The Magnitude and Rate of Change of Cell Surface Functional Groups as Function of Salinity: Implication for Environments of Microbially-Facilitated Carbonate Formation

Abstract

Microorganisms are an important component of many near surface aqueous environments with cell densities ranging between 104-107 cells ml-1. While many environments are geochemically altered by microbial metabolism, their cell surfaces, complex structures hosting functional groups, also interact with dissolved species, mineral, and organic surfaces. These interactions can influence significantly mineral equilibria of minerals in a given aqueous environment through complexation of aqueous metals and surface stabilization of mineral nuclei. While many studies have characterized the cell surface functionality of freshwater microorganisms, relatively few have focused on organsisms that inhabit fluids ranging from brackish to marine. In this study, pure cultures of Roseobacter litoralis and Halobacterium salinarum, both organisms that inhabit saline environments, were grown at a range of ionic strengths and titrated to quantify surface functional groups. Multiple generations of growth at varied growth media ionic strengths (0.5M-3.0M) were analyzed to evaluate the magnitude and rate of change in cell surface functional groups. Roseobacter litoralis and Halobacterium salinarum both displayed changes in average cell surface functional groups after growth in increased or decreased ionic strength growth media. Carboxyl groups increased by as much as 30% and 29.5% and decreased by as much as 63% and 9.8% respectively in R. litoralis and H. salinarum. Responses to various growth media ionic strength were observed rapidly, after 6 generations of growth in both microorgnisms. Data produced was evaluated in relation to previous work to provide a framework for predicting microbial functional group density at various ionic strengths. In environments such as hypersaline lagoons microorganisms have more surface functional groups, and therefore may may play an integral role in mineral nucleation and metal adsorption. Microorganisms that inhabit environments with fluctuating ionic strengths rapidly adapt their surface functional groups. A model that can predict the density of functional groups at given ionic strength environments can be valuable in metal adsorption for the purpose of bioremediation and mineral nucleation. Organisms capable of producing a functional group density above a threshold may potentially be able to facilitate mineral precipitation without regard to the specific organism.