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Absorbance measurements on intact chemolithotrophic microorganisms that respire aerobically on soluble iron are described that used a novel integrating cavity absorption meter to eliminate the effects of light scattering on the experimental results. Steady state kinetic measurements on ferric iron production by intact cells revealed that the Michaelis Menten equation described the initial rates of product formation for at least 8 different chemolithotrophic microorganisms in 6 phyla distributed equally among the archaea and the Gram negative and Gram positive eubacteria. Cell-monitored turnover measurements during aerobic respiration on soluble iron by the same 12 intact microorganisms revealed six different patterns of iron-dependent absorbance changes, suggesting that there may be at least six different sets of prosthetic groups and biomolecules that can accomplish aerobic respiration on soluble iron. Detailed kinetic studies revealed that the 3-component iron respiratory chain of Acidithiobacillus ferrooxidans functioned as an ensemble with a single macroscopic rate constant when the iron-reduced proteins were oxidized in the presence of excess molecular oxygen. The principal member of this 3-component system was a cupredoxin called rusticyanin that was present in the periplasm of At. ferrooxidans at an approximate concentration of 350 mg/mL, an observation that provides new insights into the crowded environments in the periplasms of Gram negative eubacteria that conduct electrons across their periplasm. The ability to conduct direct spectrophotometric measurements under noninvasive physiological conditions represents a new and powerful approach to examine the rates and extents of biological events in situ without disrupting the complexity of the live cellular environment.
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This content will become publicly available on May 9, 2026
Metallosphaera sedula bifurcates into two sizes when it is cultured mixotrophically on soluble iron
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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- Award ID(s):
- 2100950
- PAR ID:
- 10630215
- Publisher / Repository:
- Frontiers in Microbiology
- Date Published:
- Journal Name:
- Frontiers in Microbiology
- Volume:
- 16
- ISSN:
- 1664-302X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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