Persulfide-Responsive Transcription Factor SqrR Regulates Gene Transfer and Biofilm Formation via the Metabolic Modulation of Cyclic di-GMP in Rhodobacter capsulatus

Abstract

Bacterial phage-like particles (gene transfer agents—GTAs) are widely employed as a crucial genetic vector in horizontal gene transfer. GTA-mediated gene transfer is induced in response to various stresses; however, regulatory mechanisms are poorly understood. We found that the persulfide-responsive transcription factor SqrR may repress the expression of several GTA-related genes in the photosynthetic bacterium Rhodobacter capsulatus. Here, we show that the sqrR deletion mutant (ΔsqrR) produces higher amounts of intra- and extracellular GTA and gene transfer activity than the wild type (WT). The transcript levels of GTA-related genes are also increased in ΔsqrR. In spite of the presumption that GTA-related genes are regulated in response to sulfide by SqrR, treatment with sulfide did not alter the transcript levels of these genes in the WT strain. Surprisingly, hydrogen peroxide increased the transcript levels of GTA-related genes in the WT, and this alteration was abolished in the ΔsqrR strain. Moreover, the absence of SqrR changed the intracellular cyclic dimeric GMP (c-di-GMP) levels, and the amount of c-di-GMP was correlated with GTA activity and biofilm formation. These results suggest that SqrR is related to the repression of GTA production and the activation of biofilm formation via control of the intracellular c-di-GMP levels.

Loss of the Rhodobacter capsulatus Serine Acetyl Transferase Gene, cysE1 , Impairs Gene Transfer by Gene Transfer Agents and Biofilm Phenotypes

“… R. capsulatus biofilm production has not been extensively studied. However, one study has linked biofilm production to intracellular cyclic di-GMP (c-di-GMP) levels and the persulfide-responsive transcription factor SqrR ( 11 ). The EPS biosynthesis and export pathway has been identified, and this pathway is controlled by quorum sensing ( 12 – 14 ).…”

Formal Recognition and Classification of Gene Transfer Agents as Viriforms

“…Since the exaptation events, however, the three families have evolved as part of the host genomes (Esterman et al 2021; Lang et al 2002; Lang and Beatty 2007; Shakya et al 2017), in the case of the rhodogtaviriformids for hundreds of millions of years (Shakya et al 2017). As a result, GTAs effectively became a component of cellular genomes, integrated into cellular regulatory circuits that also control processes such as motility, quorum sensing, extracellular polysaccharide synthesis, and biofilm formation (Lang et al 2017; Pallegar et al 2020; Shimizu et al 2022). There is also mounting evidence that GTA genes experience selective pressures to be maintained in their host genomes (Kogay et al 2020; Lang et al 2012).…”

Sulfane Sulfur Is an Intrinsic Signal for the Organic Peroxide Sensor OhrR of Pseudomonas aeruginosa

“…Sulfane sulfur has been identified as the effector for gene regulators, such as FisR [ 14 ], CstR [ 15 ], and SqrR [ 16 ], which regulate sulfur metabolism in bacteria. Furthermore, SqrR also regulates gene transfer and biofilm formation in Rhodobacter capsulatus [ 17 ]. Several gene regulators that regulate other functions also respond to sulfane sulfur.…”