Chantal S. Ingham
Institute of Organismic and Molecular Evolution
phone: +49 - (0) 6131 - 39 26108
fax: +49 - (0) 6131 - 39 23731
Symbiotic associations between insects and microbes are ubiquitous in nature and are driving forces of evolutionary innovation. While nutritional symbioses have been the focus of study for the last decades, defensive symbioses have only recently been recognized as an important part of insect defense mechanisms. As such, they offer insights into the ecology of secondary metabolites and the successful long-term use of antibiotics for protection. In addition, they show great promise for the discovery of untapped resources and novel bioactive compounds.
Beewolves (Hymenoptera: Crabronidae), a group of solitary digger wasps, construct brood cells in sandy soil, where their offspring is faced with antagonistic bacteria and fungi. To circumvent this threat, they engage in a protective alliance with Streptomyces philanthi (Actinobacteria), a symbiont in the early stages of the genome erosion typically coming along with a host-associated lifestyle. The bacteria are harbored in specialized antennal glands and transferred to the larval cocoon, where they produce a complex mixture of antibiotics, conferring reliable long-term protection to their offspring.
Apart from this, the brood cell is sanitized by an emission of nitric oxide (NO), a gaseous radical, from the beewolf egg. NO plays a role in immunity of both vertebrates and invertebrates due to its toxicity to parasites and pathogens. Additionally, it helps to regulate the establishment of mutualistic interactions.
While exposure to NO effectively kills competing microorganisms, the symbionts survive the NO burst, and also show resistance to NO in vitro. However, NO is known to inflict oxidative damage on pyrimidine bases in the DNA, which can be recognized and repaired by the base excision repair (BER) machinery. Failure of correct damage repair by BER often results in point or frameshift mutations. Hence, we expect that the host-produced NO poses a mutational burden on Streptomyces philanthi, potentially playing a key role in genome erosion.
In my project, I aim to characterize the effect of host-produced nitric oxide on survival, gene expression, and genome evolution of the defensive bacterial symbiont Streptomyces philanthi.