Bacteria were cultured for 18 h on 50-mm-diameter BHI agar plates, and the lawns of S. aureus (SH1000) and S. epidermidis strains (resident and invader – Table 1) were then scraped off the agar plates and suspended in 10 mL of PBS by vortexing thoroughly.
To construct a T. reesei QM6a MAT1- 1 strain, the resident MAT1- 2 locus was replaced by the MAT1- 1 locus from T. reesei C.P.K. 1282.
So how could the Brighton Model help to lessen that strain on residents?
This relationship suggests that resistance evolution by residents may frequently impede invasion by toxin-producing strains, because resident populations are unlikely to be mutation-limited and selection for resistance progressively strengthens as an invasion proceeds.
This low-load mutant (solid line) replaces the resident strain and the average-load carrying antigenic mutant, ultimately precipitating an antigenic cluster transition.
The most compelling evidence for transposition emerged in studies of our collection of 44 strains from residents of Shimaa, a Machiguenga village (∼600 residents) in the remote Peruvian Amazon.
A large-sized antigenic mutation (σ = 0.06, dashed line) first arises in an average genetic background (k = 10) of the resident strain (dotted line).
A small antigenic mutation (σ = 0.003, dashed line) first arises in a good genetic background (deleterious mutation load k = 2) of the resident strain (dotted line).
There was also a significant difference in the strains resistance to inhibition: four of the intruders were not susceptible to inhibition by any of the resident strains and the remaining strains were inhibited by 1 5 strain(s) (on average two; Table 4, nested model: p<0.0001).
Additional variation may be introduced if novel Attamyces strains enter the nest and recombine with the resident strain; recombination appears to occur in rare cases in experimental laboratory colonies of A. texana [22, R. Sen, H.D. Ishak, and U.G. Mueller unpublished], but recombination has so far not been observed directly in natural Atta nests in the field.
