Improved hydrogen ion buffering of media for the culture of freshwater algae

Abstract

Six hydrogen ion buffers, piperazine-N, N′-bis (2-ethanesulphonic acid) (PIPES), N(-2-acetamido)-2-aminoethanesulphonic acid (ACES), N, N-bis (2-hydroxyethyl)-2-aminoethanesulphonic acid (BES), N-tris (hydroxymethyl)-methyl-2-aminoethanesulphonic acid (TES), N-2-hydroxyethylpiperazine-N′-2-ethanesulphonic acid (HEPES) and N-tris (hydroxymethyl) methylglycine (TRICINE), employed at 0·02 m concentration in freshwater media at their p ^{K _a} values, were found to have no adverse effects on the growth rates of Oscillatoria redekei van Goor, Chlorella vulgaris Beij. and Pediastrum boryanum (Turp.) Menegh. The doubling times of Aphanizomenon flos-aquae fa. gracile (Ralfs) Lemm. and Anabaena flos-aquae Bréb. were lengthened by the presence of PIPES and ACES but this was interpreted as an effect of their low p ^{K _a} values. Further results with HEPES and Oscillatoria redekei during exponential growth showed that, with a 1% CO₂-in-air gas phase, a pH variation of only 0·06 pH units was obtained compared with 2·77 units in the media alone. These results contrasted favourably with tris (hydroxymethyl) aminomethane (TRIS) buffer which severely inhibited the growth of the blue-green algae tested. This inhibition was shown to be partially counteracted in the case of Oscillatoria redekei by the addition of potassium chloride. With the other buffers, the use of the hydroxides of monovalent cations other than sodium to set the buffers at their p ^{K _S} values caused inhibition of growth. Of the buffers examined, HEPES was considered to have potentially the most versatile application because of its favourable p ^{K _a} of 7·55 and its negligible metalbinding capacity.