Siderophore-synthesizing NRPS reprogram lipid metabolic profiles for phenotype and function changes of Arthrobotrys oligospora
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Production of secondary metabolites including siderophores is yet another mechanism by which fluorescent pseudomonads acts as a biocontrol agent. Siderophores are secreted under iron limitation and have a very high affinity for ferric iron. The resulting ferric-siderophore complex is unavailable to other organisms, but the producing strain can utilize this complex via a specific receptor in its outer cell membrane. In this way, siderophore producing fluorescent Pseudomonads may restrict the growth of phytopathogens. In the present study the siderophore production by the isolated strains of fluorescent pseudomonads has been reviewed. Of the 22 isolates which showed the abilty to produce siderophores, 6 isolates were shown to produce catecholate type of siderophores and the remaining 16 isolates showed the presence of hydroxamate
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Bacteria can produce low molecular weight iron chelating compound called siderophore. Siderophore are low molecular weight iron-binding ligands which can bind to ferric ion and make it available to the producer microorganism. On account of that, an attempt was made in the present investigation to isolate potential siderophore producing bacteria from different places of Kashmir and study their effect on pea crop. A total of ten siderophore producing bacteria was isolated from rhizospheric soil sample and amongst them PGP26 was found the most efficient siderophore (18.00). The potential isolates were further characterized for their different plant growth promoting activities like Indole acetic acid production (IAA), ammonia production, phosphate solubilization, and HCN production. The potential isolates were further tried with pea to study the germination percentage, root length and shoot length by Roll towel method.
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Under iron limiting conditions, many bacteria secrete ferric iron-specific ligands, generically termed siderophore, which aid in sequestering and transport of iron. We report here the production of siderophore by selected plant growth promoting microorganisms. Production of siderophore by plant growth promoting microorganisms were detected via the chrome azurol S assay, a general test for siderophore detection, which is independent of siderophore structure. Eight bacterial isolates having better plant growth promoting traits were evaluated for siderophore production in laboratory among the isolates Pseudomonas flurescens was noted to 75 per cent siderophore production followed by Azospirillum lipoferum (67 per cent). However, Rhizobium phaseoli found to have no colour change and no siderophore production in CAS agar test.
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ABSTRACT More than 60% of species examined from a total of 421 strains of heterotrophic marine bacteria which were isolated from marine sponges and seawater were observed to have no detectable siderophore production even when Fe(III) was present in the culture medium at a concentration of 1.0 pM. The growth of one such non-siderophore-producing strain, alpha proteobacterium V0210, was stimulated under iron-limited conditions with the addition of an isolated exogenous siderophore, N , N ′-bis (2,3-dihydroxybenzoyl)- O -serylserine from a Vibrio sp. Growth was also stimulated by the addition of three exogenous siderophore extracts from siderophore-producing bacteria. Radioisotope studies using 59 Fe showed that the iron uptake ability of V0210 increased only with the addition of exogenous siderophores. Biosynthesis of a hydroxamate siderophore by V0210 was shown by paper electrophoresis and chemical assays for the detection of hydroxamates and catechols. An 85-kDa iron-regulated outer membrane protein was induced only under iron-limited conditions in the presence of exogenous siderophores. This is the first report of bacterial iron uptake through an induced siderophore in response to exogenous siderophores. Our results suggest that siderophores are necessary signaling compounds for growth and for iron uptake by some non-siderophore-producing marine bacteria under iron-limited conditions.
Marine bacteriophage
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Siderophores (in Greek: iron carriers) are low molecular weight compounds produced under iron-limiting conditions by microorganisms that chelates Fe3+ (ferric iron) with high specific activity, which in turn make it available to the plant system. Selection of efficient siderophore producing plant associated bacteria and their potential role in enhancing plant iron uptake is a strategic approach for improving plant health as Fe is an integral component and cofactor for many biomolecules. In the present study 154 bacteria associated with maize, mustard and sugarcane as endophytic or rhizospheric isolates, on screening led to the identification of 24 efficient siderophore producers (Sid+) with siderophore producing index (SPI) of 1.03-1.70 and the concentration from 0.1 to 11.25 µg/ml in Fiss glucose medium. For higher siderophore production optimization minimal and complex media were tested. Barbhaiya and Rao medium (BR), a minimal medium improved siderophore production ranging from 02.54 – 15.65 µg/ml. Complex malt extract medium produced 0.27-2.44 µg/ml of siderophores and was found to have least influence on siderophore production irrespective of bacterial culture. Differential sugars utilization pattern of 35 sugars tested was recorded with different isolates. A formulation of such siderophore producing bacterial isolates can be used for improving micronutrients availability for the plant to be more healthy and productive.
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Abstract We investigated the ability of four plant and soil‐associated fungi to modify or degrade siderophore structures leading to reduced siderophore iron‐affinity in iron‐limited and iron‐replete cultures. Pyrenophora biseptata , a melanized fungus from wheat roots, was effective in inactivating siderophore iron‐chelating moieties. In the supernatant solution, the tris‐hydroxamate siderophore desferrioxamine B (DFOB) underwent a stepwise reduction of the three hydroxamate groups in DFOB to amides leading to a progressive loss in iron affinity. A mechanism is suggested based on the formation of transient ferrous iron followed by reduction of the siderophore hydroxamate groups during fungal high‐affinity reductive iron uptake. P. biseptata also produced its own tris‐hydroxamate siderophores (neocoprogen I and II, coprogen and dimerum acid) in iron‐limited media and we observed loss of hydroxamate chelating groups during incubation in a manner analogous to DFOB. A redox‐based reaction was also involved with the tris‐catecholate siderophore protochelin in which oxidation of the catechol groups to quinones was observed. The new siderophore inactivating activity of the wheat symbiont P. biseptata is potentially widespread among fungi with implications for the availability of iron to plants and the surrounding microbiome in siderophore‐rich environments.
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Siderophores are low-molecular-weight high specificity, ferric iron chelating agents. They are produced under iron starvation by most microorganisms. Systems such as siderophores, involved in the acquisition of iron under iron limited conditions, may play a major role in microbial interactions. Some siderophores are virulence factors in animal and in plant pathogens. Moreover, siderophores have been demonstrated to play a major role in plant disease suppression by some bacterial biocontrol agents which inhibit the growth or the activity of plant pathogens by sequestering iron. This latest type of mechanism has been extensively studied in bacteria. However, the role of these iron chelating compounds in disease suppression by fungal biocontrol agents has not been clearly determined.
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ABSTRACT The growth of marine bacteria under iron-limited conditions was investigated. Neither siderophore production nor bacterial growth was detected for Pelagiobacter sp. strain V0110 when Fe(III) was present in the culture medium at a concentration of <1.0 μM. However, the growth of V0110 was strongly stimulated by the presence of trace amounts of exogenous siderophore from an alpha proteobacterium, V0902, and 1 nM N -acyl-octanoylhomoserine lactone (C 8 -HSL), which is known as a quorum-sensing chemical signal. Even though the iron-binding functionality of a hydroxamate siderophore was undetected in the supernatant of V0902, a hydroxamate siderophore was detected in the supernatant of V0110 under the above conditions. These results indicated that hydroxamate siderophore biosynthesis by V0110 began in response to the exogenous siderophore from V0902 when in the presence of C 8 -HSL; however, C 8 -HSL production by V0110 and V0902 was not detected. Direct interaction between V0902 and V0110 through siderophore from V0902 was observed in the dialyzing culture. Similar stimulated growth by exogenous siderophore and HSL was also observed in other non-siderophore-producing bacteria isolated from marine sponges and seawater. The requirement of an exogenous siderophore and an HSL for heterologous siderophore production indicated the possibility that cell-cell communication between different species was occurring.
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