How diversity of respiratory quinones affects microbial physiology

November 25, 2019

A new study provides a fundamental understanding of the diversification of small molecules called respiratory quinones and its adaptive consequences in bacterial species. Bioengineers at the University of California San Diego specifically examined how respiration is affected by different types of quinones present in bacteria growing in aerobic environments.

The team, led by Bernhard Palsson, Galletti Professor of Bioengineering at UC San Diego, and Amitesh Anand, a postdoctoral researcher in the Palsson lab, published their findings Nov. 25 in Proceedings of the National Academy of Sciences (PNAS).

The process of respiration is dependent on different types of membrane-localized, redox-active small molecules known as respiratory quinones. One type, ubiquinone, is used in modern life forms for aerobic respiration. Historically, its appearance overlaps with the emergence of oxygen on earth. Another type, naphthoquinone, is primarily used in ancient organisms (existing approximately 2.5 billion years ago when the earth had little or no oxygen) for anaerobic respiration.

This quinone diversification overlaps with the oxygenation of the earth's environment and therefore is believed to be an adaptive response to the rise in the oxygen levels. However, a large number of bacterial species still respire aerobically using the ancient respiratory quinone, naphthoquinone.

E. coli and several other bacterial species acquired the ability to produce ubiquinone while retaining the pathways to make naphthoquinone. Interestingly, these bacterial species use ubiquinone for aerobic respiration and naphthoquinone for anaerobic respiration. Bacterial species devoid of ubiquinone, such as Staphylococcus aureus and Mycobacterium tuberculosis, can efficiently respire aerobically using naphthoquinone.

To examine metabolic limitations of aerobic naphthoquinone usage in bacterial species with the ability to produce both types of respiratory quinones, researchers engineered a ubiquinone-deficient strain of E. coli to force it to respire aerobically using the ancient respiratory quinone. They then performed an adaptive laboratory evolution of this strain to understand the metabolic challenges that bacterial species face when using the ancient quinone in aerobic environments. The goal was to recreate the conditions during the rapid rise in oxygen in the earth's atmosphere, an event commonly referred to as the Great Oxygenation Event.

The E. coli strains that evolved to respire aerobically using naphthoquinone were observed to activate a subset of cellular defense systems that are primarily responsible for mitigating oxidative stress in the periplasmic space. The relatively lower redox potential of naphthoquinone makes it more prone to non-productive electron leakage during the operation of the electron transfer chain in respiration, which can result in the generation of reactive radicals and cause damage to the cell.

By activating a defense mechanism, bacteria experienced a safer operation of the electron transfer chain and showed an improvement in their oxygen consumption. However, activation of this defense mechanism required the bacteria to reallocate finite cellular resources. This restricted the growth capacity of the evolved strains. Researchers hypothesize that this so-called "fear-greed" tradeoff directed the advent of the higher redox potential quinone.

Understanding this fear-greed tradeoff not only advances the basic understanding of microbial bioenergetics evolution, it can facilitate modulation of growth and survival of bacteria, especially a broad range of pathogenic bacteria that respire aerobically using naphthoquinone, researchers said.
-end-
Paper title: "Adaptive evolution reveals a tradeoff between growth rate and oxidative stress during naphthoquinone based aerobic respiration." Co-authors include Ke Chen, Laurence Yang, Anand V. Sastry, Connor A. Olson, Saugat Poudel, Yara Seif, Ying Hefner, Patrick V. Phaneuf, Sibei Xu, Richard Szubin and Adam M. Feist.

This work was funded by the Novo Nordisk Foundation (grant NNF10CC1016517), the National Institutes of Health (grants R01GM057089 and U01AI124316).

University of California - San Diego

Related Bacteria Articles from Brightsurf:

Siblings can also differ from one another in bacteria
A research team from the University of Tübingen and the German Center for Infection Research (DZIF) is investigating how pathogens influence the immune response of their host with genetic variation.

How bacteria fertilize soya
Soya and clover have their very own fertiliser factories in their roots, where bacteria manufacture ammonium, which is crucial for plant growth.

Bacteria might help other bacteria to tolerate antibiotics better
A new paper by the Dynamical Systems Biology lab at UPF shows that the response by bacteria to antibiotics may depend on other species of bacteria they live with, in such a way that some bacteria may make others more tolerant to antibiotics.

Two-faced bacteria
The gut microbiome, which is a collection of numerous beneficial bacteria species, is key to our overall well-being and good health.

Microcensus in bacteria
Bacillus subtilis can determine proportions of different groups within a mixed population.

Right beneath the skin we all have the same bacteria
In the dermis skin layer, the same bacteria are found across age and gender.

Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.

How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.

The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?

Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.

Read More: Bacteria News and Bacteria Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.