Effect of C/N ratio on polyhydroxyalkanoates (PHA) accumulation by Cupriavidus necator and its implication on the use of rice straw hydrolysates

Abstract

The effects of carbon-to-nitrogen (C/N) ratio in simulated rice straw hydrolysates using glucose and ammonium chloride on polyhydroxyalkanoates (PHA) accumulation by Cupriavidus necator was investigated. In general, PHA accumulation rate was higher under higher degrees of N-deficient conditions (e.g., C/N ratio of 360:1) than lower degrees of N-deficient conditions (e.g., C/N ratio of 3.6:1 and 36:1). Also, the most PHA accumulation was observed during the first 12 h after the PHA accumulation initiation. This study showed that the similar PHA accumulation could be achieved by using different accumulation periods depending on C/N ratios. N source presence was important for new cell production, supported by approximately ten times greater PHA accumulation under the N-deficient condition (NH4Cl 0.01 g/L) than the N-free (without NH4Cl) condition after 96 h. C/N ratio of the rice straw hydrolysate was approximately 160:1, based on the glucose content, and this accumulated 0.

Photofermentative Poly-3-Hydroxybutyrate Production by <em>Rhodopseudomonas</em> Sp. S16-VOGS3 in a Novel Outdoor L-Shaped Row Photobioreactor

“…It is known that stressed growth conditions caused by a high C/N ratio and/or nutrient limitation (e.g. Nitrogen and Phosphorus) in the culture medium promote the accumulation of intracellular PHB [24][25][26][27]. As expected, the PHB concentration in the culture grew over time and, more significantly, when the initial lactate concentration was restored (Figure 2d).…”

“…S16-VOGS3 was cultured under lower irradiance, the amount of PHB into bacterial cells decreased significantly, indicating the dominant role of irradiance on other parameters such as C/N ratio. In fact, as elsewhere demonstrated [26,27], stressed growth conditions caused by high C/N ratios should increase the amount of PHB into bacterial cells, but this was true as far as the results of our first investigation (run 1) is concerned, but not for those of the second one (run 2) ( Figure 5). In fact, despite the similar increases in the C/N ratio for both cases (Figure 5a), the PHB content into the cells had an opposite behavior (Figure 5b): during the run 1 (direct irradiance), the PHB content rapidly increased reaching the value of 19.6 % of dry biomass weight; during the run 2 (diffuse irradiance), the PHB content decreased reaching a value of about 7 % at the end of the investigation.…”

Photofermentative Poly-3-Hydroxybutyrate Production by Rhodopseudomonas sp. S16-VOGS3 in a Novel Outdoor 70-L Photobioreactor

“…The lactate concentration restoring operations caused significant heightening of the C/N ratio in the medium since the concentration of ammonia nitrogen (NH 3 -N) in the culture broth decreased progressively over time (Figure 2c). It is known that stressed growth conditions caused by a high C/N ratio and/or nutrient limitation (e.g., Nitrogen and Phosphorus) in the culture medium promote the accumulation of intracellular PHB [25][26][27][28]. As expected, the PHB concentration in the culture grew over time and, more significantly, when the initial lactate concentration was restored (Figure 2d).…”

“…S16-VOGS3 was cultured under lower irradiance, the amount of PHB into bacterial cells decreased significantly, indicating the dominant role of irradiance on other parameters such as C/N ratio. In fact, as elsewhere demonstrated [27,28], stressed growth conditions caused by high C/N ratios should increase the amount of PHB into bacterial cells, but this was true as far as the results of our first investigation (run 1) is concerned, but not for those of the second one (run 2) ( Figure 5). In fact, despite the similar increases in the C/N ratio for both cases (Figure 5a), the PHB content into the cells had an opposite behavior (Figure 5b): during the run 1 (direct irradiance), the PHB content rapidly increased reaching the value of 19.6% of dry biomass weight; during the run 2 (diffuse irradiance), the PHB content decreased reaching a value of about 7% at the end of the investigation.…”

“…S16-VOGS3 was cultured under lower irradiance, the amount of PHB into bacterial cells decreased significantly, indicating the dominant role of irradiance on other parameters such as C/N ratio. In fact, as elsewhere demonstrated [27,28], stressed growth conditions caused by In order to evaluate the effect of the solar light intensity on the productivity of PHB accumulated in the bacterial cells, a further investigation was carried out by covering about 80% of the photobioreactor with a dark cloth as shown in Figure 3a (run 2). In this way, the light intensity impinging on the L-SRP was significantly reduced and the culture was irradiated principally by diffuse irradiance, with the exception of the U-fittings.…”