Formation of Organic Cadmium by Marine Microorganisms

This research was designed with a view to finding out whether or not there is a microbial or spontaneous transformation of inorganic cadmium into a highly toxic organic derivative of this metal by microorganism obtained from the Eastern Mediterranean marine environment. Sterile and nonsterile marine bottom sediment samples were incubated at ambient temperature for different time intervals, under aerobic and anaerobic conditions, with different concentrations of CdCl2, and the medium, the atmosphere in the incubation flasks, and the sediments were assayed for their organic cadmium contents. The results were: (a) There was microbial growth in all systems containing up to 250 μg cadmium per milliliter of growth medium; however, with higher concentrations a complete growth-inhibition was observed. (b) Organic cadmium was found in the bottom sediments, at all cadmium levels permitting considerable microbial growth, but not in the systems′ atmospheres or in the liquid growth media. (c) Under aerobic conditions higher levels of organic cadmium were found than in the anaerobic systems. (d) The microorganisms occurring in the different experimental systems were isolated and identified. The predominating species in all systems were bacteria.