Strain improvement methods

The improvement of the biocatalyst, in the form of either whole cell or isolated enzyme, can be achieved by a change in the structure of the DNA of the cell. This 

The structure of nucleic acids is discussed in Appendix 5.2, while Appendix 5.6 gives details of how information can be stored in the cell in the form of DNA, genes, plasmids, and of the mechanisms of protein synthesis. 

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One of the drawbacks in the current commercial fermentation process is that the predominant form of the product is the deprotonated lactate rather than lactic acid, requiring more expensive and wasteful product purification steps. This is because the Lactobacillus fermentation operates at a minimum pH of 5.0-5.5 which is above the pA a of lactic acid (3.87). To overcome this limitation, a powerful strain improvement method, genome shuffling, was used to improve the acid tolerance of a poorly characterized industrial strain of LactobacillusA population of strains with subtle improvement in pH tolerance was isolated using classical strain improvement methods such as chemostats, and were then shuffled by recursive pool-wise protoplast fusion to create mutant strains that grow at substantially lower pH than does the wild-type strain. 

Agents deemed to be impractical by such a collaborating team, ineffective because of biotic or other constraints, become candidates for strain improvement. Genetic enhancement of candidate potential may be by either classic methods or new genetic transformation techniques. 

Bachrach, S. M. The group equivalent reaction an improved method for determining ring strain energy, J. Chem. Ed. 1990,67,907-908. 

The value of microbial hydroxylation of steroids has long been that they allow functionalization of positions not easily accessible by normal chemical methods. For this reason yields of a few percent have often been tolerated, but yields approaching quantitative can be achieved in many instances. The objective of much current work is to improve the selectivity of microbial hydroxylations. This can be achieved in a number of ways, for example by structural modifications of the substrate, optimization of fermentation conditions and by strain improvement. The latter is most likely to yield the most significant improvements in selectivity, and has previously been discussed at length. ... 

Notice also that although the methods, compute-nonbonded-strain and compute-torsional-strain were inherited by cyclic-aliphatic, more sophisticated versions of these methods were supplied to cyclic-aliphatic. This would have been unnecessary if the original versions of these methods supported fully all cyclic configurations (i.e., a robust method given at any ring configuration). We have found that the ability to incrementally improve methods accelerates model development. 

Various techniques are employed to obtain the improved biocatalysts for potential improvement. These include the following mutation and selection, hybridization, protoplast fusion, and recombinant DNA methods. One example of strain improvement is the development of an ethanol-tolerant yeast strain, Saccharomyces 1400, through protoplast fusion of S. distaticus and S. uvarum as reported by D Amore et al. [4]. This yeast strain was used as the biocatalyst by Krishnan et al. [5] for the rapid fermentation of high concentrations of glucose... 

Polyketide natmal products are a rich source of bioactive substances that have found considerable use in hrnnan health and agriculture. Their complex structures require that they be produced via fermentation processes. This review describes the strategies and challenges used to develop practical fermentation strains and processes for polyketide production. Classical strain improvement procedmes, process development methods, and metabolic engineering approaches are described. The elucidation of molecular mechanisms that imderlie polyketide biosynthesis has played an important role in each of these areas over the past few years. 

Vinci VA, Byng G (1999) Strain improvement by nonrecombinant methods. In Demain AL, Davies JE (eds.) Manual of industrial microbiology and biotechnology. ASM Press, Washington DC, p 103... 

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