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 (Appendix Table A1). 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) (appendix, Table
2) with 35 °C/21 °C as maximum/minimum temperatures during the course of
day/night temperature ramping. The culture cultivated at constant 35 °C
(AB) was shifted to extreme summer profile (ExSP) (Table 2) 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 sample used for the DW measurement 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).