Differential Expression of Paraburkholderia phymatum Type VI Secretion Systems (T6SS) Suggests a Role of T6SS-b in Early Symbiotic Interaction

Abstract

Paraburkholderia phymatum STM815, a rhizobial strain of the Burkholderiaceae family, is able to nodulate a broad range of legumes including the agriculturally important Phaseolus vulgaris (common bean). P. phymatum harbors two type VI Secretion Systems (T6SS-b and T6SS-3) in its genome that contribute to its high interbacterial competitiveness in vitro and in infecting the roots of several legumes. In this study, we show that P. phymatum T6SS-b is found in the genomes of several soil-dwelling plant symbionts and that its expression is induced by the presence of citrate and is higher at 20/28°C compared to 37°C. Conversely, T6SS-3 shows homologies to T6SS clusters found in several pathogenic Burkholderia strains, is more prominently expressed with succinate during stationary phase and at 37°C. In addition, T6SS-b expression was activated in the presence of germinated seeds as well as in P. vulgaris and Mimosa pudica root nodules. Phenotypic analysis of selected deletion mutant strains suggested a role of T6SS-b in motility but not at later stages of the interaction with legumes. In contrast, the T6SS-3 mutant was not affected in any of the free-living and symbiotic phenotypes examined. Thus, P. phymatum T6SS-b is potentially important for the early infection step in the symbiosis with legumes.

The hologenome of Osedax frankpressi reveals the genetic interplay for the symbiotic digestion of vertebrate bone

“…Accordingly, Osedax ’s Oceanospirillales endosymbiont is metabolically versatile ( 24, 38 ), encoding a significantly larger repertoire of genes involved in sugar and lipid transport as well as carbohydrate, amino acid, and vitamin synthesis compared to the chemolithoautotrophic endosymbionts of Vestimentifera (Figure 3D). An enrichment of secretion systems likely allows the endosymbiont of Osedax to outcompete other microbes to occupy the bacteriocytes, as has been shown in other symbiotic systems such as Vibrio fischeri -bobtail squid and in the Rhizobia symbionts of legumes ( 64, 65 ). After the Osedax-Oceanospirillales symbiosis is established, the bacteria may transform the bone-derived nutrients acquired by the host into a more diverse set of macronutrients that may be either directly exported to the host or acquired through symbiont digestion ( 26 ) (Figure 9A).…”

A novel function of the key nitrogen-fixation activator NifA in beta-rhizobia: Repression of bacterial auxin synthesis during symbiosis

“…P. phymatum wild-type containing the empty pPROBE vector (WT-pPROBE) was used as negative control. As a positive control, the P. phymatum reporter strain p nodB , containing the promotor of the nodB gene (Bphy_7722) fused to gfp , was employed (WT- p nodB ) ( Hug et al, 2021 ). The gene nodB is involved in the synthesis of the backbone of NFs, and its expression is known to be induced by flavonoids secreted by the host plant ( Guerreiro et al, 1997 ).…”

Distinct genomic routes underlie transitions to specialised symbiotic lifestyles in deep sea annelid worms

“…Accordingly, Osedax's Oceanospirillales endosymbiont is metabolically versatile 24,38 , encoding a significantly larger repertoire of genes involved in sugar and lipid transport as well as carbohydrate, amino acid, and vitamin synthesis compared to the chemolithoautotrophic endosymbionts of Vestimentifera (Figure 3D). An enrichment of secretion systems compared to Vestimentiferan symbionts likely allows the endosymbiont of Osedax to outcompete other microbes as it continually colonize new bacteriocytes, as has been shown in other symbiotic systems such as Vibrio fischeri-bobtail squid and in the Rhizobia symbionts of legumes 64,65 . After the Osedax-Oceanospirillales symbiosis is established, the bacteria may transform the bone-derived nutrients acquired by the host into a more diverse set of macronutrients that may be either directly exported to the host or acquired through symbiont digestion 26 (Figure 9A).…”