Capsular polysaccharide production from Zunongwangia profunda SM-A87 monitored at single cell level by atomic force microscopy

Abstract

Polysaccharides are secreted by many marine bacteria as a strategy for growth, binding trace metals, adhering to solid surfaces, and to survive adverse conditions. Therefore, they have attracted extensive research interest due to their biological roles as well as potential industrial application. Many works have been carried out to study the growth dynamics of polysaccharides producing bacteria. Average polysaccharide production per cell during growth were usually studied in the past. However, most previous works were carried out at the population level, and the research at a single cell level was rare. Atomic force microscopy (AFM) is a powerful tool in studying single microorganisms and their extracellular polysaccharides. Here we investigated the growth dynamics and capsular polysaccharide (CPS) production of a CPS producing bacterium Zunongwangia profunda SM-A87 isolated from deep-sea sediments with AFM. Z. profunda SM-A87 exhibited slow growth rates at 10°C, which was lower than at optimum growth temperature (30°C). But the CPS production at 10°C was much higher than that at 30°C. Single cell imaging with AFM revealed rod like cell morphology at both temperatures, but filamentous bacteria could sometimes be noticed at 10°C. The CPSs surrounding bacterial cells were observed, and the fibrils of polysaccharides entangled into networks. The diameter of the capsules and the length of the polysaccharides fibrils increased as cultivation time increased. The average volume of the bacterial cells and capsular polysaccharides surrounding each cell at both temperatures were calculated. The average volume of a single bacterial cell was 0.2–0.3µm3, and it increased in exponential phase and slightly decreased in stationary phase, but the average volume of CPS produced by single cells increased during bacterial growth. CPS production increased to 0.097 ± 0.051µm3 per cell at 10°C in stationary phase, which is larger than that produced at 30°C (0.055 ± 0.013µm3 per cell). We report a novel method of estimating the average bacterial polysaccharide production with AFM. Since polysaccharides-producing bacteria are abundant in marine sediments, this method is potentially useful for studying the biological and ecological role of polysaccharides-producing bacteria from the deep sea in the future.