Abstract
There is a worldwide distribution of heavy metal pollution that can be managed with a bioremediation approach using microorganisms. Several bacterial species belonging to the Proteobacteria have been shown to tolerate heavy metal stress, including toxic salts of noblemetals. Rhodobacter sphaeroides, a model bacterium has previously been utilized for bioremediation studies. A bioinformatics approach was employed here to identify the distribution of genes associated with heavy metal tolerance among the sequenced bacterial genomes currently available on the NCBI database. The distribution of these genes among different groups of bacteria and the Cluster of Orthologous Groups (COGs) were further characterized. A total of 170,000 heavy metal related genes were identified across all bacterial species, with a majority of the genes found in Proteobacteria (46%) and Terrabacteria (39%). Analysis of COGs revealed that the majority of heavy metal related genes belong to metabolism (COG 3), including ionic transport, amino acid biosynthesis, and energy production.
Highlights
The definition of heavy metals has differed over the years, beginning with defining heavy metals as metals with a density of five times greater than water [1] and as metals with densities above 4 - 5 g/cm3 [2] [3]
This widely diverse group of bacteria is ideal for the study of heavy metal bioremediation due to the large number of genes associated with heavy metal tolerance, which encode transporter, sensor proteins, transcriptional regulators, and oxidoreductive enzymes
Results reveal that γ Proteobacteria harbors the highest frequency of metal resistance related genes, followed by α Proteobacteria, β Proteobacteria, and δ/ε Proteobacteria
Summary
The definition of heavy metals has differed over the years, beginning with defining heavy metals as metals with a density of five times greater than water [1] and as metals with densities above 4 - 5 g/cm3 [2] [3]. (Pt), arsenic (As) and chromium (Cr), which have densities that are greater than 5 g/cm3 [4] Heavy metals such as zinc, magnesium, copper, chromium, or nickelmay have a nutritional benefit to the organism as cofactors, while other metals, such as lead, cadmium, mercury, arsenic, and gold, are not yet identified beneficial to the organism [5]. Each metal has a different concentration at which it is deemed to be toxic to both the environment and the human body These toxic pollutants pose serious health risks to humans, including bone loss [9], kidney damage [10], neurological damage [11], skin cancer [12], and lung cancer [13]. Some of these metals, including chromium, cobalt, and nickel, play a vital role in metabolic processes such as essential micronutrients, stabilizing molecules [14], and catalysts in enzymatic reactions [15], help regulate osmotic balance [16], and involve redox reactions [17]
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