Recently, I saw an interesting story about bacteria called clostridia and how they might relate to peanut allergies. It seems that food allergies are on the rise in developing countries, which totally fits with my own experience. Growing up in the 1980s, I don't think I knew anybody with a serious food allergy, but I can think of a bunch of people I know now that have kids who are allergic - some severely - to various foods. What's the deal? Well, it's unexpected: a new report in PNAS by Stefka et al. suggests that clostridia might have something to do with these allergies. The researchers took some mice treated with antibiotics and compared their food sensitivity to mice that had not been exposed to antibiotics. The antibiotic-treated mice showed more sensitivity to food than untreated mice. They found that the clostridia helped the mouse's intestines keep proteins out of the blood that would otherwise cause immune reactions (allergies). So our obsession with antibiotics to cure disease (which alone is not a bad thing) might just have contributed to a rise in food allergies, because we've been killing off helpful bacteria along with the bad stuff! It sounds like we need a better strategy for coping with disease-causing bacteria. Doesn't that make sense from a design standpoint? God designed us to live with our bacteria, and when we take medicine that indiscriminately kills all bacteria (good and bad), we should expect negative consequences.
I also got an email from a reader who was interested in rhizobial symbiosis. Rhizobia are bacteria that form close relationships with legumes, like peas or clover. Rhizobia are immensely important for life on this planet because they make nitrogen available to the rest of us. Nitrogen is a colorless gas that makes up about 3/4ths of the air you breathe, but it's an extremely stable gas and very hard to use. Rhizobia are able to take that atmospheric nitrogen and make it available to the rest of us. Why is that important? Because every living thing on this planet needs nitrogen. Nitrogen is part of our proteins, which is what makes are cells do their thing. Without proteins, we couldn't live, and without nitrogen, we couldn't make proteins. See how important rhizobia are?
Now the fun thing about rhizobia and their plant symbiosis is that the bacteria seem to be able to move around from one species to another. Naively, we might expect that the rhizobia collected from a closely-related group of legume species would be closely-related themselves. That's not always the case, though. Rhizobial genomes actually contain a number of different elements that allow symbiosis genes and nitrogen-fixing genes to move around. This allows for the bacteria to share genes with other rhizobia, a process called horizontal transfer. So that boils down to this: Just about any rhizobia can form a relationship with just about any legume, provided the symbiosis genes are available from somewhere (like another rhizobia living with that legume species). It's an amazing design. It's almost like God wanted to make sure that no matter what changed in the world, there would always be nitrogen-fixing bacteria. Read all about it in Roberts's PLoS Biology paper.
One final article came from another reader interested in anthrax. Some of you might remember the anthrax letters that killed five people back in 2001. Anthrax is a nasty bacterium that infects via inhalation and quickly spreads through the body, dumping toxins everywhere and killing the host extremely quickly. Basically, if you're infected with anthrax, by the time you realize it's not just the flu, it's probably too late. Anthrax bacteria are remarkably similar to other soil bacteria, which raises an interesting question: What's anthrax doing when it's not killing people? A new paper from Ganz et al. in PLoS Neglected Tropical Diseases reports that grass grown in plots where anthrax is present in the soil was 45% taller than grass grown in control plots without anthrax. Wild! You could interpret that as an adaptation to attract a mammalian host, because cows and sheep will go for the taller grass, which increases the likelihood that they'll acquire an anthrax infection. But I just find it fascinating that anthrax is capable of doing something other than killing us. It doesn't explain everything about anthrax, but it's really interesting anyway.
So that's all for symbiosis this week. Isn't God's design amazing? Makes me glad to be a scientist.
Read all about these studies here:
Stefka et al. 2014. Commensal bacteria protect against food allergen sensitization. PNAS 111: 13145-13150.
Roberts. 2014. Symbiosis Plasmids Bring Their Own Mutagen to the Wedding Party. PLoS Biology 12(9): e1001943.
Ganz et al. 2014. Interactions between Bacillus anthracis and Plants May Promote Anthrax Transmission. PLoS Neglected Tropical Diseases 8(6): e2903.
Feedback? Email me at toddcharleswood [at] gmail [dot] com.