Modern society seems to have gone germophobic—say the word "bacteria" and most people will immediately conjure images of nasty illnesses and dangerous infections. But bacteria, fungi and other microbes underpin some of the most fundamental cycles of life and death on this planet. What's more, all kinds of beneficial microbes can be used to construct self-repairing buildings, to power batteries, to solve murder investigations and even to fight off deadly diseases.
In short, microbes are amazing, and here are just some of the ones that deserve to be celebrated:
Plants and animals require nitrogen to build the proteins and amino acids that are fundamental to biology. While nitrogen makes up almost 80 percent of our atmosphere, nitrogen gas is inert and cannot be used by most living organisms. It needs to be converted into fixed compounds, such as nitrates, nitrites and ammonia. The principal players in this biological process are free-living bacteria in the soil and bacterial species, such as Rhizobium, that live in symbiotic relationships with plants. These bacteria build nitrogen-fixing root nodules on leguminous plants like peas, beans and clover. Once the nitrogen has been fixed, it is available to build plant proteins, which are then eaten by animals and converted into animal proteins. Without these bacteria, life as we know it would not exist on Earth.
Many types of microbial decomposers break down plants and animals after their demise—including, of course, our own corpses. Bacteria such as Firmicutes and Proteobacteria are specifically associated with animal decomposition, but scientists believe that there are many more decomposers yet to be identified and described. “It is probably not just a key bacteria species or even two, but many species that work together to recycle the nutrients and energy of a decomposing body,” says Eric Benbow of Michigan State University´s department of entomology.
Finding Out Whodunit
Microbe communities living on people can have subtle differences, such as which particular species are present, in what numbers and on which parts of the body. That means humans can leave behind a trail of bacterial "fingerprints" that could potentially link a specific person to an object—such as a murder weapon. Teams at Michigan State and Texas A&M Universities are now researching how this might be applied to crime investigations in the future. According to Jeffery Tomberlin of Texas A&M, communities of bacteria may also have the potential to reveal how long someone has been dead, whether a body has been moved and where individuals have been prior to or near the time of death.
In 1928, Alexander Fleming observed that the fungus Penicillium was inhibiting the growth of Staphylococcus bacteria in petri dishes in his laboratory. In one of science´s great "Eureka!" moments, he realised the fungus had therapeutic potential, and penicillin quickly became a hospital standard. Other antibiotics that are produced from fungi include Vancomycin, first isolated in 1952 from a soil sample from Borneo, and a new antibiotic known as Teixobactin, identified in soil from Maine, which was described by a team from Northeastern University earlier this year.
Sweet New Meds
In 2005, Alejandra Vásquez and Tobias Olofsson from Lund University in Sweden identified 13 beneficial bacteria in wild honey that protect bees against pathogens. The health-giving properties of honey have been exploited by folk medicine for thousands of years, but now that scientists know the specific microbes responsible, they can develop medicines based on bee bacteria. According to Vásquez, the bacteria work together to defend their hosts by producing hundreds of antimicrobial substances. “They could become one of the best natural alternatives to antibiotics we may have in the future,” she says.
Our guts are a veritable battlefield of microbial good and evil, and each year people guzzle gallons of yogurts and drinks packed with probiotics, such as varieties of Lactobacillus, to boost the numbers of good bacteria, beat the bad, aid digestion and give other health benefits. Some probiotics can also reduce the symptoms of ulcerative colitis, a disease with an as-yet unknown cause that produces inflammation and ulcers in the colon and rectum. The Lactobacillus reuteri in human breast milk has an anti-gas effect on colicky infants, according to a study from the University of Bologna. And without the curdling effects of related healthy bacteria such as Lactococcus lactis, we wouldn´t have dairy products to enjoy with a glass of fine wine—imagine a world without Brie or Camembert.
In the lab, bacteria are increasingly used in biotechnology to manufacture large amounts of proteins. For instance, recombinant DNA technology takes fragments of human DNA that code for specific proteins and inserts them into bacteria. The individual cells then multiply exponentially, creating a colony of clones that can pump out the desired protein. Synthetic human insulin (molecular structure seen above) used by diabetics is one of the most common products of this technology.
Researchers at Stanford University have created a laboratory prototype of a battery that generates electricity from sewage using naturally occurring microbes as mini power plants—the "wired" microbes produce electricity as they digest plant and animal waste, and the team is hoping to develop the technology for commercial use in sewage treatment plants. A second Stanford team is working on ways to produce methane gas by feeding microbial colonies carbon dioxide from the atmosphere. According to team member Mark Swartz, the goal is “to create large-scale methanogen factories that produce renewable methane as an alternative to natural gas.” Meanwhile, scientists at Penn State University have produced Microbial Fuel Cells (MFCs), which use bacteria to convert organic matter to electricity.
Flying on Fungi
Fungus can also be used to produce biofuels. For example, in May a team at Washington State University published a paper describing how to make jet fuel from a common black fungus found in decaying leaves, soil and rotting fruit. When Aspergillus carbonarius fungi were fed a diet of oatmeal, wheat straw and leftovers from corn production, they formed hydrocarbons similar to those used in aviation fuels. The researchers believe that economically viable aviation biofuels could be produced in the next five years.
Researchers from Delft University of Technology in The Netherlands are making concrete with limestone-secreting bacteria, which cause the concrete to self-repair when it cracks. The bacteria are incorporated into the material in the form of dormant spores, and they wake up when water enters via cracks. The rehydrated microbes convert calcium lactate in the concrete mixture into limestone, which then seals the cracks and makes the concrete waterproof again. According to study leader Henk Jonkers, this reduces maintenance and repair costs, prolongs the life of construction projects and protects the embedded steel reinforcements from corrosion.
Our Alien Ancestors?
At the end of H-G Wells’ classic novel The War of the Worlds, humanity is saved when the invading Martians are wiped out by their lack of immunity to simple earthly bacteria. But could bacteria themselves have extraterrestrial origins? Bacterial spores can remain dormant for extraordinary lengths of time, and some microbe species can thrive in very harsh environments, like the methanogens seen here that live without any oxygen. This has led some to speculate that these extreme life-forms could survive in space. Proponents of the panspermia hypothesis even think that life on Earth began when alien spores, carried by impacting asteroids or comets, landed on our young planet.