Parvaze Ahmad Wani

Bacillus species enhance growth parameters of chickpea (Cicer arietinum L.) in chromium stressed soils

Pollution of the agricultural land by the toxic chromium is a global threat that has accelerated dramatically since the beginning of industrial revolution. Toxic chromium affects both the microbial diversity as well as reduces the growth of the plants. Understanding the effect of the chromium reducing and plant growth promoting rhizobacteria on chickpea crop will be useful. Chromium reducing and plant growth promoting Bacillus species PSB10 significantly improved growth, nodulation, chlorophyll, leghaemoglobin, seed yield and grain protein of chickpea crop grown in the presence of different concentrations of chromium compared to the plants grown in the absence of bio-inoculant. The strain also reduced the uptake of chromium in roots, shoots and grains of chickpea crop compared to plants grown in the absence of bio-inoculant. This study thus suggested that the Bacillus species PSB10 due to its intrinsic abilities of growth promotion and attenuation of the toxic effects of chromium could be exploited for remediation of chromium from chromium contaminated sites.

Toxic Effects of Heavy Metals on Germination and Physiological Processes of Plants

Pollution of the environment by toxic metals in recent years has accelerated dramatically due to rapid industrial progress. Heavy metals when taken up in amounts in excess of the normal concentration produce lethal effects on plants, on microbes, and directly or indirectly on the human health. Deleterious impact of metals on plants includes the reduction in germinability of seeds, inactivation of enzymes, damage to cells by acting as antimetabolites, or formation of precipitates or chelates with essential metabolites. Heavy metals also show unconstructive effects on other physiological processes like photosynthesis, gaseous exchange, water relations, and mineral/nutrient absorption by plants. These adverse effects may be due to the generation of reactive oxygen species which may cause oxidative stress. The impact of heavy metals on germination of legume seeds and different physiological events of plants with special reference to leguminous plants grown in distinct agroecological niches is highlighted.

Bioremediation: A Natural Method for the Management of Polluted Environment

Heavy metal contamination resulting from rapid industrialization and other sources is a growing problem worldwide. Increasing pollution of soils with heavy metals disturbs the microbial biodiversity, soil fertility, and plant production and may cause significant human health problems. The excessive accumulation of heavy metals within plant tissues can modify protein structure or replace an essential element causing chlorosis, growth impairment, browning of roots, and photosystems dysfunction. To circumvent metal toxicity, bioremediation, a process that involves the use of biological materials to detoxify the contaminated sites and brings the environment to its contaminant free (original) state, has emerged as a promising alternative to widely practiced physicochemical methods used to clean up contaminated lands. Biological materials used to remediate contaminated sites are inexpensive, are easy to operate, do not produce hazardous by-products, and can be effective even if metals are present in low concentrations. Here, we integrate the knowledge obtained so far on the removal of metals and metalloids employing bioremediation strategies for contaminated soils. The information regarding different types of bioremediation and the challenges facing bioremediation are highlighted. The role and impacts of plant-growth-promoting rhizobacteria on bioremediation efficiency are addressed.

Chromium–Plant-Growth-Promoting Rhizobacteria Interactions: Toxicity and Management

Among heavy metals, chromium is a highly toxic nonessential metal found in different environmental settings. Chromium pollution has been reported worldwide, causes undeniable damage to microbes and plant genotypes, and is carcinogenic and genotoxic for humans. Of the two most common oxidative states, hexavalent chromium is relatively more deleterious than the less-mobile trivalent form of chromium. Chromium toxicity, however, can be reduced by employing various physicochemical and biological processes. Among biomaterials, apart from plants, use of plant-growth-promoting rhizobacteria has been found effective, inexpensive, and environmentally friendly. Plant-growth-promoting rhizobacteria alleviate the metal toxicity by adopting different strategies like biosorption and bioaccumulation, bioreduction to a less-toxic state, and chromate efflux. Some of these methods have been proposed as effective biological tools for removing chromium from contaminated locations. The interaction of chromium with plant-growth-promoting rhizobacteria and the bacterial-based management of chromium toxicity is reviewed and discussed. The detoxification of chromium by plant-growth-promoting rhizobacteria is likely to reduce the adversity of chromium to various agroecosystems and may serve as a good candidate for bacterial-based bioremediation of chromium-polluted soils.