| || || Kumar, Vipra Nandani.|
| || || Inhibition of primary colonizers by marine surface-associated bacteria |
Author:Kumar, Vipra Nandani.
Institution: University of the South Pacific.
Call No.: Pac QH 91 .8 .M3 K86 2009
Copyright:Under 10% of this thesis may be copied without the authors written permission
Abstract: Surfaces immersed in seawater rapidly accumulate a complex biofouling community, of which bacteria and diatoms are among the first colonisers. However marine organisms have evolved several defence mechanisms and it has been suggested that green algae of the genus Ulva rely on microbial defence. The antibacterial properties of epiphytic bacteria are well established, but relatively little is known about their anti-diatom properties. In this study the hypothesis that surface-associated bacteria from tropical Ulva species have anti-fouling characteristics that may have a role in preventing surface fouling on the algae was investigated. Bacterial isolates from the surface of Ulva growing in tropical waters were obtained and tested for antibacterial and anti-diatom properties. It was found that 60% of the isolates expressed some inhibitory action against the remaining bacteria isolated in the study and 80% inhibited growth of the diatom Cylindrotheca fusiformis. Most effective bacteria were members of the Pseudoalteromonas genus. Also showing inhibitory properties were members of the genus Bacillus, Vibrio and Shewanella. Since Pseudoalteromonas spp. and the Roseobacter clade are model surface-associated bacteria, both groups were screened for anti-diatom property. Results showed that anti-diatom activity was present in 100% and 44% of tested Pseudoalteromonas and Roseobacter strains respectively. In order to better comprehend the anti-diatom property of marine surface-associated bacteria, a transposon mutant library of Pseudoalteromonas tunicata was generated and screened for mutants lacking in anti-diatom activity. Genetic analysis of transposon insertion sites into the P. tunicata genome was then used to identify loci linked with anti-diatom activity. Genes identified in this way include a cation/multidrug efflux pump, a beta-hexosaminidase protein, a RTX toxinlike gene and a member of the HemeO protein family. A hypothetical model for the regulation of anti-diatom activity in P. tunicata was suggested and this will form the basis of future studies that aim to identify the mechanism of anti-diatom activity in bacteria, especially in P. tunicata. Additionally, the presence of epiphytic bacteria engaged in antifouling activities on the surface of tropical Ulva sp. emphasizes the prevalence of microbial-mediated defence systems which can be manipulated to find solutions to current biofouling-associated problems.