Dr Michael Sweet
Research Associate

Historically, most studies of coral diseases have been associated with pathogenic bacteria (Richardson et al., 1998; Kushmaro et al., 2001; Ben-Haim and Rosenberg, 2002; Patterson et al., 2002; Frias-Lopez et al., 2003; Cervino et al., 2008; Sussman et al., 2008; Luna et al., 2010). Only recently have ciliates and other protozoans been associated with diseases of corals and increasing evidence indicates that ciliates act as pathogens in some diseases. Despite this, Koch’s postulates have not been fulfilled for any of the ciliates associated with coral diseases. However, several studies have shown ciliates to be pathogenic in a wide range of other organisms (Song and Wang, 1993; Bradbury et al., 1996). Some of the most ecologically important coral diseases worldwide are the poorly defined ‘white diseases/syndromes’, few of which have been satisfactorily characterised (Bythell et al., 2004). These diseases are collectively termed White Syndrome (WS) in the Indo-Pacific and include White Plague (WP) and White Band Disease (WBD) in the Caribbean. Many studies have identified bacterial pathogens involved in these white diseases (Peters et al., 1983; Barash et al., 2005; Thompson et al., 2006; Sussman et al., 2008; Efrony et al., 2009). Several vibrio species have been proposed as causal agents of WS (Sussman et al., 2008), with Vibrio harveyi being the most recently identified (Luna et al., 2010). However, recently Work and Aeby (2011) have reported that ciliates are also associated with the WS pathology. Together with Ainsworth et al. (2007) they show no bacterial populations associated with the pathogenesis and no signs of bacterial-induced necrosis. These recent studies therefore question the primary role of bacteria in WS. Our work primarily targets these 'White Diseases' around the world from the Indo-Pacific to the Caribbean. Using a variety of molecular techniques both cultured and non-cultured we can describe in detail the dominant microbial communities of healthy, apparently healthy and diseased corals along with environmental samples which may act as reservoirs for certain microbial pathogens. Other interests include any abnormalitie or diseases of any organisms, recently describing melanoma (skin cancer) for the first time in the marine fish Plectropomus leopardus.

Project Leader(s): Michael sweet
Staff: Prof. John C Bythell

Contact: michael.sweet@newcastle.ac.uk
Sponsors: NERC

My current research addresses the overall aim to fundamentally re-evaluate the emergence of reef coral diseases in the light of our recent findings that implicate ciliates rather than bacteria as primary causal agents of the most common ‘white disease’ of reef corals.

Project Leader(s): Michael sweet
Staff: Prof. John C Bythell, Dr Gordon Beakes (Newcastle University, UK)
Contact: michael.sweet@newcastle.ac.uk
Sponsors: NERC

Previous research focussed on an investigation into the controls on bacterial community development and organisation on the surface mucus layer (SML) of reef corals. Various factors influence the SML bacterial community (Brown & Bythell 2005), including production of antimicrobial chemicals, supply of bacteria from the water column, environmental conditions and mucus composition and production rates. Mucus production is particularly important as it represents both the availability of C and N and the dynamics of the SML as a physical barrier, entrapment surface and growth medium. Although the SML of corals is believed to be a highly dynamic layer, it appears to support a distinct resident bacterial community rather than one resulting from passive settlement and entrapment of water-borne bacteria. Comparisons between the bacterial species diversity found in the surrounding water column and coral mucus show little to no overlap (Rohwer et al. 2001, Frias-Lopez et al. 2002, Klaus et al. 2005). The formation, composition and rate of production of the SML in corals are not well understood, but vary considerably between coral species (Brown & Bythell 2005) and between sites subject to different environmental conditions (Guppy & Bythell 2006). It is highly likely that the bacterial community of the SML is controlled to some extent by the nature and composition of mucus secretion by the coral and this, in turn, is likely to vary in relation to environmental conditions and coral health (Brown & Bythell 2005). The study diversified into eukaryotes from the order Ciliophora, after devastation of a tank experiment by unidentified ciliates during one field trip. This lead the focus of the labs future work to look more in-depth into other causes of coral disease other than bacteria.

Conferences presented at:

International Society for Reef Studies, Amsterdam 2010, Talk: Bacterial assemblages differ between compartments within the coral holobiont

Reef Conservation UK 2010, Talk: Are ciliates the key infectious agents of White Syndrome & Investigation of the controls on bacterial community development in the reef coral A. muricata using experimental antibiotic treatment

Reef Conservation UK 2009, Talk: Bacterial Communities associated with the Surface Mucus Layer of reef corals

Environmental Marine Biology Conference 2009; Talk: A realistic measure of the supply of bacteria from the water column to the coral surface mucus layer

Delve Deeper, School of Marine Science and Technology, Dove Marine Lab 2009; Talk: Corals, Bacterial Worlds

International Coral Reef Symposium 2007; Poster presentation: Relationships between water borne and coral bacteria – a new perspective