Bacteriophages characteristics

Temperate bacteriophage, the best known being phage X, have a very different life cycle. Their DNA usually becomes integrated at a specific point into the genome of the bacterium (Chapter 27). Only rarely is an infected cell lysed. The retroviruses that attack mammals and birds have a similar characteristic. 

Within each host cell system, several independent isolates and laboratory variant strains are available, and the efficiency of expression can vary between them for reasons that are not always understood. For example, there are several independently isolated strains of E. coli, which vary in their ability to express the same protein using the same vector. Thus, it is routine to test several strains for optimal production, and this is usually achieved by screening a bank of available strains. In addition, notably in the E. coli system, there are several mutant strains which may be used to increase product yield and improve fermentation characteristics. Such mutants may have deficiencies in proteases, resulting in increased stability of the expressed protein (Kresze, 1991), cell-wall mutations permitting better secretion characteristics (Le and Trotta, 1991), or resistance to bacteriophages which can lyse bacteria leading to losses and delays in large-scale fermentation. 

A virus that infects only bacteria is called a bacteriophage, or simply a phage. Viruses that Infect animal or plant cells are referred to generally as animal viruses or plant viruses. A few viruses can grow In both plants and the Insects that feed on them. The highly mobile Insects serve as vectors for transferring such viruses between susceptible plant hosts. Wide host ranges are also characteristic of some strictly ani-... 

As shown by Komberg and coworkers, infection of Escherichia coli by these bacteriophages triggers the synthesis of new enzymes, including D-glucosyl transferases, which had been totally lacking before infection these enzymes catalyze the synthesis of the type of deoxyribonucleic acid characteristic of that phage. 

The overall effect of bacteriophage contaminations is influenced by several factors related to the characteristics of the phage itself as well as the timing of infection relative to the stage of the fermentation process. Consequently, independent infections even with the same phage can result in different outcomes. Thus, minor contaminations can only result in extended fermentation times and decreased solvent yield, whereas more severe infections can lead to complete cessation of the fermentation and/or nearly complete cell lysis within hours. 

Bacteriophages with a short latent period and large burst size tend to have the most serious consequences for the fermentation process. Such characteristics... 

Kongo, M., Aono, T., and Murata, A. (1966) Bacteriophages of Clostridium saccharoperbutylacetonicum part IV. Serological characteristics of the twelve HM-phages. Agric. Biol. Chem., 30, 399-405. 

This comprehensive collection of well-characterized Lactococcus strains facilitates fast development of new cultures in the event a strain in a commercial culture is attacked by bacteriophage. Strains that sttongly resanble the attacked strain, but with a different bacteriophage sensitivity, can simply be selected based on their previously determined phenotypic characteristics and tested for suitability for use in specific appUcalions, thus eliminating the need for new, time-consuming, strain-screening experiments. 

Probably the best examples of rod-like colloidal particles are stiff vims particles such as the plant vims tobacco mosaic virus (TMV) and the bacteriophage feline distemper (fd). In Table 6.1 we summarize the characteristics of TMV and fd, including their linear charge densities at neutral pH. 

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