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

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