Effects of nonionic surfactants on the UV/visible absorption of bacterial cells

Nonionic surfactants are used in a number of different microbiological appl ications, including solubilization of cell membranes, washing bacterial cul tures prior to experimentation, and enhancing biodegradation of low-solubil ity compounds. An important consideration in these applications is the pote ntial for the surfactant to alter the cell membrane. One potential means to monitor the impact of surfactants on the bacterial cell membrane is throug h monitoring the absorbance spectrum of the bacterial suspension. This is d ue to the colloidal nature of bacteria, where the absorbance of a bacterial suspension is related to the size and refractive index of the bacterial ce lls. Through a systematic study it was shown that there can be a significan t change in the bacterial absorbance spectrum due to the presence of nonion ic surfactants, with the effect a function of surfactant structure and conc entration, solution ionic strength and cation valence. The effects were mos t pronounced with Na+ as the cation, with surfactants having midrange hydro phile-lipophile balance (HLB) values, and with surfactant concentrations ab ove the CMC. The results indicate that measurement of the absorbance spectr um of bacterial cultures can provide a means to monitor the effects of noni onic surfactants on the bacterial cell membrane. In addition, depending on the specific application, appropriate selection of surfactant structure and media composition can be made to enhance or minimize the effects. (C) 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 74: 476-482, 2001.