In this thesis the production, isolation and purification of the kalimantacin antibiotics are described along with details of the elucidation of the structures including the relative and absolute stereochemistry. Kalimantacin A, isolated from Pseudomonas jluorescens strain BCCM_ ID9359, is biosynthesised by a trans-AT type I polyketide synthase (PKS) and exhibits strong and selective activity against multi-resistant Staphylococcus aureus (MRSA). Two mutant strains, ~batF and ~batM, have been produced from which 17- hydroxy analogue 20, 27-descarbamoyl analogue 21 and 17-hydroxy-27-descarbamoyl analogue 22 were isolated and fully characterised.