The Phospholipid N-Methyltransferase and Phosphatidylcholine Synthase Pathways and the ChoXWV Choline Uptake System Involved in Phosphatidylcholine Synthesis Are Widely Conserved in Most, but Not All Brucella Species.

Beatriz Aragón-Aranda,Amaia Zúñiga-Ripa,Ignacio Moriyón,Christian Sohlenkamp,Maite Iriarte,Raquel Conde-Álvarez,Miguel Ángel Vences-Guzmán,María Jesús De Miguel,Leticia Lázaro-Antón,Leyre Palacios-Chaves,Pilar M Muñoz,Miriam Salvador-Bescós

doi:10.3389/fmicb.2021.614243

Abstract

The brucellae are facultative intracellular bacteria with a cell envelope rich in phosphatidylcholine (PC). PC is abundant in eukaryotes but rare in prokaryotes, and it has been proposed that Brucella uses PC to mimic eukaryotic-like features and avoid innate immune responses in the host. Two PC synthesis pathways are known in prokaryotes: the PmtA-catalyzed trimethylation of phosphatidylethanolamine and the direct linkage of choline to CDP-diacylglycerol catalyzed by the PC synthase Pcs. Previous studies have reported that B. abortus and B. melitensis possess non-functional PmtAs and that PC is synthesized exclusively via Pcs in these strains. A putative choline transporter ChoXWV has also been linked to PC synthesis in B. abortus. Here, we report that Pcs and Pmt pathways are active in B. suis biovar 2 and that a bioinformatics analysis of Brucella genomes suggests that PmtA is only inactivated in B. abortus and B. melitensis strains. We also show that ChoXWV is active in B. suis biovar 2 and conserved in all brucellae except B. canis and B. inopinata. Unexpectedly, the experimentally verified ChoXWV dysfunction in B. canis did not abrogate PC synthesis in a PmtA-deficient mutant, which suggests the presence of an unknown mechanism for obtaining choline for the Pcs pathway in Brucella. We also found that ChoXWV dysfunction did not cause attenuation in B. suis biovar 2. The results of these studies are discussed with respect to the proposed role of PC in Brucella virulence and how differential use of the Pmt and Pcs pathways may influence the interactions of these bacteria with their mammalian hosts.

Highlights

Brucellosis is a worldwide extended zoonosis caused by bacteria of the genus Brucella, a group of facultative intracellular pathogens belonging to the α-2 class of Proteobacteria
Introduction of a we examined the genome sequences of other Brucella strains representing different species and biovars, we found that all of the B. melitensis and B. abortus strains examined encode pmtA alleles carrying the same mutations described in B. abortus 2308 and B. melitensis 16M
Studies employing B. abortus 2308 and B. melitensis 16M suggested that the brucellae may rely exclusively on the phosphatidylcholine synthase (Pcs) pathway for PC biosynthesis based on the presence of dysfunctional pmtA genes (Comerci et al, 2006)

Summary

Introduction

Brucellosis is a worldwide extended zoonosis caused by bacteria of the genus Brucella, a group of facultative intracellular pathogens belonging to the α-2 class of Proteobacteria. B. melitensis, B. abortus, and B. suis are the best-known Brucella species and they were divided long ago into biovars according to phenotypic criteria (Alton et al, 1988; Moreno, 2014). B. inopinata, B. vulpis, and B. papionis are species proposed for a few isolates respectively obtained from a breast implant (one strain), fox mandibular lymph nodes (2 strains), and abortion-related materials in captive baboons (two strains) (Scholz et al, 2010, 2016; Whatmore et al, 2014). All these species except B. inopinata form a core group separated from early diverging clades closer to other α-2 Proteobacteria. Diverging brucellae include B. inopinata and unnamed Brucella isolates from Australian rodents and frogs (Wattam et al, 2014; Soler-Lloréns et al, 2016; Al Dahouk et al, 2017)

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