Microscopic crustaceans called ostracods, often referred to as seed shrimp, are revealing surprising secrets about bacterial symbiosis within their reproductive systems. Researchers at the Marine Biological Laboratory (MBL) have discovered that bacteria from the genus Cardinium live inside the egg cells and tissues of ostracod ovaries, a finding published in Proceedings of the Royal Society B.
These aren’t just casual visitors; the bacteria are passed down from mothers to their offspring – a key characteristic of true endosymbiosis. This vertical transmission suggests the bacteria influence the ostracods’ asexual reproduction. While bacterial symbiosis is gaining attention in ostracod research, this type of close relationship has been extensively studied in other arthropods like insects.
Take mosquitoes, for instance. They are known to harbor Wolbachia bacteria, which play a role in mosquito reproduction and have even been explored as a tool to control the spread of mosquito-borne diseases. The discovery of similar processes in ostracods opens new avenues for understanding endosymbiosis within aquatic arthropods, creatures that form an essential part of freshwater and marine food webs.
A Multi-Lab Effort Reveals Unexpected Connections
These striking images of bacteria residing within ostracods were the result of a long-term collaboration between scientists at MBL and beyond.
Isa Schön, a senior scientist at the Royal Belgian Institute of Natural Sciences, joined the MBL as a Whitman Fellow in 2022 with a goal to establish ostracods as a new model organism for research. This focus on less conventional subjects is crucial because most biological studies rely on just a few familiar species like fruit flies or mice. Schön emphasizes that “there are endless discoveries yet to be made across the biodiverse animal kingdom.”
To pinpoint the exact location of these symbiotic bacteria within ostracods, the team needed specialized techniques. They used fluorescence microscopy and confocal microscopes at MBL’s Central Microscopy Facility, which allowed them to visualize the animals in incredible detail. This meticulous imaging required a unique combination of expertise. Schön and her colleague Koen Martens, an evolutionary biologist at the Royal Belgian Institute of Natural Sciences, teamed up with Scott Chimileski and Jessica Mark Welch from the ADA Forsyth Institute. Chimileski and Mark Welch specialize in visualizing bacteria within complex environments like the human mouth microbiome.
“This study establishes non-marine ostracods as the first fully aquatic host system for Cardinium and reinforces their value as models for evolutionary research,” said Schön.
These findings contribute significantly to our understanding of bacterial symbiosis in diverse ecosystems and highlight the importance of exploring less conventional model organisms in biological research.
