A microcin processing peptidase‐like protein of the cyanobacterium Synechococcus elongatus is essential for secretion of biofilm‐promoting proteins

Abstract

Summary Small secreted compounds, e.g. microcins, are characterized by a double‐glycine (GG) secretion motif that is cleaved off upon maturation. Genomic analysis suggests that small proteins that possess a GG motif are widespread in cyanobacteria; however, the roles of these proteins are largely unknown. Using a biofilm‐proficient mutant of the cyanobacterium Synechococcus elongatus PCC 7942 in which the constitutive biofilm self‐suppression mechanism is inactivated, we previously demonstrated that four small proteins, Enable biofilm formation with a GG motif (EbfG1‐4), each with a GG motif, enable biofilm formation. Furthermore, a peptidase belonging to the C39 family, Peptidase transporter enabling Biofilm (PteB), is required for secretion of these proteins. Here, we show that the microcin processing peptidase‐like protein encoded by gene Synpcc7942_1127 is also required for biofilm development – inactivation of this gene in the biofilm‐proficient mutant abrogates biofilm development. Additionally, this peptidase‐like protein (denoted EbfE – enables biofilm formation peptidase) is required for secretion of the EbfG biofilm‐promoting small proteins. Given their protein‐domain characteristics, we suggest that PteB and EbfE take part in a maturation‐secretion system, with PteB being located to the cell membrane while EbfE is directed to the periplasmic space via its secretion signal.

Impairment of a cyanobacterial glycosyltransferase that modifies a pilin results in biofilm development

“…Biofilms formed in standing cultures under the conditions indicated above and were quantified after 6 d growth as described (Parnasa et al, 2019), either by percentage of chlorophyll in suspension (Sendersky et al, 2017) or by crystal violet staining. For examination of biofilm formation in a flow cell system, initial cultures were diluted with BG-11 medium to OD750 of 1.0, and incubated for 48 h under 28˚C and 6 μmole photons*m −2 *s −1 .…”

“…Studies of the molecular mechanisms underlying cyanobacterial biofilm development are currently emerging (Enomoto et al, 2014;Enomoto et al, 2015;Agostoni et al, 2016;Lacey and Binder, 2016;Enomoto et al, 2018). Our previous studies revealed a mechanism that represses biofilm formation in Synechococcus elongatus PCC 7942 (hereafter S. elongatus) (Schatz et al, 2013;Parnasa et al, 2016;Nagar et al, 2017;Sendersky et al, 2017;Parnasa et al, 2019). Inactivation of the gene Synpcc7942_2071 [recently designated as pilB (Yegorov et al, 2021)], which encodes an ATPase homologue of type II protein secretion (T2S) and/or type IV pilus assembly systems (T4P), impairs the inhibitory process, resulting in a mutant (PilB::Tn5) that develops robust biofilms (Schatz et al, 2013;Parnasa et al, 2016).…”

Emerging Applications of Bacteriocins as Antimicrobials, Anticancer Drugs, and Modulators of The Gastrointestinal Microbiota

“…In some cases, microcins require post-translational modifications to be active, and they do not require a lysis process to be secreted ( Baquero et al 2019 ). Microcin production has been reported in several Enterobacteriaceae and some cyanobacteria ( Rebuffat 2016 ; Parnasa et al 2019 ).…”

Solution NMR structure of Se0862, a highly conserved cyanobacterial protein involved in biofilm formation

“…For example, four small secreted proteins, EbfG1-4 (enable biofilm formation with GG-motif), of S. elongatus PCC 7942 have been found to promote biofilm-formation. 16,17 Also, Synechocystis sp. PCC 6803 mutants lacking type IV pili (T4P) are unable to aggregate and form biofilms, 18 however, impairment of T4P formation in S. elongatus resulted in biofilm-forming-mutants, unlike the wild-type strain that grow planktonically.…”

“…Recently, there have been advances in understanding biofilm formation by cyanobacteria. For example, four small secreted proteins, EbfG1‐4 (enable biofilm formation with GG‐motif), of S. elongatus PCC 7942 have been found to promote biofilm‐formation 16,17 . Also, Synechocystis sp.…”