Interactions between marine bacteria and heavy metals

Abstract

The aim of this study was to determine the resistance of a range of marine heterotrophic bacteria to selected heavy metals. The bacteria were isolated from coastal and open regions of the Black Sea contaminated by different levels of heavy metals and other pollutants. The heterotrophic bacteria were isolated over a period of two years, 1991 and 1992. The isolates were identified as strains of Vibrio, Pseudomonas, Cytophaga, Acinetobacter, Alcaligenes, Chromobacterium, Aeromonas, Bacillus, Arthrobacter, Micrococcus and Plancococcus . The resistance of theisolates to selected heavy metals was examined and compared for 1991 and 1992 isolates. The genera Cytophaga and Pseudomonas were studied in more detail for resistance to metals and metal accumulation. Tolerance to metals was determined by point inocula onto peptone-yeast extract agar containing metal salts at a range of concentrations. The cultures were grown aerobically at 22°C for 48 hrs after which time the presence or absence of growth was determined. Metal uptake was assessed by incubating cell suspensions, containing 5 mg (wet weight) biomass in 10ml seawater or seawater with 20 mg/l FeSO 4 , Mn(CO 3 ) 2 , Ni(NO 3 ) 2 , CdCl 2 , or ZnSO 4 for 7 days at 22°C. The amount of metal accumulated under each condition was determined by flame atomic adsorption spectrophotometer. The accumulation of heavy metals by 15 Pseudomonas strains and 4 Cytophaga strains isolated from metal polluted sites varied with metal and with the strain of bacterium. The order of metal accumulation, however, was the same for both genera and was Zn>Ni>Fe>Mn>Co>Cd. The pattern of accumulation by individual strains varied between seawater and seawater with added metal ions. The resistance of the bacteria to heavy metals also varied considerably with metal and microbial type, with highest resistance shown by Pseudomonas strains. There appeared to be no relationship between the levels of metal resistance shown by Pseudomonas strains and Cytophaga strains and the accumulation of metals by the isolates. There were marked differences in the resistance shown by 1991 isolates and 1992 marine isolates.