Table 1 Overview of methods described in this review.

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

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

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

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