Biosorption of cadmium by the multiple-metal resistant marine bacterium Alteromonas macleodii ASC1 isolated from Hurghada harbour, Red Sea

Ten cadmium resistant marine bacterial isolates were isolated from seawater and sediments samples of Hurghada harbour on a seawater nutrient agar medium amended by 25 ppm of cadmium and tested for their resistance to higher cadmium concentrations (up to 200 ppm). The most resistant isolate which was able to grow at 150 ppm was identified on the basis of its morphological, physiological and biochemical characteristics as Alteromonas macleodii. Then our isolate was submitted to genotypic characterization through 16S rDNA gene technique. The sequence was compared with known sequences in the GenBank nucleotide database and identified with 96% similarity to Alteromonas macleodii NR 037127.1. Growth curves at different concentrations of cadmium (25 and 150 ppm) exhibited low growth rate and prolonged lag phase in comparison to the normal growth curve (without cadmium). Also, biosorbtion of cadmium from aqueous solution and the different factors (biomass concentration, pH, cadmium concentration, temperature and contact time) which affect on this process were optimized. The results showed that the maximum removal of cadmium (150 ppm) by A. macleodii ASC1was 68% at pH 6 and temperature 30 ° C within five hours of contact time. A. macleodii ASC1was tested for resistance to different heavy metals and the minimum inhibitory concentrations (MIC) were 175 ppm for Cd, 250 ppm for Zn, Ni and Fe, 275 for Cu, 300 for Mn and 350 ppm for Pb. Also, the response to different antibiotics was studied and showed highly sensitivity to levofloxacin, imipenem and chloramphenicol, moderate sensitivity for ampicillin and resistance against penicillin G, streptomycin, vancomycin, ceftriaxone and amikacin. Identified heavy metal resistant bacterium could be useful for the bioremediation of heavy metal contaminated sewage and waste water before drained into marine environments.