Chemical tool deciphers bacterial infections in real time

Researchers from The University of Hong Kong (HKU) have developed a novel chemical tool to reveal how bacteria adapt to the host environment and control host cells. Described in the journal Nature Chemical Biology, the tool can be used to investigate bacterial interactions with the host in real time during an infection, which cannot be easily achieved by other methods.

When bacteria meet their host (eg, human cells), they send out ‘assassins’ (virulence factor proteins) that ‘hijack’ important protein players of the host to sow chaos during an invasion. Therefore, investigating which virulence factors bacteria secrete and which host proteins are targeted is crucial for the understanding of bacterial infections. However, it can be extremely challenging to identify these key players among the ‘crowded streets’ (excessive host cellular matrix).

To tackle this challenge, researchers led by Professor Xiang David Li designed a multifunctional unnatural amino acid called photo-ANA that only labels proteins of the engineered bacteria but not the host during infection. With the help of its alkyne handle, photo-ANA can conjugate with fluorescence or biotin via ‘click chemistry’, which enables the visualisation and enrichment of the labelled bacterial proteins from the complex host environment. Thus, photo-ANA serves as an ‘undercover agent’ to gather intelligence and tag all the assassins sent by the bacteria. More importantly, photo-ANA also carries a diazirine group that can ‘handcuff’ the bacterial virulence proteins to their host target proteins upon exposure to ultraviolet (UV) light — thus catching them in the act.

Using photo-ANA, Li’s group comprehensively profiled the adaptation of Salmonella to the host environment and revealed the extensive interplay between Salmonella and the host during different infection stages, which identified known interactions and some newly discovered interactions. Moreover, the photo-ANA-based approach can be easily applied to other pathogenic bacteria and even other pathogens such as fungi.

With this new chemical tool, scientists can now investigate the activity of bacteria inside the host in real time. In the future, the tool may help us decipher the hidden interactions of deadly bacteria with the host and the mechanisms of multidrug-resistant superbugs.

International researchers have found increasing emissions of several ozone-depleting chemicals, despite their production being banned for most uses under the Montreal Protocol — and a loophole in the rules is likely responsible.

Chlorofluorocarbons, or CFCs, are chemicals known to destroy Earth’s protective ozone layer. Once widely used in the manufacture of hundreds of products including aerosol sprays, CFC production for such uses was banned under the Montreal Protocol in 2010. However, the international treaty didn’t eliminate the creation of CFCs during production of other chemicals including hydrofluorocarbons (HFCs), which were developed as ozone-friendly replacements for CFCs.

The new study focused on five CFCs with few or no known current uses — CFC-13, CFC-112a, CFC-113a, CFC-114a and CFC-115 — and that have atmospheric lifetimes ranging from 52–640 years. In terms of their impact on the ozone layer, these emissions were equivalent to around one-quarter of a recently detected rise in emissions of CFC-11, a substance controlled under the Montreal Protocol, thought to be due to unreported new production.

The researchers used measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE), in which the University of Bristol plays a pivotal role, as well as others made by Germany’s Forschungszentrum Jülich, the University of East Anglia and the US National Oceanic and Atmospheric Administration (NOAA). These were combined with an atmospheric transport model to show that global atmospheric abundances and emissions of these CFCs increased after their production for most uses was phased out in 2010.

The researchers determined that for CFC-113a, CFC-114a and CFC-115, the increased emissions may be partly due to their use in the production of two common HFCs used primarily in refrigeration and air conditioning. The drivers behind increasing emissions of CFC-13 and CFC-112a are less certain. The results were published in the journal Nature Geoscience

Emissions from these CFCs currently do not significantly threaten ozone recovery, the researchers noted — but because they’re potent greenhouse gases, they still affect the climate. According to lead author Dr Luke Western, a research fellow at the University of Bristol and researcher at NOAA, “Combined, their emissions are equal to the CO2 emissions in 2020 for a smaller developed country like Switzerland. That’s equivalent to about 1% of the total greenhouse gas emissions in the United States.”

According to the researchers, if emissions of these five CFCs continue to rise, their impact may negate some of the benefits gained under the Montreal Protocol. These emissions might be reduced or avoided by reducing leakages associated with HFC production and by properly destroying any co-produced CFCs.