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No description available.

Ocean acidification (OA) is the decrease in ocean pH due to increasing atmospheric pC02• It is predicted that by the year 2100, the pC02 will rise from ca 385 uatm today to 750 uatrn, with a corresponding decrease in surface ocean pH from 8.1 to 7.8. pH was monitored at five stations around a coastal CO2 vent site in Ischia, Italy and the utility of such areas discussed. An ecological survey of benthic macroalgae revealed a substantial community shift at lower pH toward reduced species richness and diversity. The chlorophytes became more dominant at lower pH, with cover increasing from 45-55% at pH 8.16-7.84, to 67-90% at pH 7.48-7.11. Heavily calcified species disappeared at pH 7.48-7.11, but their total cover did not change significantly between pH 8.16-7.80, suggesting some resilience over this century. At lower pH, the DMSP content in macroalgae from Ischia increased in the chlorophytes while in rhodophytes and phaeophytes it decreased. The dark-adapted algal photophysiology suggested a significant benefit when pH was 7.84-7.80, which was lost at pH 7.48-7.11. Two species of common chlorophyte macroalgae VIva lactuca and VIva clathrata, were incubated under pC02 conditions ranging from 432 to 1514 uatrn, In both species, the results indicated that by the year 2100 there could be a large decrease by 50-58% in DMS production, a reduction in chlororespiration, and increased reproductive output in these species. I conclude that increasing pC02 does not directly fertilise photosynthesis or somatic growth in the Ulvales but, reduces chlororespiration, possibly due to carbon-concentrating mechanism down-regulation. This may be the cause of the large reduction in DMS production seen and may lead to a reallocation of resources towards reproductive output. This may increase the prevalence of chlorophyte macroalgae in the future with major repercussions for coastal ecosystems.

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. This study progressed to characterise AHL production in a number of strains of Shewanella and Bacteroidetes bacteria, which, for differing reasons were deemed relevant to Ulva biology. Although data presented by this thesis showed AHL production in these bacterial groups, AHL synthase and response regulator sequences could not be identified in the published genome sequences from either Shewanella or the Bacteroidetes. This study also identified an AHL inactivating acylase enzyme in an environmental Shewanella isolate. This acylase, AacS, was shown to degrade a variety of synthetic AHLs and the AHLs produced by Yersinia pseudotuberculosis. This study has therefore increased the range of marine bacteria known to be producing AHLs, however the lack of AHL synthase and response regulator genes in the genomes of these bacteria leads to the conclusion that many marine bacteria possess novel, yet to be characterised AHL-mediated QS systems. Finally, this study screened a number of extracts from marine microalgae for compounds that act as agonists or antagonists to AHL-mediated QS. Although no AHL mimics were identified data presented by this thesis showed extracts to affect the luminescence produced in lux-based AHL bio-reporters in the presence of exogenously added signal, affect a number of QS regulated phenotypes in marine pathogens and effect QS regulated genes in the human pathogen Pseudomonas aeruginosa. As such, we hypothesise that these microalgae have the ability to produce quorum-quenching compound(s). Further characterisation of quorum-quenching compound(s) produced by microalgae may be beneficial in the bio-control of pathogenic bacteria in aquaculture and may act as candidates for novel antibiotics.

Seaweed has traditionally been used in Scotland and other countries both as food and for medicinal purposes, which has led to seaweed being investigated for their natural product content. Despite over 30 years of research, the majority of species found in Scotland have yet to have their chemistry examined. Extracts of seaweed were tested for antimicrobial activity against marine bacteria. Extracts of Palmaria palmata, Ulva linza, Chondrus crispus and Pelvetia canaliculata showed no detectable activity, while ethyl acetate extracts of Fucus serratus, Halidrys siliquosa, Osmundea pinnatifida and Polysiphonia fucoides showed activity against at least six of the seven strains. Extracts were screened for radical scavenging activity against ABTS, DPPH and superoxide radicals. At least one extract from each brown seaweed showed radical scavenging of at least 80 % towards ABTS+ with an ethyl acetate extract of P. fucoides and H siliquosa quenching DPPH by at least 90%. Radical scavenging activity appears to be dependent total phenolic content of extract. Extracts were subjected to a series of assays relevant to human health. Ethyl acetate extracts showed high antiparasitic activity against Trypanosoma brucei with a P. fucoides extract showing antibacterial activity toward Staphylococcus aureus. Extracts of H siliquosa and F. serratus showed cytotoxicity to Hela cells with extracts of H siliquosa showing cytotoxicity to LN CAP AS and PC 3 cell lines. An extract of H siliquosa underwent chromatography and by applying assay guided fractionation, several active fractions were identified. These were analysed using NMR and LC/MS and four compounds identified: (2E. 6E. 14E)-1-(l'-hydroxy-4'-methoxy-6'-methyl- phenyl)-5, 13-dihydroxy-12-one-3, 7, 11, 15-tetramethylhexadeca-2, 6, 14-triene, a known antibacterial compound, previously identified in H siliquosa; (2E, 6E, 10E, l4E)-1-(1'- hydroxy-4'-methoxy-6'-methyl phenyl)-5, 12 dihydroxy-3.7, 11, 15-tetramethyl hexadeca- 2.6, 10, l4-tetraene, previously identified in Cystoseira elegans, and now in H siliquosa; and two compounds that have not been reported before.