The Use of Plant Growth-Promoting Rhizobacteria (PGPR) to Improve Plant Growth in Heavy Metal Contaminated Soil for Phytoremediation

Plant growth-promoting rhizobacteria (PGPR) are free-living, soil-borne bacteria that colonize the rhizosphere and, when applied to crops, enhance the growth of plants. Bioremediation is the submission of biological progression for cleanup of pollutants from the environment. The main aim of this study was to use the Barely (Hordeum vulgare L.), and clover (Trifolium) metal tolerant plants with bacteria to extract metals from soil focusing on Iron (Fe) and Magnesium (Mg). Trials were conducted by incorporating them with plant growth promoting rhizobacteria (PGPR): Pseudomonas putida (UW3 and UW4). This study was conducted in two places with two experiments; the first experiment was carried out in greenhouse conditions, while the second one was conducted at the lab of An-Najah National University, Collage of Science, Nablus, Palestine, during the year 2015. The mother plant material was collected from the Palestinian Ministry of Agriculture. Iron and magnesium were taken as reference values to study the change in their concentrations after planting in vivo medium. Three types of water were used, while control seed pots used in experiments: one pot used with fresh water, another irrigated with saline with metals while the last one with saline water without metals. Pseudomonas putida strains (UW3 and UW4) possessed the direct growth promoting characteristics and the ability of strain to the uptake and accumulation of the metals. Results determined that the average barley shoot length denoted to 38cm and the average shoot weight was 10g, while the clover shoots also increased to an average length of 28cm after 30 days, and an average weight of 8g. Barley plant had the average root value biomass after 30 days (17.7cm) while the average root weight was observed to have 8g. The root growth plant height of the clover after 30 days recorded an average of 15cm length and an average weight of 6g after 30 days. PGPR inoculation also increased the average root wet weight more than root dry weight (137-141%). Accumulations and uptakes of Fe and Mg in barley which were conducted in vitro, for the treated barley seeds with bacteria C (UW3+UW4) irrigated with saline water with metals (SW) were 0.575 and 0.542 gram/liter respectively, while that of Fe and Mg in clover for the treated clover seeds with bacteria C irrigated with SW were 0.69 and 0.48 gram/liter respectively. The growth attributes were increased due to PGPR inoculation due to uptake and accumulation of heavy metals. The overall growth performance of inoculated seedlings was higher in compare to un-inoculated control. Conclusions indicated that all bacterial strains increased the average shoot and root growth of barley and clover in comparison with the untreated control, thus, this study suggests that UW3 and UW4 strains in combination have a great potential to increase photosynthesis, transpiration, leaves chlorophyll content, and could be used as crop-enhancer and bio-fertilizer for vigor seedling and production of both plantlets. This study recommended that PGPRs are the potential tools for sustainable agriculture and trend for the future. For this reason, there is an urgent need for researchers to clear definition of what bacterial traits are useful and necessary for different environmental conditions and plants, so that optimal bacterial strains can either be selected and/or improved. Furthermore, the reason to use Fe and Mg in this study is its vital importance to the plants as well as animals. Throughout the use of barley and clover, it is likely to produce feed nutrients containing enhanced excellent nutrients to the animals, consequently, instead of industrialized fodder.