Constantine Alexander's blog

New study helps predict impact of ocean acidification on shellfish

An international study to understand and predict the likely impact of ocean acidification on shellfish and other marine organisms living in seas from the tropics to the poles is published this week (date) in the journal Global Change Biology.

Ocean acidification is occurring because some of the increased carbon dioxide humans are adding to the atmosphere dissolves in the ocean and reacts with water to produce an acid.

The results suggest that increased acidity is affecting the size and weight of shells and skeletons, and the trend is widespread across marine species. These animals are an important food source for marine predators such as tropical seabirds and seals as well as being a valuable ingredient in human food production. Consequently, these changes are likely to affect humans and the ocean's large animals.

UK scientists from the British Antarctic Survey (BAS) and the National Oceanography Centre (NOC), together with colleagues from Australia's James Cook and Melbourne Universities and the National University of Singapore, investigated the natural variation in shell thickness and skeletal size in four types of marine creatures living in 12 different environments from the tropics to the Polar Regions. Their aim was to get a clearer understanding of similarities and differences between species, and to make better predictions of how these animals might respond to increasing acidity in the oceans.

The effort required by clams, sea snails and other shellfish to extract calcium carbonate from seawater to build their shells and skeletons varies from place to place in the world's oceans. A number of factors, including temperature and pressure, affect the availability of calcium carbonate for species that produce carbonate skeletons.

There is already evidence that ocean acidification is affecting the ability of some marine species to grow, especially during their early life stages, and there is mounting concern about whether or not these species can evolve or adapt to cope with increases in acidity in the coming decades.

This study shows, over evolutionary time, animals have adapted to living in environments where calcium carbonate is relatively difficult to obtain by forming lighter skeletons. Carbon dioxide from fossil fuel combustion is altering seawater chemistry in the same way, in a process called ocean acidification and this is making it harder for marine animals to make shells and skeletons.

The four different types of marine animals examined were clams, sea snails, lampshells and sea urchins. Scientists found that as the availability of calcium carbonate decreases skeletons get lighter and account for a smaller part of the animal's weight. The fact that same effect occurs consistently in all four types suggests the effect is widespread across marine species, and that increasing ocean acidification will progressively reduce the availability of calcium carbonate.

Professor Lloyd Peck of British Antarctic Survey said, "This effect is strongest at low temperatures and the results showed polar species to have the smallest and lightest skeleton, suggesting that they may be more at risk in the coming decades as the oceans change. Interestingly, where ecology requires animals to have strong skeletons - for instance to protect them from impacts from floating ice in Antarctica - skeletons are made thicker and stronger. However, they still form a smaller part of the animal's body mass, because the shape of the species changes to enclose much more body for a given amount of skeleton. Thus life finds a way, but still follows the overall trends of decreasing skeleton size in areas where the ocean chemistry makes it more difficult to obtain the necessary building blocks. If there is time for species to evolve in temperate and tropical regions it is one way they may be able to overcome some of the future effects of ocean acidification."

Dr Sue-Ann Watson, formerly of the University of Southampton and British Antarctic Survey (now at James Cook University) said, "In areas of the world's oceans where it is hardest for marine creatures to make their limestone shell or skeleton, shellfish and other animals have adapted to natural environments where seawater chemistry makes shell-building materials difficult to obtain. Evolution has allowed shellfish to exist in these areas and, given enough time and a slow enough rate of change, evolution may again help these animals survive in our acidifying oceans."

This research was funded by the Natural Environment Research Council.

Notes:

• Marine invertebrate skeleton size varies with latitude, temperature, and carbonate saturation: implications for global change and ocean acidification by Watson, S-A, Peck, LS, Tyler, PA, Southgate, PC Tan, KS, Day, RW & Morley, SA (2012) is published in Global Change Biology
• Four types of marine species were collected by scuba divers working at 12 shore-based research stations from Svalbard in the Arctic through tropical sites in Singapore and Australia and BAS Rothera Research Station in the Antarctic.
• Specimens were measured in local laboratories at these sites and the composition of shells skeleton were analysed in laboratories in the UK.
• British Antarctic Survey (BAS), a component of the Natural Environment Research Council, delivers and enables world-leading interdisciplinary research in the Polar Regions. Its skilled science and support staff based in Cambridge, Antarctica and the Arctic, work together to deliver research that uses the Polar Regions to advance our understanding of Earth as a sustainable planet. Through its extensive logistic capability and know-how BAS facilitates access for the British and international science community to the UK polar research operation. Numerous national and international collaborations, combined with an excellent infrastructure help sustain a world leading position for the UK in Antarctic affairs.
• The National Oceanography Centre, Southampton is the integrated collaboration between the Southampton-based part of the Natural Environment Research Council's National Oceanography Centre and Ocean and Earth Science at the University of Southampton.
• The Natural Environment Research Council (NERC) is the UK's main agency for funding and managing world-class research, training and knowledge exchange in the environmental sciences. It coordinates some of the world's most exciting research projects, tackling major issues such as climate change, environmental influences on human health, the genetic make-up of life on earth, and much more. NERC receives around £320 million a year from the government's science budget, which it uses to fund independent research and training in universities and its own research centres.

Contact: Athena Dinar
amdi@bas.ac.uk
44-012-232-21414
British Antarctic Survey

 

 

Out of Europe

Researchers look at the spread of dysentery from Europe to industrializing countries

Researchers have found that a bacterium that emerged centuries ago in Europe has now been spreading globally into countries undergoing rapid development and industrialization. Unlike other diarrheal diseases, this one is unlikely to be resolved by providing access to clean water. As developing countries become more industrialized the numbers of infections with dysentery-causing Shigella flexneri are known to decline, associated with improved health, lifestyle and perhaps most importantly access to clean water, but the incidence of another form of the dysentery-causing bacterium, Shigella sonnei, actually increases.

The team pinpointed that S. sonnei was first established in Europe just a few centuries ago, but in the last few decades has spread to the rest of the world. They also found that a key factor in the spread of this pathogen was a rise in multidrug resistance - the ability to survive exposure to a wide array of antibiotics. Because S. sonnei is easily transmitted and has high levels of drug resistance, the researchers suggest that drug treatment and better sanitation alone will not be sufficient for controlling the disease. Vaccine development will be crucial.

Dysentery is a disease primarily associated with developing countries and more than one million people, mostly young children, are estimated to die from dysentery caused by Shigella each year. Whilst most people have heard about dysentery, few know about the bacteria that causes it, Shigella. This is because it is relatively understudied and little is known about their population structure or its origins. Traditionally, S. flexneri has been the most common form of Shigella bacterium to cause dysentery in developing countries with S. sonnei more prevalent in industrialized countries. Yet, this is beginning to change with S. sonnei becoming increasingly common as developing countries rapidly industrialize.

"Although S. sonnei is a relatively new species of bacterium, during its spread it has diversified into an array of different distinguishable clones or strains found right across the world," says Dr Kathryn Holt, first author from the University of Melbourne. "This is hard to see using traditional methods, but by sequencing the genomes of over 100 different forms of the bacteria, we were able to get a glimpse into its past and really start to understand how it is evolving and moving around the world."

"We compared the S. sonnei family tree and geographical locations of the different strains to determine when and where this bacterium first emerged and why it has become such a problem in industrialized countries with increasing access to clean water. Traditionally we associate dysentery with contaminated water and lack of industrialization."

To investigate why the bacterium was spreading so effectively, the team looked at the S. sonnei's genetic evolution and found that only a few types of genes were selectively evolving over time, particularly those involved with drug resistance. This suggests that a major driver in the spread of this bacterium was its apparent ability to become resistant to drug treatment.

"Since S. sonnei originated, we found there have been three, independent, yet closely related lineages that have spread. The two most recent lineages have been continually evolving to become increasingly resistant to antimicrobials," says Dr Stephen Baker, a senior author from the Oxford University Clinical Research Unit in Vietnam. "Our data is consistent with antibiotic resistance as being a main driver of the spread and persistence of S.sonnei around the world, stressing that antibiotics are not a long-term solution for the elimination of this global health problem."

Despite the fact S. sonnei and S. flexneri are closely related they have very different surface antigens or coats that interact with the human immune system. S. sonnei has only one type of outer coat, while S. flexneri has many, all of which look very different from that of S. sonnei. It has been speculated for some time that S. sonnei acquired its outer coat from another bacterium that is commonly found in contaminated water, Plesiomonas shigelloides.

Both S. sonnei and P. shigelloides have an identical outer coat. It is believed that when a person is exposed to contaminated water containing P. shigelloides, there is an immune cross reaction and the body builds a natural immunity against S. sonnei. This theory may explain why the incidence of S. sonnei increases following economic development and improvements to water quality, and is consistent with the patterns of global spread described in the current report.

"One of the Millennium Development Goals is to improve drinking water and reduce water borne diseases, an undeniably important aim," says Professor Nicholas Thomson, lead author from the Wellcome Trust Sanger Institute. "This may have the unforeseen result of increasing the incidence of S. sonnei dysentery in transitional countries.

"Our research emphasises the importance of a vaccine against Shigella. The combination of increased incidence and antibiotic resistance of S. sonnei, means that a vaccine will be increasingly important for the long-term control and prevention of dysentery."

Publication Details:

• Kathryn E. Holt, Stephen Baker, François-Xavier Weill, Edward C. Holmes, Andrew Kitchen, Jun Yu, Vartul Sangal, Derek J. Brown, John E. Coia, Dong Wook Kim, Seon Young Choi, Su Hee Kim, Wanderley D. da Silveir, Derek J. Pickard, Jeremy J. Farrar, Julian Parkhill, Gordon Dougan, Nicholas R. Thomson
• 'Out of Europe: The recent global dissemination of Shigella sonnei'
  Published in Nature Genetics online on August 5 2012 DOI: XX XX

Funding:

This work was supported by the Wellcome Trust and a Victorian Life Sciences Computation Initiative (VLSCI) grant on its Peak Computing Facility at the University of Melbourne, an initiative of the Victorian Government,

Participating Centres:

• University of Melbourne, Department of Microbiology and Immunology, Royal Parade, Melbourne, Victoria, 3010, Australia
• The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam
• Institut Pasteur, Unité des Bactéries Pathogènes Entériques, Paris, France
• Center for Infectious Disease Dynamics, Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA
• Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA
• Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
• Scottish Salmonella, Shigella and Clostridium difficile Reference Laboratory, Stobhill Hospital, 133 Balornock Road, Glasgow, UK
• Molecular Biology Laboratory, International Vaccine Institute (IVI), Seoul, Republic of Korea
• Department of Pharmacy, College of Pharmacy, Hanyang University
• Ansan, Kyeonggi- do, 426-791, KoreaDepartment of Genetics, Evolution and Bioagents, Biology Institute, Campinas State
• University – UNICAMP, BrazilWellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK CB10 1SA

Links:

• Oxford University's Medical Sciences Division is one of the largest biomedical research centres in Europe, with over 2,500 people involved in research and more than 2,800 students. The University is rated the best in the world for medicine, and it is home to the UK's top-ranked medical school. From the genetic and molecular basis of disease to the latest advances in neuroscience, Oxford is at the forefront of medical research. It has one of the largest clinical trial portfolios in the UK and great expertise in taking discoveries from the lab into the clinic. Partnerships with the local NHS Trusts enable patients to benefit from close links between medical research and healthcare delivery. A great strength of Oxford medicine is its long-standing network of clinical research units in Asia and Africa, enabling world-leading research on the most pressing global health challenges such as malaria, TB, HIV/AIDS and flu. Oxford is also renowned for its large-scale studies which examine the role of factors such as smoking, alcohol and diet on cancer, heart disease and other conditions. 
• The Wellcome Trust Sanger Institute is one of the world's leading genome centres. Through its ability to conduct research at scale, it is able to engage in bold and long-term exploratory projects that are designed to influence and empower medical science globally. Institute research findings, generated through its own research programmes and through its leading role in international consortia, are being used to develop new diagnostics and treatments for human disease. 
• The Wellcome Trust is a global charitable foundation dedicated to achieving extraordinary improvements in human and animal health. We support the brightest minds in biomedical research and the medical humanities. Our breadth of support includes public engagement, education and the application of research to improve health. We are independent of both political and commercial interests. 

Contact: Aileen Sheehy
press.office@sanger.ac.uk
44-012-234-96928
Wellcome Trust Sanger Institute