Wie Bakterien funktionieren

Von dem Sauerstoff, den wir einatmen, bis hin zu den Nährstoffen, die unser Magen aus der Nahrung zieht, haben wir es Bakterien zu verdanken, dass wir auf diesem Planeten gedeihen. In unserem Körper sind Mikroorganismen, einschließlich Bakterien, 10 zu 1 zahlreicher als unsere eigenen menschlichen Zellen, was uns zu mehr Mikroben als Menschen macht [Quelle: Savage ].

Wir haben erst vor kurzem begonnen, diese mikroskopisch kleinen Organismen und ihre Auswirkungen auf unseren Planeten und unsere Gesundheit vollständig zu verstehen, aber die Geschichte legt nahe, dass unsere Vorfahren vor Jahrhunderten die Kraft von Bakterien nutzten, um Lebensmittel und Getränke zu fermentieren ( Bier und Brot, irgendjemand?).

Erst im 17. Jahrhundert begannen wir, Bakterien an einem ebenso nahen und persönlichen Ort aus nächster Nähe zu betrachten – dem menschlichen Mund. Der stets neugierige Anton van Leeuwenhoek entdeckte Bakterien, als er eine Probe der Plaque zwischen seinen eigenen Zähnen untersuchte. Er wird in seinem Schreiben poetisch und beschreibt die Bakterienkolonie auf seinem Perlmuttweiß als „eine kleine weiße Substanz, die so dick ist, als wäre es ein Teig“ [Quelle: Dobell ]. Nachdem er die Probe unter ein zusammengesetztes Mikroskop gelegt hatte, sah van Leeuwenhoek, dass sich die Mikroben bewegten. Es lebt!

Bakterien waren in der Tat bahnbrechend für die Erde und spielten eine Schlüsselrolle bei der Schaffung atembarer Luft und des biologisch reichen Planeten, den wir Heimat nennen.

In diesem Artikel geben wir Ihnen einen Überblick über diese winzigen, aber einflussreichen Mikroorganismen. Wir werden uns die guten, die schlechten und die völlig bizarren Arten ansehen, wie Bakterien die Menschheitsgeschichte und unsere Umwelt geprägt haben. Zu Beginn geben wir Ihnen einen Überblick darüber, was Bakterien von anderen Lebensformen unterscheidet.

1. Bakterien Grundlagen
2. Mikrobielle Mahlzeiten (und Miasma)
3. Eine große Familie
4. Bakterielle Reproduktion
5. Ist kein Berg hoch, ist kein Tal niedrig
6. Das Böse (für uns)
7. Bakterien als Helden

Wenn ein einzelnes Bakterium mit bloßem Auge nicht sichtbar ist, wie können wir dann so viel darüber wissen?

Wissenschaftler haben leistungsstarke Mikroskope entwickelt , um Bakterien zu vergrößern – normalerweise mit einer Länge von einem bis zu einer Handvoll Mikrometer (ein Millionstel Meter), die uns einen Einblick in ihr Innenleben geben und wie sie sich im Vergleich zu anderen Lebensformen wie Pflanzen und Tieren verhalten , Viren und Pilze.

Wie Sie vielleicht bereits wissen, sind Zellen die Bausteine ​​des Lebens, egal ob sie unser eigenes Gewebe oder einen Ast vor Ihrem Fenster bilden. Menschen, Tiere und Pflanzen haben Zellen mit genetischen Informationen, die in einer Art Membran namens Zellkern enthalten sind . Diese Zelltypen, die als eukaryotische Zellen bezeichnet werden , haben spezialisierte Organellen, von denen jede eine einzigartige Aufgabe hat, die Zelle funktionsfähig und gesund zu halten.

Bakterien haben jedoch keinen Zellkern, und ihr genetisches Material oder die DNA schwimmt frei in der Zelle. Diese mikroskopisch kleinen Zellen haben keine Organellen und verfügen über verschiedene Methoden, um genetisches Material zu reproduzieren und auszutauschen. Bakterien werden als prokaryotische Zellen klassifiziert .

Abgesehen von grundlegenden Kategorien ordnen Wissenschaftler Bakterien auch in verschiedene Lager ein, basierend auf:

Die Mikrobiologie – die Untersuchung aller verschiedenen Arten von Mikroben, einschließlich Bakterien, Archaeen, Pilzen, Viren und Protozoen – hat einen wachsenden Wissensschatz genutzt, um Bakterien weiter von ihren mikrobiellen Brüdern zu unterscheiden.

Ähnliche prokaryotische Organismen, die jetzt in der Domäne Archaea klassifiziert sind, wurden zuvor mit Bakterien zusammengeballt, aber nachdem Forscher mehr über sie erfahren hatten, gaben sie Mikroben in Archaea eine eigene Kategorie für ihre Ähnlichkeiten mit eukaryotischen Zellen.

Wie Menschen, Pflanzen und Tiere brauchen Bakterien Nahrung, um zu überleben.

Some bacteria are autotrophs, meaning they use basic inputs such as sunlight, water and chemicals from the environment to create food (think cyanobacteria, which have been turning sunlight into oxygen for roughly 2.5 million years) [source: Konhauser et al.]. Other bacteria are what researchers call heterotrophs because they draw energy from existing organic matter for food (think dead leaves on the forest floor).

The truth is, what might be appetizing to bacteria is probably repulsive to us. They've evolved to thrive on all sorts of things, from oil spills and nuclear byproducts to human waste and decaying matter.

But bacteria's penchant for a particular food source can benefit society. For instance, art experts in Italy turned to bacteria to chow down on excess layers of salt and glue threatening the longevity of priceless artwork [source: Asociación RUVID]. Bacteria's knack for recycling organic matter also comes in handy, especially considering their tremendous role as recyclers of the Earth's surface — both in soil and water.

On a daily basis, you might be all too familiar with the odor-inducing effects of hungry bacteria from that funky smell in your trashcan while they take on your leftovers, breaking them down and releasing their own gaseous by-products. It doesn't stop there, though. You also have bacteria to blame for those nature-calling moments (yes, flatulence), when bacteria in your gut release foul-smelling methane during digestion.

Bacteria grow and form colonies when given the chance. If food and environmental conditions are favorable, they'll reproduce and form sticky aggregations called biofilms to survive on a variety of surfaces, from rocks in a stream to molars in your mouth.

Biofilms have their perks and problems. On one hand, they're mutually benefiting players in nature. On the other hand, they can be a serious threat. For instance, doctors treating patients with medical implants and devices are especially concerned about biofilms because these surfaces are prime real estate for bacteria. Once colonized, biofilms can produce byproducts that are toxic — and even deadly — to the human body.

Like people in cities, cells in biofilms communicate with one another by sending messages to share information about food availability and potential dangers. But rather than calling their neighbors on the phone, bacteria send memos via chemicals to their nearby friends.

But bacteria aren't afraid to fly solo, either. In fact, some species have developed ways to stick around through rough conditions. When no food is left or conditions take a turn for the worse, these bacteria preserve themselves by creating a tough shell called an endospore, putting the cell in a dormant state that preserves the bacteria's genetic material [source: Cornell University Department of Microbiology].

One scientist even found bacteria in a time capsule that was uncovered and examined 100 years later, while other groups of scientists discovered bacteria dating back to 250 million years ago [sources: Silverman; Vreeland et al.]. This all goes to show that bacteria can self-preserve for a long time.

Now that we know bacteria are colonizers given the opportunity, let's take a look at how they get there through division and reproduction.

How do bacteria create colonies in the first place?

Bacteria, like other forms of life on Earth, need to make copies of themselves to survive. While humans and other organisms do this through sexual reproduction , it works a bit differently with bacteria.

But first, we'll discuss why diversity is a good thing.

Life undergoes natural selection , or selective forces in a given environment that allow one type to thrive and reproduce more. As you might recall from biology class, genes are the units that instruct a cell what to do — whether to make your hair color brown or blonde or your eyes green or blue. You get genes from both of your parents that provide a good mix. In addition, sexual reproduction gives rise to mutations, or random changes in the DNA, which creates diversity. The more genetic diversity from which to draw, the more likely an organism can adapt to constraints in an environment.

For bacteria, reproduction isn't a matter of meeting the right microbe and settling down; it's simply replicating its own DNA and dividing into two identical cells. This process, called binary fission, occurs when a single bacterium cleaves itself into two after it replicates its DNA and moves the genetic material into opposite ends of the cell.

Because the resulting cell is genetically identical to the one it came from, this method of reproduction isn't exactly the best way to create a diverse gene pool .

So how do bacteria get new genes?

It turns out bacteria employ tricks to get the job done, with the end result being horizontal gene transfer, or exchanging genetic material without reproducing. There are a few ways bacteria can do this. One method involves picking up genetic material from the environment outside the cell, relying on other microbes and bacteria (through molecules called plasmids). Another results from viruses that use bacteria as hosts. Upon infecting new bacteria, the viruses incidentally leave genetic material of previous bacteria in the new one [source: Marraffini ].

Swapping genetic material gives bacteria the flexibility to adapt — and some do, once they sense stressful changes in the environment such as food shortages or chemical changes.

Developing a better understanding of how bacteria adapt is tremendously important for understanding and combatting bacteria's resistance to antibiotics in medicine. Bacteria can exchange genetic material so frequently that treatments that previously worked likely won't next time.

Now that we've taken a close look at how bacteria work at a microscopic level, let's take a step back to see where you find them in the big picture.

The question isn't, "Where are bacteria?" but rather, "Where aren't bacteria?"

They're found virtually everywhere on Earth. It's impossible to have a full grasp of the number of bacteria on the planet at one time, but some estimates point to some 5 octillion microbes such as bacteria and archaea – that's 10 to the 28th power! [source: Whitman et al.]

Pinning a number on how many species, or classifiable types, of bacteria there are also remains difficult. One estimate points to approximately 30,000 formally identified species, but scientists are constantly learning and adding to their knowledge base and think we haven't scratched the surface for the true number of species out there [source: Dykhuizen].

The truth is that bacteria have been around for a long, long time. In fact, they gave rise to some of the earliest known fossils , dating back 3.5 billion years [source: University of California Museum of Paleontology]. Scientific evidence suggests cyanobacteria began creating oxygen between 2.5 and 2.3 billion years ago in the world's oceans, which gave rise to the Earth's atmosphere and abundant oxygen for us to breathe [source: Konhauser et al.].

Bacteria can survive in air, water, soil, ice and extreme heat; on plants; and even in our intestines, on our skin and on the skin of other animals.

Some bacteria are extremophiles , which means they can withstand extreme environments that are either very hot or cold or that lack the nutrients and chemicals we typically associate with life. Researchers have uncovered bacteria in the Mariana Trench , the deepest spot on Earth under the Pacific Ocean, in addition to underwater heated vents and in ice.

But the fun extends beyond the researchers in the field. Tourists are fascinated with bacteria's more beautiful natural beauty in places like Opalescent Pool at Yellowstone National Park, which features brightly colored thermophilic (heat-loving) bacteria coloring the landmark.

Houston, we have bacteria.

Bacteria that don't normally have a negative effect on human health have a leg up in forming infections among astronauts in space. To better study the effects of spaceflight on bacteria, NASA sent microbes that typically cause treatable infections on Earth to space with the Atlantis missions in 2010 and 2011. The group found that communities of these bacteria were able to form in ways they didn't on Earth, giving researchers insight into how to improve health outcomes for astronauts in space, in addition to people on Earth.

Although bacteria are valiant contributors to the health of humans and the planet, they also have a dark side. Certain bacteria have the potential to be pathogenic, meaning they can cause illness and disease.

Throughout human history, some bacteria have (understandably) gotten a bad rap, causing public anxiety and hysteria. Take the plague , for example. The bacteria causing plague, Yersinia pestis, has not only killed more than 100 million people, but it's also suggested to have shaped history, even contributing to the collapse of the Roman Empire [source: Centers for Disease Control and Prevention]. Before the advent of antibiotics, or medications capable of treating bacterial infections, infections were difficult to stop.

Even today, these pathogenic bacteria still weigh heavily on our minds. Bacteria causing a range of illnesses — from anthrax , pneumonia, meningitis, cholera, salmonella and strep throat to E. coli and staph infections — can defy our treatments thanks to antibiotic resistance.

This is especially true for Staphylococcus aureus, the bacterium responsible for staph infections . The "superbug" has posed tremendous problems for hospitals and health care clinics, where patients are more likely to be exposed to it during medical implants and catheter insertion.

In a previous section, we talked about natural selection and how some bacteria have more diverse genes to help deal with what their environment throws at them. If you have an infection, and some of the bacteria in your body are different from others, antibiotics might take care of the majority of the bacterial population. But this also gives the microbes not affected by your antibiotics the room to reproduce and take hold. This is why doctors recommend staying away from antibiotics unless you really need them.

Biological weapons are another frightening aspect of this conversation. Bacteria can be used as weapons in some cases, including being deployed in anthrax scares and embedded in aerosol sprays.

And it's not just humans taking a hit from bacteria. Indeed, bacteria even have an appetite for the sunken ocean liner Titanic, too [source: Kaufman]. The species, named Halomonas titanicae, eats away at the metal of the historic ship.

We've learned how bacteria can be harmful. In the next section, we'll look at how they can help us out.

Bacteria and Dental Health

Lo and behold, the slimy substance we call plaque on our teeth is actually from bacteria. If given free rein, these bacteria can eat away at the enamel of our teeth, eventually giving us cavities. Archaeologists have plucked knowledge from the past by studying human skulls and teeth to learn more about humans' diet and susceptibility to disease at various times [source: Watson].

Let's take a moment to examine bacteria's good side. After all, these are the microbes that bring us tasty foods such as cheese, beer, sourdough and other fermented items. They're also the unsung heroes behind medicine and advancing human health.

We also have bacteria to thank for shaping human evolution. Science is gleaning more information from the microbiota, or the microorganisms residing in our own bodies , particularly in our digestive system and gut. Research suggests that bacteria, and the diversity and new genetic materials they bring to our bodies, have allowed humans to adapt to and exploit new food sources they previously could not use [source: Backhed et al.].

Look at it this way: Lining the surfaces of your stomach and intestine, bacteria are "working" for you. When you eat, bacteria and other microbes help you break down and draw nutrients from foods, especially carbohydrates such as corn, potatoes, bread and rice. The more diverse bacteria we consume and are exposed to contribute to this diverse community in our bodies.

Although our knowledge of our own microbial communities is nascent at best, there's evidence to suggest that a lack of certain microbes and bacteria in the body can tie into a person's health, metabolism, and susceptibility to allergens and disease. Preliminary studies in mice suggest that metabolic diseases such as obesity are linked to diversity and health of the microbiome rather than our predominant view of the "calories in, calories out" approach [source: Cox].

Also in early stages, fecal transplants involving the sharing of fecal microorganisms from a healthy individual to another person show early promise. Yeah, this might not be the best mental image, but the science and options to treat certain gastrointestinal illness looks promising. Research is being done on probiotics, microbes thought to have added health benefits, but general recommendations on their use haven't been established as of November 2014.

In addition, bacteria have been game-changers in the development of scientific thinking and human medicine. Bacteria played a lead role in the 1884 development of Koch's postulates, a series of considerations that tie a given microbe to disease.

Among other contributions, researchers studying bacteria serendipitously discovered penicillin — an antibiotic that has saved countless lives — and, more recently, an easier way to edit organisms' genomes that could revolutionize medicine [source: Marraffini ]. Researchers have modified bacteria to benefit human health in many ways, including producing insulin for the treatment of diabetes.

We've only begun to understand all we can learn from our bacterial friends.

Author's Note: How Bacteria Work

Despite their status as "mindless" microbes, bacteria behave in amazing ways. Give them an obstacle, and they more than likely will find a way around it. Antibiotics on the home turf? They swap genes to better survive. Not enough food? No worries, they can catch some Zzzs and go dormant. We're only beginning to learn bacteria's secrets, and the big picture is becoming clear: A breadth of complex life teems under our very noses (and in them too).

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