The Bacillus subtilis circadian clock: its metabolic regulation and crosstalk with plants

Despite extensive knowledge of circadian clocks in mammals (including humans), plants, insects, fungi, and a single photosynthetic bacterium, little is known about circadian clocks in non-photosynthetic bacteria. In recent breakthroughs, circadian clocks were discovered in the non-photosynthetic bacteria Klebsiella aerogenes and Bacillus subtilis. The B. subtilis clock was discovered by an international team involving the laboratory of Antony Dodd (JIC), the PI of this proposal. The molecular mechanisms and functions of the B. subtilis clock remain unknown. We are developing B. subtilis as a model for the study of circadian clocks in non-photosynthetic bacteria because it has robust circadian rhythms, an exceptional set of existing research tools, photoreceptors, well-characterized physiology and behaviour, associates with plant roots, and is used in many biotechnological processes. We anticipate that knowledge of circadian clocks in non-photosynthetic bacteria, unlocked by B. subtilis as a model, could ultimately be important for gut health, pathogenicity, soil health, antimicrobial resistance, ecology and biotechnology.

All of these ecological and practical applications of bacteria involve intimate interactions between bacteria and their fluctuating environments. A common adaptation to fluctuating environments is the regulation of metabolism and development according to the 24 h day. Circadian clocks provide a biological estimate of the time of day, which allows anticipation and exploitation of 24 h changes in the environment. Circadian rhythms are generated within cells by circadian clocks, and enhance organismal fitness.

Discovery of a clock in B. subtilis has opened many questions about the mechanisms and functions of circadian clocks in non-photosynthetic bacteria. We are pursuing multiple projects on this topic, including a separate mutant screen for the B. subtilis clock components. This proposal focuses on the circadian regulation of carbon and nitrogen metabolism in B. subtilis, and its role in circadian interactions between B. subtilis and Arabidopsis thaliana. This is because key metabolic regulators in B. subtilis are PAS-domain proteins, which are clock-controlled in many organisms including B. subtilis. Our preliminary work identifies crosstalk between plant and bacterial circadian clocks, suggesting that there is circadian signalling between different kingdoms of life.

We will investigate the following:

1. The circadian regulation of central carbon and nitrogen metabolism in B. subtilis.

2. Roles for central carbon and nitrogen metabolism in the emergence and properties of circadian rhythms in B. subtilis.

3. Roles for central carbon and nitrogen metabolism in circadian clock interactions between B. subtilis and Arabidopsis.

The project uses methods established already in the Dodd lab, and is supported by expert staff and excellent facilities of JIC technology platforms. The project also benefits from ongoing collaboration with the laboratories of Martha Merrow (LMU, Munich) and Ákos Kovács (Leiden, Netherlands).

We will maximise the impact of this work by communicating our findings at industry-facing events hosted by the newly formed Norwich Centre for Microbiology, and 6-monthly meetings with the JIC Knowledge Exchange and Commercialization team to identify and act upon emerging translational opportunities within the work.