Characterization of ferredoxins involved in electron transfer pathways for nitrogen fixation implicates differences in electronic structure in tuning 2[4Fe4S] Fd activity.

Ferredoxins (Fds) are small proteins which shuttle electrons to pathways like biological nitrogen fixation. Physical properties tune the reactivity of Fds with different pathways, but knowledge on how these properties can be manipulated to engineer new electron transfer pathways is lacking. Recently, we showed that an evolved strain of Rhodopseudomonas palustris uses a new electron transfer pathway for nitrogen fixation.

Evolution of to degrade halogenated aromatic compounds involves changes in pathway regulation and enzyme specificity.

Halogenated aromatic compounds are used in a variety of industrial applications but can be harmful to humans and animals when released into the environment. Microorganisms that degrade halogenated aromatic compounds anaerobically have been isolated but the evolutionary path that they may have taken to acquire this ability is not well understood. A strain of the purple nonsulfur bacterium, , RCB100, can use 3-chlorobenzoate (3-CBA) as a carbon source whereas a closely related strain, CGA009, cannot.

Evolving a New Electron Transfer Pathway for Nitrogen Fixation Uncovers an Electron Bifurcating-Like Enzyme Involved in Anaerobic Aromatic Compound Degradation.

Nitrogenase is the key enzyme involved in nitrogen fixation and uses low potential electrons delivered by ferredoxin (Fd) or flavodoxin (Fld) to reduce dinitrogen gas (N) to produce ammonia, generating hydrogen gas (H) as an obligate product of this activity. Although the phototrophic alphaproteobacterium Rhodopseudomonas palustris encodes multiple proteins that can reduce Fd, the FixABCX complex is the only one shown to support nitrogen fixation, and R. palustris Fix mutants grow poorly under nitrogen-fixing conditions.

PioABC-Dependent Fe(II) Oxidation during Photoheterotrophic Growth on an Oxidized Carbon Substrate Increases Growth Yield.

Microorganisms that carry out Fe(II) oxidation play a major role in biogeochemical cycling of iron in environments with low oxygen. Fe(II) oxidation has been largely studied in the context of autotrophy. Here, we show that the anoxygenic phototroph, Rhodopseudomonas palustris CGA010, carries out Fe(II) oxidation during photoheterotrophic growth with an oxidized carbon source, malate, leading to an increase in cell yield and allowing more carbon to be directed to cell biomass.

Bacterial communities associated with wood rot fungi that use distinct decomposition mechanisms.

Wood decomposer fungi are grouped by how they extract sugars from lignocellulose. Brown rot fungi selectively degrade cellulose and hemicellulose, leaving lignin intact, and white rot fungi degrade all components. Many trees are susceptible to both rot types, giving carbon in Earth's woody biomass, specifically lignin, a flexible fate that is affected not only by the fungal decomposition mechanism but also the associated microbial community.

Complete Genome Sequence of Rhodopseudomonas palustris RCB100, an Anoxygenic Phototroph That Degrades 3-Chlorobenzoate.

The purple nonsulfur bacterium RCB100 anaerobically degrades 3-chlorobenzoate (3-CBA), a halogenated pollutant. RCB100 uses 3-CBA as a carbon source, while most strains cannot. We report the complete genome sequence of strain RCB100 to help gain insight into how this bacterium degrades 3-CBA.

Redox Regulation of a Light-Harvesting Antenna Complex in an Anoxygenic Phototroph.

The purple nonsulfur bacterium is a model for understanding how a phototrophic organism adapts to changes in light intensity because it produces different light-harvesting (LH) complexes under high light (LH2) and low light intensities (LH3 and LH4). Outside of this change in the composition of the photosystem, little is understood about how senses and responds to low light intensity. On the basis of the results of transcription analysis of 17 strains grown in low light, we found that strains downregulate many genes involved in iron transport and homeostasis.

The path of electron transfer to nitrogenase in a phototrophic alpha-proteobacterium.

The phototrophic alpha-proteobacterium, Rhodopseudomonas palustris, is a model for studies of regulatory and physiological parameters that control the activity of nitrogenase. This enzyme produces the energy-rich compound H , in addition to converting N gas to NH . Nitrogenase is an ATP-requiring enzyme that uses large amounts of reducing power, but the electron transfer pathway to nitrogenase in R.

Electron Transfer to Nitrogenase in Different Genomic and Metabolic Backgrounds.

Nitrogenase catalyzes the reduction of dinitrogen (N) using low-potential electrons from ferredoxin (Fd) or flavodoxin (Fld) through an ATP-dependent process. Since its emergence in an anaerobic chemoautotroph, this oxygen (O)-sensitive enzyme complex has evolved to operate in a variety of genomic and metabolic backgrounds, including those of aerobes, anaerobes, chemotrophs, and phototrophs. However, whether pathways of electron delivery to nitrogenase are influenced by these different metabolic backgrounds is not well understood.

A pathway for biological methane production using bacterial iron-only nitrogenase.

Methane (CH) is a potent greenhouse gas that is released from fossil fuels and is also produced by microbial activity, with at least one billion tonnes of CH being formed and consumed by microorganisms in a single year . Complex methanogenesis pathways used by archaea are the main route for bioconversion of carbon dioxide (CO) to CH in nature. Here, we report that wild-type iron-iron (Fe-only) nitrogenase from the bacterium Rhodopseudomonas palustris reduces CO simultaneously with nitrogen gas (N) and protons to yield CH, ammonia (NH) and hydrogen gas (H) in a single enzymatic step.

Defining Electron Bifurcation in the Electron-Transferring Flavoprotein Family.

Electron bifurcation is the coupling of exergonic and endergonic redox reactions to simultaneously generate (or utilize) low- and high-potential electrons. It is the third recognized form of energy conservation in biology and was recently described for select electron-transferring flavoproteins (Etfs). Etfs are flavin-containing heterodimers best known for donating electrons derived from fatty acid and amino acid oxidation to an electron transfer respiratory chain via Etf-quinone oxidoreductase.

Genes essential for phototrophic growth by a purple alphaproteobacterium.

Tn-seq was used to identify genes essential for phototrophic growth by the purple bacterium Rhodopseudomonas palustris. About 167 genes required for anaerobic growth on acetate in light were identified, 35 of which are annotated as photosynthesis genes. The essentiality of many of these genes by analysing the phenotypes of independently generated mutants that had altered pigmentation was verified.

Clades of Photosynthetic Bacteria Belonging to the Genus Show Marked Diversity in Light-Harvesting Antenna Complex Gene Composition and Expression.

Many photosynthetic bacteria have peripheral light-harvesting (LH) antenna complexes that increase the efficiency of light energy capture. The purple nonsulfur photosynthetic bacterium produces different types of LH complexes under high light intensities (LH2 complex) and low light intensities (LH3 and LH4 complexes). There are multiple operons that encode the α and β peptides that make up these complexes.

Genome Sequences of Eight Bacterial Species Found in Coculture with the Haptophyte Chrysochromulina tobin.

The microalgal division Haptophyta uses a range of nutritional sourcing, including mixotrophy. The genome of a member of this taxon, Chrysochromulina tobin, suggests that interactions with its bacterial cohort are critical for C. tobin physiology.

Light-driven carbon dioxide reduction to methane by nitrogenase in a photosynthetic bacterium.

Nitrogenase is an ATP-requiring enzyme capable of carrying out multielectron reductions of inert molecules. A purified remodeled nitrogenase containing two amino acid substitutions near the site of its FeMo cofactor was recently described as having the capacity to reduce carbon dioxide (CO2) to methane (CH4). Here, we developed the anoxygenic phototroph, Rhodopseudomonas palustris, as a biocatalyst capable of light-driven CO2 reduction to CH4 in vivo using this remodeled nitrogenase.

A polymorphism in the oxygen-responsive repressor PpsR2 confers a growth advantage to Rhodopseudomonas palustris under low light.

The purple nonsulfur bacterium Rhodopseudomonas palustris grows aerobically using oxidative phosphorylation or anaerobically using photophosphorylation. The oxygen-responsive transcription regulator, PpsR2, regulates the transition to a phototrophic lifestyle by repressing transcription of photosynthesis genes during aerobic growth. Whereas most R.

Apo-bacteriophytochromes modulate bacterial photosynthesis in response to low light.

Bacteriophytochromes (BphPs) are light-sensing regulatory proteins encoded by photosynthetic and nonphotosynthetic bacteria. This protein class has been characterized structurally, but its biological activities remain relatively unexplored. Two BphPs in the anoxygenic photosynthetic bacterium Rhodopseudomonas palustris, designated regulatory proteins RpBphP2 and RpBphP3, are configured as light-regulated histidine kinases, which initiate a signal transduction system that controls expression of genes for the low light harvesting 4 (LH4) antenna complex.

Genetic reporter system for positioning of proteins at the bacterial pole.

Unlabelled: Spatial organization within bacteria is fundamental to many cellular processes, although the basic mechanisms underlying localization of proteins to specific sites within bacteria are poorly understood. The study of protein positioning has been limited by a paucity of methods that allow rapid large-scale screening for mutants in which protein positioning is altered. We developed a genetic reporter system for protein localization to the pole within the bacterial cytoplasm that allows saturation screening for mutants in Escherichia coli in which protein localization is altered.

A genome-scale proteomic screen identifies a role for DnaK in chaperoning of polar autotransporters in Shigella.

Autotransporters are outer membrane proteins that are widely distributed among gram-negative bacteria. Like other autotransporters, the Shigella autotransporter IcsA, which is required for actin assembly during infection, is secreted at the bacterial pole. In the bacterial cytoplasm, IcsA localizes to poles and potential cell division sites independent of the cell division protein FtsZ.

Analysis of the amino acid sequence specificity determinants of the enterococcal cCF10 sex pheromone in interactions with the pheromone-sensing machinery.

The level of expression of conjugation genes in Enterococcus faecalis strains carrying the pheromone-responsive transferable plasmid pCF10 is determined by the ratio in the culture medium of two types of signaling peptides, a pheromone (cCF10) and an inhibitor (iCF10). Recent data have demonstrated that both peptides target the cytoplasmic receptor protein PrgX. However, the relative importance of the interaction of these peptides with the pCF10 protein PrgZ (which enhances import of cCF10) versus PrgX is not fully understood, and there is relatively little information about specific amino acid sequence determinants affecting the functional interactions of cCF10 with these proteins in vivo.