ABSCICS: Applied Bacterial Spore Control in Industrial and Clinical Settings

The bacterial endospore is one of the most highly resistant life-forms on earth and allows the bacterium to survive exposure to extremes of temperature, desiccation, disinfectants, radiation, and, in the case of anaerobes, oxygen. The longevity of survival is astounding and can be measured not in tens or hundreds of years but, in millions. These remarkable structures are the single most important feature of the bacterial genus Clostridium and underpin the spread of its disease-causing members. The vast majority of Clostridia are, however, entirely benign, and may be used sustainably to produce the chemicals and fuels society needs. Clostridia are also a source of valuable therapeutics (e.g., BoTox and Xiaflex). One of their potentially most significant uses, however, resides in their potential as therapeutic delivery vehicles for solid tumours and the microbiome through exploitation of their endospores.

Endospores are an ideal pharmaceutical. Easy to prepare and purify, once made they are admirably suited to long term storage. They are simple to administer (intravenously or orally) and once delivered rely on a natural process (germination) to be activated - conversion to vegetative cells. However, the properties that make them ideal delivery vehicles also compromise their perceived safety, as the in situ conversion of an oxygen sensitive vegetative cell to an endospore (sporulation) leads to a highly resistant agent that can be dispersed to, and survive in, the external environment. To counter this risk, the SBRC has created a clostridial strain which only produces spores under defined conditions - a conditionally sporulating (Spoc) strain. This allows the generation of high spore titres under laboratory conditions, but once germinated in the target niche (tumour or microbiome) the Clostridia remain as vegetative cells and are unable to sporulate again. Such a sophisticated form of disablement will ensure that dissemination of Clostridia is avoided, thereby satisfying the concerns of regulatory agencies.

Over and above their use in therapeutic delivery, Spoc strains are of value to commercial processes based on spore forming bacteria. This is because there is reluctance within industry to use bacteria that make spores as they are very difficult to remove from production facilities. While null mutants prevent spore production, in the case of an oxygen-sensitive anaerobe, it makes it problematic to store and maintain seed strains as vegetative cells are rapidly killed by exposure to air. A Spoc strain allows the storage and maintenance of strains in the spore state through growth in the presence of the inducers. Subsequent large-scale cultivation in the absence of inducers will prevent spore contamination of manufacturing facilities.

Our concept is to design, build and test conditionally sporulating (Spoc) strains of Clostridia specific to identified commercial applications. The ability to control bacterial sporulation has a multitude of such uses, particularly in relation to anaerobes. These relate to therapeutic delivery vehicles for niche-specific diseases and disorders, as a means of both preventing spore contamination of process facilities and limiting the dissemination of the bacterium to the environment and, in some applications, the controlled induction of sporulation.