Invited seminar-Genomic evolution in insect endosymbionts

May 12-13, 2014

Jan Roelof van der Meer

Dr Philippe Engel, University of Lausanne

Prof. Nancy A. Moran, Department of Integrative Biology,

University of Texas, USA

INVITED SEMINAR

May 12, 2013

12:15-13:00

UNIL, Biophore, Auditorium

SUMMARY

Intimate symbiotic associations between bacteria and animals have evolved often, driven by effects of symbionts on hosts, including protection from enemies and nutritional provisioning.  Although obligate symbionts typically cannot be cultured, genomic studies have illuminated their functions and have given insight into general processes of genome evolution. Insect endosymbionts are strictly maternally transmitted and clonal, a system that minimizes evolutionary conflicts of interest between symbionts and hosts. However, obligate endosymbionts experience effective population sizes much smaller than typical population sizes in environmental bacteria, making them prone to fixation of deleterious mutations and genomic erosion. One result is the accumulation of mutations that lower functionality, as reflected in protein stability and mutations that inactivate and eliminate nonessential genes. As a result, endosymbionts of insects possess the smallest known cellular genomes, and have undergone other extreme changes including rapid protein evolution and codon reassignments. The loss of essential genes in endosymbionts appears to depend on compensatory coadaptation by hosts, sometimes involving host acquisition of bacterial genes. Another outcome is the acquisition of a novel symbiont. This symbiont may replace an original symbiont with an eroded genome, or both may persist due to complementarity in their contributions to hosts. In other bacterial-animal symbioses, symbionts are horizontally exchanged and recombine, preventing or slowing genomic erosion but increasing the opportunity for "selfish" tendencies. These cases include intracellular symbionts that are usually maternally but occasionally horizontally or paternally transmitted as well as gut symbionts that show more frequent horizontal transmission.

AFTERNOON ROUND-TABLE DISCUSSION

Tuesday May 13

Location: Biophore, Bio 2917.2, 13h00-14h30

Organizer: Prof. Nancy A. Moran

1. A few papers for further reading

1.     McCutcheon JP, Moran NA (2012) Extreme genome reduction in symbiotic bacteria. Nat Rev Microbiol 10: 13–26.

2.     McCutcheon JP, McDonald BR, Moran NA (2009) Convergent evolution of metabolic roles in bacterial co-symbionts of insects. Proc Natl Acad Sci USA 106: 15394–15399.

3.     McCutcheon JP, McDonald BR, Moran NA (2009) Origin of an alternative genetic code in the extremely small and GC-rich genome of a bacterial symbiont. PLoS genetics 5: e1000565.

4.     Bennett GM, Moran NA (2013) Small, smaller, smallest: the origins and evolution of ancient dual symbioses in a Phloem-feeding insect. Genome Biol Evol 5: 1675–1688.

5.     Koga R, Moran NA (2014) Swapping symbionts in spittlebugs: evolutionary replacement of a reduced genome symbiont. ISME J. doi:10.1038/ismej.2013.235.

2. Presentation and discussion of students' projects

3. General discussion

We will discuss general aspects of bacterial genomics and evolution, microbial symbiosis, and the students work.

UNIL/DMF

0.25

6