Table 1.

Initial evaluation of the medium components’ potentials for the optimization of lipid productivity

Component	Evaluation	Reference	Variation
CaCl2	Versatile effector in plant cells; reported to be essential for induction of lipid synthesis	[50–52]	Yes
FeSO4	Influence on growth and lipid metabolism reported	[51, 53–55]	Yes
H2SO4	Sulfur supply ensured by sulfate anions from diverse other medium components; nevertheless varied as provided together with FeSO4 in one stock solution		Yesb
K2HPO4/KH2PO4	Essential phosphorus source (nucleic acid synthesis)	[54]	Yes
KOH	Potassium excess by phosphate salts; nevertheless varied as provided together with Na2EDTA in one stock solution		Yesc
MES	Trade-off between osmotic inhibition and buffer capacity; alkaline pH may inhibit cell cycle	[56]	Yes
MgSO4	Influence on growth and lipid production reported; effector of acetyl-CoA carboxylase, an essential enzyme during lipid biosynthesis; central atom of chlorophyll	[51, 57, 58]	Yes
NaCl	Reported to increase lipid production; excess may cause metabolic burden (ATP dependent sodium exporters) and thus inhibit growth	[59, 60]	Yes
Na2EDTA	Commonly used metal chelator; excess may cause growth repression due to ion depletion	[51, 55]	Yes
NaNO3	Essential nitrogen source (protein synthesis)	[54]	Yes
Penicillin-G	Support of long-time sterile conditions; not metabolized (data not shown)		No
Trace elements (CoSO4, CuSO4, H3BO3, MnCl2, Na2MoO4, ZnSO4)	Numerous studies about wastewater detoxification available, but only limited information concerning metabolism and lipid production; general pattern: little amounts essential, but high level cytotoxic (e.g., inhibition of photosynthesis); thus clustered to one input variable	[61–66]	Yesa

^aAll trace elements were clustered to one single input variable

^bVaried together with FeSO₄ as provided in one single stock solution

^cVaried together with Na₂EDTA as provided in one single stock solution