Animal-Microbe Symbioses

Hassan Salem

  • PhD 2010-2015, MPI for Chemical Ecology, Jena
  • Postdoctoral fellow, Emory University, Atlanta
  • Postdoctoral fellow, Smithsonian Institution, Washington D.C.
  • Group leader at MPI for Developmental Biology starting 2020

Research Interest

Numerous adaptations in animals are a direct consequence of symbiotic partnerships with microorganisms. We are interested in the molecular currencies driving the cooperation of species, and the genomic and metabolic consequences of coevolution between a host and its symbiont. Our emphasis is on the dynamic relationships that have evolved within leaf-feeding animals, focusing mainly on insects. We use leaf beetles (Coleoptera: Chrysomelidae) as a study system given the streamlined mutualisms they form with specialized symbionts possessing drastically reduced genomes and correspondingly limited metabolisms. These symbioses are defined by the pectin-degrading abilities of the microbe, allowing the insect host to consume, process and subsist on carbohydrate-rich leaves as a sole nutritional resource.

The widespread and convergent evolution of pectinolytic mutualisms in leaf beetles provides a highly tractable model to characterize the molecular and biochemical currencies contributing to the evolution of folivory across the Metazoa, with applications that extend to ruminants and folivorous animal groups. Our work is integrative in nature, combining genomics and fieldwork with chemical ecology and developmental biology to understand the origin of microbe-beetle interactions and the adaptive impact of pectin degradation for folivores.

Hassan Salem Figure1

Figure 1. The tortoise leaf beetle Cassida rubiginosa.

Hassan Salem Figure2

Figure 2. Florescence in situ hybridization micrograph illustrating the localization of pectinolytic symbionts (green) within the symbiotic organ of    C. rubiginosa.

Available PhD Projects

Project 1: Metabolic regulation of an obligate mutualism in leaf beetles

Recent findings from our group revealed that leaf beetles harbor an obligate bacterial symbiont throughout development. We also find that the specialized organs dedicated to housing and transmitting the symbiont exhibit unique metabolic and immunological profiles. The selected doctoral candidate will dissect the molecular factors ensuring the homeostasis of the symbiosis. Through a combination of comparative genomics and transcriptomics, with CRISPR/Cas transformations, the envisioned project is multidisciplinary in nature, and will further our understanding of a highly streamlined mutualism.

Selected Reading

1) Salem H, Kirsch R, Pauchet Y, Berasategui A et al (2020). Symbiont metabolic range shapes host dietary breadth in herbivorous beetles. Current Biology 30 (15), 2875–2886.

2)  Bauer E, Kaltenpoth M, Salem H (2020) Minimal fermentative metabolism fuels extracellular symbiont in a leaf beetle. The ISME Journal 14 (4), 866–870/p>

3)   Salem H, Bauer E, Kirsch R, Berasategui A, Cripps, M et al (2017). Drastic genome reduction in an herbivore’s pectinolytic symbiont. Cell 171 (7), 1520-15