President’s Forum: Advancing Knowledge and Innovation

Advancing Science
Presented by Rush D. Holt
American Association for the Advancement of Science (AAAS)
Science Family of Journals
Washington, DC

Philanthropy: What Can It Do for Science?
Presented by Miyoung Chun
The Kavli Foundation
Oxnard, CA
$0.00 - $25.00
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Mobile DNA and Genome Plasticity

Microbial genomes are highly dynamic, resulting in diverse variations in genetic information, which are the substrates for adaptation and selection. Multiple types of genome alterations and rearrangements underlie such genome plasticity. DNA amplification provides changes in gene copy number that can lead to changes in gene expression and, hence, alter cell growth capabilities. Such amplification occurs by alternative replication mechanisms, leading to amplification of particular DNA segments or to changes in chromosome copy number that lead to genetic diversity. DNA rearrangements also occur by excision and integration of gene cassettes often found in the genetic elements called integrons. The best-known of these cassettes encode antibiotic resistance genes, but the functions of many other diverse cassettes remain to be determined. Induction of the cellular SOS system in response to single-stranded DNA from horizontal gene transfer or DNA damage causes induction of the integrase that mobilizes gene cassettes, thus providing genetic diversity. Genetic diversity also results from genetic elements that move from place to place. Introns are RNA segments, sometimes autocatalytic, that can be excised (spliced) from a precursor RNA to form the mature RNA and Group II introns are also mobile elements whose movement between DNA molecules is mediated by both autocatalytic RNA and reverse transcriptase. Some introns also encode an endonuclease which contributes to intron mobility. Endonucleases also underlie the movement of genes encoding inteins, which are autocatalytic protein segments that can excise from a host protein. These are but a few of many strategies for genome plasticity and diversification.

"En-Lightened" Microorganisms: What's New with Phototrophic Microbes?

Phototrophic microorganisms continue to play a central role in the evolution and maintenance of Earth’s biosphere. New physiological and ecological surprises continue to be uncovered in a diverse taxonomic variety of Archaea and Bacteria – including cyanobacteria - that use light energy for growth. Oxygenic phototrophy is only one mode of light harvesting and light-dependent metabolisms may operate independent of oxygen. In addition to chlorophylls, the conversion of light energy into a proton-motive force can be based on rhodopsin-like proton pumps in a diverse array of Bacteria and Archaea. Prochlorococcus, the most abundant phototrophic organism on Earth, has highly diversified genomes that reflect the ranges of environmental conditions in the open ocean. Many novel adaptations have been found, including new classes of chlorophyll pigments in cyanobacteria. Cyanobacteria are symbiotic with a wide range of plants, animals and even other microorganisms. One of these is an unusual nitrogen-fixing anoxygenic cyanobacterium that is symbiotic with an unicellular alga and challenges the classic definition of cyanobacteria: they do not evolve oxygen, and they are not autotrophs. Rhodopsin-like proteins have been discovered in a wide-variety of bacterial and archaeal taxa in the environment, changing our perspective on the ecology and physiology of light-dependent microorganisms. The distributions and activities of phototrophic microorganisms are linked to environmental factors that may be sensitive to global climate change. The diversity of physiological and ecological aspects of phototrophs underscores the need to revise our understanding of these omnipresent microorganisms, which has implications for biotechnology, ecology and evolution.