Environmental Science and Engineering Seminar

The Cedars is a near-surface serpentinization site in northern California, where geochemistry rules!  After percolating through near-surface peridotite, the water exits in a variety of springs at pH's ranging from ≈ 11.5 to ≥ 12.  The site offers particular challenges to most microbes, having very low levels of Na⁺, which is commonly used by alkaliphiles to avoid the necessity of pumping protons.  In addition, the springs, while rich in hydrogen as an energy source, are very low in organic carbon, and CO₂ is very low at these pH levels.  Geochemical analyses showed the presence of two different types of springs: 1) shallow springs fed by young meteoric water circulating through the near-surface peridotite, and, 2) deep springs that are fed by deeper, older water that has interacted with material from the Franciscan subduction zone.  While the deep and shallow springs are geochemically quite similar, microbially they are markedly different: differences that have remained stable over several years of sampling.  Metagenomic analysis of the shallow ponds revealed that the most abundant organism is an alpha Proteobacterium, abundant not only in the Cedars shallow ponds, but in several other serpentinization sites around the globe.  We have successfully cultivated several strains of this microbe, which we have named Serpentinomonas.  These microbes have revealed a number of unexpected physiological properties that we believe make it highly adapted for terrestrial serpentinization environments.  One of the isolates is the dominant microbe in the Cedars shallow ponds, while another is virtually identical (in 16S rRNA sequence) to the dominant organism at a site in Northeast Canada (Tablelands): these data will be discussed.  In stark contrast, the deep springs community has been studied only by molecular methods, as none of the organisms have yet been cultivated.  Almost none of the taxa in the shallow springs are seen in the deep springs.  Because the diversity is low, it has been possible to assemble most of the bin-genomes, many to near completion. These genomes are extremely small, some of them at the size level of the smallest genomes known for free-living microbes.  Most of them are in candidate divisions or phyla, and those that are placed in known phyla, have no close (species level) relatives.   And finally, the distribution of ATP-synthase genes is remarkably different between the shallow and deep ponds, leading us to wonder what it is about these alkaline sites that is driving adaptation and evolution.  Of course you must come to the seminar to hear this insanity!