Hydrogen Ion Buffering of Culture Media for Algae From Moderately Acidic, Oligotrophic Waters 1

Five hydrogen ion buffers were compared for their usefulness in regulating pH in a model oligotrophic, moderately acidic (pH 6.0) algal growth medium. These were 3,3‐dimethylglutaric acid (DMGA), tricarbaliylic acid (TCA), trans‐aconitic acid (tAA), N‐2‐hydroxyethylpiperazine‐N′‐2‐ethanesulfonic acid (HEPES) and 2‐(N‐morpholino) ethanesulfonic acid (MES). All buffers (2.5 mM) except HEPES limited the reduction of pH in a NH4+‐based medium during growth of Chrysochromulina breviturrita Nich. to less than 0.12 units, compared with more than 2 units in an unbuffered medium. Long term growth of C. breviturrita in these media was significantly inhibited (P < 0.05) by TCA and tAA. MES was able to control pH with the minimum amount of NaOH (1.0 mM) added to the medium to adjust to pH 6.0. Four of five bacterial isolates were capable of utilizing tAA as a sole organic‐C source, and no isolate could metabolize HEPES or MES. No significant differences (P > 0.05) were found in the maximum growth rates of six algal species (from five classes) in a medium with or without MES buffer, although significantly greater cell yields of Ochromonas danica Prings. were obtained in the buffered medium. MES (pK4=6.15) was considered to be the most useful buffer in the pH range 5.0–6.5, due to its biological inertness, buffering capacity, the minimal requirement for excess base to adjust pH and its minimal metal complexing ability.