Vanillin production by recombinant strains of Escherichia coli

Produção de vanilina por linhagens recombinantes de Escherichia coli

INDUSTRIAL MICROBIOLOGY

Vanillin production by recombinant strains of Escherichia coli

Produção de vanilina por linhagens recombinantes de Escherichia coli

Attilio Converti^I; Danilo de Faveri^I; Patrizia Perego^I; Paolo Barghini^II; Maurizio Ruzzi^II; Luciane Sene^III

^IDepartamento de Engenharia Química e de Processo, Universidade de Genova, Genova, Itália

^IIDepartamento de Agrobiologia e Agroquímica, Universidade de Tuscia, Viterbo, Itália

^IIIDepartamento de Ciências Biológicas e da Saúde, Universidade Estadual do Oeste do Paraná, Cascavel, PR, Brasil

^{Correspondence}

ABSTRACT

Vanillin production from ferulate was studied using different recombinant strains of Escherichia coli. To prevent the occurrence of aerobic conditions and then possible product oxidation, tests were performed in Erlenmeyer flasks under mild mixing (150 rpm). Among other transformants, E. coli JM109(pBB1) appeared to be the best vanillin producer, being able to convert no less than 95% of starting ferulate to the product within 1h. This yield decreased down to 72% after 72h, likely because of a non-specific oxidase activity responsible for vanillin oxidation to vanillate.

Key words: vanillin, ferulate, Escherichia coli JM109, recombinant strains.

RESUMO

A produção de vanilina a partir de ácido ferúlico foi estudada utilizando-se diferentes linhagens recombinantes de Escherichia coli. Para prevenir a ocorrência de condições de aerobiose e a possível oxidação do produto, os ensaios foram realizados em frascos Erlenmeyer sob agitação moderada (150 rpm). E. coli JM109 (pBBI) mostrou-se o melhor produtor de vanilina entre os demais agentes transformantes, sendo capaz de converter 95% do ácido ferúlico inicial em produto após 1h, rendimento este que decresceu para 72% após 72h, provavelmente devido à atividade de uma oxidase não-específica responsável pela oxidação de vanilina a ácido vanílico.

Palavras-chave: vanilina, ácido ferúlico, Escherichia coli JM109, linhagens recombinantes.

INTRODUCTION

The increasing interest of the food industry for the use of biocatalysts, as an answer to the increased demand of natural products (1), has recently been stimulating the search for alternative ways to produce vanillin (2). Seeing that the use of a natural substrate or catalyst would allow the product itself to be classified as natural (3), we hope for a biotechnological production of this compound, which is at present synthesized chemically and mainly utilized as flavor in food industry (4). One of the most interesting biotransformations to produce vanillin is the microbial conversion of ferulate (5).

Such a bioconversion has been tested in this work using five vanillate-producing mutants of Escherichia coli, previously made unable to oxidize vanillin through deletion of the gene codifying for vanillin dehydrogenase. Among these, E. coli JM109(pBB1) was shown to be the best vanillin producer.

MATERIALS AND METHODS

Microorganisms growth and bioconversion conditions

Tests were carried out using different recombinant strains of Escherichia coli (DH5a, JM109, Novablu, SureII and XL10gold), belonging to the collection of the Agrobiology and Agrochemistry Department, Tuscia University, Viterbo, Italy. Cells were maintained at 4ºC on Petri plates containing LB medium and 0.1 g/L ampicillin. The pre-culture was prepared in 5 mL of the same medium without agar. The inoculum was cultivated over-night at 150 rpm and 37ºC. Then, 30 mL of fresh LB containing 0.1 g/L ampicillin were transferred into 300 mL Erlenmeyer flask and inoculated with 0.6 mL of the pre-culture. Cells were collected at the end of the log phase, at which O.D. (l = 600 nm) and cell concentration were 2.3-2.7 and 1.15-1.35 g_DW/L, respectively, harvested by sterile centrifugation (6000 rpm, 10 min) and washed twice with a salt solution (6 g/L Na₂HPO₄, 3 g/L KH₂PO₄, 1 g/L NH₄Cl, 0.5 g/L NaCl). The bioconversion medium was constituted by this solution supplemented with ferulate (0.3-0.4 g/L) and YE (50 mg/L) as a co-substrate. All experiments were carried out at 30ºC in triplicate using an inoculum of about 5 g/L.

Analytical determinations

Biomass concentration was determined by optical density measurements at 600 nm. Vanillate, vanillin and ferulate concentrations were determined by HPLC 1100, Hewlett Packard (Palo Alto, CA) provided with a Vydac 201TP54 C18 reverse-phase column (Hesperia, CA), maintained at 35ºC, using an UV/Vis detector, Hewlett Packard (Palo Alto, CA), set at l = 254 nm. The mobile phase, used at 0.5 mL/min flow rate, consisted of 40% methanol and 60% of a solution prepared adding 6.8 g/L KH₂PO₄ in water and adjusting the pH with H₃PO₄ up to 2.5. Data acquisition and processing were controlled by the Rev. A.09.03 ChemStation Software, Agilent Technologies (Palo Alto, CA).

RESULTS AND DISCUSSION

The experimental data of E. coli JM109(pBB1) growth were used to estimate the growth kinetic parameters of this recombinant strain, referring either to the overall growth curve (dX/dt = 1.2 g/Lh; µ = 0.29 h^-1) or only the exponential phase (dX/dt = 2.2 g/Lh; µ_max = 0.60 h^-1; t_d= 1.1 h). Comparison with literature data demonstrates that the LB medium allowed for notably slower cell growth with respect to that in simple carbon sources. For example, a duplication time of 0.5 h or even less is reported for E. coli growth on glucose under optimum conditions (6).

The ability of 4 additional strains of E. coli transformed with the pBB1 plasmid, namely DH5a, Novablu, SureII and XL10gold, was tested for vanillin production, following the same protocol as that used for E. coli JM109(pBB1). The data collected after different bioconversion times, in terms of product concentration, are illustrated in Fig. 1, while Table 1 shows the values of the kinetic parameters as well as the bioconversion yields. E. coli JM109 ensured the highest yields at the start (1h), whereas E. coli DH5a and XL10gold were the most effective at the end of bioconversion (72h).

These results on the whole suggest that most of the tested recombinant strains, but E. coli SureII and XL10 gold, may possess a non-specific oxidase activity able to oxidize vanillin and to produce NADH₂⁺, in order to sustain their own energetic metabolism. Conversely, E. coli JM109 showed the highest volumetric and specific productivities and ferulate conversion rates.

CONCLUSIONS

With the aim of minimizing vanillin oxidation and obtaining the highest productivity, the results of this work point out E. coli JM109 (pBB1) as the best recombinant strain, among others, for vanillin production from ferulate. Under aerobic conditions, a non-specific oxidase activity may be responsible for an increased production of vanillate from ferulate to the detriment of vanillin formation. Therefore, optimization of the aeration conditions is needed to improve the vanillin yield as well as to exploit this bioconversion in continuous system.

ACKNOWLEDGEMENTS

The authors thank the Italian MIUR, prot. 2001075847, for the financial support.

This paper corresponds to an "extended abstract" selected for oral presentation in the 22^nd Brazilian Congress of Microbiology, held in Florianópolis, SC, Brazil, in November 17-20, 2003

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Publication Dates

• Publication in this collection
  30 Nov 2004
• Date of issue
  Nov 2003