Microbes interacting with rock have many uses in space exploration and settlement, including:
1) Life support: the use of regolith in life support systems,
2) Soil formation: the use of microbes to break down rocks into soils for example for plant growth,
3) Biomining: the use of microbes to extract economically useful elements from rocks.
Further, by growing on rock surfaces, many microbes form biofilms. Biofilms, layers of microbes, are ubiquitous in many contexts from space exploration to medicine and one major objective is to understand how biofilm growth might change in space. In this experiment, we investigate how microbes form layers on the surface of the rock material and how they alter the release of elements from the rock.
By lowering the pH, particular microbes are able to extract cations (Fe++, Mg++, Ca++ etc.) from the rock surface which causes the break down of the rock (to form soils or release economically interesting elements in ‘biomining’). This experiment studies biofilm formation and elemental release in microgravity to investigate how space conditions will ultimately affect microbe-mineral interactions in space.
The BioAsteroid experiment investigates how gravity affects the interaction between microbes and rock in a liquid medium. The results will help to develop future equipment to support the use of microbes and their interactions with rocks on the Moon (0.17 g), Mars (0.38 g) and on asteroids (micro-g). The latter have recently been identified as the prime target for extra-terrestrial biomining. Microgravity can be considered as an end-member condition to understand how mixing regimes such as convection currents change the three-component problem of the interaction of liquid, rocks and micro-organisms. BioAsteroid is expected to gain basic physical insights into this problem, with many future applications other than mining (for example in life support systems involving microbial components).
The interaction between microbes and rocks in a medium phase can be affected by reduced gravity in more than one way. The reduction of thermal convection in low-gravity, and its absence in microgravity, will minimize the natural stirring in liquids and gases. This may restrict the supply of food and oxygen to the bacteria and hence lead to a suppression of growth, proliferation and rock attachment and leaching performance. The goal of BioAsteroid is to investigate this hypothesis.
Specific goals to be addressed
The goal of the BioAsteroid experiment is to investigate the effects of altered gravity on the rock/microbe/liquid system as a whole. The objective is not to investigate whether bacteria can detect changes in gravity (as was demonstrated for some protists - see f.i. Gravity and the behaviour of unicellular organisms, D-P. Häder, R. Hemmersbach & M. Lebert, Cambridge University Press (2005)). The questions and hypotheses that BioAsteroid seeks to address are in particular:
1. Does microgravity influence bacterial and fungal attachment (biofilm initiation) on natural asteroidal material?
Hypothesis: Microgravity has both an impact on mixing regimes and therefore on microbe-mineral interactions.
2. Does microgravity induce alterations in biofilms formed by microbes associated with rocks?
Hypothesis: Microgravity conditions change the structure and morphology of microbial biofilms formed on solid rocks substrates from which they are gathering nutrients.
3. To what extent is the ion leaching performance dependent on gravity?
Hypothesis: Microgravity will reduce mixing and thus nutrient availability to the microbes thus reducing elemental leaching from the rock.
4. How does microgravity affect the biochemistry of the organisms?
Hypothesis: Microgravity will change the lipid (membrane) composition of the organisms.
JUSTIFICATION for NEED of SPACE CONDITIONS
The minimum duration of low gravity and microgravity required for the BioAsteroid experiment is in the order of weeks. There is no technique available on ground that can offer reduced gravity conditions for such a long time.
Understanding interaction between Microbes and rocks may benefit Earth applications such as the use of microbes to extract economically useful elements from rocks (Biomining).
Understanding interaction between Microbes and rocks may benefit space exploration and settlement, including: 1) Life support: the use of regolith in life support systems, 2) Soil formation: the use of microbes to break down rocks into soils for example for plant growth, 3) Biomining: the use of microbes to extract economically useful elements from rocks.
The interaction between microbes and rock was for the first time explored under microgravity conditions in 2014 on Foton-M4 in a pilot experiment from SCK-CEN in preparation for BIOROCK.
Indirect precursors are the BIOFILTER and OCLAST experiments, performed in 2005 and 2007 on Foton-M2 (16 days in orbit) and Foton-M3 (12 days in orbit). In both cases, cell cultures interacted with and partly consumed solid substrates. In the BIOFILTER experiment (MAP AO-99-LS-019) microbes were grown on stainless steel, Kapton foil, polypropylene and aluminum tape. Especially the Kapton foil was heavily damaged by the bacteria. In the OCLAST experiment (NSS-95-5-I) osteoclasts were cultured in vitro on chips of bone. In space, the resorption of bone by the osteoclast turned out to be stronger than on ground (Tamma et al. 2009).
The BioAsteroid experiment particularly builds on the BIOROCK ESA experiment. Indeed the BioAsteroid hardware will be manufactured based on BIOROCK design. In that experiment, three organisms were investigated (Loudon et al., 2018) at microgravity, Martian gravity (0.38 g) and 1 g (simulated terrestrial gravity) to investigate biofilm formation and leaching of elements from basaltic rocks. That experiment successfully showed the use of the hardware for this experimental set up and allowed for the successfully study of biofilm growth and bioleaching in basaltic rock. BioAsteroid will use one of the same organisms as BIOROCK. The only major change in the experiment will be the change in the rock substrate to be used and the addition of a new organism.
ISS Increments 59-60 - 2019
62nd ESA Parabolic Flight Campaign - 2015
Foton-M3 - 2007
Foton-M2 - 2005
The BioAsteroid experiment is physically configured as a collection of small culturing devices, in this document referred to as Culture Chambers (CCs). Inside each CC microbial cultures are grown, attached as a biofilm onto the surface of a piece of rock.
The biofilm-covered rock is surrounded by culture medium that provides organic food, oxygen and some minerals (the missing minerals are provided by the rock).
Two microbial species have been selected to do the experiment. Each individual CC will be occupied by a single species or both mixed together.
Considering that the culture medium itself may contribute to the weathering of the rock (see f.i. Wu et al. 2008) we also include three control culture chambers in which there are no microorganisms.
All the Culture chambers (CCs) shall be at microgravity.
They will be configured as follows:
1) All CCs will contain a fragment of asteroidal material;
2) Three CCs will contain no organisms (controls);
3) Three CCs will contain Penicillium simplicissimum;
4) Three CCs will contain Sphingomonas desiccabilis;
5) Three CCs will contain a mix of Penicillium simplicissimum and Sphingomonas desiccabilis.
Twelve CCs will be required (6 experimental units) in total. They will be exposed to microgravity in the KUBIK incubator.