Modern Industrial Microbiology and Biotechnology

230 Modern Industrial Microbiology and Biotechnology(iv) The order and number of the addition of the various components of the mediumcould be important. Thus, when powders such as corn starch are to be added it isadvisable to dissolve them separately and to add the slurry into the fermentor withvigorous stirring; otherwise lumps could form. Such lumps may not only protectsome organisms, but may even render the powdered material unavailable asnourishment for the target organisms. Some commercial autoclaves therefore havean arrangement for stirring the medium to break up clumps of medium as well asdistribute the heat.Sterilization of heat labile medium: Thermolabile media may be sterilized bytyndalization. For this procedure the temperature of the medium is raised to boiling onthree consecutive days. The theory behind tydalization is that while boiling destroys thevegetative cells, the bacterial spores survive. After the first day’s boiling the vegetativecells are killed and the spores germinate. On the second day’s boiling the vegetative cellsresulting from the germinated spores surviving the first day’s boiling, are killed. In theunlikely event that any spores still survive – after two days of boiling–they will germinateand the resulting vegetative cells will be killed with the third day’s boiling. With the thirdday’s boiling the medium in all likelihood will be sterile.Chemical sterilization of the medium may be done with b-propiolactone. Filtrationmay also be used. Filtration is especially useful in the pharmaceutical industry where inaddition to sterilization it also removes pyrogens (fever-producing agents resulting fromwalls of Gram-negative bacteria), when filtration is combined with charcoal adsorption.Batch vs. continuous Sterilization: The various advantages of continuous over batchfermentation (Section 7.4) can be extended, with appropriate modifications, tosterilization. Exposure to sterilization temperature and cooling thereafter are achieved incontinuous sterilization in much shorter periods than with batch sterilization (Fig. 11.3).The two methods generally used for continuous sterilization are shown in Fig. 11.411.4 VIRUSES (PHAGES) IN INDUSTRIAL MICROBIOLOGYViruses are non-cellular entities which consist basically of protein and either DNA orRNA and replicate only within specific living cells. They have no cellular metabolism oftheir own and their genomes direct the genetic apparatuses of their hosts once they arewithin them. Viruses are important in the industrial microbiology for at least tworeasons:(i) Those that are pathogenic to man and animals are used to make vaccines againstdisease caused by the viruses.(ii) Viruses can cause economic losses by destroying microorganisms used in afermentations.It is this second aspect which will be considered in this section. We will therefore lookat those viruses which attack organisms of industrial importance, namely bacteria(including actinomycetes) and fungi. Such viruses are known as bacterophages,actinophages, or mycophages depending on whether they attack bacteria, actinomycetes,or fungi. Most of the discussion will center around baceriophages since more informationexist on them than on the other two groups.