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1 Landcare Research, Private Bag 92170, Auckland, New Zealand
2 PO Box 31425, Milford, Auckland, New Zealand
3 ‘Winton Glen’, Taylor Road, Waimauku, New Zealand
Correspondence
J. M. Young
youngj{at}LandcareResearch.co.nz
ABSTRACT
Strains now considered to represent the type strain of Arthrobacter ilicis, described as a pathogen of American holly, are not identical. The designated type strain does not represent this pathogen. However, one of the other strains sourced to the type strain of the pathogen does appear to be authentic, but is not a member of A. ilicis. It is proposed that A. ilicis is an unrelated species, not a pathogen of American holly. The nomenclature of A. ilicis can be rectified by emending the authority and by emending the species description to recognize this species as a novel species that is not a plant pathogen. The pathogen of American holly then becomes a novel pathovar, Curtobacterium flaccumfaciens pv. ilicis. The opinion of the Judicial Commission is sought.
Mandel et al. (1961)
proposed Corynebacterium ilicis as the name for a pathogen of American holly (Ilex opaca). However, they did not designate a type strain. Later, when the Approved Lists of Bacterial Names (Skerman et al., 1980) were being prepared, one requirement [Rule 18a of the International Code of Nomenclature of Bacteria (Prokaryotes), ‘the Code’; Lapage et al., 1992] was for the proposal of an existing strain as the type strain. Because Mandel's strain CR2 was already held in several culture collections, it was chosen as the type strain (Dye & Kemp, 1978). Mandel CR2 is represented in the International Collection of Microorganisms from Plants (ICMP) by strains obtained by one of the authors (D. W. Dye) from two different sources; ICMP 2607, from the National Collection of Plant-pathogenic bacteria, UK (NCPPB), as NCPPB 1228 (=Dye CJ1), and ICMP 2608, from the International Collection of Phytopathogenic Bacteria, USA (ICPB), as ICPB CI145 (=Dye CJ2). The choice of ICMP 2607 as type strain was arbitrary. Subsequently, Collins et al. (1981) examined two strains derived from Mandel CR2, NCPPB 1228 and ATCC 14264. By comparative analysis of 16S rDNA sequences, they determined that both these strains were members of the genus Arthrobacter. Their new combination, Arthrobacter ilicis, was subsequently validated (Collins et al., 1982). However, a re-examination here of the data presented by Dye & Kemp (1977) shows that ICMP 2607 (via NCPPB 1228) and ICMP 2608 (via ICPB CI145), although both ultimately sourced from Mandel CR2, are not identical. The data of Dye & Kemp (1977) showed that ICMP 2607 is in a phenon separate from all species now allocated to Clavibacter, Curtobacterium and Rhodococcus, i.e. the genera to which all other coryneform plant pathogens belong. These data showed that ICMP 2608 was indistinguishable from ICMP 2609 (=Dye CJ3, obtained via ICPB CI145), sourced from Mandel's strain Y1. The two strains ICMP 2608 and 2609 were allocated to phenon 2 of Dye & Kemp (1977). The only available information about pathogenicity [Mandel et al. (1961) did not cite specific pathogenic strains] refers to ICPB CR144 (=ICMP 2608) as pathogenic to American holly (M. P. Starr, personal communication). This phenon was later (Collins & Jones, 1983) reclassified as the new combination Curtobacterium flaccumfaciens Hedges 1922 (Collins and Jones 1984).
It seems clear that Mandel CR2 accessioned as ICMP 2607 was, for whatever reason, taxonomically different from Mandel CR2 accessioned as ICMP 2608. Therefore, the pathogen of American holly identified by Mandel et al. (1961) cannot be represented with ATCC 14264 (=ICMP 2607=NCPPB 1228) as type strain. It is concluded that the coryneform plant pathogen isolated from American holly by Mandel et al. (1961) is now authentically represented by the two strains ICMP 2608 (=Mandel CR2), which is reported to be pathogenic (Young & Fletcher, 1997), and ICMP 2609 (=Mandel Y1), both members of Curtobacterium flaccumfaciens, a species that includes only plant-pathogenic strains allocated to various pathovars (Collins & Jones, 1983). Host plants affected by this species are Beta vulgaris, Euphorbia pulcherrima, Phaseolus spp., Tulipa gesneriana and Vigna spp. According to Dye & Kemp (1977), the two strains ICMP 2608 and 2609 form a distinct subgroup within Corynebacterium flaccumfaciens. Although Dye & Kemp (1977) might have proposed their phenons as subspecies, they chose to allocate them as pathovars, later confirmed by Collins & Jones (1983). It now seems appropriate to recognize the American holly pathogen, isolated from a host unrelated to any others affected by members of Curtobacterium flaccumfaciens, as a distinct pathovar, Curtobacterium flaccumfaciens pv. ilicis. Following the Standards for Naming Pathovars (Dye et al., 1980), ICMP 2608 (=ICPB CI144), proved pathogenic to Ilex opaca, is designated here as the pathotype strain.
What is to be the fate of the binomial Arthrobacter ilicis? The intention of Mandel et al. (1961) was to name a plant-pathogenic coryneform species, as indicated by their description. By accident, this binomial is no longer connected to the original organism either by the type strain or by key elements of its original description. The Code offers no direct guide in cases like this. One seemingly plausible solution might be to have the binomial Arthrobacter ilicis declared a nomen dubium – a rejected name, whose application is uncertain. However, this solution ignores the validity of the binomial, supported by a description (although defective) and, despite its obscure provenance, a type strain (ATCC 14264). An alternative approach is to conclude that Collins et al. (1981) mistakenly created a new combination when, in fact, they were investigating novel strains and should have created a new species. If the strains had not been representatives of the type strain, then this is almost certainly what they would have done. Had they confirmed the description of the species in full, including conducting pathogenicity tests, the true situation might have revealed itself. Viewed in this light, Arthrobacter ilicis could be considered as a new species reported by Collins et al. (1981) if its formal nomenclatural connection with the pathogen of American holly reported by Mandel et al. (1961) is severed. This would entail:
(i) recognition of Collins et al. (1981) as the originators of a novel binomial Arthrobacter ilicis;
(ii) setting aside all references to Mandel et al. (1961) as authority to the name;
(iii) deletion, wherever it occurs, of reference to Mandel's strain CR2 as source of the type strain;
(iv) emendation of the description, specifically deleting reference to the species as a pathogen of American holly. In the description of the species given by Keddie et al. (1986), the sentence ‘Causes blight on the foliage and twigs of American Holly (Ilex opaca).’ should be deleted.
There is no impediment in having the same name (ilicis) for differ taxa at different nomenclatural ranks (Young et al., 2001). Nor is the specific epithet (ilicis) inappropriate because it no longer relates to a descriptive element of the species (Young, 2001).
The opinion of the Judicial Commission of the International Committee on the Systematics of Prokaryotes is requested. If this proposal is rejected, the Judicial Commission is requested to develop a preferred solution.
The binomial proposed is Arthrobacter ilicis Collins et al. 1982 emend. Young et al. 2004. The type strain is ATCC 14264T (=CFBP 1380T=ICMP 2607T=ICPB CI144T=NCPPB 1228T).
ACKNOWLEDGEMENTS
The New Zealand Foundation for Research, Science and Technology is acknowledged for funding this paper under contract C09X0201. P. K. Buchanan, E. H. C. McKenzie and S. R. Pennycook, Landcare Research, Auckland, are thanked for critically reading the manuscript and for their helpful suggestions.
REFERENCES
Collins, M. D. & Jones, D. (1983). Reclassification of Corynebacterium flaccumfaciens, Corynebacterium betae, Corynebacterium oortii and Corynebacterium poinsettiae in the genus Curtobacterium, as Curtobacterium flaccumfaciens comb. nov. J Gen Microbiol 129, 3545–3548.
Collins, M. D., Jones, D. & Kroppenstedt, R. M. (1981). Reclassification of Corynebacterium ilicis (Mandel, Guba and Litsky) in the genus Arthrobacter as Arthrobacter ilicis comb. nov. Zentbl Bakteriol Parasitenkd Infektionskr Hyg Abt 1 Orig C2, 318–323.
Collins, M. D., Jones, D. & Kroppenstedt, R. M. (1982). Arthrobacter ilicis comb. nov. In Validation of the Publication of New Names and New Combinations Previously Effectively Published Outside the IJSB, List no. 9. Int J Syst Bacteriol 32, 384–385.
Dye, D. W. & Kemp, W. J. (1977). A taxonomic study of plant pathogenic Corynebacterium species. NZ J Agric Res 20, 563–582.
Dye, D. W. & Kemp, W. J. (1978). Genus IV. Corynebacterium. In A Proposed Nomenclature and Classification for Plant Pathogenic Bacteria, pp. 156–157. Edited by J. M. Young, D. W. Dye, J. F. Bradbury, C. G. Panagopoulos & C. F. Robbs. NZ J Agric Res 21, 153–177.
Dye, D. W., Bradbury, J. F., Goto, M., Hayward, A. C., Lelliott, R. A. & Schroth, M. N. (1980). International standards for naming pathovars of phytopathogenic bacteria and a list of pathovar names and pathotype strains. Rev Plant Pathol 59, 153–168.
Hedges, F. (1922). A bacterial wilt of the bean caused by Bacterium flaccumfaciens nov. sp. Science 55, 433–434.
Keddie, R. M., Collins, M. D. & Jones, D. (1986). Genus Arthrobacter Conn and Dimmick 1947, 300AL. In Bergey's Manual of Systematic Bacteriology, vol. 2, pp. 1288–1301. Edited by P. H. A. Sneath, N. S. Mair, M. E. Sharpe & J. G. Holt. Baltimore: Williams & Wilkins.
Lapage, S. P., Sneath, P. H. A., Lessel, E. F., Skerman, V. B. D., Seeliger, H. P. R. & Clark, W. A. (editors) (1992). International Code of Nomenclature of Bacteria (1990 Revision). Bacteriological Code. Washington, DC: American Society for Microbiology.
Mandel, M., Guba, E. F. & Litsky, W. (1961). The causal agent of bacterial blight of American holly. Bacteriol Proc (1961), 61.
Skerman, V. B. D., McGowan, V. & Sneath, P. H. A. (editors) (1980). Approved lists of bacterial names. Int J Syst Bacteriol 30, 225–420.
Young, J. M. (2001). Implications of alternative classifications and horizontal gene transfer for bacterial taxonomy. Int J Syst Evol Microbiol 51, 945–953.[Abstract]
Young, J. M. & Fletcher, M. J. (1997). International Collection of Micro-organisms from Plants – Catalogue, 3rd edn. Auckland: Landcare Research. http://www.landcareresearch.co.nz/research/biodiversity/fungiprog/icmp.asp
Young, J. M., Bull, C. T., De Boer, S. H., Firrao, G., Gardan, L., Saddler, G. E., Stead, D. E. & Takikawa, Y. (2001). Classification, nomenclature, and plant pathogenic bacteria – a clarification. Phytopathology 91, 617–620.
This article has been cited by other articles:
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  Judicial Commission of the International Committee Corynebacterium ilicis is typified by ICMP 2608 =ICPB CI144, Arthrobacter ilicis is typified by DSM 20138 =ATCC 14264 =NCPPB 1228 and the two are not homotypic synonyms, and clarification of the authorship of these two species. Opinion 87 Int J Syst Evol Microbiol, August 1, 2008; 58(8): 1976 - 1978. [Abstract] [Full Text] [PDF]
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