Inter-generational transmission of microbial symbionts in the marine sponge Chondrilla australiensis (Demospongiae)
Kayley M. Usher A E , David C. Sutton A , Simon Toze B , John Kuo C and Jane Fromont DA Discipline of Microbiology, School of Biomedical and Chemical Sciences, University of Western Australia, M502, 35 Stirling Highway, Crawley, WA 6009, Australia.
B CSIRO Land and Water, Private Bag No. 5, PO Wembley, Wembley, WA 6913, Australia.
C Centre for Microscopy and Microanalysis, University of Western Australia, M010, 35 Stirling Highway, Crawley, WA 6009, Australia.
D Western Australian Museum, Locked Bag 49, Welshpool, WA 6986, Australia.
E Corresponding author. Email: kusher@cyllene.uwa.edu.au
Marine and Freshwater Research 56(2) 125-131 https://doi.org/10.1071/MF04304
Submitted: 27 December 2004 Accepted: 8 February 2005 Published: 12 April 2005
Abstract
Mechanisms for the biparental transmission of microbial symbionts to offspring in the marine sponge Chondrilla australiensis are reported. The observation of microbial mutualists in the sperm of C. australiensis is the first report of this kind in any organism, as far as we are aware. The developing eggs were shown by transmission electron microscopy (TEM) to incorporate intercellular cyanobacterial and bacterial symbionts. Nurse cells appeared to transport cyanobacterial symbionts from the surface layers of the sponge to eggs deeper in the matrix, where they were incorporated into the egg cytoplasm prior to spawning. This suggests that a host mechanism exists to actively recognise and incorporate symbionts, ensuring that larvae contain these mutualists before settlement. In addition, an average of 1.64% of mature sperm of C. australiensis contained cyanobacterial symbionts in their cytoplasm. The successful transmission of cyanobacterial symbionts to larvae was demonstrated by autofluorescent microscopy and TEM. The occurrence of organisms with functional mechanisms for transmission of symbionts from both parents to offspring provides the potential for new insights into the nature of host–symbiont interactions.
Extra keywords: cyanobacteria, symbiosis, Synechococcus spongiarum, vertical transmission.
Acknowledgments
We would like to thank the Australasian Diving Academy, Claremont, Western Australia, for subsidising diving expenses and Dr Kathy Heel for assistance with flow cytometry. This study was supported by a grant from the Australian Biological Resources Study.
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