Microbiology Editor’s Choice: AlgP in Pseudomonas aeruginosa

Posted on October 2, 2020   by Microbiology Society

Each month, a manuscript published in our flagship journal Microbiology is chosen by a member of the Editorial Board. This month, the paper is titled ‘The histone-like protein AlgP regulon is distinct in mucoid and nonmucoid Pseudomonas aeruginosa and does not include alginate biosynthesis genes’ and was chosen by Professor Gail Preston.

This thoughtful paper describes an ongoing molecular detective story to solve the mystery of AlgP. The AlgP protein of the opportunistic pathogen Pseudomonas aeruginosa originally came to attention because of its potential role in the regulation of alginate production in mucoid strains. However, in this study by Cross and collaborators, deletion of AlgP was found to have no effect on alginate production in either mucoid or non-mucoid strains. Nevertheless, AlgP expression was found to be reduced in a mucoid strain, so the authors used RNA sequencing to define the AlgP regulon. Surprisingly, AlgP was found to regulate a small, but divergent set of genes in mucoid and non-mucoid bacteria. Genes that were regulated by AlgP in non-mucoid bacteria included the operons norCBD and nosRZ involved in the synthesis of nitric oxide and nitrous oxide reductase, which were upregulated in a ΔalgP mutant, and which could contribute to the increased growth shown by this mutant in anaerobic conditions. While AlgP cannot be definitively said to lack a role in alginate biosynthesis, which may be differentially regulated according to environmental conditions, this systematic study provides a fresh perspective on the role and regulation of this intriguing protein. 

The histone-like protein AlgP regulon is distinct in mucoid and nonmucoid Pseudomonas aeruginosa and does not include alginate biosynthesis genes

The histone-like protein AlgP has long been proposed to regulate alginate production in the opportunistic bacterial pathogen Pseudomonas aeruginosa. P. aeruginosa isolates that overexpress alginate have a mucoid appearance and are often found in chronic lung infections. We reevaluated the role of AlgP by constructing a clean algP deletion mutant in a mucoid strain. Surprisingly, we found that deletion of algP did not decrease alginate production and only slightly affected the expression of a modest number of genes involved in survival under anaerobic conditions. These data suggest that the regulation of alginate production by algP is less clear cut than originally described. 

We spoke with the corresponding author Professor Joanna Goldberg to find out more:

What is your institution and how long have you been there? 

I am a Professor in the Department of Paediatrics at Emory University School of Medicine; I have a Secondary Appointment in the Department of Microbiology and Immunology. I have been here since January 2013, so almost 8 years. 

What is your research area?  

I am a “card-carrying microbiologist”.  I study bacterial pathogenesis in the context of lung infections in cystic fibrosis patients.  In particular, I try to understand how bacteria cause disease by studying bacterial physiology, genetics, and the immune response to infection.  In doing so I hope to learn how to inhibit bacterial virulence and growth, and therefore their negative effects on patient health. 

What inspired you to research this topic?  

My best friend’s daughter is living with cystic fibrosis. She and others and their families impacted by this terrible disease keep me focused on trying to find ways to combat infections. The bacteria that infect these patients are also pathogenic to other patients, so it is my hope that any mechanisms of inhibiting these microbes that we uncover will be able to be extended to infections beyond just those in cystic fibrosis.   

What is the most rewarding part of your research? 

Aside from problem solving and figuring out what makes microbes “tick”, I enjoy training the next generation of scientists. I love watching students mature scientifically and take ownership of their own projects. 

What would you be doing if you weren't a scientist? 

I would probably be a vintner, but that seems a lot like a scientist, who gets to live and work in a beautiful place and drink wine. 

Follow Professor Goldberg’s co-author Dr Ashley Cross on Twitter.