Agricultural lands are being polluted with different contaminants due to various anthropogenic activities like toxic discharge from Ni-Cd battery industry, tannery industry, alloying of metals like steel, application of agrochemicals, etc. Cadmium and lead contamination in agricultural land are directed towards global food insecurity. Bioremediation, stress alleviation, and phytostimulation by Cd and Pb tolerant PGPR is a promising eco-friendly method to develop sustainable agricultural system. At present, cadmium and lead-tolerant plant growth promoting rhizobacteria (PGPR) can be a sustainable option for heavy metal-contaminated agricultural lands. PGPRs such as Bacillus, Bradyrhizobium, Enterobacter, Klebsiella, Micrococcus, Pseudomonas, Ralstonia, etc. can survive the metal stress and stimulate the plant growth under Cd and Pb contaminated condition by direct or indirect plant growth promoting ability. So, these PGPRs could be exploited as biofertilizers and bioremediators under Cd or Pb stressed conditions for futuristic agricultural development.
TopIntroduction
Various metals such as lead, zinc, cadmium, nickel, copper and mercury are continuously being added to our soil ecosystem through different agrochemical usage, industrial waste disposal, application of urban sewage sludge, vehicle exhausts, and waste incineration and from many anthropogenic sources (Noumavo et al. 2016). These contaminations in our agricultural soils cause threat to food safety. Plants uptake different metals into their body and retains for a long days. As a result these metals can transferred to the higher tropic level like human and other animals.
Cadmium inhibits plant growth, hampers plant water relationship and ion metabolism, inhibits chlorophyll biosynthesis, inhibits many enzymes like Fructose bis-phosphatase, Fructose 6 phosphate kinase, Phosphoenolpyruvate carboxylase, NADP+ glyceraldehyde-3-phosphate dehydrogenase Ribulose-1,5-bisphosphate carboxylase oxygenase, and Carbonic anhydrase (Krantev, Yordanova, and Popova 2006; Popova et al. 2009). Cd act as a potent nephrotoxin and class-I carcinogen in animals. Lead (Pb) persists in the environment for a long time and causes anemia, reproductive impairment, renal failure, neurodegenerative damage etc. (Eslami et al. 2011). Pb badly affects plants in the seed germination, biomass production, root-shoot growth, chlorophyll content and ion distribution (Trvedi and Erdei 1992; He 1990).
These heavy metals affect a considerable harmful effect on environment, soil ecosystems and human health due to their mobility and solubility (Kabata-Pendias 1992). Frequently, the soil may be contaminated as much as a harmful waste (Berti and Jacob, 1996). In developing countries, heavy metals contamination in soil is a much talkative concern (Yanez et al., 2002; Pramanik et al. 2016; Pal and Sengupta, 2019). It is now important to remediate the contaminated soil to develop suitable agricultural land.