Role ofLeptothrix discophorain Mediating Metal Uptake in the Filter-Feeding BivalveMytilus trossulus (edulis)

Abstract

The potential for filter-feeding bivalves to accumulate metals from a wide range of food sources is an important consideration when examining trophic transfer of metals up the food chain. The objective of this study was to determine the role of Leptothrix discophora in mediating metal uptake in the filter-feeding bivalve Mytilus trossulus. The bacterium L. discophora SP-6 was cultured in the absence or presence of Mn, allowing for a naturally formed Mn oxide sheath to develop. Secondary metals (Cd and Pb) were then added to the cultures, allowing for potential Cd and Pb adsorption to the Mn oxide sheath. Resulting bacterial aggregates of known diameter were then fed to the bivalve M. trossulus using a flow-through system. Initial concentrations of both Pb and Cd on the bacterium did not differ significantly in the presence or absence of the Mn oxide; conversely both Pb (F = 7.39, p < 0.0001) and Cd (F= 33.65, p < 0.0001) were found at lower concentrations in the mussel tissue when the Mn oxide was present. To determine whether these differences in metal uptake could be attributed to sorting by the mussel based on food quality, nutritional analysis was performed. Bacterial food matrixes containing Mn oxides were found to have significantly lower levels of carbon (F = 256, p < 0.0001). Particle clearance rates for the various food matrixes were positively correlated with organic content (R2 = 0.852, p > 0.008). The results of our study suggest that metal uptake in M. trossulus was significantly decreased for Cd with a similar trend for Pb when the SP-6 sheath contained Mn oxides. The mechanism mediating this differential uptake is best explained by food quality, in that a higher quality food source enhanced metal uptake due to an increased clearance rate of organic-rich particles by M. trossulus.

Heavy Metals in Seafood Mussels. Risks for Human Health

“…via the gills or gut; subsequently, it binds to low molecular weight proteins metal-lothioneins and accumulates in the liver and kidneys, making Cd diffi cult to extract, Widmeyer et al ( 2004 ) .…”

“…Cd may act as an acute and chronic type of poison. In chronic exposure, the fi rst sign is kidney damage, usually diagnosed by increased excretion of low molecular weight proteins, Widmeyer et al ( 2004 ) . Over time, Cd can accelerate osteoporotic process, since a high calcium dose can inhibit Cd absorption.…”

“…Absorbed Pb is bound to erythrocytes in the blood and initially distributed to the liver, kidney and heart, where it preferentially binds to cell membranes and mitochondria, Widmeyer et al ( 2004 ) . Most forms of Pb are then distributed and stored in the bones.…”

“…The primary root of elimination is via the feces (90%) and the remaining via the urine (10%), Gilbert ( 2004 ) . Pb is known to cause both acute and chronic adverse effects in the hematopoietic, nervous, gastrointestinal and renal systems, Widmeyer et al ( 2004 ) . Acute poisoning causes gastrointestinal colic, often resulting in mortality, while chronic poisoning causes anemia due to a decrease in the hemoglobin levels leading to organ damage in one or all of the four above-mentioned systems, Gilbert ( 2004 ) , but Pb is not-carcinogenic, Chang ( 1996 ) .…”

Health risks of heavy metals in the mediterranean mussels as seafood

“…Moreover, Mytilus species are able to synthesize the metal-binding protein, metallothionein, for metal detoxification (Kohler and Riisgard 1982). For example, the main routes of aqueous Cd uptake in aquatic organisms are via the gills or gut; subsequently, it binds to low-molecular-weight proteins metallothioneins and accumulates in the liver and kidneys, making Cd difficult to extract (Widmeyer et al 2004). The general population is exposed to Pb through food, water, and air.…”