WHEN the Titanic sank on its maiden voyage in 1912, it became a watery grave for 1523 people. But it was attracting new residents almost as soon as the mangled hull hit the seabed. At first, these microscopic colonisers would have dined on the 10-day supply of food that remained on board. When that ran out, they started tucking into the ship itself.
Seventy-three years later, an expedition led by Robert Ballard discovered the Titanic 750 kilometres south-east of Newfoundland in 3800 metres of water. The first images the world saw of the wreck showed the bow, rusting and draped in what look like strange underwater icicles. We now know that these ārusticlesā had grown over the decades, almost like individual organisms. In fact they turned out to be very strange beasts indeed.
Each rusticle is made up of communities of bacteria, fungi and other microbes that have joined forces to build a sort of rusting tower block to sustain them and protect them from the outside world. The race is now on to uncover the secret life of rusticles. It wonāt save the Titanic, which seems doomed to biodegrade, but it could help provide clean water in the developing world, and even inspire new building materials that could be grown rather than manufactured.
Advertisement
The story began in 1996 when microbial ecologist Roy Cullimore of the University of Regina in Saskatchewan was called on to investigate biological activity on board the Titanic after the salvage company noticed the wreck seemed to be deteriorating. By carefully guiding the robotic claws of the French submarine Nautile, Cullimore was able to collect some rusticles to bring back to his laboratory for analysis. Gathering the structures without breaking them was a tricky business ā rusticles are brittle and have a tendency to snap in the fast water flow created by the propellers. A second expedition in 1998 brought up more rusticles, when a large section of hull was lifted from the seabed. The largest intact rusticle, measuring 45 centimetres long, now hangs on Cullimoreās office wall.
Each rusticle seems to contain at least five distinct microbial communities, or āconsormsā, that live in harmony, mostly clustered around water channels that run through the structure. There are also fungal growths towards the outside of the structure where the channels meet the surface. Along with the microbes, rusticles contain up to 35 per cent iron in the form of ribbons of iron compounds that permeate the entire structure in much the same way that nerves or blood vessels do in an animal. Chemically, the iron compounds are dominated by various ferric oxides, hydroxides and carbonates. The outer walls appear layered, much like the annular growth rings on trees, and there are regular patterns of channels inside. Cullimoreās work has revealed that the consorms work together to āfeedā on the ship, actively removing iron from it. In 1996, he estimated that they were mining 100 kilograms a day. As the rusticles grow, the decay rate accelerates, and Cullimore predicts that the wreck will be unrecognisable within 100 years or so.
However, the rusticles colonise some parts of the ship but leave others entirely alone. To find out why, Cullimore has placed various steel samples on the Titanicās deck. His findings suggest that the most susceptible areas are where the steel was ripped or twisted when the ship sank, because the fractures allow microbes to gain a foothold. The rusticles also seem to prefer wrought iron to steel, mining phosphorus and sulphur as well as iron. āNot only do wrought iron rivets give more easily but they essentially become a supermarket for growing rusticles,ā says Cullimore. This is bad news not just for the Titanic, but for other ships and undersea structures such as oil rigs. āWhen you take out a rivet youāre weakening the whole section,ā says Cullimore.
But the engineering implications are much wider than this. The growths on the Titanicās hull are very similar to those frequently found down water wells. āNormally boreholes are built with a supporting metal casing, with holes drilled in the sides to let water pass through,ā explains Sean Tyrrel from Cranfield Universityās Silsoe campus. āIron ochre is a common phenomenon in water courses ā you get a slimy orange goo of iron bacteria that grows and blocks the holes up.ā Scientists have used a combination of heat and chemicals to help control this unwanted plugging, but the goo can become hardened and turn into rusticles and these methods have not proved particularly effective against them, so the hunt is now on for better treatments.
Iron-loving bacteria can also be useful, however. Tyrrel has worked on projects to design iron filters for wells in developing countries, to prevent iron-rich water turning rice and clothes orange. āThereās been a great interest in using groundwater to provide safe drinking water. But if thereās a lot of iron in the water people reject it,ā he says. Tyrrel and his colleagues have found that under the right conditions they can persuade iron-loving bacteria to remove iron from the water. The rusticles research should provide more clues about how to harness these bacteria for good.
And the reach of rusticles doesnāt end there. Cullimoreās research has convinced him that microbes could be harnessed for all sorts of industrial uses. He sees rusticles as a sort of biological concrete, which has given him the idea that microbes could be added to normal concrete to improve its performance. Such bioconcrete might even be grown rather than mixed and cured. Micro-organisms could also be engineered to excrete products such as polymers and surfactants that might improve the curing process, perhaps allowing fresh concrete to be pumped more efficiently.
Scientists still have much to learn about the specific types of microbes present in rusticles and how they interact with each other. But what is certain is that the various consorms must use a common language to successfully build and sustain their mutual community. Cullimore ultimately hopes to begin to understand this language. āIf we could learn how they communicate then we could say āHey, you shouldnāt be growing here, wouldnāt you rather be growing over there?'ā
Back from the deep
Six thousand artefacts have now been removed from the Titanic and are currently on display at Londonās Science Museum. They include hundreds of flawless white porcelain gratin dishes, which were found in neat rows in the sand. The wooden crate that once held them had long since perished. In similarly pristine condition is a jar of fat green olives, looking as if it has just been plucked from a shelf in Fortnum and Masonās food hall. Perfume vials, their contents intact and still scented with roses, remain as good as new in their protective wallets. Most surprising are paper and fabric objects ā readable bank notes, letters, pyjamas and an immaculate silk top hat.
Independent textile expert David Galusha, who has helped conserve the items, believes their state of preservation has much to do with where they came to rest. Fabric objects found near metal parts of the ship colonised by rusticles show signs of biological attack. But many items found farther away remain remarkably preserved. This is particularly true of those encased in leather trunks or buried in silt, where lack of oxygen has prevented colonisation by aerobic organisms. āI was amazed,ā says Galusha. āThere are some socks that look like you could just slip them right on your feet. It really has opened the eyes of conservators. The conditions on the Titanic are so unique ā we would never have thought that something that has been down there that deep and for that long would come up intact.ā
Titanic: the Artefact Exhibition will run at the Science Museum in London until 28 September 2003.