Plasmids manipulate bacterial behaviour through translational regulatory crosstalk

Abstract

Beyond their role in horizontal gene transfer, conjugative plasmids commonly encode homologues of bacterial regulators. Known plasmid regulator homologues have highly targeted effects upon the transcription of specific bacterial traits. Here, we characterise a plasmid translational regulator, RsmQ, capable of taking global regulatory control in Pseudomonas fluorescens and causing a behavioural switch from motile to sessile lifestyle. RsmQ acts as a global regulator, controlling the host proteome through direct interaction with host mRNAs and interference with the host’s translational regulatory network. This mRNA interference leads to large-scale proteomic changes in metabolic genes, key regulators, and genes involved in chemotaxis, thus controlling bacterial metabolism and motility. Moreover, comparative analyses found RsmQ to be encoded on a large number of divergent plasmids isolated from multiple bacterial host taxa, suggesting the widespread importance of RsmQ for manipulating bacterial behaviour across clinical, environmental, and agricultural niches. RsmQ is a widespread plasmid global translational regulator primarily evolved for host chromosomal control to manipulate bacterial behaviour and lifestyle.

Compensatory mutations reducing the fitness cost of plasmid carriage occur in plant rhizosphere communities

“…These results are consistent with our earlier findings that RsmQ interferes with the host Rsm pathway (Thompson et al 2023 ), which is itself induced by gac loss-of-function mutations. Furthermore, rsmQ deletion recovers certain plasmid-induced phenotypes in SBW25 (Thompson et al 2023 ), which may slightly reduce the fitness cost of plasmid carriage in some environments, but in turn may reveal other traits to selection, as seen here for asparagine metabolism.…”

“…In addition, we observed mutations in PFLU2452 encoding a putative asparagine synthase exclusively in evolved pQBR103𝚫rsmQ carriers; two such mutations co-occurred alongside gacS mutations whereas one did not. Intriguingly, our previous work shows that acquisition of pQBR103 decreases SBW25 growth on asparagine as a sole carbon source, but that this growth defect is negated by deletion of rsmQ (Thompson et al 2023 ), suggesting that rsmQ itself alters regulation of asparagine metabolism in SBW25. These results are consistent with our earlier findings that RsmQ interferes with the host Rsm pathway (Thompson et al 2023 ), which is itself induced by gac loss-of-function mutations.…”

“…Intriguingly, our previous work shows that acquisition of pQBR103 decreases SBW25 growth on asparagine as a sole carbon source, but that this growth defect is negated by deletion of rsmQ (Thompson et al 2023 ), suggesting that rsmQ itself alters regulation of asparagine metabolism in SBW25. These results are consistent with our earlier findings that RsmQ interferes with the host Rsm pathway (Thompson et al 2023 ), which is itself induced by gac loss-of-function mutations. Furthermore, rsmQ deletion recovers certain plasmid-induced phenotypes in SBW25 (Thompson et al 2023 ), which may slightly reduce the fitness cost of plasmid carriage in some environments, but in turn may reveal other traits to selection, as seen here for asparagine metabolism.…”

“…The SBW25 Gac–Rsm regulon includes a variety of traits that may affect colonization and competitiveness on plants, including secreted secondary metabolites, motility, and biofilm formation (Cheng et al 2013 ), suggesting that loss of this system may be detrimental in complex natural environments such as plants. Interestingly, the pQBR103 sequence encodes an Rsm homologue, PQBR443 (named rsmQ ) (Tett et al 2007 , Hall et al 2015 , Thompson et al 2023 ). RsmQ interacts with Gac–Rsm signalling within SBW25 cells to alter the expression of chemotaxis, motility, and metabolic phenotypes (Thompson et al 2023 ) and could thus alter the fitness effect of pQBR103 and the potential for compensatory mutation in plant rhizosphere communities.…”

“…Interestingly, the pQBR103 sequence encodes an Rsm homologue, PQBR443 (named rsmQ ) (Tett et al 2007 , Hall et al 2015 , Thompson et al 2023 ). RsmQ interacts with Gac–Rsm signalling within SBW25 cells to alter the expression of chemotaxis, motility, and metabolic phenotypes (Thompson et al 2023 ) and could thus alter the fitness effect of pQBR103 and the potential for compensatory mutation in plant rhizosphere communities.…”