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Amstutz, J.

Publications and source records attributed to Amstutz, J..

2 recordsLinked to original sources
bioRxiv2024

Activation of the ChvG-ChvI pathway promotes multiple survival strategies during cell wall stress in Agrobacterium tumefaciens

Agrobacterium tumefaciens shifts from a free-living soil bacterium to a plant-invading state upon encountering the plant root microenvironment. The acid-induced two- component sensor system ChvG-ChvI drives this shift and triggers a complex transcriptional program that promotes host invasion and survival against host immune defenses. Remarkably, ChvG-ChvI is also activated under cell wall stress conditions suggesting that the transcriptional response may have a broader function. Here, we find that blocking cell wall synthesis either genetically or chemically leads to ChvG-ChvI activation. Mutations in key cell wall synthesis or outer membrane proteins, such as PBP1a, FtsW, and AopA1, suppress ChvG-ChvI activation suggesting that providing structural integrity is a primary function of the ChvG-ChvI regulon. Here, we investigated regulon components for this function. First, the exopolysaccharide succinoglycan confers tolerance to multiple {beta}-lactam antibiotics targeting different enzymes by forming a protective barrier around the cells. Next, a Class D {beta}-lactamase is expressed which may contribute to the high level of {beta}-lactam resistance in A. tumefaciens. Finally, outer membrane remodeling compensates for the accumulation of cell wall damage by providing structural integrity. Overall, we expand our understanding of mechanisms driving ChvG-ChvI activation and {beta}-lactam resistance in a bacterial plant pathogen. Significance Statements.O_LIActivation of the ChvG-ChvI two component system promotes survival when the bacterial cell walls are damaged by a variety of genetic or chemical approaches C_LIO_LIThe ChvG-ChvI dependent production of the exopolysaccharide succinoglycan, {beta}-lactamase Cbl activity, and outer membrane proteome remodeling all contribute to survival in the presence of {beta}-lactam antibiotics C_LIO_LIImproved understanding of bacterial stress responses that promote antibiotic tolerance and resistance has the potential to inform development of novel drug targets C_LI

microbiology↗
bioRxiv2024

Essentiality of LD-Transpeptidation in Agrobacterium tumefaciens

Peptidoglycan (PG), a mesh-like structure which is the primary component of the bacterial cell wall, is crucial to maintain cell integrity and shape. While most bacteria rely on penicillin binding proteins (PBPs) for crosslinking, some species employ LD-transpeptidases (LDTs). Unlike PBPs, the essentiality and biological functions of LDTs remain largely unclear. The Hyphomicrobiales order of the Alphaproteobacteria, known for their polar growth, have PG which is unusually rich in LD-crosslinks, suggesting that LDTs may play a more significant role in PG synthesis in these bacteria. Here, we investigated LDTs in the plant pathogen Agrobacterium tumefaciens and found that LD-transpeptidation, resulting from at least one of 14 putative LDTs present in this bacterium, is essential for its survival. Notably, a mutant lacking a distinctive group of 7 LDTs which are broadly conserved among the Hyphomicrobiales exhibited reduced LD-crosslinking and tethering of PG to outer membrane {beta}-barrel proteins. Consequently, this mutant suffered severe fitness loss and cell shape rounding, underscoring the critical role played by these Hyphomicrobiales-specific LDTs in maintaining cell wall integrity and promoting elongation. Tn-sequencing screens further revealed non-redundant functions for A. tumefaciens LDTs. Specifically, Hyphomicrobiales-specific LDTs exhibited synthetic genetic interactions with division and cell cycle proteins, and a single LDT from another group. Additionally, our findings demonstrate that strains lacking all LDTs except one displayed distinctive phenotypic profiles and genetic interactions. Collectively, our work emphasizes the critical role of LD-crosslinking in A. tumefaciens cell wall integrity and growth and provides insights into the functional specialization of these crosslinking activities.

microbiology↗