Syukur Syukur1, Marwan Majzoub1, Jadranka Nappi1, Joanna M Biazik2, Suhelen Egan1 and Torsten Thomas1
1Centre for Marine Science and Innovation, School of Biological, Earth and Environmental Sciences, The University of New South Wales, Sydney, Australia
2 Electron Microscope Unit, Mark Wainwright Analytical Centre, The University of New South Wales, Sydney, Australia
Seaweeds host many bacterial symbionts that are essential for health and performance. How these bacteria are acquired is however poorly understood. This study evaluated the presence of bacteria on the gametes of different seaweed species, including Ulva australis, Delisea pulchra, Hormosira banksii and Phyllospora comosa, using fluorescence in situ hybridization, scanning electron microscopy and 16S rRNA gene sequencing. No bacterial cells were detected on spores of U. australis showing a lack of vertical transmission of bacterial symbionts and thus indicating the need for symbiont acquisition from the surrounding seawater. In contrast, bacterial cells were visibly attached to the surface of D. pulchra tetraspores and the eggs of H. banksii and P. comosa, demonstrating the potential for vertical transmission. The bacterial community structure and composition of D. pulchra and P. comosa adults resembled those of their gametes, indicating a non-selective transfer of symbiont. In contrast, the bacterial communities associated with H. banksii eggs were significantly different from parental thalli, indicating a selective symbiont transmission. This study revealed species-dependent processes of symbiont acquisition in seaweeds ranging from selective and non-selective vertical transmission from parents to horizontal transmission from the environment.