Calder, Alan and Snyder, Lori (2024) Neisseria gonorrhoeae growth is inhibited by a type VI secretion system encoded within the genome of neisseria subflava strain KU1003-01. In: The 3rd Neisseria gonorrhoeae Research Society Conference; 3 - 6 Jun 2024, Held online. (Unpublished)

Abstract

To investigate the potential for the Type VI Secretion System (T6SS) of Neisseria subflava to inhibit Neisseria gonorrhoeae growth, we first constructed a T6SS knockout strain of N. subflava KU1003-01. Assays were then designed to allow direct competition between N. subflava and N. gonorrhoeae. Following competition with the wild-type strain, the number of recoverable N. gonorrhoeae cells was significantly reduced (p < 0.001) when compared to those recovered following competition with the T6SS knockout strain. N. subflava strain KU1003-01 has a single vgrG and EI pair encoded at one of the core T6SS gene clusters as well as nine auxiliary T6SS gene loci consisting of vgrG and effector immunity (EI) gene pairs. Seven of these auxiliary loci are encoded on a ~ 71 kb genomic island located away from the T6SS core gene clusters. Like the Gonococcal Genomic Island (GGI), the T6SS island in N. subflava is flanked by sequences similar to dif (XreCD) recombination sites. In N. gonorrhoeae, dif motifs play a role in excision of the GGI as a circular moiety as well as re-integration or even loss from the chromosome (Dillard et al., 2011). Using PCR, we show that while the vgrG EI clusters in N. subflava are present in the chromosome, these sequences also circularise and exist trachromosomally. While excision of T6SS clusters may aid in their horizontal transfer, this mechanism may also facilitate swapping of vgrG EI pairs at the core cluster and allow their expression through existing regulatory networks. Our findings so far indicate that N. subflava can outcompete N. gonorrhoea using the T6SS, however, it is not clear which effectors are responsible for the antagonism. Future understanding may help to address issues of antimicrobial resistance by utilising commensal Neisseria spp. or their secreted products as a means to control infections by the pathogens.

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