Influences of metal‐ligand complexes on the cadmium and zinc biokinetics in the marine bacterium, Bacillus firmus

Abstract

Uptake kinetics of cadmium and zinc in gram-positive bacteria, Bacillus firmus, isolated from Hong Kong sediments were examined in the present study. The metal uptake by the bacteria was measured at different ambient free metal ion concentrations (10(-12)-10(-6) M Cd(2+) and 10(-10)-10(-6) M Zn(2+)) by adding different concentrations of total dissolved Cd and Zn and hydrophilic organic ligands (ethylenedinitrilotetraacetic acid, nitrilotriacetic acid, and citrate). Our data suggest that Cd and Zn uptake by B. firmus is best predicted by Cd(2+) and Zn(2+) activities. Free metal ions were complexed with the active sites on the bacterial surface, and an equilibrium between the free metal ion and surface-metal complex was reached quickly. After binding, the metal ions were then biologically transported into the bacteria. In addition, with the presence of lipophilic organic ligands (diethyldithiocarbamate and oxine), the lipophilic metal complex was internalized rapidly into B. firmus by passive diffusion through the bacterial plasma membrane. The uptake of the lipophilic metal complex could not be predicted by the free ion activity model because the mass transport through plasma membrane was the most important metal uptake pathway. Furthermore, the efflux of Cd and Zn by B. firmus was determined in the present study. The calculated efflux rate constants of Cd and Zn were (5.55 +/- 1.96) x 10(-4)/min and (3.75 +/- 1.04) x 10(-4)/min, respectively. The present study helps us to understand the process of bioaccumulation of metals in marine bacteria, which remains a poorly studied area.

Influence of the microbial loop on trophodynamics and toxicity of cadmium complexed by cyanobacterium exudates

“…Kungolos et al 27 demonstrated that copper bioaccumulation in the photobacterium Vibrio scheri decreased with the addition of humic acid to the medium, and that free copper ions were responsible for the toxic effects. Keung et al 28 showed that Cd and Zn uptake by the bacterium Bacillus rmus correlated better with the free metal concentration than with that of hydrophilic metal complexes. Since the metals complexed in DOM are less toxic, they can be accumulated by the organisms and transferred throughout the food chain, as demonstrated in our studies.…”

Microdiversity of Deep-Sea <i>Bacillales</i> Isolated from Tyrrhenian Sea Sediments as Revealed by ARISA, 16S rRNA Gene Sequencing and BOX-PCR Fingerprinting

“…Despite the ubiquity of several Bacillus species and their ability to survive under diverse conditions, the requirement of some strains of seawater for growth suggests that they could represent obligate marine bacteria with habitats in marine sediments (19, 41, 57). Additionally, even as spores, marine Bacillus such as B. licheniformis , B. foraminis and B. firmus are involved in oceanic metal biogeochemical cycles by oxidation, precipitation, bioaccumulation and manganese-oxidizing activity in hydrothermal sediments and plumes (12, 17, 24). …”