I am confused about the origin of plaques in titering the M13 infected-bacteria mixed with LB-top agar though M13 phage is not the lytic one. Why should we see clear plaques with bacteria around eaten away?
Thanks everyone in advance
DearAlizadeh,
Theoretically what we have studied is that the development of dental plaque involves acidogenic and aciduric Gram-positive bacteria, primarily the mutans streptococci (Streptococcus mutans and S. sobrinus), lactobacilli and actinomycetes. Streptococcus mutans metabolizes sucrose in a peculiar way, producing an extra cellular adhesive polysaccharide (dextran), a sticky insoluble glucan which promotes the firm adherence of the organisms to the tooth surface contribute the formation of dental plaque. Accumulation of plaque around the gingival margin and subgingival region may lead to shift in the population of the microflora from gram positive to gram negative bacteria. Several potential Gram negative anaerobic bacteria such as Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans and Camphylobacter rectus are considered to represent a significant portion of pathogenic bacteria.
A viral plaque is a visible structure formed within a cell culture, such as bacterial cultures within some nutrient medium (e.g. agar). The bacteriophage viruses replicate and spread, thus generating regions of cell destructions known as plaques.
The appearance of the plaque depends on the host strain, virus and the conditions. Highly virulent or lytic strains give clear plaques while strains that only kill a fraction of their hosts (due to partial resistance/lysogeny) or only reduce the rate of cell growth give turbid plaques.
Even though M13 is lysogenic it has been documented to reduce bacterial growth and hence may result in a turbid plaque.
If the M13 slows down growth enough, the plaque may to the eye appear clear, even if it does not kill the bacteria. It can multiply and spread fast enough to prevent visible bacterial growth in a certain area. I guess if you would incubate the plates longer, the plaques would grow more turbid and finally "fill in" (although this could also be caused by an M13-resistant mutant or contaminant starting to grow unimpeded).
Mark is essentially correct. You have a lawn of fast growing bacteria, the M13 infected cells don't lyse but grown more slowly and so what you are observing is a zone of partial growth inhibition.
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