Screening of Silver-Tolerant Bacteria from a Major Philippine Landfill as Potential Bioremediation Agents

The field of microbial biotechnology has revolutionized the utilization of microorganisms to overcome the problems of environmental pollutions. The present study aimed to identify silver-tolerant isolates and screen their ability to synthesize silver nanoparticles for possible use as bioremediation agents. Seventeen bacterial isolates from soil collected from the Smokey Mountain landfill in Manila, Philippines, were found to tolerate 0.01 M AgNO₃ in the culture medium. Molecular and phylogenetic analyses using the 16S rRNA gene sequence identified the isolates as Bacillus cereus, Bacillus subtilis, Bacillus flexus, Bacillus thuringiensis, Alcaligenes faecalis, Achromobacter sp. and Ochrobactrum sp. The formation of silver nanoparticles was evident in the change in color of the reaction mixtures, and was detected through UV-VIS spectroscopy with absorbance peaks at 250-300 nm and 400-450 nm. Scanning electron microscopy revealed the aggregation of diverse shapes of silver nanoparticles with sizes ranging from 70 to 200 nm. The best silver nanoparticle-synthesizing isolates were Alcaligenes faecalis and Bacillus cereus. The results denote the promising microbial technology application of the 17 silver-tolerant isolates in combating the adverse effects of metals and other pollutants in the environment.