Culturing of Synechococcus clones:

Monocultures of six clones of Synechococcus were used to examine variation and controls on Si quotas and rates of Si accumulation. Cultures were procured from the National Center for Marine Algae and Microbiota (NCMA) at the Bigelow Laboratory for Ocean Sciences in Boothbay Harbor, Maine. Many of these clones are also available in other culture collections and have various strain names; here we will refer to each by their NCMA strain number (a.k.a. CCMP number).

All clones were maintained in aged surface Sargasso Sea water with f/2 media constituents with 10 – 100 uM Si depending on the experiment as detailed below. The temperature was 21C with low light 65 microeinsteins per second per square meter (uE/m2/s) on a 12 h light : 12 h dark photocycle. pH was regulated in all cultures by bubbling with humidified ambient air which was sterilized by passage through a bacterial filter prior to entering each culture vessel. Unless otherwise specified, all experiments were conducted under these temperature and light conditions. pH was monitored daily and remained below 8.5 in all experiments.

Influence of [Si(OH)4] on growth rate:

The three silicic acid levels were used: 1 uM (ambient Sargasso Sea water concentration), 60 uM and 120 uM with f/2 levels of all other medium constituents (macronutrients, trace metals, vitamins). Prior to harvest clones were maintained in exponential growth in batch culture for at least 10 generations within each treatment. Growth rates in these cultures were determined by measuring Cell fluorescence (f) to monitored changes in biomass using a TD-700 fluorometer (Turner Designs, Inc.) with a chlorophyll fluorescence filter set. Cells were transferred to fresh media while still in exponential growth. Growth rate at each concentration was determined from the slope of linear regressions of ln(f) versus time over four to six transfers to fresh culture medium. A 1-mL sample was preserved with glutaraldehyde for determining cell abundance using a Beckman Coulter Multisizer 3 coulter counter with a 20 um aperture (part 8320515, range 0.4 - 12 um).

Growth_rate.csv