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Author

P. Pittman

Bio: P. Pittman is an academic researcher. The author has contributed to research in topics: Rhizobium. The author has an hindex of 1, co-authored 1 publications receiving 48 citations.
Topics: Rhizobium

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Journal ArticleDOI
30 Aug 2013-Mbio
TL;DR: The results illustrate that chemical interactions between actinomycete bacteria exhibit high complexity and specificity and can drive differential secondary metabolite production in pairwise coculture.
Abstract: Soils host diverse microbial communities that includefilamentous actinobacteria (actinomycetes). These bacteria have been a rich source of useful metabolites, including antimicrobials, antifungals, anticancer agents, siderophores, and immu- nosuppressants. While humans have long exploited these compounds for therapeutic purposes, the role these natural products may play in mediating interactions between actinomycetes has been difficult to ascertain. As an initial step toward understand- ing these chemical interactions at a systems level, we employed the emerging techniques of nanospray desorption electrospray ionization (NanoDESI) and matrix-assisted laser desorption ionization-time offlight (MALDI-TOF) imaging mass spectrome- try to gain a global chemical view of the model bacterium Streptomyces coelicolor interacting with five other actinomycetes. In each interaction, the majority of secreted compounds associated with S. coelicolor colonies were unique, suggesting an idiosyn- cratic response from S. coelicolor. Spectral networking revealed a family of unknown compounds produced by S. coelicolor dur- ing several interactions. These compounds constitute an extended suite of at least 12 different desferrioxamines with acyl side chains of various lengths; their production was triggered by siderophores made by neighboring strains. Taken together, these results illustrate that chemical interactions between actinomycete bacteria exhibit high complexity and specificity and can drive differential secondary metabolite production. IMPORTANCE Actinomycetes,filamentous actinobacteria from the soil, are the deepest natural source of useful medicinal com- pounds, including antibiotics, antifungals, and anticancer agents. There is great interest in developing new strategies that in- crease the diversity of metabolites secreted by actinomycetes in the laboratory. Here we used several metabolomic approaches to examine the chemicals made by these bacteria when grown in pairwise coculture. We found that these interspecies interactions stimulated production of numerous chemical compounds that were not made when they grew alone. Among these compounds were at least 12 different versions of a molecule called desferrioxamine, a siderophore used by the bacteria to gather iron. Many other compounds of unknown identity were also observed, and the pattern of compound production varied greatly among the interaction sets. Thesefindings suggest that chemical interactions between actinomycetes are surprisingly complex and that co- culture may be a promising strategy forfinding new molecules from actinomycetes.

320 citations

Journal ArticleDOI
TL;DR: Eight genes have been identified that function in the regulation, biosynthesis, and transport of rhizobactin 1021, a hydroxamate siderophore produced under iron stress by Sinorhizobium meliloti, and were shown to constitute an operon that is repressed under iron-replete conditions.
Abstract: Eight genes have been identified that function in the regulation, biosynthesis, and transport of rhizobactin 1021, a hydroxamate siderophore produced under iron stress by Sinorhizobium meliloti. The genes were sequenced, and transposon insertion mutants were constructed for phenotypic analysis. Six of the genes, named rhbABCDEF, function in the biosynthesis of the siderophore and were shown to constitute an operon that is repressed under iron-replete conditions. Another gene in the cluster, named rhtA, encodes the outer membrane receptor protein for rhizobactin 1021. It was shown to be regulated by iron and to encode a product having 61% similarity to IutA, the outer membrane receptor for aerobactin. Transcription of both the rhbABCDEF operon and the rhtA gene was found to be positively regulated by the product of the eighth gene in the cluster, named rhrA, which has characteristics of an AraC-type transcriptional activator. The six genes in the rhbABCDEF operon have interesting gene junctions with short base overlaps existing between the genes. Similarities between the protein products of the biosynthesis genes and other proteins suggest that rhizobactin 1021 is synthesized by the formation of a novel siderophore precursor, 1,3-diaminopropane, which is then modified and attached to citrate in steps resembling those of the aerobactin biosynthetic pathway. The cluster of genes is located on the pSyma megaplasmid of S. meliloti 2011. Reverse transcription-PCR with RNA isolated from mature alfalfa nodules yielded no products for rhbF or rhtA at a time when the nifH gene was strongly expressed, indicating that siderophore biosynthesis and transport genes are not strongly expressed when nitrogenase is being formed in root nodules. Mutants having transposon insertions in the biosynthesis or transport genes induced effective nitrogen-fixing nodules on alfalfa plants.

191 citations

Journal ArticleDOI
TL;DR: A novel siderophore with both catecholate and hydroxamate functional groups was isolated from low-iron cultures of Acinetobacter baumannii, indicative of strain-to-strain variation in the ability to produce acinetobactin.
Abstract: A novel siderophore, called acinetobactin, with both catecholate and hydroxamate functional groups was isolated from low-iron cultures of Acinetobacter baumannii ATCC 19606. The structure was elucidated by chemical degradation, fast-atom bombardment mass spectrometry and 1H and 13C NMR spectroscopy. Acinetobactin was composed of omega-N-hydroxyhistamine, threonine and 2,3-dihydroxybenzoic acid, the last two components forming an oxazoline ring. Acinetobactin was structurally related to anguibactin, a plasmid-encoded siderophore of Vibrio anguillarum. The only difference was that acinetobactin possessed an oxazoline ring instead of a thiazoline ring. Four of 12 other clinical A. baumannii strains examined produced acinetobactin, indicative of strain-to-strain variation in the ability to produce acinetobactin. In addition, a relatively small amount of acinetobactin was also detected in A. haemolyticus ATCC 17906.

138 citations

Journal ArticleDOI
TL;DR: Synechobactins A‐C are the first structurally elucidated siderophores from marine cyanobacteria and are related to schizokinen, a previously identified sidersophore that lacks amphiphilic character, isolated from other bacteria including freshwater cyanob bacteria.
Abstract: The coastal marine cyanobacterium Synechococcus sp. PCC 7002 produces three amphiphilic siderophores, synechobactins A-C, under iron-limiting growth conditions. The synechobactins are comprised of a citric acid backbone linked to two 1, 3-diaminopropane units. The terminal amine of one diaminopropane is acetylated and hydroxylated forming one hydroxamate group. The terminal amine of the other diaminopropane is appended to one of a series of fatty acids and N-hydroxylated on the fatty acid amide forming the second hydroxamate linkage. Synechobactins A-C differ among themselves in the identity of the fatty acid residue as dodecanoic acid, decanoic acid, or octanoic acid, respectively. They are the first structurally elucidated siderophores from marine cyanobacteria and are related to schizokinen, a previously identified siderophore that lacks amphiphilic character, isolated from other bacteria including freshwater cyanobacteria.

128 citations

Journal ArticleDOI
TL;DR: The present review summarizes the structures of siderophores produced by marine bacteria and the emerging characteristics that distinguish marine siders, which are low molecular weight chelating ligands that facilitate the microbial acquisition of iron.
Abstract: Iron is essential for the growth of nearly all microorganisms yet iron is only sparingly soluble near the neutral pH, aerobic conditions in which many microorganisms grow. The pH of ocean water is even higher, thereby further lowering the concentration of dissolved ferric ion. To compound the problem of availability, the total iron concentration is surprisingly low in surface ocean water, yet nevertheless, marine microorganisms still require iron for growth. Like terrestrial bacterial, bacteria isolated from open ocean water often produce siderophores, which are low molecular weight chelating ligands that facilitate the microbial acquisition of iron. The present review summarizes the structures of siderophores produced by marine bacteria and the emerging characteristics that distinguish marine siderophores.

127 citations