Devourned' by the sea, Titanic may disappear soon

                                                                    

  When the opulent RMS Titanic set off on the road in 1912, no one could have predicted its current state - reduced to a rusty hull at the bottom of the Atlantic Ocean. But at least something remains of the ship, more than a century after its unfortunate transatlantic journey.

Only scientists believe that in a few decades, it may be that nothing else on the ship. All because of a kind of bacterium that is slowly eating its iron hull.

Robert Ballard, an oceanographer at the University of Rhode Island in Narragansett, discovered the shipwreck in 1985. What was not known at the time was that the discovery only happened because of Ballard's involvement in a secret British Navy mission to locate the remains of Two American nuclear submarines that sank during the Cold War. The Titanic was only found between the two submarines.

At the time of discovery, the ship was impressively preserved. Being 3.8 km below the surface, subjected to low light and intense pressure, it became uninhabitable for most types of life, which delayed corrosion. After 30 years, however, the hull is rusting because of bacteria that corrode metal. Some researchers now give a 14-year shelf life until the ship disappears forever.

What is known about the microorganisms responsible for this?

The story began in 1991, when scientists at Dalhousie University in Halifax (Canada) collected samples of rust formations in a pendant-like shape from the ship.

But only in 2010 another group of scientists, led by Henrietta Mann, from the same university, decided to identify what kind of life there was.

They isolated one of the species of bacteria and discovered a novelty for science. Mann and his colleagues called it Halomonas titanicae in honor of the ship.

The bacteria can survive in completely uninhabitable conditions for most forms of life on Earth: water that is completely dark and under strong pressure.

But she had another, even more impressive trick. Bacteria Halomonas are often found living in another extreme environment: salt marshes. Here, the salinity of water can vary dramatically because of evaporation, and the Halomonas bacteria have evolved to deal with the problem.

There are not many organisms that can do what the Halomonas bacteria do. Joe Saccai of the Laue-Langevin Institute in Grenoble, France, is part of an international team of scientists who looked at how the bacteria can survive under such extreme and variable conditions. They found that Halomonas use a molecule called ectoine to protect itself from osmosis pressure.

"If a cell survives in a floating salt environment, there must be a way to compensate for this by adjusting the concentration of its internal solution," says Zaccai. " Halomonas produces ectoin to counterbalance osmotic pressure from outside. As the concentration of external salt fluctuates, the ectoin concentration response will respond to it."

In other words, the more salty the water, the more ectoin the bacteria produce inside its cells to prevent water from flowing out. However, this adaptation can be highly dangerous for an organism. The more material there is inside a cell, the more it can get accumulated between water molecules, disrupting the unique properties of water.

The reason water is so necessary to life is that the unique bonds with its atoms - known as hydrogen bonds - allow it to act as a solvent. Other chemicals can be dissolved in it and react together.

The reactions of life need to happen in a solution, so all of our cells are in liquid water. In addition, RNA and DNA, the proteins and enzymes responsible for carrying out the daily work of the cell, and the membranes that give them structure, need to be surrounded by a layer of water to function.

This layer of water, known as a "hydration shell," is crucial to maintaining the correct folds of proteins for them to function. If this is interrupted, the proteins can shatter and fall, which can kill the cell.

Because the bacterium is clearly capable of accumulating extremely high concentrations of ectoin within its cells - the study found that Halomonas produces so much ectoine that it corresponds to 20% of the mass of the microbe - the molecule needs to put those important properties of water in place of someway.

To investigate how this happens, scientists led by Zaccai bombarded the bacteria with a beam of neutrons. Looking at the pattern produced by the neutron clash in the atoms in the membranes and proteins of the microbes' cells, scientists have been able to look at the structures at the molecular and atomic level.

There are few places in the world that are equipped for such experiments. The researchers worked at the Laue Langevin Institute, one of the world's largest neutron research centers.

"By observing how neutrons were scattered in different samples, we were able to demonstrate how ectoin acts on proteins and cell membranes and, more importantly, on water," says Zaccai. "Instead of interfering, ectoine actually increases the solvent properties of water that are essential to biology."

It turns out that, no matter how much dissolved ectoin exists inside the cell, the water shell surrounding proteins and cell membranes remains 100% water, which allows the metabolism to continue normal. This is because, when ectoine forms hydrogen bonds with water, it forms large clusters that will not fit on the surfaces of membranes and proteins, but only pure water can be maintained.

Initial investigations of H. titanicae have shown that it can grow in water with a weight / volume ratio between 0.5% and 25%, although it works best with a salt concentration between 2% and 8%.

However, it is unclear how, or if, this salt tolerance helped the bacteria colonize the shipwreck.

The H. titanicae is not the only bacteria that inhabit loves ships. Various types of microbes colonize ship debris immediately after shipwrecks. They quickly form sticky films over the entire available surface, called "biofilms." These biofilms are like a haven for corals, sponges and mollusks, which in turn attract larger animals.

Quickly the sunken ship becomes a type of reef with plenty of life.

Ancient remains have seen food from microbes that feed on wood, while more modern steel ships attract bacteria like H. titanicae , which love to eat iron. While H.titanicae may eventually destroy the Titanic, many of these bacteria can actually protect ships from corrosion, one reason why there are still shipwrecks dating back to the 14th century.

In 2014, a team of scientists from the American Bureau of Ocean Energy Management (BOEM) conducted what may be considered the most thorough study to date of microbial life on ships. They observed eight remains of ships in the northern Gulf of Mexico. Among the shipwrecks, there were 19th century wooden and steel ships, one from the 17th century and three steel vessels from World War II, one of which was sunk by a German submarine.

They found that the material of the ship was the crucial factor that determines the type of microbe that will be attracted. Wooden ships are full of bacteria that feed on cellulose, hemicellulose and lignin found in wood. Steel ships, on the other hand, are full of bacteria that feed on iron.

Strangely, even though the bacteria feed on the ship, they also protect it from corrosion.

Basically what happens is that any sinking vessel, be it a 19th century wooden ship or a Second World War steel ship, is vulnerable to microbes that quickly cover its entire surface," says marine archaeologist Melanie Damour, BOEM in New Orleans, one of the scientists who led the expedition.

"At first, the ship will begin to be corroded in contact with the sea water, but as the microbes begin to colonize the boat, they form a biofilm, which is a protective layer between the ship and the sea water," Says Damour.

This means that any type of mechanical impact, such as an anchor being dragged by the wreck, will break this protective surface and expose the metal to seawater once again, accelerating corrosion.

It is not just the mechanical impact that has this effect. The Deepwater Horizon disaster of 2010 knocked millions of gallons of oil into the Gulf of Mexico and much of it hit the depths of the ocean. In laboratory experiments, the team discovered that exposure to oil can accelerate corrosion of the ship's material.

This suggests that the oil from the Deepwater Horizon spill may be accelerating the corrosion of bottom-sea vessels, but researchers have yet to confirm this hypothesis.

Each bacterium, fungus and microbe has a specific function that is the result of millions of years of evolution," says Damour.

"Iron sulfate reduction bacteria are attracted to ships' steel, but others love the hydrocarbons that make up the oil, so they multiplied after the 2010 spill. However, we found that not all microbes can cope with exposure to Oil and chemical dispersants and some consider them extremely toxic.Even four years later, oil was still present in the environment and the destructive effect it had on bacteria and biofilms implies that the ships were exposed to seawater and corroded much more fast".

The finding is alarming. There are more than 2,000 ships wrecked at the bottom of the Gulf, from 16th century vessels to the remains of two German submarines from World War II. These ships are important historic monuments that give a unique view of the past. They are also home to deep sea life.

But eventually, all ships - including the Titanic in the Atlantic - will be completely devoured, either by bacteria that feed on metal or corrosion of seawater. The iron of the 47,000-ton vessel will end up in the ocean. At some point, part of it will be incorporated into the bodies of marine animals and plants. The Titanic will then have been recycled.