Response of Bacillus subtilis bacterium to environmental change monitored in an optical tweezer

We study the swimming characteristics of Bacillus subtilis by confining it in an optical trap and monitoring the rotational characteristics with high resolution by laser forward scattering onto a quadrant photo detector (QPD). Our measurements indicate that the flagella rotation rate decreases with time and this variation is in agreement with measured speed of freely swimming bacterium. The effect of change in pH of the environment were also studied. The decrease in pH of the environment lowered the rate of decrease in flagella rotation.