Microalgal photoautotrophic growth induces pH decrease in the aquatic environment by acidic metabolites secretion

Table 1 Summary of 24 candidate biomarkers in the aquatic environment of E. gracilis

BK	Super class	XBP-pKa	NNP-pKa	EXP-pKa
1-Deoxy-d-xylulose 5-phosphate	OOC	1.56	1.70	–
2,3-Dihydroxybutanedioic acid	OOC	3.13	2.86	–
Fumaric acid	OAD	3.31	3.09	3.02
trans-Aconitic acid	OAD	2.87	3.16	–
Ethyl glucuronide	OOC	3.65	3.45	–
Benzoic acid	BZO	4.15	3.54	4.21
Itaconic acid	LLM	3.48	3.65	3.9
N-Acetylglutamic acid	OAD	3.42	3.69	–
Methylsuccinic acid	LLM	3.92	3.86	–
l-Homocysteic acid	OAD	3.58	3.90	–
Homogentisic acid	BZO	4.24	4.17	4.4
3-Hydroxycapric acid	OAD	4.68	4.55	–
Dihydrolipoate	LLM	4.82	4.86	–
3-Methoxyanthranilate	BZO	4.99	4.86	–
Ochratoxin A	PPP	3.54	5.38	–
cis-Coutaric acid	OAD	2.48	5.63	–
Palmitic acid	LLM	7.02	5.81	–
16-Methylheptadecanoic acid	LLM	7.08	6.33	–
Imidazoleacetic acid	OHC	5.44	6.56	–
l-Gulonolactone	OHC	7.04	8.42	–
Uracil	OHC	9.40	8.95	9.42
N-Methylsalsolinol	OHC	9.92	9.34	–
Levoglucosan	OHC	12.37	10.64	–
6-Deoxyfagomine	OHC	11.63	15.02	–
H₂O (control)^a		14.00

The lower the pKa value, the stronger the acid; XBP- and NNP-pKa represent pKa predicted via XGBoost and Neural Network, respectively; EXP-pKa represents experimental pKa coming from the sub-database of iBonD. For more details, please click http://ibond.nankai.edu.cn. ^athe pKa value of H₂O is 14.00 instead of 15.70, according to Silverstein and Heller [46]
BK candidate biomarkers, OOC organic oxygen compounds, OAD organic acids, and derivatives, LLM lipids and lipid-like molecules, OHC organoheterocyclic compounds, BZO benzenoids, PPP phenylpropanoids, and polyketides; pKa = − log₁₀ Ka, at 25 °C

ISSN: 2731-3654