Inhibition of Xylella fastidiosa Biofilm Formation via Metal Chelators

Xylella fastidiosa (Xf) is the causative agent of Pierce's disease in a variety of commercially important plants such as citrus, coffee, and grapes. By blocking the xylem, Xf disrupts water and nutrient transport. Xf is a gram-negative phytopathogen that can form biofilms. Twelve genes have been identified in Xf that can regulate exopolysaccharides, a major component of biofilms, including aconitase, which responds to intracellular iron levels. We have employed a quantitative assay for biofilm formation referred to as minimal biofilm elimination concentration (MBEC) assay that is amenable for high-throughput screening. Biofilm formation by Xf (Napa, CA) can be blocked using iron chelators such as lactoferrin (LF), ethylenediaminetetraacetic acid (EDTA), and S,S′-ethylenediaminedisuccinic acid (EDDS). Incubation of Xf in the presence of LF at 1000μg/mL for 3.5 days showed inhibition of biofilm formation (42%) as well as inhibition (32%) of planktonic growth (liquid-phase bacteria). EDTA at a concentration of 15mg/mL inhibited 99.7% of biofilm formation and 98.9% of planktonic growth in a 24h incubation. In contrast, EDDS at a concentration of 38.2mg/mL showed 64.7% inhibition of biofilm formation and 33.6% inhibition of planktonic growth. Iron deprivation could serve as a first step toward eradication of Pierce's disease via blockage of biofilm formation.