Table 2.

Summary of ALE applied in tolerance engineering.

Microbes	Stressors	Final results	Refs
E. coli MG1655	High temperature	Maximum growth temperature was improved from 46 °C to 48 °C and Optimum growth temperature was arised from 37 °C to over 46 °C	[13]
E. coli	Temperature	30 groups of Escherichia coli evolved over 2000 generations	[14]
E. coli Bc251	Temperature	Escherichia coli evolved under high temperature condition (41.5 °C) for 2000 generations	[15]
E. coli MG1655	Temperature	E. coli evolved at 42 °C	[16]
E. coli MG1655	Temperature	E. coli could grow at max temperature at 48.5 °C	[17]
E. coli	pH, temperature or osmolarity.	By inserting evolved IS10, the expression of otsBA was shifted from RpoS-dependent to RpoS-independent, thus partially restoring the wild-type response to osmotic stress.	[18]
E. coli JCL260	isobutanol	The results showed distinction in the level of resistance to different inhibitors, with improved growth rates up to 57 %, 12 %, 22 %, and 24 % in hydrolysates, acetic acid, HMF and furfural, respectively.	[19]
E. coli	ethanol	Several of these pathways, in particular heat-shock stress response and osmoregulation, are familiar modification reagents of ethanol tolerance; while others, such as acid-stress response and fimbrial structures are emerging pathways.	[20]
E. coli	ethanol	Ethanol-induced inhibition, uncoupling of mRNA and protein synthesis through direct effects on ribosomal and RNA polymerase conformation are significant ethanol toxicity determinants in E. coli, and adaptive mutations in metJ, rho and rpsQ serve to safeguard the central dogma while the ethanol presents.	[21]
E. coli	n-butanol	Regarding studies on the potential role of iron-related genes in n-butanol tolerance, gene overexpression and deletion studies hypothesized that upregulation of iron-related genes indirectly leads to outer membrane modifications that enhance n-butanol tolerance.	[22]
E. coli	n-butanol	Additional membrane-associated and osmotic stress-related genes were identified in E. coli that confer n-butanol tolerance.	[23]
Saccharomyces cerevisiae	Acetic acid	The fraction of growing cells rose in all six mutants when transferred from a non-stressed environment to a medium with acetic acid.	[24]
Saccharomyces cerevisiae.	Acetic acid, furfural, and hydroxymethylfurfural	The results indicated differentiated degrees of resistance to different inhibitors, with increased growth rates of hydrolysates, acetic acid, HMF and furfural up to 57 %, 12 %, 22 %, and 24 %, respectively.	[25]
E. coli MG1655 and ΔlacZ strains	Five environments (osmotic, acidic, oxidative, n-butanol, and control; four biological replicates per environment)	Cross-stress dependencies are pervasive, strongly interrelated and can appear over short periods. Bacterial populations dominate a genotypic space allowing for a high degree of phenotypic plasticity as they adapt to fluctuating environments.	[26]
Saccharomyces cerevisiae	Oxidative, freezing–thawing, high-temperature and ethanol stress.	The optimal clones obtained from the populations were 102, 89, 62 and 1429 times more resistant to freezing–thawing, temperature, ethanol, and oxidative stress, respectively.	[27]