This research programme focuses on bacterial diseases of trees, both plantation and native tree species and to a lesser extent, fruit trees. We have two major research focuses – one on taxonomy and the other on pathogenicity factors exhibited by a select group of pathogens. The taxonomic research involves identifying new species using modern approaches, mainly in the Enterobacteriaceae. The majority of bacteria we have identified thus far have been opportunistic plant pathogens whilst others have been associated with plants as endophytes. This has led to a number of studies where we have attempted to understand how these opportunists can function as successful plant pathogens despite the fact that they occur in other ecological niches which are often diverse, such as in diesel fuel.

Our interest has primarily been on Pantoea ananatis and related Pantoea species, although we do have research projects on Xanthomonas spp. and Ralstonia solanacearum. P. ananatis is responsible for bacterial blight and die-back of Eucalyptus, brown stalk rot of maize and occurs on onion seed in South Africa. Our studies have centred on taxonomy and on developing rapid and reliable methods of distinguishing between the species of Pantoea. We are now expanding this research and are using a phylogenomic approach to examine this genus. Other elements currently under investigation include understanding the epidemiology and biology of primarily P. ananatis, but this has been expanded to include the other pathogens mentioned above as well. We have identified a number of pathogenicity factors in P. ananatis and this has given us some insight into its life as a phytopathogen. The approach we have used has involved both comparative and functional genomics. The pathogenicity factors investigated have included motility, Type VI secretion system, quorum sensing and exopolysaccharide production.

New Publications

Beukes CW, Sereme TK, Phalane FL, Mthombeni LS, Palmer M, Hassen AI, Chan WY, Avontuur J, van Zyl E, Steenkamp ET, Venter SN. (2019) Paraburkholderia strydomiana sp. nov. and Paraburkholderia steynii sp. nov.: rhizobial symbionts of the fynbos legume Hypocalyptus sophoroides. Antonia van Leeuwenhoek 10.1007/s10482-019-01269-5
Avontuur JR, Palmer M, Beukes CW, Chan WY, Coetzee MPA, Blom J, Stępkowski T, Kyrpides NC, Woyke T, Shapiro N, Whitman WB, Venter SN, Steenkamp ET. (2019) Genome-informed Bradyrhizobium taxonomy: where to from here?. Systematic and Applied Microbiology 10.1016/j.syapm.2019.03.006
van der Nest MA, Wingfield MJ, McTaggart AR, Van Wyk S, De Vos L, Trollip C, Santana QC, Naidoo K, Dong TA, Wilken PM, Chan W-Y, Palmer M, Soal NA, Roodt D, Steenkamp ET, Wingfield BD. (2019) Genomic analysis of the aggressive tree pathogen Ceratocystis albifundus. Fungal Biology 10.1016/j.funbio.2019.02.002 PDF
Siphathele Sibanda, Stanford Kwenda, Collins K. Tanui, Divine Shyntum, Teresa Coutinho, Lucy Moleleki. (2018) Transcriptome profiling reveals the EanI/R quorum sensing regulon in Pantoea ananatis LMG 2665T. Genes 9(3):148. 10.3390/genes9030148
Palmer M, Steenkamp ET, Coetzee MPA, Avontuur JR, Chan WY, Van Zyl E, Blom J, Venter SN. (2018) Mixta gen. nov., a new genus in the Erwiniaceae. International Journal of Systematic and Evolutionary Microbiology 68:1396-1407. 10.1099/ijsem.0.002540