Edinburgh/Yoghurt

The aim of this project is not only to produce colourful, tasty yoghurt, but to demostrate that it is possible to successfully introduce BioBricks into gram positive organisms.

We chose to produce 'self-flavouring' yoghurt, as this project enables us to genetically manipulate a range of gram positive bacteria required for yoghurt formation (see yoghurt production, below).

Bacillus subtilis

There are several advantages for using genetically engineered gram positive bacteria, over the traditionally used E. coli.

• Some Gram positive organisms (eg Lactobacillus, Lactococcus) are food grade, and therefore may be ingested. Lactobacillus are alsp common and harmless (indeed, beneficial) components of the human gut flora. Potentially this could enable their use in a range of products from medicines to milk shakes or yoghurt to deliver beneficial molecules to the body. Of course, there are also regulatory issues related to consumption of genetically modified organisms, but these will be more easily addressed in a known-harmless host with a long history of safe food use.

• Several gram positive bacteria, such as Bacillus spp. are able to form hardy endspores, which are extremely tolerant of heat, drying and other stresses, and can survive for centuries. These do not require refrigeration and can be transported and used in very hot, cold or developing countries cheaply and with ease.

• Gram positive organisms, such as the lactic acid bacteria, are much more efficient at secreting proteins and other molecules into their surrounding media than E. coli; most strains of E. coli lack the Main Terminal Branch of the General Secretory Pathway and secrete only a few proteins using specific mechanisms such as ABC transporters (eg, for hemolysin) and Type 3 Secretion Systems (in pathogenic strains).