**8. References**

268 Artificial Photosynthesis

Recently Gorbunov et al., (submitted) were able to conduct photoacoustic measurements on *Chlamydomonas reihardtii* and to determine the allocation of energy to either photosystem by using PSI or PSII deficient mutants. In these experiments the brief exciting pulses hitherto produced by lasers were generated by red light emitting diodes (Fig. 12), and the saturating,

Fig. 13. The same setup as in fig 12. The blue LEDs provide the saturating, continuous light. Recently Chengyi Yan et al. (submitted) were able to conduct photoacoustic measurements on *Chlamydomonas reihardtii* and to determine the allocation of energy to either photosystem by using PSI or PSII deficient mutants. In these experiments the brief exciting pulses hitherto produced by lasers were generated by red light emitting diodes (Fig. 12), and the saturating,

In these experiments the authors also estimated the contribution of electrostriction to the photoacoustic signal by comparing results at room temperature with ones measured at 4 oC, the temperature at which the photobaric signal is eliminated, and electrostiction is singled out.

1. Photoacoustics can be used to reliably estimate the concentration of photosynthetic

2. The efficiency of energy storage by phytoplankton photosynthesis can be estimated

continuous light was provided by blue LEDs (Fig. 13).

continuous light was provided by blue LEDs (Fig. 13).

pigments in phytoplankton cultures or assemblages.

directly, easily, rapidly and reliably by photoacoustics.

**7. Conclusions** 


**13** 

*Spain* 

**Photosynthesis in Extreme Environments** 

Angeles Aguilera1, Virginia Souza-Egipsy2 and Ricardo Amils1,3

Our ongoing exploration of Earth has led to continued discoveries of life in environments that have been previously considered uninhabitable. For example, we find thriving communities in the boiling hot springs of Yellowstone, the frozen deserts of Antarctica, the concentrated sulfuric acid in acid-mine drainages, and the ionizing radiation fields in nuclear reactors (González-Toril et al., 2003; Lebedinsky et al., 2007; Pointing et al., 2009). We find some microbes that grow only in brine and require saturated salts to live, and we find others that grow in the deepest parts of the oceans and require 500 to 1000 bars of hydrostatic pressure (Horikoshi, 1998; Ma et al., 2010). Life has evolved strategies that allow it to survive even beyond the daunting physical and chemical limits to which it has adapted to grow. To survive, organisms can assume forms that enable them to withstand freezing, complete desiccation, starvation, high levels of radiation exposure, and other physical or chemical challenges. Furthermore, they can survive exposure to such conditions for weeks, months, years, or even centuries. We need to identify the limits for growth and survival and

Biochemical studies will also reveal inherent features of biomolecules and biopolymers that define the physico-chemical limits of life under extreme conditions. Broadening our knowledge both of the range of environments on Earth that are inhabitable by microbes and of their adaptation to these habitats will be critical for understanding how life might have

The diversity of life on Earth today is a result of the dynamic interplay between genetic opportunity, metabolic capability, and environmental change. For most of their existence, Earth's habitable environments have been dominated by microorganisms and subjected to their metabolism and evolution. As a consequence of geological, climatologic, and microbial processes acting across geological time scales, the physical-chemical environments on Earth have been changing, thereby determining the path of evolution of subsequent life. For example, the release of molecular oxygen by cyanobacteria as a by product of photosynthesis as well as the colonization of Earth's surface by metazoan life contributed to fundamental, global environmental changes. The altered environments, in turn, posed novel evolutionary opportunities to the organisms present, which ultimately led to the formation

to understand the molecular mechanisms that define these limits.

**1. Introduction** 

established itself and survived.

of our planet's major animal and plant species.

*1Centro de Astrobiología (INTA-CSIC) 2Centro de Investigaciones Agrarias (CSIC) 3Centro de Biología Molecular (UAM-CSIC)* 

