Kim B. Ritchie

The etiology of white pox, a lethal disease of the Caribbean elkhorn coral, Acropora palmata

Populations of the shallow-water Caribbean elkhorn coral, Acropora palmata, are being decimated by white pox disease, with losses of living cover in the Florida Keys typically in excess of 70%. The rate of tissue loss is rapid, averaging 2.5 cm2⋅day−1, and is greatest during periods of seasonally elevated temperature. In Florida, the spread of white pox fits the contagion model, with nearest neighbors most susceptible to infection. In this report, we identify a common fecal enterobacterium, Serratia marcescens, as the causal agent of white pox. This is the first time, to our knowledge, that a bacterial species associated with the human gut has been shown to be a marine invertebrate pathogen.

Interactions of TLC1 (Which Encodes the RNA Subunit of Telomerase), TEL1, and MEC1 in Regulating Telomere Length in the Yeast Saccharomyces cerevisiae

ABSTRACT In the yeast Saccharomyces cerevisiae, chromosomes terminate with a repetitive sequence [poly(TG1–3)] 350 to 500 bp in length. Strains with a mutation of TEL1, a homolog of the human gene (ATM) mutated in patients with ataxia telangiectasia, have short but stable telomeric repeats. Mutations of TLC1 (encoding the RNA subunit of telomerase) result in strains that have continually shortening telomeres and a gradual loss of cell viability; survivors of senescence arise as a consequence of a Rad52p-dependent recombination events that amplify telomeric and subtelomeric repeats. We show that a mutation inMEC1 (a gene related in sequence to TEL1 andATM) reduces telomere length and that tel1 mec1double mutant strains have a senescent phenotype similar to that found in tlc1 strains. As observed in tlc1 strains, survivors of senescence in the tel1 mec1 strains occur by a Rad52p-dependent amplification of telomeric and subtelomeric repeats. In addition, we find that strains with both tel1 andtlc1 mutations have a delayed loss of cell viability compared to strains with the single tlc1 mutation. This result argues that the role of Tel1p in telomere maintenance is not solely a direct activation of telomerase.

High Frequency of Horizontal Gene Transfer in the Oceans

Viruslike particles enable lateral gene transfer among marine microorganisms. Oceanic bacteria perform many environmental functions, including biogeochemical cycling of many elements, metabolizing of greenhouse gases, functioning in oceanic food webs (microbial loop), and producing valuable natural products and viruses. We demonstrate that the widespread capability of marine bacteria to participate in horizontal gene transfer (HGT) in coastal and oceanic environments may be the result of gene transfer agents (GTAs), viral-like particles produced by α-Proteobacteria. We documented GTA-mediated gene transfer frequencies a thousand to a hundred million times higher than prior estimates of HGT in the oceans, with as high as 47% of the culturable natural microbial community confirmed as gene recipients. These findings suggest a plausible mechanism by which marine bacteria acquire novel traits, thus ensuring resilience in the face of environmental change.

Cause of sea fan death in the West Indies

A fungus from the genus Aspergillus is the probable agent of epizootic infections that have caused mass mortality of sea fan corals (Gorgonia ventalina) over the past 15 years,. Here we show that four strains of the fungus involved in these infections are members of the species Aspergillus sydowii, a common saprobe (an organism that lives on decaying matter) that is found in both terrestrial and marine environments. Isolates of A. sydowii taken from diseased sea fans caused new infections of sea fans in inoculation experiments, whereas isolates taken from elsewhere did not.

Florida's mystery coral-killer identified

An unusual coral disease appeared on the Florida Reef Tract in June 1995. It was distinct in its microbiology, its pattern of tissue degradation, the species susceptible to it, and its regional distribution. Symptoms included a sharp line between healthy and diseased tissue, as occurs with other coral diseases, but the pathogen responsible for the new outbreak seemed more virulent, affected a wider variety of species, and destroyed tissue much more rapidly than these other ‘line’ or ‘band’ diseases. We have identified the pathogen responsible for this new disease as a new species of Sphingomonas.

African and Asian Dust: From Desert Soils to Coral Reefs

Abstract Many hypotheses have been proposed to explain the decline of coral reefs throughout the world, but none adequately accounts for the lack of recovery of reefs or the wide geographical distribution of coral diseases. The processes driving the decline remain elusive. Hundreds of millions of tons of dust transported annually from Africa and Asia to the Americas may be adversely affecting coral reefs and other downwind ecosystems. Viable microorganisms, macro- and micronutrients, trace metals, and an array of organic contaminants carried in the dust air masses and deposited in the oceans and on land may play important roles in the complex changes occurring on coral reefs worldwide.

Microbial Communities of Coral Surface Mucopolysaccharide Layers

Microbes associated with corals form communities that differ significantly from water mass communities. Physiological and metabolic activities occurring within these close, mutualistic relationships are very different from the surrounding environment and tend to be very specific. Coral-associated microbial communities are likely to resemble microbial mats in structure. Vertical stratification of populations, from proximal toward distal regions (with respect to the surface of the coral), results in fluxes of organic and inorganic nutrients. The presence of an actively metabolizing microbiota has significant influences on overall population structure. Theoretical and observed consequences of environmental changes lead to the disruption of the ‘normal’ communities associated with healthy corals. Because it is likely that the normal microbiota protects the coral animal from invading microbes, changes in the community structure may result in the development of disease.

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

Over the last decade, significant advances have been made in characterization of the coral microbiota. Shifts in its composition often correlate with the appearance of signs of diseases and/or bleaching, thus suggesting a link between microbes, coral health and stability of reef ecosystems. The understanding of interactions in coral-associated microbiota is informed by the on-going characterization of other microbiomes, which suggest that metabolic pathways and functional capabilities define the ‘core’ microbiota more accurately than the taxonomic diversity of its members. Consistent with this hypothesis, there does not appear to be a consensus on the specificity in the interactions of corals with microbial commensals, even though recent studies report potentially beneficial functions of the coral-associated bacteria. They cycle sulphur, fix nitrogen, produce antimicrobial compounds, inhibit cell-to-cell signalling and disrupt virulence in opportunistic pathogens. While their beneficial functions have been documented, it is not certain whether or how these microbes are selected by the hosts. Therefore, understanding the role of innate immunity, signal and nutrient exchange in the establishment of coral microbiota and in controlling its functions will probably reveal ancient, evolutionarily conserved mechanisms that dictate the outcomes of host–microbial interactions, and impact the resilience of the host.

Toxicity of Deepwater Horizon Source Oil and the Chemical Dispersant, Corexit® 9500, to Coral Larvae

Acute catastrophic events can cause significant damage to marine environments in a short time period and may have devastating long-term impacts. In April 2010 the BP-operated Deepwater Horizon (DWH) offshore oil rig exploded, releasing an estimated 760 million liters of crude oil into the Gulf of Mexico. This study examines the potential effects of oil spill exposure on coral larvae of the Florida Keys. Larvae of the brooding coral, Porites astreoides, and the broadcast spawning coral, Montastraea faveolata, were exposed to multiple concentrations of BP Horizon source oil (crude, weathered and WAF), oil in combination with the dispersant Corexit® 9500 (CEWAF), and dispersant alone, and analyzed for behavior, settlement, and survival. Settlement and survival of P. astreoides and M. faveolata larvae decreased with increasing concentrations of WAF, CEWAF and Corexit® 9500, however the degree of the response varied by species and solution. P. astreoides larvae experienced decreased settlement and survival following exposure to 0.62 ppm source oil, while M. faveolata larvae were negatively impacted by 0.65, 1.34 and 1.5 ppm, suggesting that P. astreoides larvae may be more tolerant to WAF exposure than M. faveolata larvae. Exposure to medium and high concentrations of CEWAF (4.28/18.56 and 30.99/35.76 ppm) and dispersant Corexit® 9500 (50 and 100 ppm), significantly decreased larval settlement and survival for both species. Furthermore, exposure to Corexit® 9500 resulted in settlement failure and complete larval mortality after exposure to 50 and 100 ppm for M. faveolata and 100 ppm for P. astreoides. These results indicate that exposure of coral larvae to oil spill related contaminants, particularly the dispersant Corexit® 9500, has the potential to negatively impact coral settlement and survival, thereby affecting the resilience and recovery of coral reefs following exposure to oil and dispersants.

How microbial community composition regulates coral disease development.

Modeling reveals how rapid overgrowth by pathogenic microbes in the mucus layer surrounding corals, which often occurs under temporary stressful conditions, can persist long after environmental conditions return to normal.