University of New South Wales - CMB - Marine Chemical Ecology and Prokaryote/Eukaryote Interactions

Marine Chemical Ecology and Prokaryote/Eukaryote Interactions

The CMB’s research on marine chemical ecology and prokaryote/eukaryote interactions focuses on the following areas:

1. Identification of Bioactive Compounds

The identification of novel bioactive compounds is an emergent field that represents a unification of the fields of molecular biology, microbiology, natural products chemistry, and marine ecology. The field of marine chemical ecology has long been dominated by studies of plant/herbivore or predator/prey interactions. Naturally produced chemicals mediate these interactions at many levels, and in many directions. Recently, research carried out at the CMB, has begun to focus on the chemical ecology of epibiosis (colonisation of the surface of an organism by the propagules of other organisms). Using Delisea pulchra as our initial model, we were the first to quantify natural deterrents of epibiosis (halogenated furanones) on the surface of a marine organism and have in addition explored the anatomical structures of red algae that allow for release of deterrents at the surface of a plant. This has provided an ecologically realistic context for investigations of the detailed mechanisms of interference by furanones in bacterial signalling systems. Our research on natural antifoulants is now being extended to a broad array of seaweeds and other marine organisms, firstly to understand their role in the chemical ecology of these organisms and secondly to provides models for the development of novel antifouling technologies.

Surfaces of marine eukaryotes ('living surfaces') are ideal systems to explore colonization by microorganisms as they are subject to a constant bombardment from the millions of microbial cells typically found in a millilitre of seawater. The close proximity of microorganisms on surfaces drives intercellular interactions. Space and nutrients limitation create a highly competitive environment, which has allowed

surface microbes to evolve both defensive and antagonistic strategies, including the production of toxins and other biologically active secondary metabolites to evade predators and/or prevent the colonisation and growth of competitors. From a biotechnological point to view, this represents a unique reservoir for the discovery of new drugs and bioactive molecules with applications across medical, industrial and environmental settings. Thus one of the major research goals in the CMB is to capture the phylogenetic and functional diversity of marine surface associated microbes and to understand the chemical interactions, which occur within these communities. This research platform is based on our capacity to link our understanding of microbial interactions with the targeted isolation of novel bioactive compounds with a range of biological activities including but not limited to antibacterial, antifungal antiagal, antilarval, antiprotozoan and antihelminthic.

2. Identification of inducers of settlement of invertebrate larvae

The converse of natural antifoulants are chemical inducers of settlement, which act as cues for settling propagules (larvae, spores, etc.), enabling these planktonic forms to settle in an appropriate habitat for resumption of the benthic (bottomdwelling) phase of their life history. The analysis of cues which control settlement in marine organisms and understanding the generality or specificity at which these cues operate is fundamental to advancing our understanding of adult distribution and abundance, population and community variability and hence our ability to manage natural marine systems. Examples of this research include our investigations of settlement cues for the common Australian sea urchins Holopneustes purpurascens and Heliocidaris eryrthrogramma. More recently, we addressed the question of why the larvae of many wild, harvested and even farmed species, such as sea urchins, starfish, oysters, abalone and corals, settle preferentially on coralline algae or biofilms associated with these plants. These observations suggest a potentially significant role of coralline algae in establishing and structuring marine benthic communities.

Although a paradigm of coralline algae as general mediators or cues for induction of larval settlement has long been recognized, no common, natural chemical settlement cue has been identified so far. Our aim is to identify common chemical cues that enable these plants to be such a widespread settlement substrate for larvae. Mariculture and marine conservation stand to benefit from knowledge of these cues as many commercially valuable and environmentally significant species (abalone, sea urchins and corallivorous crown-of-thorns starfish) rely on them.

3. Diseases of marine and aquatic organisms

In the last ten years the effects of disease on natural marine communities have become increasingly apparent, with organisms as diverse as seagrasses, seals and corals suffering from major disease-related die-offs. In a number of these instances human impacts via pollution or environmental change are thought to have played a major role in the impact of these diseases. Recent evidence indicates that "bleaching" of Delisea pulchra is due to a bacterial disease. In a comprehensive approach, we investigate the interplay between bacterial virulence, environmental factors (temperature and UV light), and the seaweed's natural bacterial inhibitors to understand the epidemiology and ecology of this disease.

Understanding these marine prokaryote/ eukaryote interactions has implications for a remarkably diverse array of endeavours, from the preservation of marine biodiversity to an understanding of diseases of marine and aquatic organisms to the development of novel antibiotics.

4. Protozoan grazing

The CMB is involved in several projects with the aim to understand in detail the interactions of microbial biofilms and protozoan and nematode grazers. Recent findings in the CMB indicate that, depending on the species of the protozoan used, biofilm development can be encouraged (e.g. predation induces microcolony formation) or conversely, protozoans can be used to reduce microbial biomass through predation pressure.

It is our hypothesis that the production of toxic factors and expolysaccharide are essential in the resistance of Vibrio cholerae to grazing pressure and hence, persistence in the environment. Protozoan grazing has been identified as one of the key environmental pressures faced by bacteria and thus, the survival and persistence of bacteria depends on their ability to adapt to this pressure. In particular, the ability to survive and persist is especially relevant to Vibrio cholerae, where the environmental reservoir is mediated by attachment and biofilm formation on zooplankton. Indeed, removal of zooplankton from contaminated water by filtration is 48% effective in reducing infection. Exopolysaccharide (EPS) production and quorum sensing (QS) have been shown to affect biofilm formation in V.cholerae.

Preliminary data from our laboratory indicate that V. cholerae biofilms produce an extracellular product that is toxic to protozoa. In contrast to V. cholerae biofilms, planktonic cultures are rapidly eliminated, suggesting that biofilms serve as a potent predation refuge relevant for the environmental persistence of V. cholerae. Thus, we propose that EPS production and bacterial QS systems are not only important for the formation of biofilms but also for resistance to grazing by protozoans in the aquatic environment. We further propose that these resistance mechanisms also have a role in attachment and cytotoxicity to cells of the human host, suggesting that some virulence factors play dual roles in survival and persistence of the organism in the environment or human host. Therefore, the specific aims of this project are:

To identify toxic exoproduct(s) produced by V. cholerae biofilms that inhibit protozoan grazing
To determine if exopolysaccharide plays a role in protection from grazing
To determine if biofilms of V. cholerae are protected from grazing in situ using environmental chambers placed in the marine environment
To determine the role of factors (e.g. production of inhibitors and EPS) providing grazing protection in the environment as virulence factors to human epithelial cells and phagocytes

For any queries on this project please contact Dr. Tilmann Harder