The nine most frequent bacterial strains out of 127 were isolated form ten drinking
water samples collected from tap water and bottled water in sharqia governorate. The
nine isolates were purified and examined for their resistance to increasing concentrations
of two heavy metal ions, lead (Pb+2) and iron (Fe"3). Four stains out of the
nine isolates encoded I, II, IV, and VIII showed the highest efficiency of both Pb+2 and
Fe +3 uptake from nutrient broth media containing 100 ppm of the heavy metal ions.
The four bacteria were preliminary identified and then confirmed by the Biolog
examination as Corynebacterium jeikeium, Pseudomonas putida biotype A, Acinetobacter
calcoaceticus and Acidovorax delafieldii. The increased concentrations of Pb+2 ions (from
100 to 500 ppm) in nutrient broth media had deleterious effect on the process of heavy
metal uptake (biosorption) by all the four selected isolates. Whereas percentage of Pb+2
uptake decreased from 42.9 to 24%; from 72.6 to 42%, from 78.9 to 37% and from 68.8
to 45%, for the four selected isolates, respectively. Meanwhile there was slight
decrease change in Fe+3 uptakes percentage accompanying the increase in heavy metal
ion concentration. Optimization of the cultural conditions releaved maximum uptake
op pb+2 and Fe+3 by the four tested strains in presence of 100 ppm heavy metal
concentration when incubated at 25°C except for Acinetobacter calcoaceticus at 35°C in
case of Pb+2 uptake, when pH, was adjusted at 5 under static conditions. Upon addition
of 50 ppm Cu+2 ions to broth media supplemented with 100 ppm Pb+2 ions, the
percentage of metal biosorption by the four tested isolated decreased between 41.11%
and 48.45% according to type of strain. Similarly presence of Cu+2 ions caused
decrease in Fe+2 uptake by the four isolates ranging between 29.14-45.1%. Percentage
of Pb+2 ions uptake by the tested bacteria sharply decreased when a sterile tap water
sample was used as natural medium for cell-metal contact. The percentage of uptake
inhibition of Pb*2 ranged between 57-65.23% and between 75.1-84.27% for Fe+3 ions.
Cell hydrolysate of three tested bacteria appeared to be free from plasmid DNA
proving that the genetic character of heavy metal resistance is plasmidless and related
to chromosmal DNA in |
