The Effects of Lead (II) Nitrate on EPS Production by Colwellia psychrerythraea 34H and the Metal-Binding Capacity of the EPS under Freezing Conditions

Abstract

We examined how [Pb2+] affects the growth of the bacterium, Colwellia psychrerythraea as well as the bacterium’s ability to produce extracellular polysaccharide substances (EPS). In addition, we explored the potential binding capacity of EPS and [Pb2+] through freezing trials that included both ice and liquid phases. Earlier studies have explored the effects of EPS on other bacteria or algae. In these experiments we focused on bacterial growth and the impacts on EPS production using the phenol-sulfuric acid method of Dubois et al. (1956) to measure EPS, an ICPMS machine to measure [Pb2+], and a series of freezing experiments to examine selective retention of EPS or lead in ice. The growth data suggests that there may be a threshold or “tipping point” between 0.1 mg/L and 1 mg/L of [Pb2+] up to which there is more EPS produced than when there is no lead present. However, at a high lead amount (1 mg/L), the culture was completely unable to grow or produce EPS. At low levels of lead (0.1 mg/L) there was possible binding activity between EPS and the heavy metal. This effect was not evident when 1 mg/L of lead was introduced to the system, which we attribute to as an oversaturation of the EPS such that no binding could take place.