Lead-Tolerant Bacillus Strains Promote Growth and Antioxidant Activities of Spinach (Spinacia oleracea) Treated with Sewage Water

Najm-Ul-Seher Najm-Ul-Seher,Fahad S Alotaibi,Mohamed A Mattar,Muhammad Zahid Mumtaz,Farheen Nazli,Ahmed A El-Shafei,Mobarak S Al-Mosallam,Maqshoof Ahmad,Muhammad Latif,Iqra Ahmad,Ahmed Z Dewidar

doi:10.3390/agronomy11122482

Abstract

Irrigation with sewage-contaminated water poses a serious threat to food security, particularly in developing countries. Heavy metal tolerant bacteria are sustainable alternatives for the removal of wastewater contaminants. In the present study, four lead (Pb)-tolerant strains viz. Bacillus megaterium (N8), Bacillus safensis (N11), Bacillus sp. (N18), and Bacillus megaterium (N29) were inoculated in spinach and grown in sewage water treated earthen pots separately and in combination with canal water. Results showed that Pb-tolerant strains significantly improved plant growth and antioxidant activities in spinach and reduces metal concentration in roots and leaves of spinach plants irrigated with treated wastewater. Strain Bacillus sp. (N18) followed by B. safensis (N11) caused the maximum increase in shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, and leaf area compared to the uninoculated control of sewage water treated plants. These strains also improved antioxidant enzymatic activity including catalase, guaiacol peroxidase dismutase, superoxide dismutase, and peroxidases activities compared to the uninoculated control under sewage water conditions. Strain Bacillus sp. (N18) followed by B. safensis (N11) showed the highest reduction in nickel, cadmium, chromium, and Pb contents in roots and leaves of spinach compared to the uninoculated control plants treated with the sewage water. Such potential Pb-tolerant Bacillus strains could be recommended for the growth promotion of spinach after extensive evaluation under field conditions contaminated with wastewater.

Highlights

Irrigation with sewage wastewater is a common practice in rural and urban areas of the majority of emerging countries
After harvesting the plant samples were collected for the determination of plant growth, antioxidant activities, and heavy metal uptake in plant roots and leaves
The current study showed that inoculation with Pb-tolerant Bacillus strains reduces the heavy metals (Ni, Cr, Cd, and Pb) concentration in roots and leaves of spinach compared to the uninoculated control treated with sewage water (Tables 5 and 6)

Summary

Introduction

Irrigation with sewage wastewater is a common practice in rural and urban areas of the majority of emerging countries. Natural water resources for irrigation have been diminishing due to diverse human activities. In these areas, polluted water is often the only supply of water for irrigation. The application of untreated wastewater in agriculture creates key risks to the health of the community due to chemical and microbial contaminants. It can produce ecological risks in terms of soil and groundwater contamination. It causes the accumulation of metals in various crops and vegetables [5]. The sewage sludge contains moderate to toxic concentrations of metals including zinc (Zn), copper (Cu), mercury, chromium (Cr), cadmium (Cd), nickel (Ni), and lead (Pb) [6]

Methods

Results

Discussion

Conclusion