THE BOSS EXPERIMENT OF THE EXPOSE-R2 MISSION: BIOFILM VERSUS PLANKTONIC CELLS

In the BOSS experiment (biofilm organisms surfing space), which was performed in the context of the successfully finalized EXPOSE-R2 mission, an international consortium of scientists investigated the ability of a variety of organisms to survive in space and on Mars as a function of their life style. The question in focus is whether there are different strategies for individually living microorganisms (planktonic state) compared to a microbial consortium of the same cells (biofilm state) to cope with the unique mixture of extreme stress factors including desiccation, gamma-, ionizing- and UV radiation in this environment. Biofilms, in which the cells are encased in a self-produced matrix of excreted extracellular polymeric substances, are one of the oldest clear signs of life on Earth. Since they can become fossilized they might also be detected as the first life forms on other planets and moons of the solar system and are therefore ideal candidates for astrobiological investigations. As an example for the organisms that attended the EXPOSER2 mission the results of the ight and mission ground reference analysis of Deinococcus geothermalis are presented. Deinococcus geothermalis is a non-spore-forming, gram-positive, orange-pigmented representative of the Deinococcus family which is unparalleled in its poly-extreme resistances to a variety of environmental stress factors on Earth. The results demonstrate that Deinococcus geothermalis remains viable in the desiccated state over almost 2 years, whereas culturability was preserved in biofilm cells at a significantly higher level than in planktonic cells. Furthermore, cells of both sample types were able to survive simulated space and Martian conditions and showed high resistance towards extra-terrestrial UV radiation. Additionally results of cultivation-independent investigations of pigment stability, membrane integrity, enzyme activity, ATP content and DNA integrity will be discussed.To conclude, biofilms exhibit an enhanced rate of survival compared to their planktonic counterparts when exposed to space and Martian conditions. This seems to indicate an advantage of living as a biofilm when facing the poly-extreme conditions of space or Mars. The findings will contribute to the understanding of the opportunities and limitations of life under the extreme environmental conditions of space or other planets as function of the state of life and aims to contribute to the understanding of the adaptation mechanisms that allow microorganisms to survive in extreme environments, possibly including space and the surface of Mars

Water in bacterial biofilms:pores and channels, storage and transport functions

Bacterial biofilms occur in many natural and industrial environments. Besides bacteria, biofilms comprise over 70 wt% water. Water in biofilms occurs as bound- or free-water. Bound-water is adsorbed to bacterial surfaces or biofilm (matrix) structures and possesses different Infra-red and Nuclear-Magnetic-Resonance signatures than free-water. Bound-water is different from intra-cellularly confined-water or water confined within biofilm structures and bacteria are actively involved in building water-filled structures by bacterial swimmers, dispersion or lytic self-sacrifice. Water-filled structures can be transient due to blocking, resulting from bacterial growth, compression or additional matrix formation and are generally referred to as "channels and pores." Channels and pores can be distinguished based on mechanism of formation, function and dimension. Channels allow transport of nutrients, waste-products, signalling molecules and antibiotics through a biofilm provided the cargo does not adsorb to channel walls and channels have a large length/width ratio. Pores serve a storage function for nutrients and dilute waste-products or antimicrobials and thus should have a length/width ratio close to unity. The understanding provided here on the role of water in biofilms, can be employed to artificially engineer by-pass channels or additional pores in industrial and environmental biofilms to increase production yields or enhance antimicrobial penetration in infectious biofilms

EPS—Then and Now

“Slime” played a brief and spectacular role in the 19th century founded by the theory of primordial slime by Ernst Haeckel. However, that substance was never found and eventually abandoned. Further scientific attention slowly began in the 1930s referring to slime as a microbial product and then was inspired by “How bacteria stick” by Costerton et al. in 1978, and the matrix material was considered to be polysaccharides. Later, it turned out that proteins, nucleic acids and lipids were major other constituents of the extracellular polymeric substances (EPS), an acronym which was highly discussed. The role of the EPS matrix turns out to be fundamental for biofilms, in terms of keeping cells in proximity and allowing for extended interaction, resource capture, mechanical strength and other properties, which emerge from the life of biofilm organisms, including enhanced tolerance to antimicrobials and other stress. The EPS components are extremely complex and dynamic and fulfil many functional roles, turning biofilms into the most ubiquitous and successful form of life on Earth

Bacteria and archaea on Earth and their abundance in biofilms

Biofilms are a form of collective life with emergent properties that confer many advantages on their inhabitants, and they represent a much higher level of organization than single cells do. However, to date, no global analysis on biofilm abundance exists. We offer a critical discussion of the definition of biofilms and compile current estimates of global cell numbers in major microbial habitats, mindful of the associated uncertainty. Most bacteria and archaea on Earth (1.2 × 10³⁰ cells) exist in the 'big five' habitats: deep oceanic subsurface (4 × 10²⁹), upper oceanic sediment (5 × 10²⁸), deep continental subsurface (3 × 10²⁹), soil (3 × 10²⁹) and oceans (1 × 10²⁹). The remaining habitats, including groundwater, the atmosphere, the ocean surface microlayer, humans, animals and the phyllosphere, account for fewer cells by orders of magnitude. Biofilms dominate in all habitats on the surface of the Earth, except in the oceans, accounting for ~80% of bacterial and archaeal cells. In the deep subsurface, however, they cannot always be distinguished from single sessile cells; we estimate that 20-80% of cells in the subsurface exist as biofilms. Hence, overall, 40-80% of cells on Earth reside in biofilms. We conclude that biofilms drive all biogeochemical processes and represent the main way of active bacterial and archaeal life

Growth of the acidophilic iron–sulfur bacterium Acidithiobacillus ferrooxidans under Mars-like geochemical conditions

The question of life on Mars has been in focus of astrobiological research for several decades, and recent missions in orbit or on the surface of the planet are constantly expanding our knowledge on Martian geochemistry. For example, massive stratified deposits have been identified on Mars containing sulfate minerals and iron oxides, which suggest the existence of acidic aqueous conditions in the past, similar to acidic iron- and sulfur-rich environments on Earth. Acidophilic organisms thriving in such habitats could have been an integral part of a possibly widely extinct Martian ecosystem, but remains might possibly even exist today in protected subsurface niches. The chemolithoautotrophic strain Acidithiobacillus ferrooxidans was selected as a model organism to study the metabolic capacities of acidophilic iron–sulfur bacteria, especially regarding their ability to grow with in situ resources that could be expected on Mars. The experiments were not designed to accurately simulate Martian physical conditions (except when certain single parameters such as oxygen partial pressure were considered), but rather the geochemical environment that can be found on Mars. A. ferrooxidans could grow solely on the minerals contained in synthetic Mars regolith mixtures with no added nutrients, using either O₂as an external electron acceptor for iron oxidation, or H₂as an external electron donor for iron reduction, and thus might play important roles in the redox cycling of iron on Mars. Though the oxygen partial pressure of the Martian atmosphere at the surface was not sufficient for detectable iron oxidation and growth of A. ferrooxidans during short-term incubation (7 days), alternative chemical O₂-generating processes in the subsurface might yield microhabitats enriched in oxygen, which principally are possible under such conditions. The bacteria might also contribute to the reductive dissolution of Fe³⁺-containing minerals like goethite and hematite, which are characterized by a high thermodynamic stability. Even in a desiccated environment, A. ferrooxidans survived for one week under simulated Martian shallow subsurface conditions (6 hPa, −20 °C, 0.13% O₂) in the form of dried biofilms without loss of viability. Low temperature and low oxygen pressure were favorable to survival. Thus, the acidophilic iron–sulfur bacterium A. ferrooxidans may be considered a plausible candidate of a potential Martian food web based on its metabolic capacities. As an autotroph it would be located at the base of such a food web, providing organic carbon

A Comprehensive View of Microbial Communities in the Laundering Cycle Suggests a Preventive Effect of Soil Bacteria on Malodour Formation

Microorganisms are an important factor in the wash-and-use cycle of textiles since they can cause unwanted aesthetic effects, such as malodour formation, and even pose health risks. In this regard, a comprehensive view of the microbial communities in washing machines and consideration of the microbial contamination of used textiles is needed to understand the formation of malodour and evaluate the infection risk related to laundering. So far, neither the compositions of washing machine biofilms leading to the formation of or protection against malodour have been investigated intensively, nor have microbial communities on used towels been analysed after normal use. Our results link the qualitative and quantitative analysis of microbial communities in washing machines and on used towels with the occurrence of malodour and thus not only allow for a better risk evaluation but also suggest bacterial colonizers of washing machines that might prevent malodour formation. It was shown that soil bacteria such as Rhizobium, Agrobacterium, Bosea, and Microbacterium in particular are found in non-odourous machines, and that Rhizobium species are able to prevent malodour formation in an in vitro model