The versatile TolC‐like Slr1270 in the cyanobacterium Synechocystis sp. PCC 6803

Abstract

Here we report on the functional characterization of the hypothetical protein Slr1270, a TolC homologue in Synechocystis sp. PCC 6803. Analysis of a slr1270 insertion deletion mutant and respective wild-type revealed that the mutant presents increased susceptibility to antibiotics. In addition, a detailed study of the exoproteome showed that Slr1270 mediates protein secretion. Among the protein substrates dependent on Slr1270 function, we found the S-layer structural component. Electron microscopy studies of the slr1270 mutant showed that the S-layer is indeed absent. The requirement of functional Slr1270 for protein secretion and drug resistance mechanisms suggests that Slr1270 plays a role similar to that described for TolC in other bacteria. Additional phenotypic traits could also be observed, including slower growth rates at low temperature, impairment in biofilm formation and increased activity of enzymes detoxifying reactive oxygen species. Furthermore, an increased capacity of outer membrane vesicles (OMVs) formation and release was also found in the slr1270 mutant, a feature that has not yet been observed in bacteria lacking TolC. This work highlights the marked physiological fitness that the TolC-like Slr1270 bestows to the photosynthetic model Synechocystis sp. PCC 6803 and presents a valuable model for studying OMVs formation and release.

Identification of inner membrane translocase components of TolC‐mediated secretion in the cyanobacterium Synechocystis sp. PCC 6803

“…S3). To establish whether the proteins encoded by the disrupted genes have any effect on cell growth or viability, the wild‐type and mutant strains (including the Δ tolC strain, previously generated and characterized by us (Oliveira et al ., ) were cultivated under standard conditions. Most of the mutants' growth was similar to that observed for wild‐type cells (Supporting Information Fig.…”

“…). Sll1951 is the main constituent of the S‐layer (Trautner and Vermaas, ) and was recently identified as a substrate of the T1SS in Synechocystis (Oliveira et al ., ). In order to further investigate the presence/absence of the S‐layer in the various Synechocystis strains, two additional approaches were taken.…”

“…PCC 6803 (hereafter referred to as Synechocystis ) is one of the most commonly studied cyanobacteria. In 2014, a TolC homologue (Slr1270) was identified in this microorganism (Agarwal et al ., ) and it was demonstrated in another work that this protein is involved in the export of antibiotics and proteins (e.g., S‐layer protein) (Oliveira et al ., ). In addition, a TolC‐mutant was shown to release more outer membrane vesicles (OMVs) than the wild‐type (Oliveira et al ., ).…”

“…In 2014, a TolC homologue (Slr1270) was identified in this microorganism (Agarwal et al ., ) and it was demonstrated in another work that this protein is involved in the export of antibiotics and proteins (e.g., S‐layer protein) (Oliveira et al ., ). In addition, a TolC‐mutant was shown to release more outer membrane vesicles (OMVs) than the wild‐type (Oliveira et al ., ). OMVs represent a largely overlooked secretion mechanism, in which biologically active molecules (including toxins, enzymes and nucleic acids) can be trafficked to distant targets in a concentrated, protected and targeted manner (Kulp and Kuehn, ).…”

Type 4 pili are dispensable for biofilm development in the cyanobacterium Synechococcus elongatus

“…PCC 7120 (Oliveira et al ., ) and Synechocystis sp. PCC 6803 (Oliveira et al ., ). Other functional categories were not statistically significantly enriched (false discovery rate < 0.1) in the WT exo‐proteome or the T2SEΩ exo‐proteome compared to the total detected exo‐proteome.…”