s research showed that starvation can induce large-scale genomic rearrangements. Interestingly, many of the yeast so affected have a higher resistance to starvation than wild-type yeast, suggesting that these rearrangements may provide a route to rapid adaptation in the face of stressful environmental conditions. A few of the yeast isolates from these experiments exhibited a multicellular phenotype. About two thirds of these result from mutations in the Ace2 gene, the same gene that causes the multicellular phenotype in Will Ratcliff‘s ‘snowflake’ yeast.
Today is the last day of the conference, and I have to catch the Empire Builder back to Montana this afternoon. It has been fun seeing friends and colleagues from other institutions and hearing talks both in and outside of my field. Summer in Montana is glorious, though, and I’m looking forward to getting back.
*I realize that not everyone considers them ambiguous.