Bacteria

Mouthless, Gutless Worms

In the deepest sea, where not a single photon of sunlight ever penetrates, life persists in eternal darkness, crowded around chemical- and lava-spewing fissures in the ocean’s floor. Life around these hydrothermal vents includes shrimp, crabs, and tall, slender tubeworms.

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These worms have no mouths, no stomachs, and no intestines, yet they clearly thrive, some species growing up to eight feet in length.

They need no eating apparatus because their bodies house billions of bacteria that feed them.

The tubeworms’ tissues are lined with bacteria that convert hydrogen sulfide from the hydrothermal vents into molecules that serve as usable nutrients for the worms.

The worm’s gills look like a red plume sticking out from its protective tube. Its blood contains a special type of hemoglobin that transports sulfides, oxygen, and carbon dioxide into its tissues, where the bacteria turn them into food for themselves and their host. In return, the worms provide the bacteria with a protected and stable home.

 

Mitochondria and Chloroplasts

The Partnerships That Led to Higher Life

If you could peer deep into one of the many cells in your body, you’d see little blobs, squiggles, and coils. These are the cell’s organelles, structures that perform specialized functions in cells the same way that the lungs, heart, and other organs do in a body.

Mitochondria are the energy factories found in each cell of fungi, protozoa, insects, and animals. Once nutrients are absorbed or digested, they move in the form of minuscule molecules into the mitochondria, which convert the molecules into chemical energy to power the cell.

Chloroplasts undertake a similar function in the cells of plants, algae, and some protozoa. They capture sunlight and, through a series of chemical reactions called photosynthesis, use the light to make energy.

These organelles are absolutely essential to the existence of all higher life forms on Earth. If all of the mitochondria in our bodies were to suddenly shut down, we would die. The same is true for plants were they to lose their chloroplasts.

So where did they come from?

As microscopes improved over the years, scientists began noticing striking similarities in the appearances of mitochondria, chloroplasts, and bacterial cells. They discovered that these two organelles contain their own DNA, or gene set, organized very much like the DNA in bacterial cells.

Mitochondria and chloroplasts also reproduce independently from the cells in which they reside, in a manner very like bacterial fission.

Many microbiologists think it is likely that mitochondria and chloroplasts were once free-living prokaryotes (cells that lack a nucleus and organelles) that somehow took up residence in larger cells.

An Invading bacterium may have infected a cell, then become a permanent resident as it adapted to become less virulent, or the target cell became less susceptible. Or both.

Chloroplasts likely first entered a host cell as food before establishing a successful merger with the cell so they were not digested.

Lichens

Lichens: When Fungi and Algae (or Cyanobacteria) Merged

Fungi feed themselves quite ably, absorbing nutrients from organic materials. Algae and cyanobacteria are also adept at providing for their own nutritional needs by turning sunlight into energy through photosynthesis.

Yet many thousands of years ago, some fungi merged with some algae (or cyanobacteria in some cases) to create a new kind of partnership called a lichen.

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Some 20,000 different kinds of lichens live in such diverse habitats as the surfaces of rocks in arctic tundra and desert sands as well as the bark of trees in bayous and the sides of buildings.

 

 

 

 

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Lichen formation enables each of the partners to expand into habitats and environments they might not survive alone, such as wind-whipped tundra or sun-scorched desert.

Fungi provide the shelter and stability while the algae or cyanobacteria provide the food. The fungal filaments surround the algal or bacterial cells and make up the majority of the lichen’s bulk and shape. Meanwhile, the photosynthetic algae or bacteria churn out nutrients in the form of carbons, with up to 60% of what they produce being devoured by the fungal cells.

Lichens have an amazing capacity to withstand drought. Like very efficient sponges, lichens absorb moisture from fog, dew and even humid air. They can take in as much as 35 times their weight in water. They also retain water well, drying out very slowly. This ability enables them to survive in places like bare rock surfaces, deserts and tundra.

Some lichen partners are dependent upon one another for survival, but in many cases, the fungus and the algal or cyanobacterial species can each be found living independently.

Ant Farmers and Gardens of Fungi

Ant Farmers and Their Gardens of Fungi

It’s not clear precisely how and why some ancestral species of ant first took up fungus farming, but scientists have determined by genetic testing that it happened about 50 million years ago.

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Today, several species of ant (including the famed leaf-cutters of Central and South America) carefully tend and nurture gardens of fungi in vast underground nests.

Ants lack the necessary enzymes to digest leaves and stems themselves, so they cut them up and feed them to the fungi, which break down cellulose (the tough fibrous material in plant tissues), making nutrients available to the ants.

The ants excavate nests and build nice, cozy, safe chambers for their fungal gardens; they clean off debris and parasites from the fungi; and even produce special antibiotics in their bodies to ward off or kill infectious organisms that might attack their crops.

In return, the fungi produce swellings at the tips of their hyphae (long strings of fungal cells) that are rich in proteins, sugars and other nutrients. The ants dine on these nutritious swellings, called gongylidia.

The fungi are ensured a copious food supply and a stable, nurturing environment in which to live.

The fungi rely upon the ants for reproduction. Before new queen ants fly off to mate and found their own colonies, they tuck a bit of fungus in their mandibles to start their new gardens. The fungi growing in virtually every leaf-cutter garden are actually clones of the same fungus farmed by ants 25 million years ago.

Fungi and Bacteria

Ages ago, as land plants were evolving, they ran into a few impediments. Soil can sometimes prove a nutrient-poor and inhospitable environment. In order to grow and thrive, plants need nitrogen to make proteins, but they lack the chemistry set to convert free nitrogen in the air into a form their cells can use.

To overcome these obstacles, early plants struck deals with co-evolving bacteria and fungi.

Some early bacteria developed the chemical tools to harvest free nitrogen from the air and convert it into forms such as ammonia and nitrate through a process called nitrogen fixation. The catch is that they need sufficient amounts of energy in the form of carbohydrates to power these conversions, and the supply of carbohydrates in the soil can be limited.

On the other hand, plants produce copious amounts of carbohydrates as a product of photosynthesis. And ammonia and nitrate are perfect protein-building nitrogen forms for plants.

Fungi and Bacteria: The Fundamental Fertilizers

Ages ago, as land plants were evolving, they ran into a few impediments. Soil can sometimes prove a nutrient-poor and inhospitable environment. In order to grow and thrive, plants need nitrogen to make proteins, but they lack the chemistry set to convert free nitrogen in the air into a form their cells can use.

To overcome these obstacles, early plants struck deals with co-evolving bacteria and fungi.

Some early bacteria developed the chemical tools to harvest free nitrogen from the air and convert it into forms such as ammonia and nitrate through a process called nitrogen fixation. The catch is that they need sufficient amounts of energy in the form of carbohydrates to power these conversions, and the supply of carbohydrates in the soil can be limited.

On the other hand, plants produce copious amounts of carbohydrates as a product of photosynthesis. And ammonia and nitrate are perfect protein-building nitrogen forms for plants.

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A group of enterprising plants called the legumes (these include all beans and peas as well as clover and alfalfa) entered into a merger agreement with nitrogen-fixing bacteria called Rhizobium.

The bacteria moved into the plants’ roots, forming bumps on the roots called nodules that supply the fixed nitrogen plants need. In exchange, the plants supply the bacteria with the carbohydrates they require. Because Rhizobia can still dwell independently in the soil, plants are more dependent upon them than the microbes are on plants.m_rhizo2

Animals need nitrogen for protein building, too. We humans get our nitrogen by eating plants (or by eating animals that eat plants).  Another partnership teams plants with soil-dwelling fungi called mycorrhizae. Virtually all plants from flowers to towering trees like Sequoias have partner mycorrhizae.

Some species of mycorrhizae cover the surface of plants’ root hairs; others settle down inside the plant roots. The fungi act as extensions of the plants’ roots, vastly increasing the surface space of their nutrient-absorbing network.

Mycorrhizae increase the plants’ uptake of water and essential nutrients, particularly phosphorous, which doesn’tspread readily in soil. Inexchange, the plants provide the fungi energy in the form of carbohydrates.

This partnership enables both plants and fungi to survive in nutrient-poor places where they otherwise might die.

Algae: The Invisible Partner

Major development projects are taking place in oceans across the globe all the time, enterprises that will provide shelter and food for a vast number of fish, mussels, urchins, and other marine life.

While credit is regularly and duly given to the visible construction crew — coral polyps — recognition is also due the polyps’ invisible, but very active algal partners, the zooxanthelle.

These algae (a type called dinoflagellates) live inside the body tissues of coral polyps. Coral polyps take care of some of their nutritional needs on their own by catching tiny protists and organic matter that drift past their tentacles. Their partnership with the chlorophyll-containing algae enable them to also get food from sunlight as if they were plants.

The zooxanthelle do the actual work of converting the sunlight into energy via photosynthesis. The by-products they generate (organic carbons such as glycerol and sugars) are excellent nutrients for their polyp hosts.

The zooxanthellae supply much of the polyps’ energy needs. In turn, the polyps provide the algae a protected, stable environment and nutrients they need for growth, such as nitrates and phosphates. Zooxanthellae also increase the rate of coral calcification, the growth of the hard shells that form the actual reef structures.

Microbial Mergers

Collaborations on a Minute Scale

Over millions of years of evolution, we humans have worked out a mutually beneficial partnership with the microbes that came to inhabit our guts. In return for their aid in digestion, we give them a stable, protected home and plenty of nutrients via the food we eat. We need them as much as they need us.

Microbes break down food molecules our body’s enzymes and acids can’t dissolve, helping us squeeze all the nutrients out of our food. Some make valuable vitamins that our body needs.

Many microbial species have proved to be consummate evolutionary wheelers and dealers, arranging collaborations, mergers, and acquisitions that usually serve both partners well.

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The pea root sends a chemical message that attracts Rhizobia, then surrounds the bacteria, whcih set up housekeeping inside the root's cells.

MERGERS OF NOTE

Rhizobia are bacteria that form nodules on the roots of legumes to supply them with nitrogen; in return, the plants provide the bacteria with carbohydrates.

Mycorrhizae are soil-dwelling fungi that act as extensions of plants’ roots, enabling them to vastly increase their nutrient-absorbing network. The plants provide the fungi energy in the form of carbohydrates.

Zooxanthelle are photosynthetic algae that live inside the body tissues of coral polyps. They provide nutrients to their polyp hosts in exchange for a protected, stable environment and nutrients they need for growth.

Lichens are an alliance of fungi and algae that allows each to grow in environments where neither could survive alone, like deserts, rocks, or tree bark.

 

 

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