Phosphorus limitation increases attachment in Agrobacterium tumefaciens and reveals a conditional functional redundancy in adhesin biosynthesis

Abstract

Bacterial responses to phosphorus limitation, commonly inorganic phosphate (Pi), are important survival mechanisms in a variety of environments. The two-component sensor kinase PhoR and its cognate response regulator PhoB are central to the Pi limitation response of many bacteria and control the large Pho regulon. Limitation for Pi significantly increased attachment and biofilm formation by the plant pathogen Agrobacterium tumefaciens, and this was driven by PhoB. Surprisingly, it was also found that both phoR and phoB were essential in A. tumefaciens. Expression of a plasmid-borne copy of the low affinity Pi transporter (pit) from Sinorhizobium meliloti in A. tumefaciens abolished the phoB and phoR essentiality in A. tumefaciens and allowed direct demonstration of the requirement for this regulatory system in the biofilm response. Increased attachment under Pi limitation required a unipolar polysaccharide (UPP) adhesin. Mutation of a polyisoprenylphosphate hexose-1-phosphate transferase (PHPT) called uppE abolished UPP production and prevented surface attachment under Pi-replete conditions, but this was rescued under Pi limitation, and this rescue required phoB. In low Pi conditions, either uppE or a paralogous gene Atu0102 is functionally redundant, but only uppE functions in UPP synthesis and attachment when Pi is replete. This conditional functional redundancy illustrates the influence of phosphorus availability on A. tumefaciens surface colonization.

Agrobacterium-Mediated Plant Transformation: Biology and Applications

“…The UPP consists of at least two types of sugars, N-acetylglucosamine and N-acetylgalactosamine (Tomlinson and Fuqua, 2009;Xu et al, 2012). The A. tumefaciens UPP biosynthetic mutant uppE is defective in both bacterial attachment and biofilm formation, supporting the idea that the UPP plays an important role in bacterial attachment (Xu et al, 2012;Heindl et al, 2014). Interestingly, while A. tumefaciens attachment to plant tissues often leads to biofilm formation and is required for virulence, A. tumefaciens strains lacking UPP or impaired in biofilm formation remain efficient in T-DNA transfer.…”

“…Aside from the cellulose and cyclic β-1,2-glucan, A. tumefaciens produces an additional exopolysaccharide, unipolar polysaccharide (UPP), that participates in bacterial attachment (Tomlinson and Fuqua, 2009;Li et al, 2011;Xu et al, 2012;Heindl et al, 2014). The unipolar polysaccharide helps A. tumefaciens cells attach to the plant surfaces in a polar fashion because the UPP is mainly produced at the cell pole.…”

“…The unipolar polysaccharide helps A. tumefaciens cells attach to the plant surfaces in a polar fashion because the UPP is mainly produced at the cell pole. The UPP is rarely observed in A. tumefaciens planktonic cells or in colonies on solid media, suggesting that the production of UPP is a signature of A. tumefaciens permanent attachment (Li et al, 2011;Xu et al, 2012;Xu et al, 2013). The UPP consists of at least two types of sugars, N-acetylglucosamine and N-acetylgalactosamine (Tomlinson and Fuqua, 2009;Xu et al, 2012).…”

“…The UPP is rarely observed in A. tumefaciens planktonic cells or in colonies on solid media, suggesting that the production of UPP is a signature of A. tumefaciens permanent attachment (Li et al, 2011;Xu et al, 2012;Xu et al, 2013). The UPP consists of at least two types of sugars, N-acetylglucosamine and N-acetylgalactosamine (Tomlinson and Fuqua, 2009;Xu et al, 2012). The A. tumefaciens UPP biosynthetic mutant uppE is defective in both bacterial attachment and biofilm formation, supporting the idea that the UPP plays an important role in bacterial attachment (Xu et al, 2012;Heindl et al, 2014).…”

Enhancement of Biofilm Formation on Pyrite by Sulfobacillus thermosulfidooxidans

“…Phosphorus is a very important element for organisms, but the response of bacteria to limited phosphate can be different. Phosphorus limitation can increase attachment in case of Agrobacterium tumefaciens [28]. Bellenberg et al also described that growth under phosphate starvation conditions resulted in an enhancement of EPS production and well-formed biofilms of A. ferrooxidans [29].…”