Abstract

Development of methods for quantification of cellular association and patterns in growing bacterial colony is of considerable current interest, not only to help understand multicellular behavior of a bacterial species but also to facilitate detection and identification of a bacterial species in a given space and under a given set of condition(s). We have explored quantitative spectral light scattering polarimetry for probing the morphological and structural changes taking place during colony formations of growing Bacillus thuringiensis bacteria under different conditions (in normal nutrient agar representing favorable growth environment, in the presence of 1% glucose as an additional nutrient, and 3 mM sodium arsenate as toxic material). The method is based on the measurement of spectral 3×3 Mueller matrices (which involves linear polarization measurements alone) and its subsequent analysis via polar decomposition to extract the intrinsic polarization parameters. Moreover, the fractal micro-optical parameter, namely, the Hurst exponent H, is determined via fractal-Born approximation-based inverse analysis of the polarization-preserving component of the light scattering spectra. Interesting differences are noted in the derived values for the H parameter and the intrinsic polarization parameters (linear diattenuation d, linear retardance δ, and linear depolarization Δ coefficients) of the growing bacterial colonies under different conditions. The bacterial colony growing in presence of 1% glucose exhibit the strongest fractality (lowest value of H), whereas that growing in presence of 3 mM sodium arsenate showed the weakest fractality. Moreover, the values for δ and d parameters are found to be considerably higher for the colony growing in presence of glucose, indicating more structured growth pattern. These findings are corroborated further with optical microscopic studies conducted on the same samples.

Highlights

  • The corresponding variations of the light scattering signal for the bacteria colonies growing in normal nutrient agar environment and in presence of 3 mM sodium arsenate are shown in Fig. 4(b) and 4(c), respectively

  • The corresponding results of fractal analysis of the light scattering signal for the bacteria colonies growing in normal nutrient agar environment and in presence of 3 mM sodium arsenate are shown in Fig. 4(b) and 4(c), respectively

  • We have explored the use of quantitative spectral light scattering polarimetry to probe the morphological and structural changes of growing Bacillus thuringiensis bacteria colonies under different environments

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Summary

Introduction

As living organisms, are unicellular in nature, but in order to cope with environmental conditions, under an unfavorable one, bacterial cells of the same species have evolved with time to develop cooperative behavior among them for survival.. As living organisms, are unicellular in nature, but in order to cope with environmental conditions, under an unfavorable one, bacterial cells of the same species have evolved with time to develop cooperative behavior among them for survival.1–3 This cooperative behavior have caused further evolving complex growth patterns in a bacterial colony.. Specific bacterial associations and colony growth patterns under different conditions have enabled us to identify and detect specific bacterial species and helped us to understand cellular and molecular basis of signaling network for bacterial competition and cooperation..

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