I. Microbial Diversity and Evolution
II. Microbial Respiration of Arsenate (As(V))
III. Interpreting Molecular Fossils of Oxygenic Photosynthesis
Part II: Microbial Respiration of Arsenate [As(V)]
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Microbes are diverse, ancient, numerous and ubiquitous. In part 1, Newman gives an overview of these four key points. She presents mind-boggling data on the numbers of microbes inhabiting the earth, as well as the environments in which they can survive, and indeed, thrive. Both fossilized and modern microbes come in fantastically diverse physical forms and this diversity extends to their metabolism. Newman explains how geobiologists can deduce information about ancient microbial life by studying rocks formed on earth billions of years ago.
In Part 2, Newman continues to describe microbes with unusual metabolisms. Her lab identified the first known enzymatic pathway that allows microbes to respire arsenic compounds. This work has direct environmental relevance because in Bangladesh and other regions, drinking water often contains very high levels of toxic arsenic compounds. Arsenite [As(III)], a particularly toxic form of arsenic, is often released into the water by bacteria that reduce arsenic complexes in river sediments. Understanding this metabolic pathway may help to address the problem of arsenic poisoning.
In the last part of her lecture, Newman describes efforts to date the evolution of oxygenic photosynthesis (photosynthesis that uses water as a substrate and produces oxygen as a product) in the ancient rock record using a particular type of a molecular fossil, or “biomarker”. She explains the importance of identifying a robust biomarker, and describes various criteria that should be applied to this pursuit.
Dr. Newman is a Professor in the Divisions of Biology and Geological and Planetary Sciences at the California Institute of Technology. When Newman began her undergraduate studies at Stanford University she wasn’t sure she was going to be a scientist because she was interested in a variety of different fields. In fact, she received her B.A. in German studies. Unable to forego a scientific way of thinking, however, she decided to enroll in a PhD program in environmental engineering at MIT. While in graduate school, she took a class in environmental microbiology and she has been studying it ever since.
Newman’s group is interested in the co-evolution of life and Earth. Specifically, they take an interdisciplinary approach to studying the molecular mechanisms that underlie putatively ancient forms of metabolism. By understanding the way extant organisms function at the molecular level, they hope eventually to gain insights into the evolution of ancient metabolic and biomineralization pathways, interpret the chemical signatures of early life found in the geologic record, and understand how multicellular bacterial communities survive in various contexts (including some relevant to infections).
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H. Ehrlich and D.K. Newman (2008) Geomicrobiology 5th edition, CRC Press, New York, NY.
A.L. Sessions, D.M. Doughty, P.V. Welander, R.E. Summons, D.K. Newman (2009) The continuing puzzle of the great oxidation event, Current Biology, 19:R567-574.
J.A. Gralnick and D.K Newman (2007) Extracellular respiration, Mol. Microbiol., 65(1):1-11.
L.E.P. Dietrich, M. Tice, D.K. Newman (2006) The co-evolution of life and earth, Current Biology, 16:R395 R400.
Primary literature relevant to part 2:
D. Malasarn, C.W. Saltikov, K.M. Campell, J.M. Santini, J.G. Hering, D.K. Newman (2004) arrA is a reliable marker for As(V)-respiration, Science, 306:455.
C. W. Saltikov and DK. Newman (2003) Genetic identification of a respiratory arsenate reductase, Proc. Nat. Acad. Sci., 100:10983-10988.
C. W. Saltikov, A. Cifuentes, K. Venkateswaran, D.K. Newman (2003) The ars detoxification system is advantageous, but not required, for As(V) respiration by the genetically tractable Shewanella species, strain ANA-3, Appl. Environ. Microbiol., 69:2800-2809.
Primary literature relevant to part 3:
P. Welander, M. Coleman, A. Sessions, R. Summons and D.K. Newman (2010) Identification of a methylase required for 2-methylhopanoid production and implications for the interpretation of sedimentary hopanes, Proc. Nat. Acad. Sci., 107(19):8537-8542.
P.V. Welander, R.C. Hunter, L. Zhang, A.L. Sessions, R.E. Summons, D.K. Newman (2009) Hopanoids play a role in membrane integrity and pH homeostasis in Rhodopseudomonas palustris TIE-1, J. Bacteriol., 191(19):6145-6156.
D.M. Doughty, R.C. Hunter, R.E. Summons, D.K. Newman (2009) 2-Methylhopanoids are maximally produced in akinetes of Nostoc punctiforme: geobiological implications, Geobiology, 7:1-9.
S.E. Rashby, A.L. Sessions, R.E. Summons, D.K. Newman (2007) Biosynthesis of 2-methylbacteriohopanepolyols by an anoxygenic phototroph, Proc. Nat. Acad. Sci., 104(38): 15099-15104.