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.