Symbiotic associations with bacteria are found virtually everywhere in nature. In order for host-microbe associations to evolve, the symbiosis must be stably re-established by each new generation of host. We are investigating the mechanisms involved in helping to maintain host-microbe specificity from the broad evolutionary scale down to the molecular level. To do so, we primarily study a highly specific, binary symbiosis between a coral reef fish (Siphamia tubifer) and a luminous bacterium (Photobacterium mandapamensis).
We have determined that unique aspects of the host’s life history and behavioral ecology, play important roles in promoting specificity of the bioluminescent association between host generations. We also characterized the degree of specificity of the association throughout the host’s broad Indo-Pacific distribution and across all 25 species in the host genus. Future work will focus on defining the genetic mechanisms that regulate symbiont recognition and the establishment of the association.
The bioluminescent symbiosis between the sea urchin cardinalfish, Siphamia tubifer, and the luminous bacterium, Photobacterium mandapamensis, is highly specific - the fish seem to only associate with members of a sub-clade of the bacterial symbiont. We are investigating key ecological factors that help to promote the specificity and stability of this association between host generations, including the possibility of local symbiont enrichment by a local host fish population.
Over recent years, it has become increasingly apparent how important the microbiome is to human health and disease. But relatively little is known about the molecular mechanisms employed by symbiotic bacteria to stably colonize the gut, as they are difficult to experimentally study in isolation. At the California Academy of Science’s Steinhart Aquarium, we are currently developing the Siphamia-Photobacterium symbiosis as a simple binary model to disentangle the complexities underlying gut-associated vertebrate-bacteria associations. We recently assembled the genome of Siphamia tubifer, unlocking the potential for exciting new research projects addressing the molecular mechanisms that regulate the symbiosis.
Ongoing research in the lab is focused on identifying the factors that regulate complex host-microbe interactions in highly dynamic and rapidly changing ocean environments. Specifically, we are studying the role of temperature on aspects of the Siphamia-Photobacterium symbiosis, including the specificity of the association as well as phenotypic traits of the microbial symbionts and the process of symbiont community assembly. This work also involves characterizing and comparing the symbionts of the temperately-distributed Siphamia species to those in more tropical regions.
The symbiotically luminous cardinalfish genus Siphamia is comprised of 25 described species. However, little is known of the biology and ecology of this fascinating group of coral reef fishes, including which luminous bacteria they harbor in their gut-associated light organs. Most Siphamia sp. are habitat specialists, associating closely with a particular substrate, such as branching coral or sea urchins. We are investigating various ecological drivers of speciation in the host, including the fish’s association with luminous bacteria, throughout it’s broad Indo-Pacific distribution.
