Publication Search Results

Now showing 1 - 10 of 18
  • (2007) Yee, Lachlan Hartley; Holmström, Carola; Fuary, Evi; Lewin, Nigel; Kjelleberg, Staffan; Steinberg, Peter
    Journal Article
    Antifouling solutions that leave little or no impact in the world’s oceans are constantly being sought. This study employed the immobilisation of the antifouling bacterium Pseudoalteromonas tunicata in k-carrageenan to demonstrate how a surface may be protected from fouling by bacteria, i.e. a ‘living paint’. Attempts so far to produce a ‘living paint’ have been limited in both longevity of effectiveness and demonstration of applicability, most noticeably regarding the lack of any field data. Here survival of bacteria immobilised in k-carrageenan for 12 months in the laboratory is demonstrated and evidence presented for inhibition of fouling for up to 7 weeks in the field (Sydney Harbour, NSW, Australia).

  • (2009) Jayawardena, Menuk Birendra
    During the last few decades, systems incorporating immobilised enzymes have been used prevalently in many industrial and commercial applications. Normally, enzyme-based applications are expensive and have limited operating times, hence low cost operating systems and reusability of the biocatalyst are valuable factors that need consideration. All biocatalytic coatings are composed of two distinct components, categorised as the catalytic and the non-catalytic component. In order to have a stable and long lasting biocatalytic system both these components need to withstand varying conditions and to operate synergistically. Two commercially produced lipases, Greasex (LIPHLL) and NS81042 (LIPCA) were scrutinised for their ability to operate as immobilised biocatalysts in household based paint coatings. The two enzymes were first characterised in solution and in paint to determine their ability to withstand conditions that are considered foreign. The capability of these enzymes to withstand thermal denaturation was then analysed both in paint (in-can stability) and after entrapment in paint coatings, demonstrating significantly greater stability in the latter. The first part of the work described in this thesis was aimed at improving the thermostability of both lipases (the catalytic component). Chemical modifications were chosen over more expensive genetic modification techniques. The chemically modified variants showed improved thermostability both in buffer and in paint emulsion. The second part of the thesis addressed the modification and optimisation of the non-catalytic component (the support). Two strategies were successfully implemented to overcome the mass transfer limitations commonly experienced by many immobilised biocatalysts, including enzymes. The surfactant and solvent based improvements provided compelling evidence that they were practical approaches to direct the location of enzymes to a desired position in the surface layer of the polymer coating. The third part involved the use of the optimised lipase-based paint coatings to determine their detergency against natural substrates such as oils and ester/fat-based commercial stains. The lipase-based paint coatings indicated increased hydrolysis of oils and increased detergency towards the removal of ester-based stains on polymer surfaces. Overall, self-cleaning paint coatings were developed in this project to target fouling by fat material and these films offer great potential in a variety of applications and surroundings. It is proposed that the initial steps required for the development of a commercially available household paint with self-cleaning capabilities have been successfully undertaken.

  • (2012) Tebben, Jan
    In the marine environment chemical signals play critical roles at every organisational level. One emerging area of interest in the field of Marine Chemical Ecology is the role of bacterially derived chemical signals, in particular for the induction of larval settlement of marine invertebrates. Although bacteria have long been recognised to induce larval settlement, to date no inducer of bacterial origin has been fully characterised. In Chapter 2, I describe the isolation of the bacterium Pseudoalteromonas J010 from the surface of crustose coralline algae, which trigger the larval settlement of acroporid corals. In a bioassay-guided fashion, I characterised the metamorphic inducer in this bacterium as tetrabromopyrrole (TBP). TBP rapidly induces larval metamorphosis, however the larvae fail to attach to the substratum when exposed to TBP. The toxic nature of this compound suggests that larval metamorphosis to TBP is a stress response, rather than an evolved response to a habitat specific cue. The production of TBP may provide Pseudoalteromonas J010 with an advantage to persist in the highly competitive biofilm environment. To further explore this hypothesis, I screened the allelochemical profile of this strain and characterised further bioactive metabolites, including novel korormicin derivatives and a polybrominated pyrrole with anti-larval, anti-bacterial, anti-fungal and anti-protozoal properties (Chapter 3). Because, TBP did not explain the inductive properties of CCA on coral larval settlement, I addressed the origin and characteristics of inductive cues from CCA (Chapter 4). This resulted in the isolation of purified fractions that readily induced complete larval settlement, including i) low molecular weight organic-soluble compounds identified as glycoglycerolipids and ii) high molecular weight polymeric aqueous-soluble cue(s). These common algal metabolites may explain the highly inductive properties of CCA on acroporid coral larval settlement. I further demonstrated that these settlement inducers can be immobilised, enabling controlled settlement of coral larvae on target surfaces. Targeted larval settlement on substrata is common practise in reef rehabilitation, particularly for techniques based on sexual reproduction of corals. To improve current reef rehabilitation techniques, I explored methods to enhance post settlement survival of settled coral spat (Chapter 5).

  • (2005) Koppi, Anthony; Lowe, Colin
    Conference Paper

  • (2006) Allen, Belinda; Crosky, Alan; McAlpine, Iain; Hoffman, Mark; Munroe, Paul
    Conference Paper

  • (2006) McAlpine, Iain; Reidsema, Carl; Allen, Belinda
    Conference Paper

  • (2016) Ye, Jun
    Organic farming relies on the activities of bacterial communities for optimal soil productivity. Understanding the responses of bacterial communities to different soil amendments, including organic fertilizers and biochars, can provide information for soil management. This thesis firstly describes the bacterial diversity and functions that are central to soil processes of organic soils and their responses to fertilizers with different C/N ratios. Secondly, this thesis analyzes the effect of a mineral-enhanced biochar (MEB) on the bacterial community of organically amended soil. Finally, the thesis investigates the direct interactions between biochar and bacteria that underpin metabolic processes in the soil. Bacterial taxa that are resilient to different fertilizers were identified and defined as the core community of organic soil. The phyla Bacteroidetes and Planctomycetes, the family Cytophagaceae and the class Acidobacteria-5 were thus found in organic soil regardless of the type of fertilizer being applied. These core bacterial taxa were further linked to the functional potential of organic soil. The C/N ratio of fertilizer was also found to have a positive correlation with microbial N assimilation in organic soil. MEB was applied in combination with compost to soil and this resulted in synergistic effects on soil properties. Specifically, the soil nitrate content was increased, which correlated with an enrichment of bacterial nitrifiers due to the MEB addition. As a consequence, plants produced larger leaves, which demonstrates that MEB could be used to manipulate specific agricultural outcomes in organic farming. To understand the detailed mechanism that supports the beneficial effects of biochar and MEB, a novel method was developed to visualize the in situ interactions between bacteria and surfaces on a single-cell level. Distinct bacterial communities were found to exist on the surface of biochar and MEBs compared to surrounding soils and surface-associated bacteria were found to have the capacities to fix carbon dioxide using chemolithotrophic processes. This provides a bacterial mechanism on how biochar and MEBs can drive carbon sequestration into the soil environment. Together, the discoveries and models presented in this thesis provide new insights into the functions of soil microbiomes in organically amended soil.

  • (2013) Ling, Gee Chong
    In all ecosystems bacteria predominantly live on surfaces, encapsulated within an extracellular matrix, and readily establish a multicellular and most often a multispecies organisation known as a biofilm. Microbial biofilm formation is sequential, involving multiple developmental stages and resulting in dynamic communities with cooperative traits resembling those of multicellular organisms. Such traits enable biofilms to survive in harsh environments and increase bacterial tolerance to antimicrobials, leading to a range of negative impacts such as fouling on industrial surfaces and bacterial infections. This study investigates the impact of micro-fabricated poly-dimethyl siloxane (PDMS) surfaces on initial biofilm formation as well as subsequent development, to explore the utility of surface modification and patterning for biofilm control. Bacterial populations establishing biofilms on different micro-fabricated PDMS surfaces, with micro-scale trenches from 1 to 10 μm, and smooth control surfaces, were first studied using the model biofilm forming bacterium Pseudomonas aeruginosa. Surface micro-fabrication had significant effects on several important biofilm traits, such as reduced microcolony formation, biofilm height, and biovolumes. Similar outcomes were observed for P. aeruginosa grown in other culture conditions, including the use of different culture media such as Luria Broth (LB), Vaatanen Nine Salt Solution (VNSS) and M9 Minimal Media (M9), which displayed broader impacts of different physiological conditions for biofilm development, as well as in studies using two model marine surface colonising organisms, Phaeobacter gallaeciensis and Pseudoalteromonas tunicata. Altered biofilm formation of P. aeruginosa biofilms on micro-fabricated PDMS surfaces also showed decreased chemical resistance of their biofilm populations, compared to biofilms established on control surfaces. Marine field experiments allowing diverse biofilm community formation similarly showed a marked impact on biofilm development by the modified surfaces. In addition to altered biofilm traits similar to those observed for biofilm populations, the biofilm community composition analysed using terminal restriction fragments (T-RF) for phylogenetic fingerprinting, was significantly changed at different times during the long term exposure, as revealed by the changes in T-RF profiles, and hence biofilm development. The effects of micro-fabricated PDMS surfaces on microbial biofilm formation and development are pronounced, both in laboratory settings and in marine field trials. The findings contribute to ongoing and future research for the delivery of novel biofilm control tools.

  • (2013) Ballestriero, Francesco
    Marine bacteria produce a wide array of biologically active metabolites involved in defence strategies and pathogenesis against a range of metazoans target organisms. In return bacteriovorous metazoans, including nematodes, have developed sophisticated strategies to neutralise or avoid such bioactives. The overall objective of this study was to investigate the antagonistic activities of bacteria-eukaryote interactions. The first aim of this thesis was to develop a novel functional (meta) genomic screen for the identification of inhibitors that target the nematode Caenorhabditis elegans. Environmental DNA from marine habitats was expressed in Escherichia coli and the resulting functional (meta) genomic libraries were screened by selective grazing of the nematode C. elegans, in a simple, rapid, high-throughput manner. Next, this project aimed at characterizing antagonistic activities that target C. elegans and study their toxic effect in the nematode. Genetic and microscopic analysis uncovered known and novel bioactive compounds including the small molecules tambjamine and violacein, which appear to facilitate bacterial colonisation and induce apoptosis in the nematode. An array of genes and gene products involved in antinematode activities was also identified including a gene encoding for a novel protein involved in a fast killing activity. Finally, this study investigated the sophisticated strategies that the nematode mounts to neutralize or avoid bacterial toxic compounds. The role of both C. elegans behavioural and immune system strategies in mediating the nematode defence in response to toxic bacterial compounds were investigated. In the nematode, a complex behavioural strategy known as aversive learning is employed to avoid violacein toxicity. When noxious violacein cannot be avoided, the toxic compound appears to activate the insulin-like signaling cascade, an evolutionary conserved innate immunity pathway. In summary, this work combines functional (meta) genomics and C. elegans genetics to identify bioactive compounds from marine bacteria and uncover animal defence strategies in response to bacterial secondary metabolites.

  • (2013) Hui, Janice Gee Kay
    Prophage have been identified in most sequenced bacterial genomes, however the effects of prophage genes on the host are poorly understood. Bacteriophage have been shown to play a role in the cell death phenomenon observed during biofilm development of Pseudomonas aeruginosa PAO1. The filamentous Pf4 prophage is important for mediating cell death within microcolonies, dispersal events and variant formation during biofilm development. Further, these effects were shown to result from the establishment of a superinfective phage phenotype. These observations have demonstrated the importance of phage activity in bacterial biofilms and their effects leading to biofilm variant formation and bacterial adaptation. However, little is known about the genetic mechanisms and triggers that lead to the conversion from lysogenic to the superinfective Pf4 phage. The aim of this study was to determine the factors and genes that induce the conversion of the lysogenic Pf4 phage into its lytic, superinfective form during P. aeruginosa PAO1 biofilm development. Here, the mechanisms in the induction into the superinfective phage and the gene responsible for variant formation in the biofilm were demonstrated.Two morphotypic variantswere isolated during the cell death and dispersal phase of the biofilm. These variants, the small colony variant SCV2 and spreader variant S4, carrya superinfective Pf4 phage and exhibited changes in motility and biofilm formation. Genetic analysis of these variants identified mutations within the immunity region of the Pf4 prophage genome. The mutations were identified to lie within the putative repressor c gene of the prophage and the putative promoter of the gene. Moreover, meta-genomic sequencing of pre- and post- dispersal biofilm populations identified the same mutations. The majority of the mutations were within the prophage genome at a frequency of up to 79% in contrast to mutations atless than 7% within the PAO1 genome. Collectively, these results suggest a role of the repressor C in superinfective phage conversion and strong selection for mutations within the immunity region of the phage to facilitate adaptation to biofilm lifecycle in the presence of phage infection. Variant formation is a common trait during biofilm development, as a result of genetic changes in the biofilm community. Furthermore, it has been observed that the appearance of variants from the biofilm correlated with the occurrence of the conversion into the superinfective phage. Environmental stresses have previously shown to cause phenotypic variants and were here tested for induction of the superinfective phage of PAO1 biofilm. Reactive oxygen and nitrogen species have been shown to accumulate within the biofilm microcolonies. Biofilms exposed to oxidative stress induced the conversion of the superinfective phage. Phenotypic variants are a commonly isolated cystic fibrosis patients suffering from lung infection, and have shown to exhibit mutator phenotypes with lost of mut genes of the mismatch repair system. DNA damaging agent mitomycin C and mutS mutant biofilms have also shown to induce superinfective phage. These results have indicated that the oxidative stress and DNA damage are triggers to induce mutations within the biofilm resulting in the conversion into the superinfective form. Interestingly, the OxyR oxidative stress response regulator binds within the repressor c gene, suggesting a potential role of OxyR in the conversion of the superinfective phage. Biofilms have been estimated to be associated with 80% of chronic bacterial infections and have been a challenge for treatment and therapy. While the mechanisms contributing to the conversion into the superinfective Pf4 phage remains elusive, this study has demonstrated the complexity involved in the study of phage infection in biofilms. Phage genes play a major role in the ability of the phage to cause infection against the host and provide resistance for host against infection. The proposed modelinvolves oxidative stress induced mutations within the repressor C region of the prophage andlead to selection for variants that are resistant against superinfective phage. Thus, biofilm variants carrying the superinfective Pf4 phage persist within the biofilm.As P. aeruginosa is known to be a pathogenic bacterium and is involved in several biofilm-related diseases such as chronic infections and cystic fibrosis, it is important to understand the mechanism of biofilm development and to further improve the current treatments conducted.