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Abstract A soil bacterium in the Serratia genus, carrying a 153 kb conjugative amber disease‐associated plasmid (pADAP), is commercially exploited for population control of the New Zealand endemic pest beetle Costelytra giveni (Coleoptera: Scarabaeidae). The main insecticidal elements are an anti‐feeding prophage and the Sep ABC toxin complex (Tc). Homologs of pADAP, encoding variant Tcs, convey different beetle disease phenotypes. To investigate the correlation between variable bioactivity and the Tc variant, 76 Serratia plasmids were sequenced, resulting in the identification of four additional tc variants. All Serratia tc variants were found to be colocated with a conserved type 1 sef fimbrial‐like operon, indicating a conserved sef‐tc genetic island not observed outside of the Serratia genus. The conserved co‐location of the fimbrial and tc genes suggests the fimbriae somehow contribute to the lifestyle of Tc‐producing cells. Expression of the sef operon in a fim‐null Escherichia coli strain revealed fimbriae presence while a constructed sef‐deficient mutant showed no reduction of virulence or host colonization. Although no detectable contribution of Sef to amber disease in C. giveni was observed, the Sef adhesin sequences clustered similarly to the Serratia species encoding it, suggesting Sef has a species‐specific function.

[Display omitted] • The genomes of histamine- and biofilm-producing L. parabuchneri strains were compared. • Only strong biofilm-producers harbour a pilus-encoding gene cluster (PGC). • Heterologous PGC expression reflects its role in adhesion and biofilm formation. • The PGC is located on a plasmid and is flanked by insertion sequences. • Strong biofilm-forming capacity could be transferred by horizontal gene transfer. Histamine is a biogenic amine synthesized through the enzymatic decarboxylation of the amino acid histidine. It can accumulate at high concentrations in foods through the metabolism of certain bacteria, sometimes leading to adverse reactions in consumers. In cheese, histamine can accumulate at toxic levels; Lentilactobacillus parabuchneri has been identified the major cause of this problem. Previous studies have shown some L. parabuchneri strains to form biofilms on different surfaces, posing a contamination risk during cheese production, particularly for cheeses that are processed post-ripening (e.g., grating or slicing). The food contamination they cause can result in economic losses and even foodborne illness if histamine accumulates in the final product. The aim of the present work was to identify the genes of L. parabuchneri involved in biofilm formation, and to determine their function. The genomes of six strains with different biofilm-production capacities (strong, moderate and weak) were sequenced and analysed. A cluster of four genes, similar to those involved in sortase-mediated pilus formation, was identified in the strong biofilm-producers, suggesting it to have a role in surface adhesion. Cloning and heterologous expression in Lactococcus cremoris NZ9000 confirmed its functionality and involvement in adhesion and, therefore, in biofilm formation. PacBio sequencing showed this cluster to be located on a 33.4 kb plasmid, which might increase its chances of horizontal transmission. These findings provide insight into the genetic factors associated with biofilm formation in histamine-producing L. parabuchneri , and into the risks associated with this bacterium in cheese production. [ABSTRACT FROM AUTHOR]