Role of RamA on biofilm formation of Klebsiella variicola

Abstract

Klebsiella variicola (Kv) is a bacterium which occupies diverse natural niches, colonising different hosts, including humans. Initially isolated from plants and the broader environment, Kv is now considered as an emerging pathogen causing human infections with a high mortality rate. One of the main microbiological features of Kv, allowing it to survive in the environment, is biofilm formation. In the human host, biofilm-associated infections are hard to treat as they display high resistance to immune cells and antibiotics. It is, therefore, vital to determine the factors involved in the biofilm formation mechanisms.

Aspects regarding Kv’s biofilm formation and virulence traits remain to be elucidated. RamA is an AraC-transcriptional protein regulator described in Klebsiella pneumoniae, responsible for bacterial multidrug resistance and virulence. Studies in Salmonella and Klebsiella pneumoniae show that RamA can also influence the expression of genes involved in biofilm formation. Despite the genetic similarity between Klebsiella variicola and Klebsiella pneumoniae, the regulatory role of RamA in Klebsiella variicola is not fully characterised. Our hypothesis is that the RamA plays a role in the biofilm formation in Kv. To test this hypothesis, our aim was to determine the possible role of RamA in biofilm formation of Kv. We compared the biofilm formation between strains presenting with different levels of RamA, both using the crystal violet staining technique and by growing strains on Congo Red plates. We found that the ramA expression levels were inversely correlated with biofilm formation. We also found that RamA altered biofilm formation independent of the mrk operon and capsule (wcaJ) in Kv. We undertook transcriptomic analyses, to establish the genes necessary for biofilm formation. Transcriptomic analyses allowed us to identify pspA & pspG as genes participating to this RamA-dependant variations in biofilm formation. In conclusion, our work showed that RamA plays a role in the biofilm formation of Kv independently of the mrk operon.