Tardigrades: Water bears in space

In 2007, a little known creature called a tardigrade became the first animal to survive exposure to space.

It prevailed over sub-zero temperatures, unrelenting solar winds and an oxygen-deprived space vacuum.

On Monday, this microscopic cosmonaut has once again hitched a ride into space on the Nasa shuttle Endeavour.

Its mission: to help scientists understand more about how this so-called "hardiest animal on Earth" can survive for short periods off it, the redObit reported in its website on May 18.

Tardigrades join other microscopic organisms selected to be part of a project into extreme survival.

Endeavour climbs into the sky on Monday Project Biokis is sponsored by the Italian Space Agency and will investigate the impact of short-duration spaceflight on a number of microscopic organisms.

The project will use seven experiments to investigate how spaceflight affects organisms on a molecular level.

The team will be using molecular biology to evaluate any changes in the organisms' genetic information, as well as investigating how cells physically adapt to cope with extreme dehydration, caused by the space vacuum, and damage caused by cosmic radiation.

One of these experiments, the Tardkiss experiment, will expose colonies of tardigrade to different levels of ionising radiation, determined using an instrument called a dosimeter, at different points during the spaceflight mission.

The results from Tardkiss will enable researchers to determine how radiation dosage effects the way cells work.

Tardigrades are of particular interest following the 2007 European Space Agency (Esa) Foton-M3 mission, during which their ability to survive space conditions was discovered.

Tardigrades are microscopic animals more commonly known by their non-scientific name, the water bear.

Their stocky bodies and gait have all the hallmarks of a bear. But this isn't a typical bear encounter.

These bears are less than 1mm long and are found in the sea, in fresh water and on land.

Genetic studies have shown that they originally lived in freshwater environments before adapting to colonise the land, seeking out moist habitats such as soil, mosses, leaf litter and lichen.

Tardigrades earned the "hardiest animal on earth" tag having evolved elaborate dormancy strategies that allow them to shut down all but the essential biological processes when conditions are not conducive to supporting life.

Coloured scanning electron micrograph of the water bear Echiniscus granulatus Professor Roberto Guidetti from the University of Modena and Reggio Emilia believes their ability to suspend life and withstand freezing and desiccation may explain why they can survive in space.

"Tardigrades can be found all over the world from the Arctic to the Antarctic, from high mountains to deserts, in urban areas and backyard gardens," he explained.

"In terrestrial environments, they always require at least a film of water surrounding their bodies to perform activities necessary for life."

But if these conditions change, tardigrades are capable of entering an extreme form of resting called cryptobiosis.

In this state, they are capable of withstanding freezing, a process called cryobiosis, and desiccation, a process called anhydrobiosis.

Arid state

"This capability [to withstand desiccation] involves a complex array of factors working at molecular, physiological and structural levels," Professor Guidetti told BBC News.

"The physiology and biochemistry of anhydrobiosis is bound to a complex system that involves many different molecular components working together as bioprotectants."

Sugars and heat stress proteins, which are expressed when cells become stressed, act as "molecular chaperones" protecting important molecules within the cell.

The disaccharide sugar called trehalose plays a role in the protection of cells and biomolecules from dehydration by replacing water that is normally bonded to hydrogen.

During dehydration, loss of water increases the ionic concentration leading to the formation of reactive oxygen species (ROS) which damage important biomolecules including DNA.

A water bear egg, imaged by coloured scanning electron micrograph To counter this attack, organisms produce antioxidants that can mop up ROS minimising cell damage.

The regulation of antioxidant metabolism represents a crucial strategy to avoid damage during dehydration.

"Tardigrades can persist for months, or even for years, in the anhydrobiotic state. When in the desiccated state, tardigrades show a high resistance to physical and chemical extremes," explains Professor Guidetti.

"For example, very low and high temperatures, exposure to high pressure or vacuum, as well as contact with organic solvents and ionising radiation."

Exposure to the conditions found in space induces rapid changes in living systems.

The TARDKISS study may help researchers such as Professor Guidetti develop techniques to protect other organisms, including humans, from the extreme stresses found under space conditions.

It may also help with the future long-term goal of extending the exploration of the Solar System.

영하 273도, 영상 151에도 견디는 괴생물 우주간다

지난 16일 미국 플로리다주 케네디 우주센터에서 가브리엘 기퍼즈 미 연방 하원의원의 배웅을 받으며 마지막 비행을 떠난 우주왕복선 인데버호에는 기퍼즈 의원의 남편 마크 켈리 선장을 포함한 6명 우주인 말고도 특별한 생명체가 동승했다.

이름은 타디그레이드(Tardigrade·사진). '느림보 동물'이란 뜻의 이 생명체는 일반인들에게는 잘 알려져 있지 않지만 과학자들 사이에서는 극한의 생존 조건에서도 살아남는 놀라운 생명력으로 유명한 '동물'이다. 타디그레이드는 16일간 우주비행에 나선 인데버호에서 중요한 임무를 수행한다.

우주라는 극한의 환경에서 생명을 어떻게 유지할 수 있는지 정보를 축적하고 이를 과학자들에게 제공해 인간을 포함한 유기체의 생명을 보존하는 과학기술을 발전시키도록 하는 일이다.

타디그레이드는 번데기 같은 몸체에 여덟 개의 다리를 가지고 있다. 다 자란 성체(成體)의 크기는 1.5㎜ 정도다. 현미경으로 본 얼굴 모습과 걷는 모양이 곰과 비슷하다고 해서 '물곰(water bear)'으로도 불린다. 5억3000만년 전 캄브리아기에 출현한 생물로 과학자들은 '완보동물(緩步動物)'이라는 독자적인 생물군으로 분류한다.

타디그레이드는 기체의 부피가 '제로'가 되는 절대영도(영하 273도)에서도 생존하며 끓는 물 온도보다 높은 151도에서도 살 수 있는 것으로 보고되고 있다. 6000m가 넘는 히말라야 산맥이나 깊이 4000m 바다 속에서도 발견된다. 남극과 북극, 사막과 적도지역 등 전 세계 어느 곳에서도 살아간다. 생물에게 치명적인 농도의 방사성 물질 1000배에 달하는 양에 노출돼도 생명을 이어간다. 전 세계에1000여종이 있는 것으로 파악되고 있다. 이끼 같은식물의 세포액을 빨아먹고 산다.

타디그레이드의 우주비행은 이번이 처음은 아니다. 지난 2007년 9월 유럽우주국(ESA) 무인우주선 포톤-M3호를 타고 지구 밖으로 날아가 진공상태의 우주 공간에서 10일간 있다가 돌아왔다. 당시 지구로 다시 돌아온 타디그레이드는 물도 산소도 없는상태를 견디며 살아남았고 정상적으로 알을 낳아 번식도 해 과학자들을 놀라게 했다.

이번 인데버호 우주비행에서는 더욱 극한의 조건을 견디는 실험을 진행하고 이들 데이터를 갖고 귀환할 예정이다.

타디그레이드 연구자인 로베르토 귀데티 이탈리아 모데나대학 교수는 17일 BBC와의 인터뷰에서 "타디그 그레이드의 생존 메커니즘 연구는 인류의 생존 연장, 태양계를 비롯한 우주 탐험 등 미래에 달성할 목표에 다가가는 데 도움을 줄 것"이라고 말했다.