Cyanobacterial mats were critical in the evolution of Earth?s chemistry and biology. They have long been recognized as drivers of the ?great oxidation event? (GOE), and may have also perpetuated a prolonged period of intermediate redox state in the early Earth's time period call the Proterozoic. However, the types of cyanobacteria that could have mediated such geochemical transitions are poorly understood because whereas Proterozoic oceans were characterized by low oxygen, stratified and/or fluctuating redox conditions, oxygen is required by most modern cyanobacteria studied to date. Further, traditional tools used for study of microbial mats provide limited information regarding metabolic or physiological diversity of cyanobacteria. In this proposal, the PIs propose an exploratory project that will combine cutting-edge single-cell and community genome sequencing technologies with elemental and isotopic geochemistry to address questions focused on facultatively oxygenic/anoxygenic cyanobacteria dominating modern microbial mats that are excellent analogs of Proterozoic mat ecosystems. This EAGER proposal is motivated by two recent, disparate developments that together provide unique opportunities to investigate metabolically versatile cyanobacteria: (i) discovery of an easily accessible modern mat ecosystem in northern Lake Huron that is a novel analog of Proterozoic geochemistry and biology, and (ii) the advent of new genome sequencing technologies that enable unprecedented insights into uncultivated single cells as well as whole microbial communities.
Broader Impacts: Undergraduate students will conduct the primary research focused on physiology (GVSU) and geochemistry (UM) and a PhD student will lead the genomics effort (UM). The discovery-driven and exploratory nature of this project provides outstanding opportunities for translating research into educational opportunities and public outreach. The PIs will take advantage of video resources (underwater dive footage, microscopic cell separations), time-lapse photography of motility, and recent coverage on the Discovery Channel (http://watch.discoverychannel.ca/daily-planet/september-2009/daily-planet-september-22-2009/#clip216315) and local news stations to develop multi-media materials (?microbes in motion? and ?laser roundup? movies). These will be integrated into outreach activities at UM and GVSU, and geobiology exhibits at TBNMS?s Visitor Center.
Cyanobacteria are microorganisms that release oxygen (O2) as a waste product of photosynthesis. Billions of years ago, these organisms oxygenated Earth, transforming it from a planet that was largely free of O2 into a world with an O2-rich atmosphere and oceans that is habitable for life as we know it. Despite the importance of cyanobacteria in the history of Earth and life, little is known about the cyanobacteria that thrived under the low-O2 conditions that characterized much of their evolutionary history. The goal of this project was to better understand low-O2 adapted cyanobacteria by studying an unusual modern environment that harbors such organisms - submerged sinkholes of northern Lake Huron. Here, brilliant purple cyanobacterial mats thrive in low- O2 groundwater emerging from sinkholes onto the lake floor. This project resulted in six key outcomes. First, we showed that sinkhole microbial mats dominated by cyanobacteria are not a net source of oxygen. This finding has important implications for understanding the role of cyanobacteria in the evolution of planetary redox chemistry; cyanobacterial mats, which are common in the geologic record, should not necessarily be considered as a source of O2. Second, our project showed that there are currently no isotopic, mineralogical, elemental, or molecular organic biomarkers of anoxygenic (not oxygen producing) cyanobacterial mats that could be uniquely recognized in the geologic record. Considering that these types of cyanobacterial mats likely played important biogeochemical roles through long stretches of Earth history, including critical geobiological turning points, this outcome highlights the importance of exploring and identifying new signatures of such ecosystems. Fourth, our work revealed evidence of extensive viral predation in the sinkhole cyanobacterial mats. These results provide new views into the importance of viruses in shaping diversity of cyanobacterial mat systems. We now suspect that viral predation is a major cause of mortality, driver of carbon and nutrient cycling, and source of evolutionary selection in extreme microbial mat systems, especially those from which eukaryotic grazers are excluded. Fifth, by analyzing the genome sequences of the major mat-forming cyanobacteria we discovered that they are a rich source of novel genes for the biosynthesis of natural products – biological molecules that kill or inhibit the growth of other organisms. These genes and the molecules they encode are of potential value for development of new pharmaceutical drugs such as antibiotics or anti-cancer compounds. More broadly, the genome-sequencing techniques that we have developed in this project will be useful for exploring other microbial communities for such genes and biochemicals that could benefit humanity. Finally, this project provided opportunities for outreach and training and professional development to three PhD students, two Masters students, 9 undergraduate students, one technician, and one postdoc at the University of Michigan. Research results were disseminated through two peer-reviewed journal publications, three more currently in preparation, one PhD dissertation, and nine presentations at regional, national, and international meetings. This project also served as the centerpiece for outreach activities targeting undergraduate and high school students, especially those from backgrounds that are under-represented in the geosciences.
