Host range specificity

Recently, bacteriocins produced by LAB and associated bacteria have been identified that exhibit expanded host ranges, specifically with added activities against Gram-negative bacteria (Svetoch and Stern 2010 Lee et al. 2011). Both class I and class Ila bacteriocins have been identified. 

Widner, W.R. and H.R. Whiteley. 1989. Two highly related insecticidal crystal proteins of Bacillus thuringiensis subsp. kurstaki possess different host range specificities. J Bacteriol. 171 965-74. 

The sindbis virus is simple, robust, capable of infecting non-dividing cells and generally supports high levels of gene expression. However, it does display a broad host range and, hence, lacks the inherent targeting specificity characteristic of an idealized viral vector. 

Hashemolhosseini, S., Montag, D., Kramer, L., and Henning, U. (1994). Determinants of receptor specificity of coliphages of the T4 family. A chaperone alters the host range./. Mol. Biol. 241, 524-533. 

Host range (bacteriophage p) Gin/gix Site-specific Alternative expression of two sets of tail fiber genes affects host range. 

As pointed out above, the bioassay design depends on the objective(s) of the study. A bioassay to determine allelopathic interactions in the field or in an ecological setting may have a quite different design than one used to determine PGR activity of a compound or to determine its molecular mode of action. Specific bioassays can be used to follow the isolation/purification of allelochemicals, evaluate their phytotoxic (or growth simulation) effects (i.e., visual effects), determine their host range/selectivity, evaluate allelopathic action of volatile compounds, or examine physiological/biochemical effects, such as photodynamic and membrane effects, effects on photosynthesis, specific enzyme sites, and effects at the ultrastructural level to locate receptor sites or sites of injury. Several examples of useful bioassays will be presented later. 

To achieve successful infection a virus depends on the encounter rate and thus on the abundance of its host species. The Phaeocystis virus isolates have, however, not only a species-restricted host ranges but most often also a strain-specific spectrum of infection (Jacobsen et al. 1996 Baudoux and Brussaard 2005). Thus, not all strains of a Phaeocystis species (e.g., P. globosa) will become infected, even when coexisting in the same water mass. Factors influencing this are the ability of the virus to bind optimally to a proper host cell, as well as the sensitivity of the host to infection. 

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