TRIS NOT ONLY CONTROLS THE PH IN MICROALGAL CULTURES, BUT ALSO FEEDS BACTERIA

Tris (Tris(hydroxymethyl)amino methane), a compound often used as a bu ffer in microalgal culture media, sustains active bacterial growth in non-axenic microalgal cultures when sodium phosphate is present. The l ow pH levels caused by bacterial growth and probably the depletion of phosphorus in the medium caused the collapse of Phaeodactylum tricornu tum cultures resulting in a reduction of microalgal growth from 32 x 1 0(6) to 1.1 x 10(6) cells ml(-1). This emphasizes the need for care wh en interpreting thf results of non-axenic microalgae cultures in which Tris or other organic buffer is added.