Presence of Extracellular DNA during Biofilm Formation by Xanthomonas citri subsp. citri Strains with Different Host Range

Abstract

Xanthomonas citri subsp. citri (Xcc) A strain causes citrus bacterial canker, a serious leaf, fruit and stem spotting disease of several Citrus species. X. alfalfae subsp. citrumelonis (Xac) is the cause of citrus bacterial spot, a minor disease of citrus nursery plants and X. campestris pv. campestris (Xc) is a systemic pathogen that causes black rot of cabbage. Xanthomonas spp. form biofilms in planta that facilitate the host infection process. Herein, the role of extracellular DNA (eDNA) was evaluated in the formation and stabilization of the biofilm matrix at different stages of biofilm development. Fluorescence and light microscopy, as well as DNAse treatments, were used to determine the presence of eDNA in biofilms and bacterial cultures. DNAse treatments of Xcc strains and Xac reduced biofilm formation at the initial stage of development, as well as disrupted preformed biofilm. By comparison, no significant effect of the DNAse was detected for biofilm formation by Xc. DNAse effects on biofilm formation or disruption varied among Xcc strains and Xanthomonas species which suggest different roles for eDNA. Variation in the structure of fibers containing eDNA in biofilms, bacterial cultures, and in twitching motility was also visualized by microscopy. The proposed roles for eDNA are as an adhesin in the early stages of biofilm formation, as an structural component of mature bacterial aggregates, and twitching motility structures.

Mechanistic insights into host adaptation, virulence and epidemiology of the phytopathogenXanthomonas

“…eDNA has long been considered to be an integral part in bacterial biofilms (Okshevsky and Meyer 2015) but only recently shown to play a role in Xanthomonas biofilm formation. Specifically, Sena-Vélez and colleagues have shown that eDNA is highly abundant in Xanthomonas citri mature biofilm and accumulates throughout biofilm development (Sena-Vélez et al 2016). In addition, extracellular DNase treatment was able to inhibit biofilm formation but only partially dispersed mature biofilm, suggesting that eDNA plays a significant role in early stage of biofilm establishment (Sena-Vélez et al 2016).…”

“…Specifically, Sena-Vélez and colleagues have shown that eDNA is highly abundant in Xanthomonas citri mature biofilm and accumulates throughout biofilm development (Sena-Vélez et al 2016). In addition, extracellular DNase treatment was able to inhibit biofilm formation but only partially dispersed mature biofilm, suggesting that eDNA plays a significant role in early stage of biofilm establishment (Sena-Vélez et al 2016). Other factors that were reported to be critical for Xanthomonas biofilm formation include cell surface LPS and lipoproteins (Li and Wang 2011a;Li and Wang 2011b;Petrocelli et al 2012;Yan, Hu and Wang 2012), the bacterial flagellum and type IV pili (Malamud et al 2011;Dunger et al 2014).…”

Extracellular DNA in natural environments: features, relevance and applications

“…Other biofilms formed by environmental microorganisms, plant pathogens (Sena-Velez et al 2016), or in the activated sludge during wastewater treatment have been studied to a lesser extent (e.g. Dominiak et al 2011).…”

Recent advances in the understanding of Xanthomonas citri ssp. citri pathogenesis and citrus canker disease management

“…These microcolonies are tightly packed bacteria, sometimes in regular hexagonal formation, separated by channels of water (Rigano et al, 2007). Xanthan and the presence of extracellular DNA are important during the early stages of biofilm formation (Rigano et al, 2007;Sena-V elez et al, 2016). The xanthan in the biofilm provides protection from both desiccation and plant antimicrobial compounds (Dow et al, 2003).…”