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

Abstract

The life cycle of the plant pathogen Erwinia amylovora comprises periods inside and outside the host in which it faces oxidative stress caused by hydrogen peroxide (H O ) and other compounds. The sources of this stress are plant defences, other microorganisms and/or exposure to starvation or other environmental challenges. However, the functional roles of H O -neutralizing enzymes, such as catalases, during plant-pathogen interactions and/or under starvation conditions in phytopathogens of the family Erwiniaceae or closely related families have not yet been investigated. In this work, the contribution of E. amylovora catalases KatA and KatG to virulence and survival in non-host environments was determined using catalase gene mutants and expression, as well as catalase activity analyses. The participation of E. amylovora exopolysaccharides (EPSs) in oxidative stress protection was also investigated. Our study revealed the following: (i) a different growth phase regulation of each catalase, with an induction by H O and host tissues; (ii) the significant role of E. amylovora catalases as virulence and survival factors during plant-pathogen interactions; (iii) the induction of EPSs by H O despite the fact that apparently they do not contribute to protection against this compound; and (iv) the participation of both catalases in the detoxification of the starvation-induced intracellular oxidative stress, favouring the maintenance of culturability, and hence delaying the development of the viable but non-culturable (VBNC) response.

Chromosomally Encoded hok-sok Toxin-Antitoxin System in the Fire Blight Pathogen Erwinia amylovora: Identification and Functional Characterization

“…Reactive oxygen species, including hydrogen peroxide, are common sources of DNA damage during bacterial stress (57,58), and supplementation with hydrogen peroxide or deletion of catalase genes is a trigger of filamentation in some species (59,60). During infection, E. amylovora must contend with ROS generated by the host defense response (40,(61)(62)(63). Regulation of bacterial catalase activity has been previously shown in the type II TA systems MqsR/MqsA and YafQ/DinJ in E. coli, where the antitoxins MqsA and DinJ both affect bacterial catalase by decreasing the level of RpoS, a positive regulator of katG and katE catalase genes (64)(65)(66).…”

“…7B). Catalase activity in E. amylovora has recently been shown to be conferred by two genes, katA and katG, with katA playing the major role (40). To further explore the mechanism of how the hok-sok locus affects catalase activity in E. amylovora, we constructed transcriptional fusions of each of the katA and katG promoters to a green fluorescent protein reporter.…”

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

“…The yjeK required for full Erwinia amylovora virulence reduced amylovoran production in the yjeK::Tn5 mutant could contribute to its decreased virulence. Although EPS production correlates with survival in H 2 O 2 in plant-associated bacterial species (Lehman and Long, 2013), the existence of a correlation between exopolysaccharide (amylovoran and levan) production and H 2 O 2 sensitivity is unclear in E. amylovora (Santander et al, 2017). In any case, it is unlikely that the moderately decreased amylovoran production by yjeK::Tn5 by itself can account for its increased H 2 O 2 sensitivity, as the yjeK::Tn5 mutant is more sensitive to H 2 O 2 than an amylovoran-deficient E. amylovora mutant without detectable amylovoran.…”

Three Hfq‐dependent small RNAs regulate flagellar motility in the fire blight pathogen Erwinia amylovora

“…When E. amylovora invades plant host tissue, the host induces defense mechanisms, such as production of reactive oxygen species to fight back against the bacteria (Venisse et al ., ; Kamber et al ., ). E. amylovora suppresses these host defenses via the action of effector proteins translocated into host cells via the type III secretion system and mitigates the effects of host defenses with its own counter‐defenses, such as catalases that neutralize the damaging potential of reactive oxygen species (Kim et al ., ; Bogdanove et al ., ; Santander et al ., ). However, overcoming host defenses is insufficient for infection, because E. amylovora cells must actively move into host plant tissues.…”