The amount of PM production in

cells harvested at OD = 0.2 were comparable to the control culture whereas only negligible amounts were observed in cells harvested at ODs above 40. An inhibitory effect was also observed when Fed-Batch culture supernatants were applied as cultivation medium for fresh cells (white bars, Figure 2A). Figure 2 Effect of culture supernatants, obtained at various optical densities, on photosynthetic membrane production (A) and cell growth (B) of R. PF-3084014 solubility dmso rubrum. A: PM production during microaerobic cultivation using sterile filtered culture supernatants and cells harvested from an aerobic Fed-Batch cultivation. Black bars represent production in cells harvested from the Fed-Batch cultivation, washed and resuspended in fresh medium. White bars indicate cells harvested from an aerobic pre-culture, this website washed and resuspended in supernatant from the same Fed-Batch cultivation. B: Initial growth rate under microaerobic conditions after cells were inoculated into filtered culture supernatant harvested from the same aerobic

Fed-Batch cultivation. As a control for both A and B, cells harvested from an aerobically grown preculture were washed and resuspended in fresh medium (striped bars). Rates were calculated from data during HSP990 mw the growth phase of the cultivation. The shown data represents the mean of three measurements. Error bars were calculated by error propagation with accumulated deviations of three equivalent experiments. (Cells and culture supernatants from three Fed-Batch cultivations were treated as described above). The results Galeterone summarized in Figure 2A therefore suggest the presence of one or more factors in the supernatant that restrict PM production. Furthermore, in the resuspended culture, PM production diminished with increasing OD from the point of harvest/resuspension until complete inhibition at OD >40. However, when samples taken at different OD levels were plated on minimal or lysogeny broth (LB) medium, all colonies had the PM-producing phenotype of the wild-type strain. Therefore, loss of PM production through

mutation could be ruled out. Another interesting observation was that fresh cells inoculated in culture supernatant grew with a higher initial growth rate than the control (aerobic cells/fresh cultivation medium, Figure 2B). However, this effect declined for cells cultivated in culture supernatants harvested at OD >25. These initial results showed that cells provided with fresh growth medium were capable of producing higher PM levels and that substances which accumulated in the culture supernatant have an influence on the initial growth rate and the PM production. As the changes in cell behaviour were strongly dependent on the culture density, we suspected that a quorum sensing system could be responsible for the observed phenomena.