Table 1.

Overview of methods described in this review.

Method used	Advantages	Disadvantages	Topic	Aim
Random mutagenesis	Little knowledge required. Especially useful for elimination of specific characteristics where direct selection is not possible.	Use of dangerous chemicals. Mutation bias and hot spots. Second site mutations will be created. Requires screening of a large number of survivors.	Pyrimidine auxotrophy	Bacteriophage resistance
			Elimination of antibiotic resistance	Eliminating unwanted property
			Elimination of citrate metabolism	Eliminating unwanted property
			Urease negative mutants of S. thermophilus	Eliminating unwanted property
			Lactobacillus strains with low post acidification	Improving product stability
Directed evolution	Little knowledge required. Especially useful for complex phenotypes. Mutagens normally not required.	Multiple mutations may occur. May require complex experimental setups. Slow process requiring long time frames. Selection is at population level, isolated strains must be characterized.	Increasing the growth yield during fermentation	Increased efficiency in culture production
Dominant selection	Mutagens not required. Often results in a single mutation.	Requires considerable insight into physiology of the cell. Analogues may be toxic to humans.	Bacteriophage receptors	Bacteriophage resistance
			Conjugation	Bacteriophage resistance
			Modifying bacterial cell surfaces	Improving texture
			Optimizing the metabolic pathway of EPS	Improving texture
			Bacteriophage resistant mutants	Improving texture
			Lactobacillus strains with improved ethanol or bile tolerance	Improving survival and efficacy
			Lb. helveticus producing succinate	Improving flavor
			Altering acidification properties by adapting the carbohydrate metabolism	Overcoming effect of a mutation
Recombinant DNA technology	Extremely accurate targeted methods.	Consumer acceptance. Regulatory approval. Can be difficult to apply to industrial strains.	Potentially all of the above	Potentially all of the above