Mr Alan Calder

Research project: The Type VI Secretion System in commensal Neisseria spp.


A type 6 secretion system (T6SS) was recently identified in the genome sequence data of an isolate sourced from a throat swab of a volunteer that is believed to be N. subflava. The T6SS is one of the most recently discovered bacterial secretion systems and this is the first time it has been reported in Neisseriaceae. Since this discovery, genome sequences analysis for a number of other commensal Neisseria spp. has identified that in fact, two distinct T6SS types exist across Neisseriaceae. The two T6SS types are clearly defined and are different to one another in both their core gene sequences and organisation. These two systems also differ in the number of VgrG proteins required for the delivery of toxic effector proteins as well as type of effectors associated with them. While the two T6SS types in Neisseria spp. form two separate lineages, the core gene sequences for each type show a high degree of homology across the different species where they occur. Analysis of the VgrG and effector proteins within a single species containing the same T6SS type has highlighted a wide range of diversity in these components between strains. The VgrG/effector combinations identified in the genomic data for our isolate are not common across all members of the same species and specific combinations of genes encoding these proteins have been identified within the genomic data for other commensal Neisseria spp. The data provides possible evidence of Neisseria spp. acquiring new VgrG/effector combinations horizontally through killing of their competitors. A number of putative effectors have so far been identified within the genome of our original isolate that include hydrolases, phospholipases, and nucleases. While these effectors are predicted to be antibacterial in nature, the conditions under which the T6SS system is activated, as well as demonstration of the function of the effectors still needs to be investigated experimentally.  


I worked from 1996 - 2010 in industry labs, these included molecular biology research, forensics, genotyping and trace residue analysis. I came to Kingston to study after finally working in the NHS for a short while. Following my graduation from Kingston, I have worked full time as a Graduate Teaching Assistant and I am currently studying part time for a PhD.

Areas of research interest

  • Microbiology
  • Genetics
  • Toxin / Antitoxin systems
  • Secretion systems


  • BSc


Churchward, Colin P., Calder, Alan and Snyder, Lori A. S. (2018) Mutations in 'Neisseria gonorrhoeae' grown in sub-lethal concentrations of monocaprin do not confer resistance. PLoS One, 13(4), e0195453. ISSN (online) 1932-6203

Zelewska, M.A., Pulijala, M., Spencer-Smith R., Mahmood H.A., Norman B., Churchward, C.P., Calder, C. and Snyder, L.A.S. (2016). Phase variable DNA repeats in Neisseria gonorrhoeae influence transcription, translation, and protein sequence variation. Microbial Genomics 2.

Alan Calder, Chukwuma Jude Menkiti, Aylin Ça?da?, Jefferson Lisboa Santos, Ricarda Streich, Alice Wong, Amir H Khakbazan, Ebrima Bojang, Karththeepan Yogamanoharan, Nivetha Sivanesan, Besma Ali, Mariam Ashrafi, Abdirizak Issa, Tajinder Kaur, Aisha Latif, Hani A Sheik Mohamed, Atifa Maqsood, Laxmi Tamang, Emily Swager, Alex J Stringer, Lori A S Snyder (ORCiD 0000-0003-3172-3984)* (2020) Virulence genes and novel gene clusters in four commensal Neisseria spp. isolated from the human throat expands the neisserial gene repertoire. Microbial Genomics

Conference papers

Abstract and Poster Microbiology Society Annual Conference 2020, published online in Access Microbiology: The Type VI Secretion System in Commensal Neisseria spp.