Dataset Information

Extraction and Detection of Structurally Diverse Siderophores in Soil.

ABSTRACT: Although the biochemistry of bacterial and fungal siderophores has been intensively studied in laboratory cultures, their distribution and impacts on nutrient cycling and microbial communities in soils remain poorly understood. The detection of siderophores in soil is an analytical challenge because of the complexity of the soil matrix and their structural diversity. Liquid chromatography-mass spectrometry (LC-MS) is a suitable method for the sensitive analysis of siderophores in complex samples; however, siderophore extraction into liquid phases for analysis by LC-MS is problematic because of their adsorption to soil particles and organic matter. To determine extraction efficiencies of structurally diverse siderophores, spike-recovery experiments were set up with standards representing the three main siderophore classes: the hydroxamate desferrioxamine B (DFOB), the ?-hydroxycarboxylate rhizoferrin, and the catecholate protochelin. Previously used solvent extractions with water or methanol recovered only a small fraction (< 35%) of siderophores, including < 5% for rhizoferrin and protochelin. We designed combinatorial chemical extractions (22 total solutions) to target siderophores associated with different soil components. A combination of calcium chloride and ascorbate achieved high and, for some soils, quantitative extraction of DFOB and rhizoferrin. Protochelin analysis was complicated by potential fast oxidation and interactions with colloidal soil components. Using the optimized extraction method, we detected ?-hydroxycarboxylate type siderophores (viz. rhizoferrin, vibrioferrin, and aerobactin) in soil for the first time. Concentrations reached 461 pmol g-1, exceeding previously reported concentrations of siderophores in soil and suggesting a yet unrecognized importance of ?-hydroxycarboxylate siderophores for biological interactions and biogeochemical processes in soil.

SUBMITTER: Rai V

PROVIDER: S-EPMC7527475 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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Extraction and Detection of Structurally Diverse Siderophores in Soil.

Rai Vineeta V Fisher Nathaniel N Duckworth Owen W OW Baars Oliver O

Frontiers in microbiology 20200917

Although the biochemistry of bacterial and fungal siderophores has been intensively studied in laboratory cultures, their distribution and impacts on nutrient cycling and microbial communities in soils remain poorly understood. The detection of siderophores in soil is an analytical challenge because of the complexity of the soil matrix and their structural diversity. Liquid chromatography-mass spectrometry (LC-MS) is a suitable method for the sensitive analysis of siderophores in complex samples ...[more]

PMID: 33042099

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Project description:The siderophore synthetic system in Shewanella species is able to synthesize dozens of macrocyclic siderophores in vitro with synthetic precursors. In vivo, however, although three siderophores are produced naturally in Shewanella algae B516, which carries a lysine decarboxylase (AvbA) specific for siderophore synthesis, only one siderophore can be detected from many other Shewanella species. In this study, we examined a siderophore-overproducing mutant of Shewanella oneidensis which lacks an AvbA counterpart, and we found that it can also produce these three siderophores. We identified both SpeC and SpeF as promiscuous decarboxylases for both lysine and ornithine to synthesize the siderophore precursors cadaverine and putrescine, respectively. Intriguingly, putrescine is mainly synthesized from arginine through an arginine decarboxylation pathway in a constitutive manner, not liable to the concentrations of iron and siderophores. Our results provide further evidence that the substrate availability plays a determining role in siderophore production. Furthermore, we provide evidence to suggest that under iron starvation conditions, cells allocate more putrescine for siderophore biosynthesis by downregulating the expression of the enzyme that transforms putrescine into spermidine. Overall, this study provides another example of the great flexibility of bacterial metabolism that is honed by evolution to better fit living environments of these bacteria.IMPORTANCE The simultaneous production of multiple siderophores is considered a general strategy for microorganisms to rapidly adapt to their ever-changing environments. In this study, we show that some Shewanella spp. may downscale their capability for siderophore synthesis to facilitate adaptation. Although S. oneidensis lacks an enzyme specifically synthesizing cadaverine, it can produce it by using promiscuous ornithine decarboxylases. Despite this ability, this bacterium predominately produces the primary siderophore while restraining the production of secondary siderophores by regulating substrate availability. In addition to using the arginine decarboxylase (ADC) pathway for putrescine synthesis, cells optimize the putrescine pool for siderophore production. Our work provides an insight into the coordinated synthesis of multiple siderophores by harnessing promiscuous enzymes in bacteria and underscores the importance of substrate pools for the biosynthesis of natural products.

Dataset Information

Extraction and Detection of Structurally Diverse Siderophores in Soil.

Publications

Extraction and Detection of Structurally Diverse Siderophores in Soil.

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