Isolation of Lead Resistant Bacteria from Spent Mushroom Compost and Their Impact on Growth and Biochemical Parameters of Safflower.

Spent mushroom compost (SMC) is a favored waste because of its nutrients for plant growth and useful microbial communities. The aim of this study was to isolate the lead resistant bacteria from SMC and to evaluate the effects of SMC extract on the growth and biochemical parameters of safflower under lead stress including fresh and dry weights, photosynthetic pigments, protein content, and enzymatic activities. Four bacterial strains including Bacillus licheniformis, Bacillus cereus, Bacillus aerius, and Brevibacterium frigoritolerans were identified in the SMC extract; from which B. licheniformis offer the most resistance to lead. The highest total chlorophyll content of the plant was seen by treatment with 100 mM lead; the highest carotenoid content observed by treatment with 100 mM lead in association with 10% and 5% SMC extract; and the highest increase in protein content was seen in the presence of 5% SMC. The safflower seeds germination was reached the highest level in the presence of 20% SMC extract associated with 50 and 100 mM lead. The highest dry weights of the plant roots (33%) and stems (85%) were shown in the presence of 100 mM lead in association with 5% SMC extract. The highest antioxidant enzymes activity was seen by polyphenol oxidase (0.135 OD/min/mg) in the presence of 100 mM lead in association with 10% SMC extract. It is concluded that by induction of lead bioremediation via improving lead resistant bacterial communication, and the addition of 10-20% SMC extract to the agricultural soil, safflower may undergo the lead stress.