Psychrophilic and psychrotrophic respiratory metabolism in antarctic microplankton

Abstract

The activity of the respiratory Electron Transfer System (ETS) was measured in total microplankt on (<200-μm size fraction) and nanoplankton (<20-μm size fraction) from the Bransfield Strait, during the ECOANTAR 1993–1994 cruise of the Spanish B.I.O.Hespérides in January 1994. Activity variation in response to temperature was measured at three stations belonging to three different water masses that showed in situ temperatures ranging from — 0.57 to 1.30°C. Subsamples from each station were assayed for ETS activity at 11 temperatures in the — 3 to 20°C range. The results showed a bimodal activity-temperature variation in plankton from the lower in situ temperatures, with a peak in activity at 0°C, and a minimum at 3°C, with subsequent continuous increase up to absolute maxima at 15°C. The water mass with higher than 0°C temperature did not show the 0°C activity peak. The results suggest the existence, in water masses with in situ temperature near or below 0°C, of psychrophilic microbial populations with a narrow temperature range of respiratory enzyme activity, coexisting with more numerous and widespread psychrotrophs, or cold-tolerant populations, whose ETSs showed a continuous increase in activity in the — 3 to 15°C temperature range. Arrhenius activation energies (E_a) of total microplankton ranged from 3 to 17 kcal mole⁻¹, and the Q₁₀ from 1.2 to 3.5. These facts point to the existence of differentiated biochemical adaptations and acclimations to low temperature in polar plankton, an issue that has been much discussed in the recent past.