Outdoor Simulation: Phase III
Phase III involved exposing the cultures to dynamic temperature profiles
with hourly changes in temperature that are representative of outdoor
summer culture temperature profiles (Supplementary Material). This final
phase of cultivation was carried out from day 33-43 with scheduled
alternate day dilutions and with no adaptation period. The cultures
grown at constant 20 °C (EF) and one set of the constant 30 °C (CD)
cultures were shifted to average summer profile (AvSP) with 35 °C/21 °C
as maximum/minimum temperatures during the course of day/night
temperature ramping. The cultures at constant 35 °C (AB) were shifted to
an extreme summer profile (ExSP) with 39 °C/26 °C as maximum/minimum
temperatures, and the final set of two photobioreactors at constant 30
°C (GH) were shifted to constant summer profile (CtSP) where day/night
temperature were maintained at constant 31 °C/21 °C, selected based on
Fort Myers summer profile and averaging the day and night temperatures
separately.
The average pre-dilution cell concentration in gDW L-1for the temperature profile treatments are shown in Table 1. The
relative dilution rates were about 0.16 day-1 in AvSP
(CD), AvSP (EF) and CtSP (GH), and about 20% lower (0.135
day-1) for ExSP (AB).
From visual observations, it is worth noting that during the processing
of biomass samples for the various analyses, agglomeration or clumping
of the algal cultures occurred for cultures grown at higher temperature
(constant 35 °C and ExSP). This is attributed to a stress response. In
addition, the dried samples from these temperature exposures showed a
flaky texture on the dry weight plate membrane surface. In
cyanobacteria, high temperature stress can result in a rise in fluidity
of membranes which can cause disintegration of the lipid bilayer and
many other alterations in the physical properties of the cells that
result in the loss of functionality of photosynthetic machinery
(Panyakampol et al., 2015; Panyakampol et al., 2016).