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.
A recent study led by Professor Tracy Palmer at the University of Dundee discovered a new way by which bacteria can insert proteins into membranes, using two different transport machines. Here she gives us the lowdown on what it’s all about…
All cells are surrounded by lipid membranes; they keep the insides in, and the outsides out, but sometimes bacteria need to bring a molecule from the environment into the cell, or vice versa. The membrane itself is pretty much impermeable, so the cell uses specialised proteins to make channels in the membrane so they can control what moves from one side to the other.
Imaging technologies have come a long way since the invention of the microscope 400 or so years ago. Now we can look at the circulatory system in a developing chicken embryo or the hair cells on a terrapin’s inner ear, but there’s one very familiar place that remains a mystery: the inside of a plant pot.
There’s a good reason why it would be great to have a peek into the peat – to learn what’s going on between the plant roots and soil-dwelling microbes in situ (something we’ve written about before). These interactions are environmentally and economically important, and many have been intensely studied. The symbiosis between rhizobia and plant roots allows nitrogen fixing, and many pathogens, such as fungi of the genus Phytophthora, use roots as a route into a plant.
So what’s stopping us looking at the roots? The answer’s fairly obvious: you can’t see through soil. You can overcome this hurdle by using non-optical imaging techniques such as MRI to look at root structures, much as you can use them to see inside your head – but they can’t pick up light emitted by fluorescent proteins, for example.
I read a short paper this week that is making early inroads into another option: make soil see-through. Well, not soil precisely, but lumps of Nafion – a polymer invented in the 1960s that’s used in fuel cells. By grinding the Nafion down, researchers in Scotland have made it into particles similar to those found in soil.
Nafion isn’t normally see-through, but it has a refractive index very close to that of water. What that means in practice is that when you add water, the polymer disappears (this video shows something similar).
The Nafion particles that have been produced aren’t totally identical to soil, but they’ve been altered to have similar water and nutrient availability. It seems to work: plant growth in the transparent soil is comparable to growth in the real thing.
The researchers have already visualised GFP-labelled E. coli O157:H7 colonising the roots of lettuce seedlings. This bacterium, which is an important human pathogen, can grow quite happily on salad vegetables. The above picture is from the paper, showing the fluorescent E. coli on the lettuce roots.
This demonstrates how useful this technology could become. Although the authors concede that it’s not perfect for every type of plant–microbe interaction, there’s so much we don’t know about life in the loam that any insights we can get should advance both plant science and microbiology significantly.
Downie H, Holden N, Otten W, Spiers AJ, Valentine TA, & Dupuy LX (2012). Transparent soil for imaging the rhizosphere. PloS one, 7 (9) PMID: 22984484
Image Credit: PLOS ONE
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.
The hepatitis B virus (HBV) causes potentially life-threatening diseases, including cirrhosis and liver cancer. The virus is transmitted by bodily fluids and is thought to infect around two billion people, causing approximately 600 000 deaths a year.
HBV has at least ten genotypes. Each genotype, which refers to the arrangement of genetic material in a virus, is divided into multiple subgenotypes, each localised to a particular area or population.
In Korea, where HBV infection is endemic, most viruses isolated are from the C2 (HBV/C2) genotype. The big question is, ‘Where did HBV/C2 come from?’ Now, remarkably, a 16th-century mummy is helping scientists solve the mystery.
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.