Normal alluvial (FFS), calcareous (WNS) as well as sewage farm (ARS) soil samples amended with peptone nutrient solution were subjected to increasing concentrations of Pb, Cd, Zn and Ni then incubated for 7 days at 25 o C. Total bacteria recorded the highest colony forming unites (cfug-1) in Abu-Rawash soils (ARS) even in the presence of increasing levels of Cd, Zn and Pb followed by the normal alluvial (FFS) and calcareous (Wadi-El-Natrun) soils. Under Ni stress, calcareous soil showed the highest population density which may be due to the lime effect. In the alluvial soil, counts were substantially reduced to 1% compared to plain soil applying only 3 mg Cd/kg soil while it was 10% in Abu-Rawash soil. For Pb-and Zncontaminated soils, microbial density in alluviall soil recorded almost the same density as in Abu-Rawash and was higher than in calcareous soil. Dehyrogenase activity (DEH) decreased by 32% in the FFS, 35% in ARS and 17% in WNS as the applied Cd increased from 3 to 8 mg/kg soil. Increased amounts of Zn and Ni inhibited dehydrogenase (DEH) activity by higher 36-44% in FFS and ARS compared to that of WNS (17-22%). A significant positive correlation coefficient (P<0.05) was observed between microbial counts and DEH activity in almost all examined heavy metalpolluted soil. Sixty-seven bacterial isolates from the three heavy-metal-contaminated soils were in vitro examined for their ability to tolerate increasing concentrations of Cd, Zn, Pd and Ni in their culture media. A screening of 67 bacterial isolates was conducted on solid nutrient agar medium supplemented with increasing concentrations of the investigated metals. Nineteen isolates were selected according to their heavy metal tolerance. Some isolates were found to be able to grow in a medium containing up to 700 mg Pb/kg others were tolerant to 75 mg Zn/kg. A maximum tolerable level of 25 mg Ni/kg soil was recorded with the isolates Nos. B-1, B-24, B+27, B-30, B+41, B+55 and B+64. The cultural, morphological and physiological characteristics of the heavy metal-resistant isolates were examined. The majority were Gram-positive long rod-shaped motile sporeforming isolates belonging to the genus Bacillus. The minimum inhibitory concentrations (MIC) of the examined heavy metals were designated for these isolates in submerged liquid cultures. For all examined isolates, culture OD600 increased with time reaching a maximum after 10 day and declined thereafter. Among the examined isolates, the two Gram-positive Bacillus isolates Nos. B-48 and B+41 were the most tolerant to all heavy metals. The identities of these isolates were analyzed using the Sole-Carbon Cource Utilization Profile (Biolog, Inc., Hayward, CA2000). The isolate No. B-48 was identified as Bacillus amyloliquefaciens and No. B+41 as Bacillus thuringiensis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.