GAPDH, rhbC, and vapA gene expression in Rhodococcus equi cultured under different iron concentrations.

The research article is about an investigation into the effects of different iron concentrations on the expression of three specific genes – GAPDH, rhbC, and vapA – in a bacteria called Rhodococcus equi, which causes pneumonia in young horses.

Background

• The study focuses on the bacterium Rhodococcus equi, which is known for causing pneumonia in foals. R. equi’s virulence, or its ability to cause disease, depends heavily on two genes: vapA and rhbC.
• These genes are responsible for producing a virulence-associated protein A (VapA) and a siderophore known as rhequichelin, respectively.
• The researchers previously knew that the bacteria require iron, obtained from the protein transferrin, to survive inside host cells (macrophages), but the exact mechanisms of this iron acquisition were unclear.

Objectives

• The aims of the study were to explore the role of the gene GAPDH in iron homeostasis, analyze the expression of the GAPDH, rhbC, and vapA genes under various iron conditions, and record the presence of the rhbC gene in different R. equi isolates.

Methodology

• R. equi was grown in conditions with high, normal, and low iron concentrations. The researchers taken quantitative measurements of the cultures and documented gene expression.
• They used qPCR, a technique for quantifying gene expression, to analyze the relative expression of GAPDH, rhbC, and vapA after 48 hours of growth.
• The presence of the rhbC gene was determined through DNA extraction from different sources of R. equi, including clinical isolates from ill foals, healthy horses and soil samples.

Findings

• On limiting iron, the growth rate of R. equi was reduced. This stress condition also induced high levels of GAPDH and vapA gene expression. This suggests a possible role for GAPDH in iron homeostasis within R. equi.
• The rhbC gene was found to be significantly up-regulated or increased in activity, under conditions of both iron excess and severe iron deprivation.
• All clinical isolates and soil samples carried the rhbC gene. However, two samples from healthy horses did not have the gene, leading the researchers to infer that rhequichelin might not be necessary for R. equi to colonize the nasal and intestinal areas of horses.