interestingly, although the growth and pigments production
were greatly inhibited when nitrate was used as nitrogen source at
pH 6.5, the spectrum of the intracellular extract, with its maximum
at 471 nm, was almost identical to the spectra observed at pH 2.5
and 4.0, suggesting that, differently from what observed for
ammonium and peptone, the intracellular extract consisted mainly
of orange pigments. The spectrum of the extracellular broth presented
two peaks at 407 nm and 492 nm, suggesting that they
might mainly consist of red pigments derivatives.