Saturated and Polyunsaturated Fatty Acids Production by Aurantiochytrium limacinum PKU#Mn4 on Enteromorpha Hydrolysate

Abstract

Thraustochytrids are unicellular marine heterotrophic protists, which have recently shown a promising ability to produce omega-3 fatty acids from lignocellulosic hydrolysates and wastewaters. Here we studied the biorefinery potential of the dilute acid-pretreated marine macroalgae (Enteromorpha) in comparison with glucose via fermentation using a previously isolated thraustochytrid strain (Aurantiochytrium limacinum PKU#Mn4). The total reducing sugars in the Enteromorpha hydrolysate accounted for 43.93% of the dry cell weight (DCW). The strain was capable of producing the highest DCW (4.32 ± 0.09 g/L) and total fatty acids (TFA) content (0.65 ± 0.03 g/L) in the medium containing 100 g/L of hydrolysate. The maximum TFA yields of 0.164 ± 0.160 g/g DCW and 0.196 ± 0.010 g/g DCW were achieved at 80 g/L of hydrolysate and 40 g/L of glucose in the fermentation medium, respectively. Compositional analysis of TFA revealed the production of equivalent fractions (% TFA) of saturated and polyunsaturated fatty acids in hydrolysate or glucose medium. Furthermore, the strain yielded a much higher fraction (2.61-3.22%) of eicosapentaenoic acid (C20:5n-3) in the hydrolysate medium than that (0.25-0.49%) in the glucose medium. Overall, our findings suggest that Enteromorpha hydrolysate can be a potential natural substrate in the fermentative production of high-value fatty acids by thraustochytrids.

Keywords: Enteromorpha; fatty acids; fermentation; hydrolysate; reducing sugars; thraustochytrids.

Figure 1

Time course of (a) DCW and (b) total reducing sugars, and (c) experimental and estimated (modified Gompertz model) total fatty acids (TFA) during the cultivation of the PKU#Mn4 strain on Enteromorpha hydrolysate and glucose media. EH stands for Enteromorpha hydrolysate.

Figure 2

Effects of various concentrations of (a–c) Enteromorpha hydrolysate and (d–f) glucose on the DCW, TFA content, and TFA yield of PKU#Mn4 strain. The significant codes indicate the results of multiple comparisons, where the mean of each group was compared to all (i.e., base mean) by a paired t-test. The significant codes *, **, ***, and **** represented significance at p < 0.05, p < 0.01, p < 0.001, and p < 0.0001, respectively. The data represent the mean ± SD of triplicate samples (n = 3).

Figure 3

Effects of various concentrations of Enteromorpha hydrolysate (EH) and glucose (Glu) on the relative concentrations of fatty acids produced by PKU#Mn4 culture. The number after EH and Glu represents the concentration of EH and Glu.