Fine-tuned regulation of photosynthetic performance via γ-aminobutyric acid (GABA) supply coupled with high initial cell density culture for economic starch production in microalgae

Table 3 Net increase (Δ) of starch yield and starch theoretical productivity based on GABA supply and net extra benefit from GABA addition and ICD increase in T. subcordiformis exposed to nitrogen deprivation under NICD and HICD conditions on Day 4

ICD	GABA (mM)	ΔStarch yield/GABA (mg mmol⁻¹)	ΔStarch theoretical productivity/GABA (mg day⁻¹ mmol⁻¹)	Benefit from starch production ($ m⁻³ culture)	Net extra benefit from GABA addition and ICD increase^a ($ m⁻³ culture)
NICD	0	–	–	25.56	0
	2.5	184.34	46.08	36.18	7.65
	5	145.98	36.50	41.08	9.59
	10	80.44	20.11	42.29	4.87
HICD	0	–	–	33.37	3.14
	2.5	159.91	39.98	42.84	9.64
	5	23.53	5.88	36.65	0.48
	10	− 28.65	− 7.16	27.29	− 5.91

^aThe net extra benefit was estimated by assuming a biomass seed production cost of 2.71 $ kg⁻¹ (Muhammad et al. 2021) and GABA cost of 11.5 $ kg⁻¹ (Xiong et al. 2017)