Cell proliferation and growth inZoothamnium niveum (Oligohymenophora, Peritrichida) — Thiotrophic bacteria symbiosis

Abstract

Chemolithoautotrophic, sulphide-oxidizing (thiotrophic) symbioses represent spectacular adaptations to fluctuating environmental gradients and survival is often accomplished when growth is fuelled by sufficient nourishment through the symbionts leading to fast cell proliferation. Here we show 5'-bromo-2'deoxyuridine (BrdU) pulse labelling of vegetative growing Zoothamnium niveum, a colonial ciliate obligately associated with thiotrophic ectosymbionts, and demonstrate age related growth profiles in three heteromorphic host cell types. At the colony's apex, a large top terminal zooid performed high proliferation activity, which decreased significantly with increasing colony age but was still present in old colonies indicating that this cell possesses lifelongcell division potential. In contrast, terminal branch zooids proliferated independent of colony age but appeared to be limited by their cell division capacity predetermined by branch size, thus leading to the strict, feather-shaped colony form. Appearance of labelled terminal branch zooids allowed us to distinguish a highly proliferating apical colony region from an almost inactive, senescent basal region. In macrozooids attached to the colony, extensive BrdU labelling suggests that DNA synthesis occurs in preparation for a new generation. As motile swarmers, the macrozooids seem to be arrested in the cell cycle and mitosis and cell division occur when the swarmer settles and transforms into a top terminal zooid buildingup a new colony.

Bacterial Symbiosis Maintenance in the Asexually Reproducing and Regenerating Flatworm Paracatenula galateia

“…This is consistent with other studies [17], [57]. Fuhrman & Azam [58] found evidence that some autotrophic bacteria do not incorporate thymidine analogues.…”

Thiotrophic bacterial symbiont induces polyphenism in giant ciliate host Zoothamnium niveum

“…Although the percentage of recruited aposymbiotic colonies is low, in nature the high density of symbiotic populations producing large numbers of swarmers might nevertheless allow survival of aposymbiotic host populations. Based on an average number of 15.5 ± 2.8 (mean ± standard error) macrozooids per colony 63 and 1,200 colonies m −2 on mangrove peat 64 ) we estimate that well over 150 aposymbiotic colonies would be produced under oxic conditions from populations inhabiting a single square meter. Equally densely colonized wood (Supplementary Fig.…”

“…Individual cells (termed zooids) of the colony are differentiated with different functions for division (terminal zooids), feeding (microzooids), and asexual reproduction (macrozooids). The terminal zooid on the tip of the stalk produces the terminal zooids on each branch, which in turn produce feeding microzooids and the macrozooids on the branches 63 . Vertical transmission of the ectosymbiont is through macrozooids that leave the colony as swarmers 43,44 , recruit to sulphide-emitting surfaces and grow into new colonies 64,65 .…”

Ediacaran pre-placozoan diploblasts in the Avalonian biota: the role of chemosynthesis in the evolution of early animal life

“…The giant epibenthic ectosymbiotic colonial ciliate Zoothamnium niveum (Bauer-Nebelsick et al 1996;Rinke et al 2006) had a uniaxial frond-like morphology (Kloiber et al 2009;Fig. 4) that is superficially reminiscent of the frondose Ediacaran taxa (e.g.…”