Exploring new roles for therpoSgene in the survival and virulence of the fire blight pathogenErwinia amylovora

Abstract

Erwinia amylovora causes fire blight in economically important plants of the family Rosaceae. This bacterial pathogen spends part of its life cycle coping with starvation and other fluctuating environmental conditions. In many Gram-negative bacteria, starvation and other stress responses are regulated by the sigma factor RpoS. We obtained an E. amylovora rpoS mutant to explore the role of this gene in starvation responses and its potential implication in other processes not yet studied in this pathogen. Results showed that E. amylovora needs rpoS to develop normal starvation survival and viable but nonculturable (VBNC) responses. Furthermore, this gene contributed to stationary phase cross-protection against oxidative, osmotic, and acid stresses and was essential for cross-protection against heat shock, but nonessential against acid shock. RpoS also mediated regulation of motility, exopolysaccharide synthesis, and virulence in immature loquats, but not in pear plantlets, and contributed to E. amylovora survival in nonhost tissues during incompatible interactions. Our results reveal some unique roles for the rpoS gene in E. amylovora and provide new knowledge on the regulation of different processes related to its ecology, including survival in different environments and virulence in immature fruits.

An Erwinia amylovora yjeK mutant exhibits reduced virulence, increased chemical sensitivity and numerous environmentally dependent proteomic alterations

“…Similarly, the reduced abundance of several flagellar proteins, including FliC and FliL, in yjeK ::Tn 5 , compared with the wild‐type, could contribute to the reduced motility of the mutant. Interestingly, the sigma factor protein RpoS (GI 291200225) was moderately decreased in yjeK ::Tn 5 in both rich and minimal media, and rpoS is required for normal stationary phase cross‐protection against acid and oxidative stress, as well as normal swimming motility and amylovoran production in E. amylovora (Santander et al ., ).…”

“…Similarly, the reduced abundance of several flagellar proteins, including FliC and FliL, in yjeK::Tn5, compared with the wild-type, could contribute to the reduced motility of the mutant. Interestingly, the sigma factor protein RpoS (GI 291200225) was moderately decreased in yjeK::Tn5 in both rich and minimal media, and rpoS is required for normal stationary phase crossprotection against acid and oxidative stress, as well as normal swimming motility and amylovoran production in E. amylovora (Santander et al, 2014). Notably, the ability of yjeK::Tn5 to elicit an HR on tobacco leaves suggests that the T3SS is intact and functional, at least sufficiently for the delivery of HrpN, which is primarily responsible for the HR caused by E. amylovora in tobacco (Wei et al, 1992).…”

Erwinia amylovora catalases KatA and KatG are virulence factors and delay the starvation‐induced viable but non‐culturable (VBNC) response

“…In the latter case, immature pears ( Pyrus communis cv. Devoe) were surface disinfected with 2% (w/v) sodium hypochlorite (NaOCl), as described previously (Santander et al ., ), sliced into 1‐cm‐thick pieces and surface inoculated with 0.2 mL of E. amylovora overnight (stationary phase) culture in MBMANic + 0.2% Glc. Fruits were incubated for 72 h at 28 °C inside a wet chamber, and bacterial cells recovered from the inoculated slice surface were resuspended in fresh medium (MBMANic + 0.2% Glc).…”

“…To confirm the results, E. amylovora was re‐isolated from symptomatic fruits and identified by specific PCR, as described elsewhere [European and Mediterranean Plant Protection Organization (EPPO), ; Santander et al ., ].…”

“…In addition, starvation and other stresses causing growth arrest, which are experienced during epiphytic stages, in soil, rainwater, vectors, etc., lead to the intracellular accumulation of H 2 O 2 (McDougald et al, 2002). Related to this, the starvationinduced viable but non-culturable (VBNC) response (Oliver, 2010;Ordax et al, 2012Ordax et al, , 2015Santander et al, 2012Santander et al, , 2014a, characterized by the inability of viable cells to grow on routine solid media (Oliver, 2010;Ramamurthy et al, 2014), has been linked to the inability to detoxify H 2 O 2 (Flores-Cruz and Allen, 2011;Imamura et al, 2015;Kong et al, 2004Kong et al, , 2014Zhong et al, 2009). However, the exact contribution of catalases to this process has not yet been determined.…”