The mutualism between the thioautotrophic bacterial ectosymbiont Candidatus Thiobius zoothamnicola and the giant ciliate Zoothamnium niveum thrives in a variety of shallow-water marine environments with highly fluctuating sulfide emissions. To persist over time, both partners must reproduce and ensure the transmission of symbionts before the sulfide stops, which enables carbon fixation of the symbiont and nourishment of the host. We experimentally investigated the response of this mutualism to depletion of sulfide. We found that colonies released some initially present but also newly produced macrozooids until death, but in fewer numbers than when exposed to sulfide. The symbionts on the colonies proliferated less without sulfide, and became larger and more rod-shaped than symbionts from freshly collected colonies that were exposed to sulfide and oxygen. The symbiotic monolayer was severely disturbed by growth of other microbes and loss of symbionts. We conclude that the response of both partners to the termination of sulfide emission was remarkably quick. The development and the release of swarmers continued until host died and thus this behavior contributed to the continuation of the association.

Observations of swarmers and colonies were done visually or under dissection microscope. SEM observations on a Philips XL 20 scanning electron microscope (acceleration voltage of 20kV). Data was processed with R.

Missing values are indicated with NA.

The following files contain the original data:

Countings.csv (md5=ad4fbe105ad390b59aaf377d87732e3a)

Environment.csv (md5=05054f9bb9e3dae612ef2d551c710aaf)

Experiments.csv (md5=d03f17a6c28576117724ebad5c667833)

Measurements.csv (md5=c15d58269847d58dfc1f7876df2f46c5)

StarvingColonies.csv (md5=37eaf6e908ee85c4ff4a940ecf10d46c)

StarvingSwarmers.csv (md5=cec73153f2d8a64a81af794e59b7bb4c)

SulfidicControlColonies.csv (md5=fc32b11cb7bb6c28e7998c7b12ad53f1)

SulfidicControlSwarmers.csv (md5=77bb8d685b37eda69ee21beaab8fd25b)

SulfidicControlTimes.csv (md5=7665737b0b0f57ea2784da69b1b920e4)

The RMarkdown code is in the file Espada-Hinojosa_et_al_2022.Rmd (md5=627344bfbed0a78846ff2abe6517b061)

The outcome of the RMarkdown report in html format is in the file Espada-Hinojosa_et_al_2022.html (md5=4e0bf9f974613b40db9405f34677b2db)