Cultivation of Pichia capsulata as a whole-cell biocatalyst with NADH-dependent alcohol dehydrogenase activity for R -1-phenylethanol production

An odorant binding protein is involved in counteracting detection-avoidance and Toll-pathway innate immunity

INTRODUCTION

Odorant-binding proteins (OBPs) are a class of small molecular weight soluble proteins that exist as expanded gene families in all insects, acting as ligand carriers mediating olfaction and other physiological processes. During fungal infection, a subset of insect OBPs were shown to be differentially expressed.

OBJECTIVES

We tested whether the altered expression of insect OBPs during pathogenic infection plays a role in behavioral or immune interactions between insect hosts and their pathogens.

METHODS

A wide range of techniques including RNAi-directed knockdown, heterologous protein expression, electrophysiological/behavioral analyses, transcriptomics, gut microbiome analyses, coupled with tandem mass spectrometry ion monitoring, were used to characterize the function of a locust OBP in host behavioral and immune responses.

RESULTS

The entomopathogenic fungus Metarhizium anisopliae produces the volatile compound phenylethyl alcohol (PEA) that causes behavioral avoidance in locusts. This is mediated by the locust odorant binding protein 11 (LmOBP11). Expression of LmOBP11 is induced by M. anisopliae infection and PEA treatment. LmOBP11 participates in insect detection of the fungal-produced PEA and avoidance of PEA-contaminated food, but the upregulation of LmOBP11 upon M. anisopliae infection negatively affects the insect immune responses to ultimately benefit successful mycosis by the pathogen. RNAi knockdown of LmOBP11 increases the production of antimicrobial peptides and enhances locust resistance to M. anisopliae infection, while reducing host antennal electrophysiological responses to PEA and locust avoidance of PEA treated food. Also, transcriptomic and gut microbiome analyses reveal microbiome dysbiosis and changes in host genes involved in behavior and immunity. These results are consistent with the elevated expression of LmOBP11 leading to enhanced volatile detection and suppression of immune responses.

CONCLUSION

These findings suggest a crosstalk between olfaction and immunity, indicating manipulation of host OBPs as a novel target exploited by fungal pathogens to alter immune activation and thus promote the successful infection of the host.

Rational design of the carbonyl reductase EbSDR8 for efficient biosynthesis of enantiopure (R)-3-chloro-1-phenyl-1-propanol

(R)-3-Chloro-1-phenyl-1-propanol ((R)-CPPO) is an important chiral intermediate for antidepressants. For its efficient biosynthesis, the carbonyl reductase EbSDR8 was engineered to asymmetrically reduce the unnatural substrate 3-chloro-1-phenyl-1-propanone (3-CPP) at high concentrations. Molecular docking and molecular dynamics simulations of the resulting mutants suggested enlarged substrate binding pocket and more reasonable interactions between the enzyme and the substrate or cofactor as the reasons for the enhanced catalytic activity and thus the remarkably improved conversion of high-concentration 3-CPP. Using the best mutant EbSDR8^{G94A/L153I/Y188A/Y202M} as the whole-cell biocatalyst, reduction of 3-CPP (1.0 M) was conducted using 100% isopropanol as both the solvent and co-substrate for NADH regeneration, delivering (R)-CPPO with ˃ 99% ee_p and 95.5% conversion. This result suggests EbSDR8^{G94A/L153I/Y188A/Y202M} as a potential biocatalyst for green production of (R)-CPPO at the industrial scale. KEY POINTS: • Rational design of EbSDR8 by modulating steric hindrance and molecular interactions; • Non-aqueous biocatalysis using isopropanol as both the solvent and co-substrate; • Whole-cell catalyzed production of 161 g/L enantiopure (R)-CPPO from 1.0 M of 3-CPP. Graphical Abstract.

Biotransformation of β-hydroxypyruvate and glycolaldehyde to l-erythrulose by Pichia pastoris strain GS115 overexpressing native transketolase

Transketolase is a proven biocatalytic tool for asymmetric carbon-carbon bond formation, both as a purified enzyme and within bacterial whole-cell biocatalysts. The performance of Pichia pastoris as a host for transketolase whole-cell biocatalysis was investigated using a transketolase-overexpressing strain to catalyze formation of l-erythrulose from β-hydroxypyruvic acid and glycolaldehyde substrates. Pichia pastoris transketolase coding sequence from the locus PAS_chr1-4_0150 was subcloned downstream of the methanol-inducible AOX1 promoter in a plasmid for transformation of strain GS115, generating strain TK150. Whole and disrupted TK150 cells from shake flasks achieved 62% and 65% conversion, respectively, under optimal pH and methanol induction conditions. In a 300 μL reaction, TK150 samples from a 1L fed-batch fermentation achieved a maximum l-erythrulose space time yield (STY) of 46.58 g L^-1 h^-1 , specific activity of 155 U gCDW-1, product yield on substrate (Y_p/s ) of 0.52 mol mol^-1 and product yield on catalyst (Y_p/x ) of 2.23g gCDW-1. We have successfully exploited the rapid growth and high biomass characteristics of Pichia pastoris in whole cell biocatalysis. At high cell density, the engineered TK150 Pichia pastoris strain tolerated high concentrations of substrate and product to achieve high STY of the chiral sugar l-erythrulose. © 2017 The Authors Biotechnology Progress published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers Biotechnol. Prog., 34:99-106, 2018.