Effect of Bacillus pumilus Strains on Heavy Metal Accumulation in Lettuce Grown on Contaminated Soil

Abstract

Increasing number of heavy metal on land needs to be addressed through sustainable ways and various species of Bacillus can be used to mitigate heavy metals. The research work entitled “Effect of Bacillus pumilus strains on heavy metal accumulation in lettuce grown on contaminated soil” focuses on functional role of Bacillus pumilus strains inoculated with lettuce seed in mitigating heavy metal present in chromite mining soil. This experiment was conducted at ornamental horticulture nursery, the University of Agriculture Peshawar. In this experiment, factor A was three Bacillus pumilus strains (sequence C-2PMW-8, C-1 SSK-8 and C-1 PWK-7) while soil used for this experiment was collected from Prang Ghar mining site and lettuce seeds were grown in three levels of chromite mining soil (2.27, 4.65 and 7.14 %).The experimental design used during this research was randomized complete block design with two factors and was replicated thrice. The collected data related to effect of chromite mining soil and Bacillus pumilus strains indicated that these both factors have significant influence on growth parameters. For mining soil minimum days to germinate (14 days) was noted in lettuce grown on garden soil inoculated with sequence. Maximum germination percentage noted was (100%) for C-1 SSK-8 grown on garden soil, dry weight of lettuce leaf (5.0 g) for lettuce inoculated with C-1 SSK-8 and C-1 PWK-7 strains, survival percentage (77.9%) for C-1 SSK-8 treated lettuce for sequence C-2 PMW-8. Maximum germination percentage noted was (88%) for garden soil, fresh leaf weight (17.3g), dry leaf weight (6.5g), number of leaf per plant (16), leaf area (49.0 cm2) were noted in garden soil with no chromite mining soil. Results related to heavy metals accumulation showed that minimum chromium was (2.3 mg kg-1) in lettuce and (1.9 mg kg-1) in soil for all three sequences. It can be concluded that chromite mining soil significantly reduced the growth and survival of lettuce, but when lettuce was inoculated with Bacillus.pumilus strains it enhances the growth and survival. Similarly, minimum heavy metal accumulation in plant and soil, regardless of type of B. pumilus used, all three sequences has same mitigating effect on heavy metal in both soil and lettuce. All the three Bacillus pumilus strains ensured reduction in heavy metals content (Cr) in lettuce, below the maximum permissible limits of WHO/FAO 2011.