Table 2.

Genes engineered by different microorganisms for improving acid tolerance

Mechanisms	Genes	Microorganisms	Acid stress	References
F0F1-ATPase proton pumps	AtMtATP6	S. cerevisiae	Pyruvic acid	(Zhang et al. 2008)
	atpA	P. acidipropionici	Propionic acid	(Guan et al. 2014)
	CgAMD1	C. glabrata	Hydrochloric acid	(Wu et al. 2018)
Decarboxylation and deamination	cad	E. coli	Acetic acid	(Noh et al. 2018)
	ybaS, gadC	E. coli	Hydrochloric acid	(Lu et al. 2013)
	hdcAPB	L. lactis	Hydrochloric acid	(Trip et al. 2012)
	arcA, arcC, gdh, gadB, ybaS	P. acidipropionici	Propionic acid	(Guan et al. 2016)
Cell membrane modification	cfa	E. coli	Hydrochloric acid	(Chang and Cronan 1999)
	murG	L. lactis	Lactic acid	(Zhang et al. 2016)
	FPS1	S. cerevisiae	Acetic acid	(Zhang et al. 2011)
	Yro2, Mrh1	S. cerevisiae	Acetic acid	(Takabatake et al. 2015)
Metabolic regulation	gshA, gshB	L. lactis	Lactic acid	(Zhang et al. 2007)
	trePP, pgmB, otsB	L. lactis	Lactic acid	(Carvalho et al. 2011)
	BetL	Bifidobacterium breve	Gastric acid	(Sheehan et al. 2007)
	ACS2	S. cerevisiae	Acetic acid	(Ding et al. 2015b).
Macromolecule protection and repair	dnaK	L. lactis	Lactic acid	(Abdullah-Al-Mahin et al. 2010)
	shsp	L. lactis	Lactic acid	(Tian et al. 2012)
	RecO	L. lactis	Lactic acid	(Wu et al. 2013)
	UvrA	A. pasteurianus	Acetic acid	(Zheng et al. 2018)
Protection from organelle	COX20	S. cerevisiae	Acetic acid	(Kumar et al. 2015)
	PEP3	S. cerevisiae	Acetic acid	(Ding et al. 2015a)
	RTT109	S. cerevisiae	Acetic acid	(Cheng et al. 2016)