Quantitative spectral light scattering polarimetry for monitoring fractal growth pattern ofBacillus thuringiensisbacterial colonies

Abstract

ABSTRACT It is of considerable current interest to develop various methods which help to understand and quantif y the cellular association in growing bacterial colon ies and is also important in terms of detection and identification of a bacterial species. A novel approach is used here to probe the morphological structural changes occurring during the growth of the bacterial colony of Bacillus thuringiensis under different environmental conditions (in normal nutrient agar, in presence of glucose - acting as additional nutrient and additional 3mM arsenate as additional toxic materia l). This approach combines the quantitative Mueller matrix polarimetry to extract intrinsic polarization properties and inverse analysis of the polarization preserving part of the light scattering spectra to determine the fractal parameter H (Hurst exponent) using Born approximation. Interesting differences are observed in the intrinsic polarization parameters and also in the Hurst exponent, which is a meas urement of the fractality of a pattern formed by bacteria while growing as a colony. T hese findings are further confirmed with optical microscopic studies of the same sample and the results indicate a very strong and distinct dependence on the environmental condition s during growth , which can be exploited to quantify different bacterial spe cies and their growth patterns. Keywords: Optical polarization, Turbid medium polarimetry, Mueller matrix, Light scattering spectroscopy, Biological and medical applications, Fractals, Multiple scattering, Bacillus thuringie nsis