Angewandte
Communications
Chemie
Biocatalysis
Hot Paper
Temperature-Directed Biocatalysis for the Sustainable Production of
Aromatic Aldehydes or Alcohols
Abstract: The biosynthesis of aromatic aldehydes and alcohols
from renewable resources is currently receiving considerable
attention because of an increase in demand, finite fossil
resources, and growing environmental concerns. Here, a tem-
perature-directed whole-cell catalyst was developed by using
two novel enzymes from a thermophilic actinomycete. Ferulic
acid, a model lignin derivative, was efficiently converted into
vanillyl alcohol at a reaction temperature at 308C. However,
when the temperature was increased to 508C, ferulic acid was
harbor many characterized and uncharacterized ADHs, and
selecting the correct target genes for eliminating this activity
is challenging.[5c,6]
Herein, we propose a novel strategy inspired by cell-free
systems for the efficient biosynthesis of aromatic aldehydes,
which does not require purified enzymes or knockout/knock-
down of ADHs. The use of whole cells for biocatalytic
reactions is an effective method for the production of value-
added products.[7] We assumed that endogenous ADHs might
lose their activity at high temperatures while the activities of
functional enzymes from thermophilic strains can be retained
in artificial whole-cell catalysis. To confirm the feasibility of
this strategy, a model aromatic aldehyde, vanillin (1), was
chosen as the target product.[8] Ferulic acid (FA, 2), an easily
available component of lignin, was used as the feedstock for
the production of vanillin.[9] Normally, feruloyl-CoA synthe-
tase (Fcs, encoded by fcs) and enoyl-CoA hydratase/aldolase
(Ech, encoded by ech) are found in most FA-degrading
strains. These strains convert 2 into 1 via a coenzyme A-
dependent, non-b-oxidative pathway (Scheme 1). However,
the instability and inefficiency of enzymes from mesophilic
bacteria hamper their application.[10]
mainly converted into vanillin with
a productivity of
1.1 gLÀ1 hÀ1. This is due to the fact that the redundant
endogenous alcohol dehydrogenases (ADHs) are not active
at this temperature while the functional enzymes from the
thermophilic strain remain active. As the biocatalyst could
convert many other renewable cinnamic acid derivatives into
their corresponding aromatic aldehydes/alcohols, this novel
strategy may be extended to generate a vast array of valuable
aldehydes or alcohols.
R
ecent years have witnessed a rising demand for bio-based
polymers owing to the restricted availability of petrochemical
resources and increasing environmental concerns.[1] In poly-
meric backbones, aromatic units offer rigidity, hydrophobic-
ity, and fire resistance.[2] However, aromatic aldehyde mono-
mers are predominantly produced by energy-intensive che-
mocatalysis of non-renewable petroleum feedstocks.[3] The
use of microorganisms for converting renewable substances
into aromatic monomers would provide a low-energy sustain-
able and green alternative. Unfortunately, aromatic alde-
hydes are rapidly converted into undesirable aromatic
alcohols by numerous endogenous alcohol dehydrogenases
(ADHs) with broad substrate specificity.[4] Recently, several
attempts have been made to overcome this primary barrier in
the biosynthesis of aromatic aldehydes.[5] For example, an
Escherichia coli strain was generated by the deletion of six
genes that contribute to benzaldehyde reduction, and used to
increase the production of vanillin (1), benzaldehyde, and
l-phenylacetylcarbinol.[5c] Nevertheless, microorganisms
Scheme 1. Proposed route for the catabolism of ferulic acid into
vanillin in A. thermoflava. Fcs =feruloyl-CoA synthetase, Ech=enoyl-
CoA hydratase/aldolase, Vdh =vanillin dehydrogenase.
First, we attempted to identify efficient and thermostable
enzymes for converting 2 into 1. A thermophilic actino-
mycete, Amycolatopsis thermoflava N1165, was found to
rapidly degrade more than 35 mm FA (2) at 508C and produce
approximately 61.3 mgLÀ1 of vanillin (1; Figure 1A). To the
best of our knowledge, this is the first report of microbial
production of 1 at 508C. In addition, a small amount of
vanillic acid (3) was also detected, which indicated that
1 could be degraded further. According to phylogenetic
analysis, A. thermoflava N1165 is closely related to Amyco-
latopsis sp. ATCC39116 (see the Supporting Information,
Figure S1). Hence, we speculated that similar to Amycola-
topsis sp. ATCC39116, the catabolism of 2 in A. thermoflava
N1165 was also catalyzed by Fcs and Ech (Scheme 1).[11]
Furthermore, the enzymes involved in the degradation of 2
in the thermophilic bacterium might be more stable.
[*] Dr. J. Ni,[+] Y. Y. Gao,[+] Dr. F. Tao, H. Y. Liu, Prof. P. Xu
State Key Laboratory of Microbial Metabolism and School of Life
Sciences & Biotechnology
Shanghai Jiao Tong University
Shanghai 200240 (P. R. China)
E-mail: taofei@sjtu.edu.cn
[+] These authors contributed equally to this work.
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
1214
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2018, 57, 1214 –1217