Archive for the ‘Ecology and Environment’ Category
Recently, I found a paper published in mBIO that describes how antibiotic use in farming is involved in the spread of resistance genes. In this case the work focuses on the humble honeybee (Apis mellifera). Since the 1950s, beekeepers in the USA have been using the antibiotic oxytetracycline – a ‘broad-spectrum’ antibiotic that kills most species of bacteria – to prevent infections that can cause ‘foul brood’, a disease that kills bee larvae. As you can imagine, using a single antibiotic for more than 50 years has led to some selective pressure. In this work, researchers from Yale University were investigating the prevalence of disease resistance in bee gut bacteria.
This might seem like a strange place to look, but it actually has its advantages. Unlike the supremely complex ecosystem of the human gut microbiome, the bee’s is pretty simple, with eight species making up over 95% of the gut bacteria in adult worker bees. The small number of species and the knowledge of how hives have been treated allowed the researchers to monitor the impact of decades of antibiotic use.
Sometimes you find a paper with a title so intriguing you just have to find out a little more about it. Recently, I came across a paper about ‘entombed pigs’, so how could I possibly ignore it? I learned a fair bit about animal-disease control methods in Asia and the use of quicklime to decompose corpses , a fairly standard weekend for me.
The work centres on foot-and-mouth disease (FMD), a viral infection of hoofed animals caused by Aphthovirus. It causes significant suffering in animals and has serious economic consequences: a 2001 outbreak is estimated to have cost the UK £8 billion.
Millions of infected animals were culled in South Korea in 2010/11, then buried (rather than burnt, as they are in the UK). The slaughtered animals were placed in five-metre-deep pits and covered with quicklime and copious amounts of soil to prevent the FMD spreading. Problem solved? Well, perhaps not.
It’s tempting to think of amoebae as the single, fried-egg-shaped animal cells we learned about in biology at school – and when there’s plenty of food around, that’s pretty much right. But what happens when the food runs out? For the soil-dwelling Dictyostelium discoideum, things get a little weird.
These amoebae usually feed on bacteria and live quite happily as individual cells when food is plentiful. However, when there’s no bacteria around, the amoebae stick together, or ‘aggregate’, to form slug-like super colonies.
The job of these 4 mm ‘slugs’ is to migrate to a good spot, where they transform again, this time into fruiting bodies – tiny hand grenades filled with spore-like cells – that burst, transporting future amoebae to areas where more food is present, starting the cycle all over again.
Biofilms get a pretty bad rep, and rightly so. Colloquially known as ‘slime’, these sticky scaffolds of polysaccharides, proteins and DNA are produced by colonies of bacteria and let them cling to wet surfaces, whether those are crustacean shells, water pipes or artificial cardiac valves.
Bacteria within biofilms are difficult to kill, which makes them a real problem in hospitals. The bacterial colonies are often more resistant to antibiotics than their free-living relatives, perhaps because the biofilm cocoons the bacteria in the centre and prevents drugs from reaching them. Biofilms are also tricky to remove by cleaning and are impervious to many detergents. Once they’re there, you’re kind of stuck with them, if you’ll excuse the pun.
But what if we could harness the adhesive power of biofilms for good? Could we use them to deliver useful molecules or drugs? A group of researchers is working on that very problem, right now.
Poor old Vibrio vulnificus, it just can’t catch a break. This Gram-negative marine bacterium (and occasional human pathogen) is the first species found to be infected by both a virus and a predatory bacterium.
Let’s step back a moment and look at the smaller picture. Just like humans, bacteria are regularly infected by viruses. These viruses are known as bacteriophages, and they are the most abundant and diverse organisms on Earth: nobody really knows how many exist, but estimates suggest that there might be as many as 1031 on the planet (that’s more viruses than there are stars in the universe). Sometimes, after infection, the viruses integrate their genetic material into the host bacterial chromosome but remain dormant; other times, they force the bacteria to make multiple copies of themselves until the host cell can’t take any more and explodes.
Like bacteria, viruses have existed for millions of years, yet even after all this time we still don’t really know when or how they evolved. Viruses are grouped into families based on their genome, which can be either DNA or RNA.
Like all other organisms on Earth, viruses evolve, and they mix their genomes with each other in the environment to form new strains – which is why new flu strains appear each year. It was thought that viruses only mixed with others of the same family or with their close relatives, but researchers have discovered a new virus that seems to be a bit of a rule-breaker…
This virus, provisionally named BSL RDHV (Boiling Springs Lake RNA–DNA hybrid virus), is unusual because it seems to be a mix of both DNA and RNA viruses. A typical virus consists of genetic material (DNA or RNA) surrounded by a protein shell; the genetic material in this newly discovered virus is DNA, yet its shell contains a protein similar to those found in RNA viruses.
Through an unusual recombination event, the DNA virus seems to have picked up a gene from an RNA virus. Whereas DNA–DNA and RNA–RNA recombinations are well understood, we don’t understand how DNA–RNA recombinations work.
The new virus was discovered by researchers in the acidic Boiling Springs Lake at Lassen Volcanic National Park, USA. The researchers collected and analysed samples of DNA from the lake’s sediment, identifying the virus and its unusual RNA-derived gene. This technique, known as metagenomics, allows scientists to investigate genetic material from environmental microorganisms directly, instead of first growing them in the lab.
This new discovery is an important step in understanding virus evolution: it seems likely that RNA viruses evolutionarily preceded DNA viruses, so the authors speculate that the incorporation of RNA genes by DNA viruses might help to explain this branch of evolution.
Sruthi is a freelance science writer
Diemer, G., & Stedman, K. (2012). A novel virus genome discovered in an extreme environment suggests recombination between unrelated groups of RNA and DNA viruses Biology Direct, 7 (1) DOI: 10.1186/1745-6150-7-13
Image Credit: Dave Faris on Flickr
Last year, I was lucky enough to visit the Wellcome Collection’s Dirt exhibition, which featured several microbiology treasures. Among other objects, I saw an original van Leeuwenhoek microscope and a first edition of Robert Hooke’s Micrografia. I also had the chance to get close to an original copy of John Snow’s cholera map.
Snow, who is commonly considered to be the father of modern epidemiology, is most famous for identifying where cases of cholera were occurring during an epidemic in London in 1854. This allowed him to trace the source of the outbreak – a contaminated water pump on Broad Street.
Today, very few cases of cholera are reported in the UK; however, it is endemic in many other countries and resulted in more than 100 000 deaths in 2010. It is caused by the bacterium Vibrio cholerae, which produces toxins in the small intestine of an infected person, causing them – if untreated – to produce more than ten litres of diarrhoea a day. Death comes as a result of dehydration.
As shown by Snow in 1854, people get the disease through drinking contaminated water. This is a real problem in much of the world, where clean drinking water is not accessible for local populations.