2.1 Algal incubation and mineral treatments
C. reinhardtii (CC-125) was purchased from the Chlamydomonas
Resource Center, Department of Plant and Microbial Biology, University
of Minnesota, United States. It was initially cultured in
Tris-Acetate-Phosphate (TAP) medium at (25 ± 2) oC
(light/dark 12/12h, light intensity 2000 Lux) [22]. The algal strain
was then purified by streaking on an agar plate with TAP medium and
forming algal colonies. A 0.5 cm x 0.5 cm algal sample was collected
from the plate, and then placed in a 100 mL liquid TAP medium prior to
the mineral treatments.
Mt (STx-1) and Pal (PFl-1) were purchased from the Clay Minerals
Society. For Mt, its cation exchange capacity (CEC) was 84.4 meq/100g
and the specific area was 83.79 ± 0.22 m2/g. For Pal,
the CEC was 19.5 meq/100g and the specific area was 136.35 ± 0.31
m2/g (data taken from the website of Clay Minerals
Society, https://www.clays.org/sourceclays_data/).
The two minerals were added into a 100 mL TAP medium to obtain the Mt
and Pal concentrations (0, 200, and 500
mg/L). For the mineral exposure,
1 mL suspension of C. reinhardtii (in the logarithmic phase of
growth) was incubated in the above mineral-TAP
composite. The mineral treatments
were denoted as Mt0, Mt200,
Mt500, Pal0, Pal200,
Pal500, respectively. All the samples were cultured by
shaking three times every day during four-day incubation. Additionally,
in order to explore the ability of phosphorus (P) uptake by C.
reinhardtii under mineral treatments, we set two P concentrations, 3.15
mg/L and 31.5 mg/L, respectively in the algal culture. For other
analyses, the P concentration in the culture medium was 3.15 mg/L. Three
replicates were prepared for each treatment.