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Iron in Neisseria meningitidis: minimum requirements, effects of limitation, and characteristics of uptake
Abstract:
A simple defined medium (neisseria defined medium) was devised that does not require iron extraction to produce iron-limited growth of Neisseria meningitidis (SDIC). Comparison of this medium to Mueller-Hinton broth and agar showed nearly identical growth rates and yields. The defined medium was used in batch cultures to determine the disappearance of iron from the medium and its uptake by cells. To avoid a number of problems inherent in batch culture, continuous culture, in which iron and dissolved oxygen were varied independently, was used. Most of the cellular iron was found to be nonheme and associated with the particulate fraction in sonically disrupted cells. Nonheme and catalase-heme iron were reduced by iron starvation far more than cytochromes b and c and N,N,N',N'-tetramethylphenylenediamine-oxidase. The respiration rate and efficiency also decreased under iron limitation, whereas generation times increased. The iron-starved meningococcus took up iron by an energy-independent system operating in the first minute after an iron pulse and a slower energy-dependent system inhibited by respiratory poisons and an uncoupler. The energy-dependent system showed saturation kinetics and was stimulated nearly fourfold by iron privation. In addition, to determine the availability to the meningococcus of the iron in selected compounds, a sensitive assay was devised in which an iron-limited continuous culture was pulsed with the iron-containing compound.
Insights
Researchers developed a new iron-limited growth medium for Neisseria meningitidis, revealing insights into iron uptake and cellular iron distribution under nutrient stress.
Area of Science:
- Microbiology
- Bacterial Physiology
- Nutritional Biochemistry
Background:
- Neisseria meningitidis requires iron for growth.
- Previous studies faced challenges in controlling iron availability for bacterial cultures.
- Understanding iron metabolism is crucial for Neisseria meningitidis pathogenesis.
Purpose of the Study:
- To develop a defined medium for iron-limited Neisseria meningitidis growth.
- To investigate iron uptake mechanisms and cellular iron distribution.
- To assess the impact of iron limitation on bacterial respiration and growth.
Main Methods:
- Devised a novel iron-limited defined medium (neisseria defined medium).
- Utilized batch and continuous culture systems to study iron metabolism.
- Analyzed cellular iron content (heme vs. nonheme) and respiration rates.
- Characterized iron uptake systems using iron pulses and kinetic analysis.
Main Results:
- The defined medium supported iron-limited growth comparable to standard media.
- Iron starvation significantly reduced nonheme and catalase-heme iron levels.
- Respiration rates decreased, and generation times increased under iron limitation.
- Identified both energy-independent and energy-dependent iron uptake systems.
Conclusions:
- The developed defined medium is effective for studying iron-limited Neisseria meningitidis.
- Iron limitation impacts cellular iron distribution and respiratory function.
- Neisseria meningitidis employs distinct mechanisms for iron acquisition.
- Further research can utilize this system to explore iron compound availability.