It is easy to find algae, but finding algae suitable for biotechnology is difficult. Currently, insufficient attention is paid to the selection of algal strains that could be cultivated inexpensively by growing them in wastewater and under ambient condi­tions of light and temperature. It is necessary for entrepreneurs of microalgal bio­technology to invest in selecting algal strains and optimizing their cultivation. The choice of commercial algal strains is of paramount importance and merits rigor­ous investigation. Local species are well adapted to local environmental conditions, and their utility contributes to more successful cultivation than nonnative species; for example, a consortium of Actinastrum, Chlorella, Chlorococcum, Closterium, Euglena, Golenkinia, Micractinium, Nitzschia, Scenedesmus, and Spirogyra, and two unidentified species concentrated from local ponds grew well at a dairy farm in municipal wastewater and yielded 2.8 g m-2 lipid day-1, which would be equivalent to 11,000 L ha-1y-1 (Pitman et al., 2011). Microalgal cultivation in wastewaters is cost effective in producing algal biomass for biofuel, and it also helps in the removal of nutrients (Craggs et al., 2011).

To date, few native species have been studied for their growth and photosyn­thetic efficiencies; with extremophiles, this is seldom the case. For example, pho­tosynthetic rates of the extremophiles Chlamydomonas plethora and Nitzschia frustule, isolated from a semi-arid climate, approached their theoretical maxima corresponding to 22.8 and 18.1 mg C mg chl a-1 h-1 and high photosynthetic effi­ciencies (Subba Rao et al., 2005). Based on their specific growth rates at 10°C, 15°C, 25°C, and 30°C and threshold (I0) and saturation (S) values of irradiance and saturation irradiance for growth, Kaeriyama et al. (2011) demonstrated the existence of physiological races in Skeletonema species isolated from Dokai Bay, Japan. Cultures of microalgae from tropical, subtropical, and semi-arid climates that may have unique physiological characteristics should be studied in detail. Of note, a marine diatom, Navicula sp. strain JPCC DA0580, and a marine green alga, Chlorella sp. strain NKG400014, isolated in Japanese ocean waters (Matsumoto et al., 2009) had a cell composition that yielded energy of 15.9 ± 0.2 MJ kg-1 and

26.9 ± 0.6 MJ kg-1, respectively, which is equivalent to coal energy. Also of inter­est is the Strain B32 Dunaliella isolated from the Bay of Bengal, which yielded a maximum 0.68 pg carotene cell-1 while strain I3 yielded 17.54 pg carotene cell-1 (Keerthi et al., in press).

Extremophile algae stressed by high temperatures, light, salinity, and nutrients seem to have physiologically adapted to their harsh environmental conditions even under high irradiation, as evidenced by a chlorophycean microalga in the storage pools of nuclear reactors (Rivasseau et al., 2010). Because of their resilience, cultur­ing these algae under ambient environmental conditions reduces the dependency on seasons for cultivation and the need to shut off operations during extreme climatic conditions. This will be cost-effective and enhance their utility in biotechnology. The thermo-acidophilic red alga Galderia sulphuraria isolated from environments with pH 0 to 4 pH and temperatures up to 56°C can survive both autotrophically and heterotrophically (Weber et al., 2004). This alga has a repertoire of metabolic enzymes with high potential for biotechnology. Its tolerance for high concentra­tions of cadmium, mercury, aluminum, and nickel supports its potential for biore­mediation. The desert crusts seem to support extremophile members of five green algal classes; these unicellular algae growing under selective pressures of the desert appear to have high desiccation and photophysiology tolerance (Cardon et al., 2008). The extremophile cyanobacteria, mostly Microcoleus sp. living in the desert crust, are remarkably resistant to photo-inhibition, in contrast to Synechocystis sp. strain PCC 6803, and, within minutes of rehydration, recover their photosynthetic activ­ity (Harel et al., 2004). Comparison of the extremophile Chlamydomonas rauden — sis Ettl UWO 241 isolated from an ice-covered Antarctic lake with its mesophilic counterpart C. raudensis Ettl. SAG 49.72 (SAG) isolated from a meadow pool in the Czech Republic, showed different abilities for acclimation (Pocock et al., 2011). The UWO 241 strain, unlike the other, relied on a redox sensing and signaling system for growth that bestows better success under stressful environmental conditions.

Nannochloris sp., isolated from the Great Salt Plains National Wildlife Refuge, grew in salinities from 0 to 150 PSU (practical salinity unit) and temperatures up to 45°C; growth and photosynthesis saturation were at 500 mol photons m-2s-1. Although the division rates in this alga were equal, in cells acclimated to low or high salinity and temperature, the former had a higher photosynthetic performance (Pmax) than the latter (Major and Henley, 2008).

The extremophile Coccomyxa acidophila (pH < 2.5) accumulated more lutein (3.55 mg g-1) when grown in urea (Casal et al., 2011). In another extremophile, Chlamydomonas acidophila (pH 2-3.5), stringent limitation of phosphate resulted in higher total fatty acid levels and lower percentages of polyunsaturated fatty acids (Spijkeman and Wacker, 2011). C. acidophila cultures grown on urea as a carbon source yielded high biomass levels (~20 g dry biomass m-2d-1) compared to ~14 g dry biomass m-2d-1 grown mixotrophically utilizing glucose as a carbon source (Cauresma et al., 2011). Mixotrophic growth of C. acidophila on glucose resulted in better accumulation of carotene and lutein (10 g kg-1 DW), the highest recorded for a microalga (Cauresma et al., 2011). In Dunaliella salina living under high light and salt stress, carotenogenesis shifted to higher salinity and increased substantially under nutrient-limiting conditions (Coesel et al., 2008); nutrient availability seems to control carotenogenesis and messenger-RNA levels. The extremophile (photopsychrophile) Chlorella sp. Strain BI isolated from Antarctica is unique in retaining the ability for dynamic short-term adjustment of light energy distribution between Photosystem II and Photosystem I, and can grow as a heterotroph in the dark (Morgan-Kiss et al., 2008).