Ogataea parapolymorpha (Hansenula polymorpha DL-1) is
a thermotolerant methylotrophic yeast with biotechnological
applications. Here, O. parapolymorpha genes whose expression
is induced in response to heat shock were identified by
transcriptome analysis and shown to possess heat shock elements
(HSEs) in their promoters. The function of O. parapolymorpha
HSF1 encoding a putative heat shock transcription
factor 1 (OpHsf1) was characterized in the context of heat
stress response. Despite exhibiting low sequence identity
(26%) to its Saccharomyces cerevisiae homolog, OpHsf1 harbors
conserved domains including a DNA binding domain
(DBD), domains involved in trimerization (TRI), transcriptional
activation (AR1, AR2), transcriptional repression (CE2),
and a C-terminal modulator (CTM) domain. OpHSF1 could
complement the temperature sensitive (Ts) phenotype of a
S. cerevisiae hsf1 mutant. An O. parapolymorpha strain with
an H221R mutation in the DBD domain of OpHsf1 exhibited
significantly retarded growth and a Ts phenotype. Intriguingly,
the expression of heat-shock-protein‒coding genes harboring
HSEs was significantly decreased in the H221R mutant
strain, even under non-stress conditions, indicating the importance
of the DBD for the basal growth of O. parapolymorpha.
Notably, even though the deletion of C-terminal domains
(ΔCE2, ΔAR2, ΔCTM) of OpHsf1 destroyed complementation
of the growth defect of the S. cerevisiae hsf1 strain,
the C-terminal domains were shown to be dispensable in O.
parapolymorpha. Overexpression of OpHsf1 in S. cerevisiae
increased resistance to transient heat shock, supporting the
idea that OpHsf1 could be useful in the development of heatshock‒
resistant yeast host strains.
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α-Glucosidase is a crucial enzyme for the production of isomaltooligosaccharide.
In this study, a novel method comprising
eosin Y (EY) and α-D-methylglucoside (AMG) in glass
plates was tested for the primary screening of α-glucosidaseproducing
strains. First, α-glucosidase-producing Aspergillus
niger strains were selected on plates containing EY and AMG
based on transparent zone formation resulting from the solubilization
of EY by the hydrolyzed product. Conventional methods that use trypan blue (TB) and p-nitrophenyl-α-Dglucopyranoside
(pPNP) as indicators were then compared
with the new strategy. The results showed that EY-containing
plates provide the advantages of low price and higher specificity
for the screening of α-glucosidase-producing strains.
We then evaluated the correlation between the hydrolytic activity
of α-glucosidase and diffusion distance, and found that
good linearity could be established within a 6–75 U/ml enzyme
concentration range. Finally, the hydrolytic and transglycosylation
activities of α-glucosidase obtained from the
target isolates were determined by EY plate assay and 3,5-
dinitrosalicylic acid-Saccharomyces cerevisiae assay, respectively.
The results showed that the diameter of the transparent
zone varied among isolates was positively correlated with
α-glucosidase hydrolytic activity, while good linearity could
also be established between α-glucosidase transglycosylation
activity and non-fermentable reducing sugars content. With
this strategy, 7 Aspergillus niger mutants with high yield of
α-glucosidase from 200 obvious single colonies on the primary
screen plate were obtained.
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