Optimized inorganic carbon regime for enhanced growth and lipid accumulation in Chlorella vulgaris

Table 3 C. vulgaris culturing characteristics when grown under various inorganic carbon regimes

Treatment	Cell concentration (×10⁷ cells mL⁻¹)	Specific growth rate (μ _max day⁻¹)	Biomass productivity (g L⁻¹ day⁻¹; DCW)^a	Maximum chlorophyll (mg L⁻¹)
Air only	2.31 ± 0.09^*	0.61 ± 0.09^*	0.04 ± 0.00^*	3.52 ± 1.0^*
Air + 5 mM NaHCO₃	3.53 ± 0.2^*	0.82 ± 0.02^*	0.06 ± 0.01^*	5.72 ± 1.0^*
Air + 5 % (v/v) CO₂ pH control	14.21 ± 4.67^**	0.76 ± 0.05^*	0.11 ± 0.02^*	8.01 ± 1.23^*
5 % (v/v) CO₂ continuous	23.92 ± 1.55^**	1.02 ± 0.02^*	0.11 ± 0.01^*	8.13 ± 1.46^*
Optimized scenario	5.93 ± 0.61^b	1.72 ± 0.06	0.14 ± 0.00	10.7 ± 0.84

Experimental conditions: (1) continuous sparge of atmospheric air, (2) continuous sparge of atmospheric air and supplemented with 5 mM NaHCO₃ at inoculation, (3) continuous sparge of atmospheric air supplemented periodically with 5 % CO₂ (v/v) to maintain pH between 8.4 and 8.7, (4) continuous sparge of atmospheric air supplemented with 5 % CO₂ (v/v) during daytime hours, and (5) the optimized scenario of a continuous sparge of atmospheric air supplemented periodically with 5 % CO₂ (v/v) to maintain pH between 8.4 and 8.7 and an initial addition of 5 mM NaHCO₃ at inoculation plus an additional 50 mM NaHCO₃ just prior to nitrogen depletion to stimulate TAG accumulation (n = 3). All growth yields are calculated for the exponential growth phase (i.e., from inoculation until depletion of nitrogen)
^* p value <0.05 as determined by a two-tailed t test, statistically significantly lower (difference between treatment and optimized scenario)
^** p value <0.05 as determined by a two-tailed t test, statistically significantly higher (difference between treatment and optimized scenario)
^aDry cell weight (DCW) determined gravimetrically with lyophilized biomass
^b50 mM NaHCO₃ addition results in cessation of cellular division

ISSN: 2731-3654