High Cell Density Cultivation of Paracoccus sp. on Sugarcane Juice for Poly(3-hydroxybutyrate) Production

Abstract

High cell density cultivation is a promising approach to reduce capital and operating costs of poly (3-hydroxybutyrate) (PHB) production. To achieve high cell concentration, it is necessary that the cultivation conditions are adjusted and controlled to support the best growth of the PHB producer. In the present study, carbon to nitrogen (C/N) ratio of a sugarcane juice (SJ)-based medium, initial sugar concentration, and dissolved oxygen (DO) set point, were optimized for batch cultivation of Paracoccus sp. KKU01. A maximum biomass concentration of 55.5 g/L was attained using the C/N ratio of 10, initial sugar concentration of 100 g/L, and 20% DO set point. Fed-batch cultivation conducted under these optimum conditions, with two feedings of SJ-based medium, gave the final cell concentration of 87.9 g/L, with a PHB content, concentration, and yield of 36.2%, 32.1 g/L, and 0.13 g/g-sugar, respectively. A medium-based economic analysis showed that the economic yield of PHB on nutrients was 0.14. These results reveal the possibility of using SJ for high cell density cultivation of Paracoccus sp. KKU01 for PHB production. However, further optimization of the process is necessary to make it more efficient and cost-effective.

Keywords: bioplastic; high cell density cultivation; paracoccus sp.; process optimization; sugarcane.

FIGURE 1

Growth of Paracoccus sp. KKU01 on sugarcane juice-based medium (A) and total sugar consumption (B) at C/N ratios of 4 to 53.

FIGURE 2

Growth of Paracoccus sp. KKU01 on sugarcane juice-based medium (A) and total sugar consumption (B) at initial total sugar concentration of 30–150 g/L.

FIGURE 3

Growth profiles of Paracoccus sp. KKU01 on sugarcane juice-based media (A), specific growth rate of the bacterium (B), and total sugar consumption (C) at DO setpoints ranging from 10 to 50%.

FIGURE 4

Cell dry mass (CDM), PHB, residual CDM (A), total sugar and ammonia nitrogen concentrations (B), and total sugar consumption rate and PHB production rate (C) during fed-batch fermentation of Paracoccus sp. KKU01 in SJ-based medium. The solid lines in (A) represent data predicted by the modified Gompertz model (Eq. 2). The dashed lines represent the time at which fresh medium was fed into the bioreactor.

FIGURE 5

Concentrations of sucrose, glucose, and fructose at the beginning, before and after first and second feedings of the feed, and the end of the process. The dashed lines represent the time at which fresh medium was fed into the bioreactor.