Pigments production and cell growth at pH 6.5 with
different nitrogen sources At pH 6.5 both cell growth and
pigments production were significantly inhibited independently to
the nitrogen source employed, especially when nitrate was used.
Because of the extremely low DCW and pigments yield for nitrate,
the data were not shown. The maximum DCW for ammonium and
peptone were approximately 4.5 g/L in both cases (Fig. 3A1 and
B1), corresponding to less than half of the values observed at pH
2.5 and 4.0. The yield of intracellular pigments was also much
lower, around 1/5 to 1/4 of that at pH 2.5 and 4.0 (according to
the absorbance at 410 nm). However, extracellular pigments
secretion was greatly increased and the ratios of intracellular to
extracellular pigments concentration at 132 h (according to the
absorbance at 410 nm) were approximately 5.51 and 0.36 for
ammonium and peptone, respectively (Fig. 3A2 and B2). Unlike
other fermentation conditions, for peptone at pH 6.5 the
concentrations of extracellular pigments were higher than the
intracellular pigments and the absorbance of extracellular
pigments at 510 nm reached 68.11 AU. It was noteworthy that
the absorbance spectra of intracellular and extracellular pigments
(Fig. 3A3 and B3) exhibited large differences from those recorded
at pH 2.5 and pH 4.0. When ammonium was the nitrogen source,
the absorbance spectrum of the extracellular broth presented a
maximum at 475 nm and a shoulder at about 410 nm, whereas
the intracellular extract showed two maxima at 527 nm and
413 nm, with the absorbance at 413 nm slightly higher than that
at 527 nm. The spectrum of the intracellular extract match the