Background: Pigment production is regulated by quorum-sensing
(QS) in certain bacteria which are being widely used as model organisms in different
QS labs. This paper emphasizes importance of selecting an appropriate
wavelength for quantification of bacterial growth and pigmentation. While
screening different natural/synthetic preparations for their possible QSmodulating
potential, it becomes very much necessary to establish that the observed
effect is truly QS-associated, and not falsely inflated owing to inaccurate
quantification of bacterial cell density/ pigment intensity.
Methods: Pigments were extracted in suitable organic solvents, whereas quantification
of bacterial growth and extracted pigments was done photometrically.
Results: Findings reported in this paper, suggest that while quantifying cell density in a pigmented
bacterial suspension, such a wavelength (e.g. 764 nm) should be selected at which pigment interference
is either absent or minimum. Additionally, importance of appropriate dilution of the bacterial
cell suspensions, prior to photometric measurement has been highlighted.
Conclusion: This work indicates that while working with pigmented bacteria, it is important to pay
attention to the absorption spectrum of the pigment(s) involved, and also to dilute the dense bacterial
suspensions appropriately prior to measuring optical density, so as to avoid any major deviation
of OD from the proportionality to the cell density. Besides presenting the experimental data in this
paper, patents regarding measurement of cell growth, as well as those indicating the potential of
commercialization of various aspects of QS research have been mentioned.