Enhanced degradation of polyhydroxyalkanoates (PHAs) by newly isolated Burkholderia cepacia DP1 with high depolymerase activity

Abstract

The contribution of microbial depolymerase has received much attention because of its potential in biopolymer degradation. In this study, the P(3HB) depolymerase enzyme of a newly isolated Burkholderia cepacia DP1 from soil in Penang, Malaysia, was optimized using response surface methodology (RSM). The factors affecting P(3HB) depolymerase enzyme production were studied using one-variable-at-a-time approach prior to optimization. Preliminary experiments revealed that the concentration of nitrogen source, concentration of carbon source, initial pH and incubation time were among the main factors influencing the enzyme productivity. An increase of 9.4 folds in enzyme production with an activity of 5.66 U/mL was obtained using optimal medium containing 0.028% N of di-ammonium hydrogen phosphate and 0.31% P(3HB-co-21%4HB) as carbon source at the initial pH of 6.8 for 38 h of incubation. Moreover, the RSM model showed great similarity between predicted and actual enzyme production indicating a successful model validation. This study warrants the ability of P(3HB) degradation by B. cepacia DP1 in producing higher enzyme activity as compared to other P(3HB) degraders being reported. Interestingly, the production of P(3HB) depolymerase was rarely reported within genus Burkholderia. Therefore, this is considered to be a new discovery in the field of P(3HB) depolymerase production.

Keywords: Biodegradable; Extracellular P(3HB) depolymerase enzyme; P(3HB-co-4HB); Poly(3-hydroxybutyrate) [P(3HB)]; Polyhydroxyalkanoates (PHAs); Response surface methodology (RSM).

Fig. 1

P(3HB) depolymerase enzyme activity from various isolates; values are the mean ± SD of three replicates

Fig. 2

Phylogenetic tree based on 16S rRNA gene sequences, showing the positions of Burkholderia cepacia DP1 and the related genera using neighbouring joining tree method. Maximum sequence different = 0.02

Fig. 3

Effect of different inorganic nitrogen sources on the production of P(3HB) depolymerase enzyme by Burkholderia cepacia DP1; Values are the mean ± SD of three replicates

Fig. 4

Effect of different concentrations of di-ammonium hydrogen phosphate on the production of P(3HB) depolymerase enzyme by Burkholderia cepacia. DP1, incubation time (36 h); Values are the mean ± SD of three replicates

Fig. 5

Effect of different concentrations of P(3HB) on the production of P(3HB) depolymerase enzyme by Burkholderia cepacia DP1, incubation time (36 h); Values are the mean ± SD of three replicates

Fig. 6

Effect of different initial pH of medium on the production of P(3HB) depolymerase enzyme by Burkholderia cepacia DP1; values are the mean ± SD of three replicates

Fig. 7

Effect of different carbon sources on the production of P(3HB) depolymerase enzyme by Burkholderia cepacia DP1; values are the mean ± SD of three replicates

Fig. 8

Effect of different concentrations of P(3HB-co-21%4HB) on the production of P(3HB) depolymerase enzyme produced by Burkholderia cepacia DP1, incubation time (60 h); Values are the mean ± SD of three replicates

Fig. 9

3D response surface Interactive effect of a different concentrations of nitrogen and substrate at pH 6.8, b different concentrations of nitrogen and pH at 0.31% of substrate and c different concentration of nitrogen and incubation time at 0.31% substrate on the production of P(3HB) depolymerase enzyme