Modern Industrial Microbiology and Biotechnology

232 Modern Industrial Microbiology and Biotechnology11.4.1 Morphological Grouping of BacteriophagesBacteriophages can be divided into six broad morphological groups (Table 11.3). Mostphages attacking industrial organisms are to be found in groups A, B, C. Groups D, E, andF attack industrial organisms less frequently if at all.11.4.2 Lysis of Hosts by PhagesThe growth cycle of a phage has three steps: adsorption onto the host cell, multiplicationwithin the cell, and liberation of the prepotency phages by the lysis of the host cell.Phages may be classified as virulent or temperate according to how they react to theirhost. In temperate phages, the phage genome (known as a prophage) integrates with thegenetic apparatus of the host, replicates with it and can be lysogenic and are known aslysogons.Temperate phages may become virulent and lyse their hosts, either spontaneously orafter induction by various agents e.g. mitomyin C or UV light. They may also mutate tolytic phages, complete the virus growth cycle and lyse their hosts. It is for this reason thatlysogenic phages should be avoided in industrial microorganisms.The nature of the disturbance caused by phages in an industrial fermentationdepends on a number of factors.(i) The kinds of phages.(ii) The time and period of phage infect.(iii) The medium composition.(iv) The general physical and chemical conditions of the fermentor.The manifestation of infection is variable and the same phage does not always causethe same symptom. In general the symptom of infection could be a slowing down of theprocess resulting in poor yield, this being the case when the infection is light. When it isheavy, the cells may be completely lysed. The length of time taken before a phagemanifests itself is variable depending on its latent period (i.e., the period before the cell islysed) and the number of phages released. In a continuously operated fermentation,phages may take up to three months to manifest themselves. In general, however, theperiod is much shorter, being noticeable in a matter of days.11.4.3 Prevention of Phage ContaminationPhages are as ubiquitous as microorganisms in general and are present in the air, water,soil, etc. The first cardinal rule in avoiding phage contamination therefore is routinegeneral cleanliness and asepsis. Pipes, fermentors, utensils, and media, should all bewell sterilized. The culture should be protected from aerial phage contamination, aninsidious situation, which unlike bacterial or fungal contamination cannot be observedon agar. Air filters should be replaced or sterilized regularly.Aerosol sterilization of the factory with chlorine compounds, and other disinfectants,as well as UV irradiation of fermentation halls should be done routinely.