This paper reports on the THz frequency characterization of highly diluted mixtures of Bacillus Subtilis (BG) cells and spores pressed into pellets with high densities of polyethylene (PE) micro-powders. This technique of forming matrices of sparsely distributed biological (bio) materials by mixing them into larger concentrations of PE is one that has been previously applied to study spectral signature phenomenology. In particular, previously results have suggested that isolating the microscopic bio-particles leads to an enhancement of the THz signatures - i.e., yielding sharper and stronger absorption resonances. However, it is important to minimize the influence of etalon effects because they can introduce sharp artificial fringes in the transmission spectra that obscure the underlying THz signatures. This paper will present results from optimally prepared PE matrices containing reduced concentrations of BG cells and spores. Here, the BG-PE matrices are of thickness of approximately 30 micrometers and contain BG concentrations from 0.1 to 0.3 %. As will be shown, these thinner layers allow for the more accurate characterization of smaller amounts of bio samples and reveal new information on the THz signatures of BG cells and spores. In particular these results show very close correlations between the spectra of BG cells and spores and suggest both contain common genetic components. These studies provide new information that will be useful in the future development of THz-based sensors.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.