Effect of short- and medium-chain fatty acid mixture on polyhydroxyalkanoate production by Pseudomonas strains grown under different culture conditions

Abstract

Short- and medium-chain fatty acids (SMCFAs) derived from the acidogenic anaerobic mixed culture fermentation of acid whey obtained from a crude cheese production line and their synthetic mixture that simulates a real SMCFA-rich stream were evaluated for polyhydroxyalkanoate (PHA) production. Three individual Pseudomonas sp. strains showed different capabilities of growing and producing PHAs in the presence of a synthetic mixture of SMCFAs. Pseudomonas sp. GL06 exhibited the highest SMCFA tolerance and produced PHAs with the highest productivity (2.7 mg/L h). Based on these observations, this strain was selected for further investigations on PHA production in a fed-batch bioreactor with a SMCFA-rich stream extracted from the effluent. The results showed that PHA productivity reached up to 4.5 mg/L h at 24 h of fermentation together with the ammonium exhaustion in the growth medium. Moreover, the PHA monomeric composition varied with the bacterial strain and the type of the growth medium used. Furthermore, a differential scanning calorimetric and thermogravimetric analysis showed that a short- and medium-chain-length PHA copolymer made of 3-hydroxybutyric, -hexanoic, -octanoic, -decanoic, and -dodecanoic has promising properties. The ability of Pseudomonas sp. to produce tailored PHA copolymers together with the range of possible applications opens new perspectives in the development of PHA bioproduction as a part of an integrated valorization process of SMCFAs derived from waste streams.

Keywords: Pseudomonas sp.; biopolymers; medium-chain fatty acids; polyhydroxyalkanoates; short-chain fatty acids.

FIGURE 1

Biomass concentration (g/L) of Pseudomonas sp. Gl01, Pseudomonas sp. Gl06, and P. antarctica at 48 h cultured on three different growth media (MSM 1, MSM 2, and MSM 3) in shake flask experiments under non-limited and N-limited conditions using SMCFA_synthetic-rich stream.

FIGURE 2

PHA production from SMCFA_synthetic-rich stream by Pseudomonas sp. GL01, Pseudomonas sp. GL06, and P. antarctica at 48 h cultured on three different growth media (MSM 1, MSM 2, and MSM 3) in shake flask experiments under non-limited and N-limited conditions. (A) PHA concentration (g/L) and (B) PHA productivity (mg/L h).

FIGURE 3

PHA production, cell, ammonium and phosphate concentration during Pseudomonas sp. GL06 cultivation on SMCFA_extracted-rich stream in the bioreactor fermentation.

FIGURE 4

Monomeric composition of extracted PHAs from shake flasks (A) and bioreactor (B).

FIGURE 5

FTIR spectra of P(3HB-co-3HHx-co-3HO-co-3HD-co-3HDD) extracted from the Pseudomonas sp. GL06 cells at 48 h cultured in the bioreactor.

FIGURE 6

DSC curves (A) and TG curves (B) of P(3HB-co-3HHx-co-3HO-co-3HD-co-3HDD) extracted from the Pseudomonas sp. GL06 cells at 48 h cultured in the bioreactor.