Isolation and Identification of Heavy-Metal Resistant Soil Bacteria

Abstract

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.

Monitoring and molecular characterization of bacterial species in heavy metals contaminated roadside soil of selected region along NH 8A, Gujarat

“…The accumulation of heavy metals content in the roadside soil is of enormous environmental apprehension as it can cause alteration in the biological activities occurring in the soil system (Singh and Yadav, 2019). The diversity and activity of soil bacterial populations are diminished as a result of the environmental stress instigated by heavy metals, prompting a reduction in the total microbial biomass, a decline in the number of the explicit populace, and a shift in microbial structure (Abd et al, 2013;Wang et al, 2010). Anthropogenic activities, including automobile emissions and the industrial process, cause the raised load of heavy metals in the environment, thus creating pollution (Singh and Yadav, 2019).…”