Surface Charge Properties of and Cu(II) Adsorption by Spores of the Marine Bacillus sp. Strain SG-1

Abstract

Spores of marine Bacillus sp. strain SG-1 are capable of oxidizing Mn(II) and Co(II), which results in the precipitation of Mn(III, IV) and Co(III) oxides and hydroxides on the spore surface. The spores also bind other heavy metals; however, little is known about the mechanism and capacity of this metal binding. In this study the characteristics of the spore surface and Cu(II) adsorption to this surface were investigated. The specific surface area of wet SG-1 spores was 74.7 m2 per g of dry weight as measured by the methylene blue adsorption method. This surface area is 11-fold greater than the surface area of dried spores, as determined with an N2 adsorption surface area analyzer or as calculated from the spore dimensions, suggesting that the spore surface is porous. The surface exchange capacity as measured by the proton exchange method was found to be 30.6 μmol m−2, which is equal to a surface site density of 18.3 sites nm−2. The SG-1 spore surface charge characteristics were obtained from acid-base titration data. The surface charge density varied with pH, and the zero point of charge was pH 4.5. The titration curves suggest that the spore surface is dominated by negatively charged sites that are largely carboxylate groups but also phosphate groups. Copper adsorption by SG-1 spores was rapid and complete within minutes. The spores exhibited a high affinity for Cu(II). The amounts of copper adsorbed increased from negligible at pH 3 to maximum levels at pH >6. Their great surface area, site density, and affinity give SG-1 spores a high capability for binding metals on their surfaces, as demonstrated by our experiments with Cu(II).

Removal of Heavy Metals from the Environment by Biosorption

“…The negatively charged groups (carboxyl, hydroxyl, and phosphoryl) of the bacterial cell wall adsorb metal cations, which are then retained by mineral nucleation [64]. For example, one study showed that the spores of the Bacillus species strain SG-1 remove copper from waste streams containing mixed metals by precipitation followed by passive adsorption [65].…”

“…With some species, both processes may occur. In a study of Pseudomonas aeruginosa, for instance, was found that copper uptake initially resulted from an extracellular adsorption of Cu 2+ ions, which was followed by intracellular accumulation that resulted from the exchange of copper ions with calcium and magnesium ions across the cell wall [65,66].…”

“…Other studies of single-solute solutions containing copper ions have also demonstrated that uptake is rapid and reversible in most cases. In research involving marine Bacillus species, 60 % of the Cu 2+ was bound to the bacteria within the first minute at pH 7.2 and the adsorption equilibrium was reached within 10 min [65]. In another study, planktonic Thiobacillus ferrooxidans cells in aqueous solutions with Cu 2+ reached the adsorption equilibrium within 15 min [69].…”

Chemical and structural status of copper associated with oxygenic and anoxygenic phototrophs and heterotrophs: possible evolutionary consequences

“…In the simplest form of uptake by phytoplankton, metals are adsorbed onto sites in cell walls and cell membranes without being transported into cytoplasm (Hudson, 1998;Xue et al, 1988). To address the first step of metal interaction with live cells, a significant amount of work has been devoted to copper binding to algal and bacterial surfaces using macroscopic techniques (Gonzales-Davila et al, 1995;Gonzalez-Davila et al, 2000;He & Tebo, 1998;Xue & Sigg, 1990). Nevertheless, provision of Cu limitation vs. toxicity for different aquatic micro-organisms remains largely unknown.…”

NanoSIMS imaging ofBacillusspores sectioned by focused ion beam

“…For example, P and Ca are known to be abundant in the spore core because that is where DNA, RNA, phosphorylated nucleotides and Ca-dipicolinic acid are located, respectively. Trace elements are known to bind to the spore coat (Stewart et al, 1980;He & Tebo, 1998), but the controls on these elements are less well understood. Elemental distributions and abundances may be directly related to spore production, purification and stabilization methodologies, which are of particular interest for forensic investigation.…”