Strains, growth conditions and growth physiology
Cultures of the psychrophilic Chlamydomonas sp. UWO 241
(CCMP1619) and a mesophilic strain, Chlamydomonas raudensis SAG
49.72, were grown in Bold’s basal medium (BBM) (Nichols & Bold, 1965)
under ambient CO2 conditions in 250 mL Pyrex tubes
submerged in temperature-regulated aquaria as described in Morgan-Kiss
et al. (2008). The mesophilic SAG 49.72 was chosen for comparison as it
has been used in several comparative studies with UWO 241 (Pocock,
Vetterli, & Falk, 2011; Szyszka-Mroz et al., 2019; Szyszka-Mroz et al.,
2015; Szyszka, Ivanov, & Hüner, 2007). Cultures were grown under either
control (C) conditions or exposed to one of three long-term stress
treatments: high light (HL), low temperature (LT) or high salt (HS). For
control conditions, cultures were grown under temperature/light regimes
of 8oC/50 μmol -2s-1 and 20oC/50 μmol-2 s-1 for UWO 241 and SAG 49.72,
respectively, and NaCl levels of 0.43 mM for both strains (Table 1).
Long-term stress conditions were chosen based on previous studies
(Morgan-Kiss et al., 2006; Pocock et al., 2011; Szyszka et al., 2007) to
reflect the maximum level of a particular stress to which the organism
could fully acclimate, that is achieve exponential growth and high
photochemical activity (maximum photosynthetic efficiency values,
FV/FM, above 0.5). Long-term stress
conditions for UWO 241 and SAG 49.72, respectively, were: i) high light,
250 μmol m-2 s-1 and 500 μmol
m-2 s-1; ii) low temperature, 2° C and 11 ° C; iii) high salinity, 700 mM NaCl and 100
mM NaCl.
Growth kinetics were monitored as change in optical density at 750 nm.
All other measurements were performed on mid-log phase cultures.
Chlorophyll a and b concentrations were determined from whole cell
extractions in 90% acetone according to Jeffry & Humphrey (1975).