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1. Ferrimicrobium acidiphilum Exchanges Electrons With a Platinum Electrode via a Cytochrome With Reduced Absorbance Maxima at 448 and 605 nm

   https://doi.org/10.3389/fmicb.2021.705187  

   Blake, Robert C.; Nautiyal, Amit; Smith, Kayla A.; Walton, Noelle N.; Pendleton, Brealand; Wang, Zhe (July 2021, Frontiers in Microbiology)

   null (Ed.)

   Ferrimicrobium acidiphilum is a Gram-positive member of the Actinobacteria phylum that can respire aerobically or anaerobically with soluble Fe(II) or Fe(III), respectively, in sulfuric acid at pH 1.5. Cyclic voltammetry measurements using intact F. acidiphilum at pH 1.5 produced fully reversible voltammograms that were highly reproducible. The maximum current observed with the anodic peak was considerably less than was the maximum current observed with the cathodic peak. This difference was attributed to the competition between the platinum electrode and the soluble oxygen for the available electrons that were introduced by the cathodic wave into this facultative aerobic organism. The standard reduction potential of the intact organism was determined to be 786 mV vs. the standard hydrogen electrode, slightly more positive than that of 735 mV that was determined for soluble iron at pH 1.5 using the same apparatus. Chronocoulometry measurements conducted at different cell densities revealed that the intact organism remained in close proximity to the working electrode during the measurement, whereas soluble ionic iron did not. When the cyclic voltammetry of intact F. acidiphilum was monitored using an integrating cavity absorption meter, the only small changes in absorbance that were detected were consistent with the participation of a cellular cytochrome with reduced absorbance peaks at 448 and 605 nm. The cytochrome that participated in the exchange of electrons between the intact organism and extracellular solid electrodes like platinum was the same cytochrome whose oxidation was previously shown to be rate-limiting when the organism respired aerobically on extracellular soluble iron. 

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2. Metallosphaera sedula bifurcates into two sizes when it is cultured mixotrophically on soluble iron

   https://doi.org/10.3389/fmicb.2025.1455423  

   Blake, Robert C; Painter, Richard G; Pham, Nghi; Griswold, Olivia; White, Brooke; White, Richard A (May 2025, Frontiers in Microbiology)

   Metallosphaera sedulais a thermoacidophilic archaeon that obtains all of its energy for growth from aerobic respiration and oxidative phosphorylation at the expense of selected organic and inorganic sources of electrons. Initial velocities for the oxidation of soluble ferrous ions by intact cells at 60 °C and pH 1.5 were determined using an integrating cavity absorption meter that permitted accurate absorbance measurements to quantify the increase in soluble ferric iron in the presence of turbid suspensions of the live organisms.M. sedulathat was cultured on yeast extract either in the absence or the presence of 20 mM soluble ferrous iron exhibited turnover numbers for soluble iron oxidation of 304 ± 26 and 333 ± 31 attamoles/cell/min, respectively. These functional data were consistent with the transcriptomic evidence presented by others, that the proteins presumably responsible for aerobic respiration on soluble iron are expressed constitutively inM. sedula. Intact cells ofM. sedulawere characterized by electrical impedance, laser light diffraction, and transmission electron microscopic measurements. All three types of measurements were consistent with the surprising observation that cells cultured on yeast extract in the presence of soluble iron bifurcated into approximately equal numbers of coccoidal cells of two sizes, smaller cells with an average diameter of 0.6 μm and larger cells with an average diameter of 1.35 μm. Cells cultured on the same concentration of yeast extract but in the absence of soluble iron comprised a single cell size with an intermediate average diameter of 1.06 μm. This unexpected bifurcation of a clonal cell population into two demonstrably different sizes when the extracellular nutrient environment changes has not previously been reported forM. sedula, or any other single-celled archaeon or eubacterium. 

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3. Oxidation of cytochrome 605 is the rate-limiting step when Ferrimicrobium acidiphilum respires aerobically on soluble iron

   https://doi.org/10.1128/AEM/01906-20  

   Blake, II; Guidry, J.J.; Anthony, M.D.; Ban, B.; Smith, K.A.; Walton, N.N.; Painter, R.G. (October 2020, Applied and environmental microbiology)

   Atomi, Haruyuki (Ed.)

   Proteins that oxidize extracellular substrates in Gram-positive bacteria are poorly understood. Ferrimicrobium acidiphilum is an actinobacterium that respires aerobically on extracellular ferrous ions at pH 1.5. In situ absorbance measurements were conducted on turbid suspensions of intact Fm. acidiphilum using an integrating cavity absorption meter designed for that purpose. Initial velocity kinetic studies monitored the appearance of product ferric ions in the presence of catalytic quantities of cells. Cell-catalyzed iron oxidation obeyed the Michaelis-Menten equation with values for KM and Vmax of 71 µM and 0.29 fmol/min/cell, respectively. Limited-turnover kinetic studies were conducted with higher concentrations of cells to detect and monitor changes in the absorbance properties of cellular redox proteins when the cells were exposed to limited quantities of soluble reduced iron. A single a-type cytochrome with reduced absorbance peaks at 448 and 605 nm was the only redox-active chromophore that was visible as the cells respired aerobically on iron. The reduced cytochrome 605 exhibited mathematical and correlational properties that were consistent with the hypothesis that oxidation of the cytochrome constituted the rate-limiting step in the aerobic respiratory process with a turnover number of 35 ± 2 s-1. Genomic and proteomic analyses showed that Fm. acidiphilum could and did express only two a-type heme copper terminal oxidases. Cytochrome 605 was associated with the terminal oxidase gene that is located between nucleotides 31090 and 33039, inclusive, in the annotated circular genome of this bacterium. 

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4. Homogeneous Cytochrome 579 Is an Octamer That Reacts Too Slowly With Soluble Iron to Be the Initial Iron Oxidase in the Respiratory Chain of Leptospirillum ferriphilum

   https://doi.org/10.3389/fmicb.2021.673066  

   Blake, Robert C.; Shively, John E.; Timkovich, Russell; White, Richard Allen (May 2021, Frontiers in Microbiology)

   null (Ed.)

   The exact role that cytochrome 579 plays in the aerobic iron respiratory chain of Leptospirillum ferriphilum is unclear. This paper presents genomic, structural, and kinetic data on the cytochrome 579 purified from cell-free extracts of L. ferriphilum cultured on soluble iron. Electrospray mass spectrometry of electrophoretically homogeneous cytochrome 579 yielded two principal peaks at 16,015 and 16,141 Daltons. N-terminal amino acid sequencing of the purified protein yielded data that were used to determine the following: there are seven homologs of cytochrome 579; each homolog possesses the CXXCH heme-binding motif found in c -type cytochromes; each of the seven sequenced strains of L. ferriphilum expresses only two of the seven homologs of the cytochrome; and each homolog contains an N-terminal signal peptide that directs the mature protein to an extra-cytoplasmic location. Static light scattering and macroion mobility measurements on native cytochrome 579 yielded masses of 125 and 135 kDaltons, respectively. The reduced alkaline pyridine hemochromogen spectrum of the purified cytochrome had an alpha absorbance maximum at 567 nm, a property not exhibited by any known heme group. The iron-dependent reduction and oxidation of the octameric cytochrome exhibited positively cooperative kinetic behavior with apparent Hill coefficients of 5.0 and 3.7, respectively, when the purified protein was mixed with mM concentrations of soluble iron. Consequently, the extrapolated rates of reduction at sub-mM iron concentrations were far too slow for cytochrome 579 to be the initial iron oxidase in the aerobic respiratory chain of L. ferriphilum . Rather, these observations support the hypothesis that the acid-stable cytochrome 579 is a periplasmic conduit of electrons from initial iron oxidation in the outer membrane of this Gram-negative bacterium to a terminal oxidase in the plasma membrane. 

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5. Antifouling Activity of Bottlebrush Network Hydrogels

   https://doi.org/10.1021/acsabm.5c00291  

   Chiang, Meng-Chen; Clarke, Brandon R; Tew, Gregory N; Schiffman, Jessica D (April 2025, ACS Applied Bio Materials)

   Mitigating the attachment of microorganisms to polymer biomaterials is critical for preventing hospital-acquired infections. Two chemical strategies to mitigate fouling include fabricating fouling-resistant surfaces, which typically present hydrophilic polymers, such as polyethylene glycol (PEG), or creating fouling-release surfaces, which are generally hydrophobic featuring polydimethylsiloxane (PDMS). Despite the demonstrated promise of employing PEG or PDMS, amphiphilic PEG/PDMS copolymer materials remain understudied. Here, for the first time, we investigated if phase-separated amphiphilic copolymers confounded microbial adhesion. We used bottlebrush amphiphilic PEG/PDMS co-networks and homopolymer networks to study bacterial adhesion across a library of gels (ϕPEG = 0.00, 0.21, 0.40, 0.55, 0.80, and 1.00). Hydrated atomic force microscopy measurements revealed that most of the gels had low surface roughness, less than 5 nm, and an elastic modulus of ∼80 kPa. Interestingly, the surface roughness and elastic modulus of the ϕPEG = 0.40 gel were twice as high as those of the other gels due to the presence of crystalline domains, as confirmed using polarized optical microscopy on the hydrated gel. The interactions of these six well-characterized gels with bacteria were determined using Escherichia coli K12 MG1655 and Staphylococcus aureus SH1000. The attachment of both microbes decreased by at least 60% on all polymer gels versus the glass controls. S. aureus adhesion peaked on the ϕPEG = 0.40, likely due to its increased elastic modulus, consistent with previous literature demonstrating that modulus impacts microbial adhesion. These findings suggest that hydrophilic, hydrophobic, and amphiphilic biomaterials effectively resist the early attachment of Gram-negative and Gram-positive microorganisms, providing guidance for the design of next-generation antifouling surfaces. 

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