Project DEFEND has yielded a number of discoveries in terms of adaptive and innate immune systems of bacteria. Below I will highlight three of these discoveries:
Throughout the the DEFEND project, our team has conducted extensive research, uncovering significant insights into the immune systems of bacteria. Three notable discoveries have been made, advancing our understanding of bacterial defenses against phage assaults.
Firstly, a novel variant of CRISPR mechanisms, known as CRISPR-controlled proteases, has been identified. Unlike the traditional CRISPR systems that employ nucleases to cleave nucleic acids, these specialized systems utilize a guide RNA to pinpoint phage messenger RNA and subsequently activate proteases. The activation of these proteases represents an alternative pathway, augmenting the bacterial immune response against phage predation through protein degradation cell suicide pathways. This discovery may lead to further molecular biology tools that can edit proteomes in the future.
Secondly, research has uncovered an innovative evasion strategy employed by phages: the encoding of tRNAs that are resistant to cleavage by host defense systems. These phages produce specific tRNAs that function as uncleavable components of the translation machinery, evading bacterial defense systems that typically target and degrade tRNA molecules to deplete the host from the ability to produce proteins, thereby stopping bacteriophage infection. This mechanism of escape signifies a sophisticated level of adaptive evolution among phages, presenting a challenge to the effectiveness of bacterial immune systems. Furthermore, this finding may solve the 50 year old mystery why phages encode their own tRNAs.
Lastly, an a detailed bioinformatic analysis uncovered an accumulation of defense systems in clinical strains of Pseudomonas aeruginosa, resulting in heightened resistance to phage infection. This accumulation signifies a robust defensive stance, enhancing the bacterium's survival against phage attacks. This phenomenon underscores the importance of understanding the dynamics of bacterial immune responses, particularly in clinically relevant contexts where antibiotic resistance is prevalent.
These discoveries, together, contribute to a more comprehensive understanding of the intricate interplay between bacterial defenses and phage offensive strategies. This knowledge is crucial in advancing the development of phage therapies, especially as a potential solution to combat antibiotic-resistant bacterial infections.
