Description of copper tolerantXanthomonas citrisubsp.citriand genotypic comparison with sensitive and resistant strains

Abstract

The copper-based products widely used for control of citrus canker may lead to the development of Xanthomonas citri subsp. citri (X. citri) resistant to copper (Cu R ). However, the study of copper sensitivity of X. citri strains from Paran a state, Brazil, did not reveal the existence of Cu R , but copper tolerant (Cu T ) strains. The aim of this study was to describe for the first time the existence of Cu T X. citri and compare the genetic determinants that differentiate the Cu T strains from the sensitive (Cu S ) and Cu R strains. Cu T strains supported intermediate concentrations of copper in comparison to Cu S and Cu R . Cu T strains lack the gene clusters copLAB or copABCD responsible for copper resistance in Cu R strains and the large plasmids (c. ≥200 kb) that normally carry these genes. The nucleotide sequences of chromosomal homologous genes cohLAB, involved in copper homeostasis, were 100% similar in strains of all phenotypes. Cu T strains differed from Cu S strains by the higher expression of the homologous chromosomal genes cohA and cohB in the presence of copper. Cu T X. citri strains are not precursors of Cu R strains and do not pose a threat to the efficient use of copper-based bactericides for management of citrus canker in citrus orchards. Copper resistance and tolerance are distinct phenotypes and should not be used as synonyms. The proper characterization of the sensitivity to copper leads to a more confident monitoring of the distribution of copper resistant populations of X. citri and adoption of containment measures only when necessary.

Copper Kills Escherichia coli Persister Cells

“…Unlike many antibiotics, copper resistance is unlikely to occur spontaneously [70], requiring the acquisition of plasmid-based operons to enhance copper homeostasis [71]. This may explain our unsuccessful attempts to recover copper-resistant mutants using both KEIO and ASKA libraries; however, more testing is required using longer times for mutants to occur and strains that are more medically relevant.…”

Diversity and copper resistance of Xanthomonas affecting citrus

“…The CuT strains differ from CuR strains by the lack of copper resistance genes and the large plasmids that normally carry these genes. Moreover, CuT strains differed from CuS isolates by the higher expression of the homologous chromosomal genes, mainly cohA and cohB, in the presence of copper (Marin et al 2019).…”

“…However, recently, copper tolerant (CuT) strains of X. citri subsp. citri have been described for the first time (Marin et al 2019). The characterization of reference strains for sensitivity or resistance to copper in previous studies (Basim et al 2005;Behlau et al 2011;2012a, 2012b contributed to the description of CuT strains.…”

“…This is probably due to the fact that, in contrast to resistance, which may be assessed by the presence of specific cop genes, tolerance is more difficult to characterize due to the lack of a strong or evident genetic marker (Brauner et al 2016). More importantly, CuT strains are not precursors of CuR X. citri, nor do they pose a threat to the efficient use of copper-based bactericides for management of citrus canker in orchards (Marin et al 2019).…”

Xanthomonas citri subsp. citri: host interaction and control strategies

“…However, this control measure has posed considerable risks to the environment, as residual amounts of copper can cause unwanted damage to the soil and plants (Hippler et al 2018). Moreover, copper resistance in X. citri has already been reported (Behlau et al 2010(Behlau et al , 2013Marin et al 2019), which raises concerns about its widespread use in citrus plantations.…”