微生物与生化技术杂志

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Changes in Cell Structure, Morphology and Activity of Streptomyces venezuelae during the Growth, Shocking and Jadomycin Production Stages

Marianne S Brooks, Tracey J Burdock, Abdel E Ghaly and Deepika Dave

Streptomyces venezuelae have the ability to synthesize a group of novel benzoxazolophenanthridine antibiotics called jadomycin. The aim of the study was to investigate the changes in activity, cell structure and morphology of Streptomyces venezuelae while subjected to different environmental conditions during the growth, ethanol shocking, and jadomycin production stages. The activity of S. venezuelae was measured using the triphenyl tetrazolium chloride (TTC) technique while the microbial population was measured using the optical density and plate count techniques. Samples from each stage were viewed under the scanning electron microscope (SEM) and transmission electron microscope (TEM). The specific TF yield was calculated by dividing the TF yield by the number of cells. The specific TF yield remained constant at 2.44 x 10-8(μmol/CFU) during the growth period in nutrient rich medium and decreased to 0.25 x 10-8 μmol/CFU and 0.28 x 10-8 μmol/CFU during the acclimatization to the nutrient deprived-amino acid rich production medium and after shocking and then increased to 3.67 x 10-8 μmol/CFU during jadomycin production. The ethanol shock did not cause 100% of the cells to change their morphology. Remarkable changes were observed in the morphology and structure (cell diameter, vacuoles present and septation/sporulation) of S. venezuelae during the four consecutive stages (growth, acclimatization, shocking and jadomycin production). The elemental analysis provided information for verifying jadomycin B purity (97.86%). However, it was not possible to detect jadomycin B within cells. It is probable that jadomycin was produced outside the cells by extracellular enzymes as opposed to intracellularly by the uptake of isoleucine and glucose. The white pellets (cells), obtained by centrifugation of production medium, supports the idea that jadomycin B is produced outside the cells as jadomycin is highly coloured compound. It is also possible that the cells were highly efficient at excreting the secondary metabolites. These hypotheses need further investigation.