It has previously been reported that a certain Pi concentration will
repress yeast phytase production differently in different media and
pH, and that the temperature has a strong effect of phytase activity
(Andlid et al., 2004; Li et al., 2009; Ushasree et al., 2014). Our findings
on P. kudriavzevii are not in agreement with Quan et al. (2001) which
showed that phytase production by P. kudriavzevii occurs in the late
stage of exponential growth phase. As previously mentioned, this
might be due to different growth conditions of the strains. However,
considering that the enzyme has been secreted during 48 hwe expected
the highest extracellular activity to be at the end of cultivation. At the
moment, we do not have a clear explanation for that.
Expressions of other genes than PHYPk also seemto play a role in the
activity of P. kudriavzevii. Further studies are therefore necessary to better
investigate the molecular basis of the phytase production in P.
kudriavzevii, the presence and interactions with other phytase genes
and a more detailed investigation of the genetic system responsible
for transcriptional regulation of phytases. The identification and study
of regulatory genes in P. kudriavzevii and the identification of appropriatemutants
in the autochthonous strainsmay be an opportunity to improve
even more phytate degradation in fermented foods.
Considering the importance of this species in African traditional
fermentation and the occurrence of micronutrient deficiencies in
African countries, studying phytase production during yeast growth in
fermented foods is of significant importance. In the present work, for
the first time, a phytase-coding gene of P. kudriavzevii PHYPk was identified,
its expression level quantified and correlated with enzyme activity.
Furthermore, the phytase gene expression was for the first time
investigated during growth. The identified gene PHYPk seemed to be
involved in the hydrolysis of phytate allowing the yeast growth in the
absence of free phosphate.
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.ijfoodmicro.2015.04.011.