Recently, C9-1 has been reassigned from find more P. agglomerans to the novel species P. vagans based on its gyrB sequence

(Brady et al., 2009; Rezzonico et al., 2009). Pantoea agglomerans and P. vagans isolates are generally considered nonpathogenic. Most P. agglomerans isolates lack virulence determinants such as type III secretion systems (T3SS), while some contain a T3SS described as a nonpathogenic type (Rezzonico et al., 2009). The phytopathogenicity of subspecies P. agglomerans pv. gypsophilae and pv. betae can be attributed to recently acquired large plasmids that carry a pathogenic type of T3SS and other virulence determinants (Ezra et al., 2000; Mor et al., 2001; Guo et al., 2002; Manulis & Barash, 2003; Nissan et IDH inhibitor al., 2006). Virulence and ecological fitness genes in phytopathogenic P. agglomerans pathovars, Pantoea stewartii and Pantoea ananatis are regulated by an autoinducer-1 quorum-sensing system involving N-acyl-homoserine lactone (AHL) signals (von Bodman et al., 2003; Morohoshi et al., 2007; Chalupowicz et al., 2008, 2009). Several Pantoea species are yellow pigmented (Grimont & Grimont, 2005) due to production of carotenoids (Sandmann et al., 1990; Hundle et al., 1994). Nonpigmented variants have been reported, arising spontaneously at a low frequency (10−2–10−3) after extended cultivation on nutrient-rich laboratory media (Chatterjee

& Gibbins, 1971; Gantotti & Beer, 1982; Lindh et al., 1991). These reports described physiological changes, such as thiamine deficiency and negative reactions with citrate or maltose, and lack of

reversion to a wild-type phenotype, suggesting that such phenotypic changes are due to plasmid loss, although this has never been confirmed experimentally. We have found that P. vagans C9-1 carries three plasmids: two plasmids of 168 kb (pPag1) and 166 kb (pPag2), and the 530-kb megaplasmid named pPag3 (Smits et al., 2009). The phenotypic effects of these plasmids in P. vagans C9-1 have not been described previously. Sequence analysis of the megaplasmid revealed that carotenoid biosynthesis Thymidylate synthase is encoded on plasmid pPag3. We obtained a nonpigmented variant of P. vagans C9-1 that lost the ability to synthesize thiamine and metabolize maltose, features that were also encoded by plasmid pPag3 genes. The aim of this study was to use the nonpigmented variant that lacks pPag3, representing over 10% of the total genome, in order to confirm functional phenotypes for annotated plasmid genes. Bacteria were routinely grown at 28 °C on Luria–Bertani (LB) (Sambrook et al., 1989). Carbon source (glucose, sorbitol, maltose or sucrose) and thiamine (5 μg mL−1) utilization assays were conducted in amended M9 minimal medium (Sambrook et al., 1989). Resistance to ampicillin (2.5–200 μg mL−1) or tellurite (50 μg mL−1) was determined on amended LB agar.