Characteristics of Surface Adsorbed Bacterial Luminescence

Abstract

ABSTRACTPhotobacterium kishitanii is one species of luminescent bacteria. This bacterium is known to convert chemical energy into light; it glows in the dark with a visible peak wavelength (ca. 475 nm) that is easily recognized. Luminescent bacteria produce autoinducers and respond to this molecule to switch on the luciferase structural operon. Luminescence is, therefore, controlled by the cell-population density.If bacterial cells are viewed as enzyme bags, substrates, such as oxygen or autoinducers, diffuse into the bags through a semipermeable cell wall and are catalyzed by the enzyme. Oscillation in the product concentration is often observed in systems where a semipermeable membrane separates the substrate and the enzyme. Such behavior is simulated using a reaction-diffusion model.We have reported several characteristics of the luminescence from a bacterial suspension. For example, in a batch culture, higher initial bacteria density resulted in an earlier luminescence starting time [1]. Apart from such linear characteristics, we have reported an oscillation in the luminescence intensity both spatially and temporally [2]. We hypothesize that a group of bacteria behaves differently from a sum of single cells. The nonlinearity of the bacterial luminescence might be a key to understanding the phenomenon. In a previous experiment, we separated bacteria into small groups that showed similar characteristics, such as motility and adsorption activity. For example, bacteria separated according to their motility using a microfluidic device were proved to show different bioluminescent intensities for each cell [3]. On an agar plate, the luminescence intensity from actively dividing cells was less than that from mature cells [4]. In addition to this basic study to understand the oscillation in bacterial luminescence, reactors were designed to realize stable bacterial luminescence. In a PDMS cell, only the parts of the suspension that faced the wall were illuminated [5]. This result suggested that the geometrical symmetry of oxygen supply to the suspension helped maintain spatial stability without convection of the bacterial luminescence.Here, we report the luminescence behavior of bacteria that adsorbed on material surfaces. In this work, we show experimentally that the bacteria adsorb on the inner surfaces of a polyethylene terephthalate (PET) or polystyrene (PS) bottle and start to emit light when a liquid broth is added. We also show that the luminescence from the suspension oscillates. Experimentally, using a self-made luminescence detector, measurement of luminescence intensity from well-stirred bacterial suspensions in the bottles of different materials (PVC, PET, or PS) was performed. After the observation of oscillation in luminescence, the bottles were washed three times using the same broth, followed by the luminescence measurement. Such washing and measurements were repeated, and oscillation was repeatedly observed. The chemical condition of adsorption on the surface was investigated using surface analysis methods, such as AFM or FTIR, and the material characteristics with regard to cell adsorption and oscillation mode were discussed.