Dynamic light scattering by cultures of heterotrophic marine bacteria

Dariusz Stramski; Marian Sedlak; David Tsai; Eric J. Amis; Dale A. Kiefer

doi:10.1117/12.140688

31 December 1992 Dynamic light scattering by cultures of heterotrophic marine bacteria

Dariusz Stramski, Marian Sedlak, David Tsai, Eric J. Amis, Dale A. Kiefer

Proceedings Volume 1750, Ocean Optics XI; (1992) https://doi.org/10.1117/12.140688
Event: San Diego '92, 1992, San Diego, CA, United States

Abstract

Heterotrophic bacteria may play a significant role in the scattering of light in the ocean. The scattering properties of these microbes are very sensitive to cell size, which is difficult to measure in the submicron size range by common electronic and microscopic techniques. Assessment of bacterial contribution to light scattering is further complicated by the fact that the size of the cells may change under differing conditions of growth. We examined the size of bacterial cells that were either fast-growing or starving by application of the dynamic light scattering (DLS) method. Laboratory cultures of mixed populations of bacteria from oceanic waters off Southern California were measured. In the DLS method, the autocorrelation function of the time-dependent intensity of light scattered by small suspended particles is a measure of Brownian motion which, via the diffusion coefficient, provides information about the particle size distribution. The scattered intensity weighted sizes of formalin-preserved bacteria obtained from DLS were generally consistent with average cell sizes determined by epifluorescence microscopy. This consistency was supported by simulation of the intensity weighted size distribution by means of Mie scattering calculations for microscopically determined size distribution. In addition, the microscopic analysis showed that while the equivalent spherical diameter of fast-growing bacteria was on average 0.85 micrometers , the diameter of starved cells was 40 to 50% less. The starved cells were thus quite similar in size to bacteria found in the nutrient-poor open ocean environments. The cultures of starved bacteria contained small numbers of yeast cells (2 - 4 micrometers in size), and the sensitivity of the DLS analysis to such relatively large scatterers was evident. Our study indicates that the dynamic light scattering, a fast and noninvasive technique, offers new perspectives to study bacteria and other oceanic microparticles.

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Dariusz Stramski, Marian Sedlak, David Tsai, Eric J. Amis, and Dale A. Kiefer "Dynamic light scattering by cultures of heterotrophic marine bacteria", Proc. SPIE 1750, Ocean Optics XI, (31 December 1992); https://doi.org/10.1117/12.140688

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