Specific metal containing enzymes involved in cell division are targeted. Desferrioxamine interacts by various mechanisms with ribonucleotide reductase and thereby inhibit DNA synthesis. Targets involved in cancer progression, such as molecules involved in cell cycle control, angiogenesis and metastatic suppression may get affected by the depletion of iron by DFO and other chelators (Kontoghiorghes et al., 2008). Clinical studies on chelating drugs and experimental chelators have shown some positive results regarding use in anticancer treatment. Desferrioxamine has been used synergistically with other anticancer drugs for neuroblastoma and leukemia treatments (Kontoghiorghes et al., 2008).
Siderophore – antibiotic conjugates:
Integration of two functional molecule parts into one structural scaffold i.e. formation of siderophore-antibiotic conjugates are the Trojan Horse antibiotics. The siderophore part of these compounds performs scavenging of iron and is recognized by cellular Fesiderophore uptake systems and the other part has an antibiotic activity where the Fesiderophore uptake system is used as entry gate into the pathogen interior where the drug can have its effect. Microcins isolated from enteric bacteria, albomycins, ferrimycins, danomycins, and salmycins from Streptomycetes or actinomycetes are the examples of natural siderophore antibiotic conjugates (Miethke and Marahiel, 2007). These compounds have strong protein synthesis inhibiting activity for Gram positive bacteria such as staphylococci and streptococci.
Siderophores can be considered to be an eco-friendly alternative to hazardous chemical pesticide in the agricultural sector by the following ways.
Siderophore promotes plant growth
Iron starvation significantly reduces the quantity and quality of crop production. This reduction in crop production also alters the natural food web of the ecosystem. The level of available iron required by plants at neutral pH is around 10?17 mol/L while the level of available iron required by microorganism is 10?6 mol/L under the similar condition (Omidvari et al. 2010). Siderophore produced by an endophytic Streptomyces sp. isolated from the roots of a Thai jasmine rice plant induced plant growth and markedly elevated root and shoot biomass and lengths (Rungin et al., 2012). Recently, Trichoderma asperellum was found to produce siderophore which had a potential role in enhancing cucumber growth by ameliorating salt stress (Qi and Zhao 2013).
Siderophore as potential biocontrol agent
Siderophores play a significant role in the biological control mechanism against certain phyto-pathogens (Fig. 3). Siderophores bind with the iron tightly and reduce the bioavailable iron for the plant pathogens, thus facilitating the killing of phyto-pathogens (Ahmed and Holmstrom 2014).
Siderophore as biosensor
Fluorescent siderophore to act as a photoactive sensor for the biologically available iron content in aquatic systems (Orcutt et al., 2010). Although some of the siderophores have been used as potential biosensors, most of them have not yet been characterized.Thus, it could be hypothesized that some of the uncharacterized siderophores may turn out to be novel and potential biosensors.
Siderophores and heavy metal stress
In the presence of heavy metals, it causes destruction in membrane bound ferric reductase enzyme, and thereby declines the Fe uptake in plant. This Fe deficiency exhibits as young leaf chlorosis. Hence, inoculation of plants with siderophore producing bacteria prevent iron deficiency even under heavy metal polluted conditions (clowley and kralmer 2007). For instance, with inoculation of siderophores producing Pseudomonas sp on Vigna radiate showed a reduction of chlorotic symptoms and increase in chlorophyll level (Sharma et al. 2003).
Bioremediation of environmental pollutants
Metals play a vital role in the development of human civilizations (Jonhson et al., 2002), but the manufacturing industry, sludge applications, nuclear power stations and mining have led to metal pollution (Wasi et al., 2013). Siderophores are extremely effective in solubilizing and increasing the mobility of a wide range of metals such as Cd, Cu, Ni, Pb, Zn, and the actinides Th(IV), U(IV) and Pu(IV) (Schalk et al., 2011). This ability of siderophores mainly depends on their ligand functionalities, by which means siderophores may have a strong affinity or selectivity for a particular metal other than Fe with regards to the stability constants of this metal–siderophore complex (Hernlem et al., 1999).Thereby, siderophores become a useful tool in bioremediation, which is a cost-effective and environmentally friendly technique (Rajkumar et al., 2010).
Bioremediation of heavymetal polluted soils
Bioremediation is the use of organisms(microorganisms and/or plants) for the treatment of polluted soils. Bioremediation of heavymetals can be achieved via the use of microorganisms , plants ,or the combination of both organisms.
To achieve the most desired results in the detoxification of soil,the plant that should be selected for phytoremrdiating purposes has to be based on multiple plants characters(Favasetal.,2014)
Overall ability to take up and degrade contaminatnts in the soil
Ability to accumulate organic and inorganic contaminatnts in its cells cells and intercellular spaces
Extraction of exudates to stimulates the multiplication of soil microorganisms and secretion of enzyme participating in the initial transformations of the contaminatnts
Existence within the cell of contaminatntsdegrading or conjugation enzyme
High resistance against contaminatnts
The root system (main or fibres)
Whether the plants are endemic and non-agricultural
Tolerance to salty soil
Appropriate adaptation to warm or cold condition
Techniques/strategies of phytoremediation
Phytoremediation is a general term including several processes, in function of the plant-soil-atmosphere interactions.Techniques of phytoremediation include
Rhizodegradation (Alkorta et al., 2004).
Phytoextaction is the main and most useful phytoremediation technique for removal of heavy metals and metalloids, from polluted oils, sediments or water. The efficiency of phytoextracton depends on many factors like bioavailability of the heavy metals in soil, soil properties, speciation of the heavy metals and plant species concerned.(Adesodum te al 2010)
Phytoextraction is amethod that employs plant roots to absorb heavymetals.resulting in their translocation within the plant.this method has grown in popularly and extensively used worldwide for the last twentyyears. Phytoextraction is usually used for extracting heavymetals rather than organic contaminatnts. A plant which is able to plant extract a certain heavymetal is known as a hyper accumulator of said heavymetal(Rajoo etal.,2013a)
This is the most common form of phytoremediation .It involves accumulation of heavymetals in the roots and shoots of phytoremediation plants.these plants are later harvested and incinerated.plants used for phytoextraction usually possess the following characteristics.rapid growth rate,high biomass,extentive rootsystem,and ability to tolerante high amounts of heavymetals. This ability to tolerate high concentration of heavymetals by these plants may lead to metal accumulation in the harvestable part:this maybe problematic through contamination of the foodchain.(Marques et al., 2009)
Rhizodegradation refers to the breakdown of organic polluta in the soil by microorganisms in the rhizosphere (Mukhopadhy and Maiti, 2010).
Phytodegradation is the degradation of organic pollutants plants with the help of enzymes such as dehalogenase and oxygenase; it is not dependent on rhizospheric microorganisms (Vishn and Srivastava, 2008).
Phytodegradation is the use of plants and microorganisms to uptake, metabolize, and degrade the organic contaminant. In this approach, plant roots are used in association with microorganisms to detoxify soil contaminated with organic compounds (Garbisu and Alkorta, 2001).