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NANCY A. MORAN, Principal Investigator
My long-term interests are in the evolution of biological complexity, such as that apparent in complex life histories, in intimate interactions among species, and in species-diversity of clades and communities.
My focus is on symbiosis, particularly that between multicellular hosts and microbes. Symbioses are central in the evolution of complexity; have evolved many times and are critical to the lifestyles of many animals and plants and also to whole ecosystems, in which symbiotic organisms are key players. The primary reason that symbiosis research is suddenly active, after decades at the margins of mainstream biology, is that DNA technology and genomics give us enormous new ability to discover symbiont diversity, and more significantly, to reveal how microbial metabolic capabilities contribute to the functioning of hosts and biological communities.
My ongoing projects, mostly collaborations with students and postdoctoral associates, include
- Phylogenetic and genomic studies of previously unstudied insect symbioses
- Experiments on gene expression of symbionts within hosts
- Computational reconstruction of the content and arrangement of genes in bacterial ancestors
- Experimental investigations of facultative symbioses that are heritable but more labile within host lineages.
SOME RECENT WORK
The Smallest Cellular Genome: Carsonella ruddii
Nakabachi A, Yamashita A, Toh H, Ishikawa H, Dunbar HE, Moran NA, Hattori M. 2006. The 160-kilobase genome of the bacterial endosymbiont Carsonella. Science. 314(5797):267
University of Arizona press release: UA Researchers Find Smallest Cellular Genome
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The bright yellow structure inside this newly hatched psyllid insect is the bacteriome, the special structure that houses the endosymbiotic bacteria, Carsonella ruddii. |
Bacterial Symbionts of the Glassy-Winged Sharpshooter (Homalodisca literata)
Three-Way Symbiosis Supplies Insect Pest With Well-Rounded Diet (UA news release, June 8, 2006)
Wu, D., S.C. Daugherty, S. E. Van Aken, G. H. Pai, K. L. Watkins, H. Khouri, L. J. Tallon, J. M. Zaborsky, H. E. Dunbar, P. L. Tran, N. A. Moran, and J. A. Eisen. 2006. Metabolic complementarity and genomics of the dual symbiosis of sharpshooters. PloS-Biology 4(6):e188
Moran, N. A., P. Tran, and N. M. Gerardo. 2005. Symbiosis and insect diversification: an ancient symbiont of sap-feeding insects from the bacterial phylum Bacteroidetes. Applied and Environmental Microbiology, 71(12):8802-10
NATIONAL SCIENCE FOUNDATION-FUNDED PROJECTS
Go to National Science FoundationEnvironmental Genomics: "Mutation in Genomes of Obligate Symbionts and Impacts on the Ecological Tolerances and Distributions of Hosts: Buchnera and Pea Aphids"
(PI is Nancy Moran)
The health and survival of most animals and plants depends on specialized symbiotic microorganisms, mostly bacteria. Symbionts can affect the tolerances of hosts to environmental factors such as heat, parasites or nutritional stress. In many cases, symbionts are transferred from mother to offspring before birth, with maternal transmission especially common in insects. This project focuses on mutations affecting symbiont genomes and on how these mutations impact the functioning and environmental tolerances of hosts.
Full genome resequencing will be carried out for Buchnera, the bacterial symbionts of aphids and one of the best studied examples of symbiosis. These data will reveal the overall frequency of mutations in the symbiont genome and the frequency of mutations that affect functions important to hosts, such as production of essential nutrients or tolerance to heat.
To quantify the effects of these mutations on hosts, lab experiments with live insects containing different symbiont genotypes will be conducted. Preliminary evidence indicates that even a single change in the symbiont DNA sequence can have a massive effect on the aphid's ability to survive heat exposure. The new results will show the extent of such mutations across the entire symbiont genome. The results will add to understanding of fundamental processes determining the distribution of a major group of crop pests (aphids) and will have implications for similar symbiotic systems found in many other insect pests.
The study has direct implications for predicting how organisms respond to climate change. Educational components, from the high school to graduate level, are integrated into the research. Graduate and undergraduate students will conduct significant portions of the primary research. In addition, high school students will participate through a sustained collaboration between Dr. Moran and Tucson High Magnet School, a large urban high school with a majority of students from groups underrepresented in science and in the university.
Microbial Genomics: "Highly Reduced Genomes of Coresident Bacterial Symbionts of Xylem-Feeding Insects: Ecological and Evolutionary Implications"
(PI is Nancy Moran; co-PI is Rod Wing (U. Arizona))
The aim of this project is to sequence the highly reduced genomes of bacteria that live as symbionts in xylem-feeding insects. Symbiotic bacteria are critical to the development and reproduction of many plants and animals, and their roles are now being explored using genomic approaches. In many animals, symbionts provision nutrients that are lacking in food. Many plant-feeding insects contain specialized bacterial symbionts that are required for normal development and reproduction. These bacteria have been difficult to study in the past because they cannot be grown outside their hosts. However, the capability to sequence their genomes now allows major new understanding of how these organisms function within their hosts.
This project will determine and analyze the genomic sequence of symbionts that live in two insect species called sharpshooters, and a spittlebug species, all of which feed on plant xylem and that vector diseases of many crop plants. Each of these hosts contains a pair of symbiotic bacterial species. New approaches to genome sequence determination will be used in this collaboration between Dr. Moran, who investigates bacterial symbiont genomes, and Dr. Wing, who runs a sequencing and genome analysis center focused on plants. Analysis of the genomic sequence potentially will reveal critical aspects of symbiont biology that can be useful in the control of the hosts, which are significant agricultural pests. Results will be integrated in ongoing science education and outreach projects for college students as well as high school teachers and students.
Biocomplexity in the Environment, Genome-Enabled: "Response of host and symbiont genomes to environmental stress and its ecological consequences"
(PI is Nancy Moran; co-PIs are Katrina Mangin (U. Arizona) and Anthony Ives (Univ. Wisconsin))
The ubiquity of symbiosis in nature has become increasingly apparent during the last decade, due to both molecular and ecological studies. Many eukaryotic species represent not unified genetic entities but aggregations of organisms having heterogeneous evolutionary origins and distinctive metabolic capabilities as well as major differences in genetic systems.
This multidisciplinary investigation is assessing how these genomic responses jointly determine tolerances and how these sensitivities link with other ecological pressures to determine population persistence and geographic distributions. The focus is on tolerance to thermal stress and the implications of this tolerance for host densities and distributions in natural and human-influenced habitats.
Our experiments exploit the genomic resources now available for the aphid Acyrthosiphon pisum and for its multiple bacterial symbionts; this system provides a model for bacterial-animal symbiosis. Previous work has demonstrated that both obligate and facultative symbionts have significant effects on the heat tolerance of aphid hosts.
Host and symbiont responses to heat are being examined using gene microarray and quantitative PCR experiments and using experimentally manipulated combinations of host and symbiont genotypes. The work involves the determination of the genomic sequence for a widespread facultative symbiont that has been experimentally demonstrated to affect both thermal tolerance and parasite resistance in aphids and that occurs in a wide variety of insect species.
Because symbionts influence host nutrition, amino acid and sugar pools are being measured to determine how heat and symbionts mediate nutritional status.
To address the ecological consequences of variable heat sensitivities resulting from genetic differences in hosts and/or symbionts, lab and field experiments are being conducted; these will address how complex patterns of heat sensitivity and parasite resistance determine population dynamics in field situations at different temperatures.
Results will be used to construct predictive models of population performance under different climate conditions.
This grant also includes an educational outreach component. An intensive summer course in biotechnology/molecular biology has been offered for high school teachers in 2004-2006, and and the course was opened to high school students in 2006. The summer course was also offered in 2007. A molecular biology laboratory (BLAST) with state-of-the-art equipment purchased with the NSF grant funding was established at Tucson High Magnet School, adjacent to the UA campus, in 2006. The laboratory is available for school-year use.
Biodiversity Surveys and Inventories, "Discovery and characterization of bacterial endosymbiont diversity in Drosophila"
(PI is Nancy Moran; co-PI is Therese Markow (U. Arizona))
Go to the Drosophila Endosymbiont Database
Among the most remarkable recent developments in our knowledge of biological diversity is the increase in understanding of the phylogenetic relationships and the ecological distributions of microbes. A prominent instance of this increased knowledge concerns symbionts living in the tissues and cells of eukaryotes. For example, members of all major insect orders harbor heritable symbiotic bacteria, often having substantial consequences for the biology and reproduction of hosts.
One limitation on progress in understanding the role of symbiosis in host ecology, genetics and development is the lack, to date, of general surveys for bacterial symbionts of those host taxa most amenable to genetic and experimental studies. This issue is addressed here through a program of surveying and characterizing symbiotic bacteria occurring naturally in the genus Drosophila and relatives. These flies are among the most intensively studied of all animals and provide an ideal group for which to obtain a worldwide inventory of symbiotic bacteria. The community of scientists using Drosophila to address biological questions is both huge and diverse, spanning the disciplines of genetics, development, molecular biology, ecology, and behavior.
The database of genetic and other knowledge for these insects provides unique opportunities for exploring intimate interactions between bacteria and eukaryotes, so a catalog of symbionts and their features would be invaluable. There has been no major effort to catalog symbionts in Drosophila, although a variety of symbiont lineages have been documented in specific studies.
Symbionts are being surveyed primarily in newly collected insects and are also being screened in established cultures from the Drosophila Species Stock Center, located at the University of Arizona. The collection scheme is designed to reveal the extent to which symbiont distributions are governed by host phylogeny, habitat, resource type, or geographic location. New collections will be made in Asia, Central America, Europe as well as several sites in the US and Mexico; they will include tropical, subtropical, temperate and boreal sites.
Symbiont screens are based on molecular features, primarily sequences of bacterial ribosomal DNA and several additional bacteria genes. For each symbiont type, vertical transmission is being tested with live insects; in situ hybridizations based on diagnostic sequences are being used to localize bacteria within host tissues; real-time PCR is being used to quantify abundance in specific tissues and individuals; and efforts are being made to establish bacterial cultures. The most studied insect symbiont, Wolbachia pipientis, is being screened, but other, little-known, symbiont lineages are the primary focus of the survey.
In addition to providing an overview of the distribution and diversity of symbionts of Drosophila, the project will yield data and materials of use to the scientific community. This will be achieved by providing online images of flies and symbionts (via a web page linked to that of the Stock Center), DNA samples of known symbionts, living lines of Drosophila harboring symbionts, and any established bacterial cultures. Fly stocks of interest will be submitted to and distributed by the Stock Center. An added value of the project will be the expansion of the living inventory of the Stock Center.