The enzymes that enable bacteria to make themselves at home

torrentsFig2_webIBEC researchers have come a step closer to understanding how bacteria can cause chronic infections by identifying the key enzymes that allow them to create the right conditions for infection.

When P. aeruginosa bacteria cause chronic lung infections in patients with cystic fibrosis or chronic obstructive pulmonary disease (COPD), it means they have been able to form a mature biofilm in situ that lets them grow and adapt. This biofilm not only enhances cell-to-cell communication for the bacteria, thus allowing the infection to increase and thrive, but it also increases the chances of developing new antibiotic resistance and escape from the body’s immune system.

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Image: Detailed microscopy observations of structured biofilms from P. Aeruginosa PAO1 wild-type, ETS102, ETS103 and ETS125 strains. On the left side, a scheme of the longitudinal structure of P. aeruginosa biofilm is represented, labelled with indications of the oxygen concentration along the biofilm (Stewart and Franklin, 2008). On the right, images taken from the aerobic region of the biofilm (top part, superficial biofilm) and from the anaerobic region (bottom part, deeper in the biofilm structure) are shown.

Oxygen concentration throughout the biofilm is a crucial parameter for bacterial growth. In a mature biofilm, the oxygen concentration becomes reduced in its lower layers, resulting in strict anaerobic conditions in its depths – an oxygen-free microenvironment. Knowing this, the IBEC researchers looked at the effect on P. aeruginosa of three difference classes of an important enzyme, ribonucleotide reductase (RNR), that is critical for the formation of the building blocks needed for DNA synthesis and repair.

P. aeruginosa is one of the few bacteria encoding all three known RNR classes: Ia, which is oxygen dependent, II, which is oxygen independent, and III, which is oxygen sensitive and can only function under strict anaerobic conditions,” explains Eduard Torrents, who heads the IBEC research group that carried out the study. “These RNRs are likely to increase the capacity of this bacterium to grow in the different aerobic and anaerobic environments generated throughout biofilms.”

The scientists modeled a P. aeruginosa biofilm as a set of layers with different RNR expression profiles. “We found that the bacteria had difficulties forming a biofilm when class II and III RNRs – the oxygen independent and oxygen sensitive ones – were missing,” explains Anna Crespo, first author on the paper. “Classes II and III are clearly essential for anaerobic growth, and without them, fully mature biofilms will not be able to establish themselves.”

Their findings bring researchers a step closer to the understanding of this complex growth pattern and play an important role in understanding the virulence of bacterial biofilms, which will help towards the better design of specific antibacterial drugs.

Source article: Anna Crespo, Lucas Pedraz, Josep Astola, Eduard Torrents (2016). Pseudomonas aeruginosa exhibits deficient biofilm formation in the absence of class II and III ribonucleotide reductases due to hindered anaerobic growth. Frontiers in Microbiology 7:688. doi: 10.3389/fmicb.2016.00688.

IBEC in the media:

La Vanguardia, “Investigadores abren nuevas vías para mejorar los fármacos antibacterianos”
NCYT, “Cómo evitar que las bacterias se sientan como en casa”
Gaceta Médica, “RNRII y III son clave para que las bacterias formen la biopelícula”
Agencia SINC, “Cómo evitar que las bacterias se sientan como en casa”
Fármaco Salud, “Cómo evitar que las bacterias se sienta como en casa”