The limits for life under multiple extremes

Aerobically respiring prokaryotic strains exhibit a broader temperature–pH–salinity space for cell division than anaerobically respiring and fermentative strains

“…Indeed, global metagenome surveys to date have focused on pelagic marine habitats [83 -85]. Additionally, attempts to define the habitable parameter space on the Earth have necessarily been restricted to data obtained for isolates [9][10][11][12]. As the vast majority of microorganisms are unculturable in the laboratory [86], it remains unclear how representative the taxa employed in our study are of those that define the temperature, pH and salinity limits for cell division within natural environments.…”

“…Additionally to research into the in situ activities of microbial communities under extreme conditions [6 -8], the isolation and physiological characterization of microbial strains has been essential to our knowledge of the physico-chemical limits for life, as it has enabled us to investigate the growth phenotypes of extremophilic taxa in detail. Based on cardinal growth data (minimal, optimal and maximal conditions for cell division), several efforts to characterize the global-scale boundary space for bacterial and archaeal cell division have now been made, using two-and three-dimensional maps of habitability [9][10][11][12].…”

“…Adaptation to low-energy conditions has additionally been proposed as a factor that distinguishes between the temperature and the pH preferences of thermophilic bacteria and archaea [23,24]. Global-scale limits to cell division, however, have not been determined for individual modes of catabolism, particularly with reference to multiple-stress conditions that characterize the majority of extreme environments on the Earth [12,25,26]. For instance, as aerobic respiration frequently results in high cellular growth yields [27] and can enable ATP yields up to an order of magnitude higher than those attained anaerobically (with up to 36 ATP molecules for each oxidized glucose molecule), could this type of metabolism enable cell division over a broader range of physical and chemical extremes than other catabolic pathways?…”

“…While culture-based data are characterized by several biases, other types of data are currently insufficient for estimating global-scale boundaries for cell division, with in situ limits to microbial activity only having been described for a small selection of environments (see [12] and Discussion section). Three-dimensional approximations of the window for cell division on the Earth were constructed using a modification of a previously described method [12]. To enable plotting, the mean of the strain-specific growth minimum and maximum was used in the absence of optimal growth data.…”

Space as a Tool for Astrobiology: Review and Recommendations for Experimentations in Earth Orbit and Beyond

“…Low pressure down to space vacuum, exceptionally low relative humidity, and in particular highly ionizing and short-wavelength solar UV radiation are quite common in space and on the surfaces of Solar System bodies, and can only partly be simulated due to their complexity . In particular it is important to study the response of extremophiles to multiple extremes (Harrison et al 2013).…”