The signal based relationship between the green seaweed Ulva and its indigenous bacterial community
Twigg, Matthew (2013) The signal based relationship between the green seaweed Ulva and its indigenous bacterial community. PhD thesis, University of Nottingham.
This project has focused on the relationship between the green seaweed Ulva, commonly found in the intertidal zone of the UK coastline and its cognate bacterial community. It has previously been reported that motile Ulva zoospores are attracted to N-Acylhomoserine lactones (AHLs), signalling molecules utilised by Gram-negative bacteria in a density dependent form of cellular communication termed quorum sensing (QS) and produced by several biofilm dwelling species of marine bacteria. The species represented in the bacterial community associated with Ulva spp. were identified by generating a 16S rDNA phylogenetic clone library from bacterial DNA isolated from the surface of the seaweed. These data revealed that the majority of the population belonged to the Proteobacteria or Bacteroidetes phyla. In order to investigate whether QS signalling affected the rate of zoospore germination in addition to zoospore attraction, Ulva zoospores were settled and allowed to grow on synthetic AHLs, biofilms derived from AHL-producing model organisms and strains relevant to the Ulva epiphytic population which were shown to produce AHLs. Results from these experiments revealed that AHLs affected zoospore germination and the early growth of the Ulva germling as zoospores germinated and grown in the absence of AHLs were significantly longer than those germinated in the presence of AHLs. We therefore hypothesise that reduced germling growth in the presence of AHLs allows Ulva to obtain a healthy epiphytic bacterial community that is vital for the seaweed’s later development. Further understanding of Ulva growth biology could have potential applications in preventing marine biofouling by this genus of seaweed.
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