Pantoea ananatis: an unconventional plant pathogen

Abstract

Pantoea ananatis causes disease symptoms in a wide range of economically important agricultural crops and forest tree species worldwide. It is regarded as an emerging pathogen based on the increasing number of reports of diseases occurring on previously unrecorded hosts in different parts of the world. Its unconventional nature lies in the fact that, unlike the majority of plant pathogenic microbes, P. ananatis is capable of infecting humans and occurs in diverse ecological niches, such as part of a bacterial community contaminating aviation jet fuel tanks and contributing to growth promotion in potato and pepper.

Taxonomy: Bacteria; Gammaproteobacteria; family Enterobacteriaceae; genus Pantoea.

Microbiological properties: Gram-negative; facultatively anaerobic; most strains are motile and produce a yellow pigment in culture; indole positive. BIOLOGY: Pantoea ananatis is a common epiphyte; it also occurs endophytically in hosts where it has been reported to cause disease symptoms and in hosts where no such symptoms have been described. Some strains are ice-nucleating, a feature which has been used as a biological control mechanism against some insect pests of agricultural crops and by the food industry.

Disease symptoms: Pantoea ananatis infects both monocotyledonous and dicotyledonous plants. The symptoms are diverse depending on the host infected, and include leaf blotches and spots, die-back, and stalk, fruit and bulb rot. BIOLOGICAL CONTROL AGENT: Pantoea ananatis has both antifungal and antibacterial properties. These characteristics have the potential of being exploited by biological control specialists.

Figure 1

Maximum likelihood tree based on the gyrB sequences of Pantoea species and their closest phylogenetic neighbours. Bootstrap values after 1000 replicates are expressed as percentages. Citrobacter rodentium was included as an outgroup. BD 333 and 336 were isolated from onion seed in South Africa, ATCC 35400 from honeydew melons in the USA, LMG 2676 and 2678 from Puccinia graminis in the USA and Zimbabwe, respectively, LMG 2668 and 2665 from pineapple in Hawaii and Brazil, respectively, LMG 20103, 20104, 20106 and BD 114 from Eucalyptus in South Africa, LMG 24190 from onion in the USA, and BD 561, 577, 588, 602, 622, 640, 647 and LMG 24191 and 24192 from maize in South Africa.

Figure 2

Disease symptoms caused by Pantoea ananatis. (A) Bacterial blight of Eucalyptus. (B) Brown stalk rot of maize (photograph courtesy of Dr Teresa Goszczynska, Agricultural Research Council‐Plant Protection Research Institute, Pretoria, South Africa). (C) Centre rot of onion (photograph courtesy of Professor Ron Gitaitis, University of Georgia, Tifton, GA, USA).