Effects of temperature, nutrients, organic matter and coral mucus on the survival of the coral pathogen, Serratia marcescens PDL100

Abstract

Serratia marcescens is an enteric bacterium that causes white pox disease in elkhorn coral, Acropora palmata; however, it remains unclear if the pathogenic strain has adapted to seawater or if it requires a host or reservoir for survival. To begin to address this fundamental issue, the persistence of strain PDL100 was compared among seawater and coral mucus microcosms. Median survival time across all conditions ranged from a low of 15 h in natural seawater [with a first-order decay constant (k) = -0.173] at 30°C to a maximum of 120 h in glucose-amended A. palmata mucus (k = -0.029) at 30°C. Among seawater and mucus microcosms, median survival time was significantly greater within Siderastrea siderea mucus compared with seawater or mucus of Montastraea faveolata or A. palmata (P < 0.0001). In seawater, the addition of phosphate and especially glucose resulted in significant improvements in survival (P < 0.001), while only the addition of glucose resulted in significant improvement in survival in A. palmata mucus (P < 0.0001). Increasing the temperature of seawater to 35°C resulted in a significantly slower decay than that observed at 30°C (P < 0.0001). The results of this study indicate that PDL100 is not well-adapted to marine water; however, survival can be improved by increasing temperature, the availability of coral mucus from S. siderea and most notably the presence of dissolved organic carbon.

Human Pathogen Shown to Cause Disease in the Threatened Eklhorn Coral Acropora palmata

“…For example, saltwater tolerant strains may be more likely to become persistent or even resident on the reef whereas less halo-tolerant strains may either die off before reaching the reef or may be responsible for discrete outbreaks over short time periods. Our data from microcosm studies suggest that PDL100 (isolated in 1999) follows the latter pattern [26] and is supported by the fact that this strain has never been re-isolated from the marine environment [13]. On the other hand, strain PDR60, which has been recovered from multiple marine sources [13], is highly persistent in marine waters (KP Sutherland and EK Lipp unpublished data), suggesting that this may be an endemic disease strain.…”

“…, Solenastrea bournoni ) [13], may serve as a reservoir for the acroporid pathogen in the reef environment. Previous work suggests that PDL100 is poorly adapted for survival in the marine environment, persisting in seawater for only 15 h [26], but survival and proliferation of this strain is enhanced when it is grown in A. palmata SML and S. siderea SML [26], [27]. Our results indicate that PDL100 survived for at least 11 days in association with A. palmata ; PDL100 was recovered from an APS lesion on day 19 of the experiment (Table 2), 11 days after the second experimental inoculation.…”

“…, ability to persist and/or grow in seawater) and in genetic differences leading to increased virulence. S. marcescens vary widely in their survival in seawater with strain PDL100 surviving for 15 h or less at 30°C [26] and marine-derived isolates of the PDR60 pathogen strain persisting for up to 20 days under the same conditions (KP Sutherland and EK Lipp unpublished data). Fitness of different S. marcescens strains in seawater may also shed light on the mode of APS transmission.…”

“…This “reverse zoonosis” is all the more interesting because it involves the jump of a pathogen from vertebrate to invertebrate and from terrestrial to marine. Furthermore, disease incidence or severity may increase with rising temperatures [26], [43], [44], reinforcing the importance of near-shore water quality under climate change scenarios. Given a reliance on tourism by most Caribbean countries and the widespread lack of consistent wastewater treatment in the region, the APS disease system is of great economic interest and public health concern to developing nations and has particular significance for sustainable development activities and coastal-zone carrying capacity studies world-wide, especially under changing climatic conditions.…”

Coral-associated micro-organisms and their roles in promoting coral health and thwarting diseases

“…In addition to carbon and nitrogen sources discussed above, coral mucus also contains potent antimicrobials [78]. Therefore, when crude preparations of fresh mucus are used as growth substrate, declining bacterial viability is sometimes reported [79]. To establish within presumably robust coral surface microbial communities, invading pathogens-in addition to dealing with host defence molecules present in mucusmust be able to outcompete members of native microbiota within the surface mucopolysaccharide layer, and then penetrate mucus to reach host tissues.…”