Table 2 PHB production under a two-stage (photoheterotrophy, then heterotrophy) culture.
Nutrient condition | Acetate supply % (w/v) | PHB content (% w/w DW) | PHB production (mg/L) | % w/w [PHB product/ACT supply]a |
|---|---|---|---|---|
NORMAL | 0.00 | 0.1 ± 0.0 | 1 ± 1 | na |
0.05 | 0.1 ± 0.0 | 2 ± 1 | 0.0 ± 0.0 | |
0.10 | 0.6 ± 0.4 | 9 ± 5 | 0.7 ± 0.5 | |
0.20 | 1.5 ± 0.9 | 22 ± 13 | 0.1 ± 0.6 | |
0.40 | 1.8 ± 0.8 | 28 ± 15 | 0.7 ± 0.3 | |
-N | 0.00 | 1.4 ± 0.8* | 19 ± 10* | na |
0.05 | 0.4 ± 0.2* | 6 ± 5 | 0.8 ± 0.9 | |
0.10 | 2.2 ± 0.9* | 30 ± 11* | 2.8 ± 1.0* | |
0.20 | 8.6 ± 1.9* | 121 ± 23* | 6.0 ± 1.1* | |
0.40 | 19.5 ± 2.0* | 267 ± 16* | 6.6 ± 0.4* | |
-P | 0.00 | 1.3 ± 0.1* | 18 ± 4* | na |
0.05 | 1.8 ± 1.0* | 25 ± 17* | 4.6 ± 3.3* | |
0.10 | 7.5 ± 1.5* | 97 ± 11* | 9.5 ± 1.1* | |
0.20 | 14.3 ± 2.5* | 203 ± 30* | 10.0 ± 1.5* | |
0.40 | 36.0 ± 2.8* | 531 ± 75* | 13.2 ± 1.8* | |
-N-P | 0.00 | 4.9 ± 1.6* | 65 ± 24* | na |
0.05 | 8.3 ± 1.9* | 108 ± 30* | 21.2 ± 6.0* | |
0.10 | 21.4 ± 2.4* | 295 ± 37* | 29.3 ± 3.7* | |
0.20 | 30.7 ± 2.8* | 431 ± 45* | 21.5 ± 2.2* | |
0.40 | 28.5 ± 1.9* | 395 ± 9* | 9.8 ± 0.2* |
- Cells were pre-grown under normal photoautotrophy for 16 d and transferred to the specified heterotrophic conditions using the 6-d time culture period yielding the highest PHB contents (Fig. 3). Data are the average ± 1 SD from three to five independent cultures. Asterisks indicate significantly higher levels (P < 0.01, two-tailed t-test) than those obtained from NORMAL nutrient condition and the same acetate supply. na, not applicable. a = [(PHB production, mg/L)]/(ACT supply in the culture medium, mg/L)] × 100, where PHB production is the difference in production at a second-stage heterotrophic culture and at the end of the first-stage photoautotrophic culture.
Figure 3 
Conversion efficiency (CE) of acetate to PHB in the two-stage cultures of C. fritschii.
Sixteen-d photoautotrophy-grown cells were transferred to the heterotrophic -N-P medium in the dark up to 10 d with an initial acetate (ACT) concentration of 0.05% or 0.1% (w/v). The residual available ACT level in the culture medium and CE of acetate to PHB was determined at the indicated time points. Data are the average ± 1 SD from six independent cultures.
