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Bacillus thuringiensis: Evolution of a taxonomic conception
42,295~198 (19831
JOURNAL OF INVERTEBRATE PATHOLOGY
GUEST Bacillus
thuringiensis:
EDITORIAL
Evolution
of a Taxonomic
Conception
OLEG LYSENKO Insect
Pathology,
Institute of Entomology, Czechoslovak 166 09 Prague 6, Czechoslovakia
Academy
of Sciences,
Received November 5, 1982
Invertebrate pathology can be defined by the subject it examines rather than by the methods applied. In this branch there work people with different scientific and educational backgrounds. From time to time this heterogeneous scientific community behaves as a system with a tendency to separate itself from other systems, even when it uses the same methods and deals with similar problems. This would imply that analogous problems that had been solved elsewhere could be solved smoothly in this system. But time and time again it is not so because under specific conditions, analogous algorithms produce the same errors. This is not due to an absence of relevant information, but to overestimating the exclusivity of particular problems and ignoring a common experience of analogous
dencies and to demonstrate where and why what has happened has occurred. The name Bacillus thuringiensis was introduced by Berliner who validly described this bacterium in 1915. The interest in this bacillus has been proportional to attempts to use it in biological control of insects. In the classical taxonomic scheme of the genus Bacillus (N. R. Smith, R. E. Gordon, and F. E. Clark, USDA Agric. Monogr. 16, l-148, 1952), because of its pathogenicity to insects, this organism was classified as a variety of Bacillus cereus. Later, when some former varieties of this species were elevated in rank to species, the original combination, B. thuringiensis (sensu lacto), was used again to name insect pathogenic strains of B.cereus in taxonomic schemes of the genus Bacillus.
296
GUEST EDITORIAL
able, in our experience this is not the case with crystal-forming bacteria pathogenic for Lepidoptera.” Despite experience in other fields of microbiology these criteria were accepted by insect pathologists and they have been used for over 20 years. In 1962, A. Bonefoi and H. de Barjac (Entomophaga 8, 223-229, 1963) showed that strains of B.thuringiensis can be distinguished by their flagellar antigens and they proposed a taxonomic scheme based on serotypes. J. R. Norris (J. Appl. Bacterial. 27, 439-447, 1964) showed that different serotypes have different esterase patterns. Thus two separate specialized taxonomic schemes were proposed: one based on specific toxicity and toxins, the other on serotypes. Each scheme had its pros and cons. The first operated with properties (specific toxicity and toxins), which in practice were difficult to define and standardize. The second one gave clear-cut results when only serotyping was involved, but required specific sera and a specialized laboratory. When it was believed that serotypes were in correlation with specific pathogenicities, an improved scheme was widely accepted by insect pathologists. From the nomenclatural point of view, descriptions as given by A. M. Heimpel and T. A. Angus were validly published and had standing in nomenclature. This could not be
venient even for a specialized purpose, because specific pathogenicity could not be fully correlated with serotypes and should be used only as one of several taxonomic criteria. Also an experience from medical microbiology implied possible trouble if a subgeneric subdivision was based on serotypes. These arguments were later supported by A. Krieg (J. Invertebr. Parhol. 12, 366-378, 1968) and from the view point of general bacteriological taxonomy reviewed by R. E. Gordon (1975, in “Biological Regulation of Vectors,” J. D. Briggs, ed., US DHEW Publ. No. NIH-77-1180, pp. 67-82). This kind of critique, however, had no chance of being accepted by the majority of insect pathologists because it made a unity between specific pathogenicity and serotypes (or any other simple phenotypic marker) problematic. Within the last 5 years it was demonstrated that (1) besides flagellar antigens. strains can also be grouped according to crystal antigens; (2) within a given H serovar, different crystovars can occur; (3) there is no strict correlation between H antigenicity and specific pathogenicity. For further details see H. T. Dulmage (1981, in “Microbial Control of Pests and Plant Diseases, 1970-1980,” H. D. Burges, ed., Academic Press, New York/London, pp. 193-222). The discoverv of a relatinnhin
291
GUEST EDITORIAL
ON SOME
TAXONOMIC
ATTRISUTES
Combination Attributesu Determinationb NO.
1
CR P Ha
2b 3
+ + ? + + + - -
4 5 6 7 8
t - + - -t --
2a
+
t+
t + + -
Bath. typical strain Bath, new serovar Bath, not motile, WU Bath, not motile, new serovar ?, FO Bath, unknown host. Fl Bath, CR- mutant Bath, CR- mutant Bate?, Bath Cr- not motile Bate. typical strain
mosiuitoes and blackfliesc.oILAxI ;II Nigeria, it was found that approximately 50% of isolated strains can be classified as B.cereus, and 30% as B.thuringiensis. The summary of this examination is presented in Table 2 (0, Lysenko, unpubl.). If the same set of strains were to be routinely examined, i.e., all strains for CR, and those CR+ for P and/or Ha, only strains in combination Nos. 1-4 could be taken as l?.thuringiensis.
As was mentioned above, from the nomenclatural point of view several names of crystaliferous bacteria were not validly published and this would require some action. The last edition of Bacteriological Code and the Approved Lists of Bacterial Names (Int. J. Syst. Bacterial. 30,225-420, bined and a table can be constructed con- 1980) has made things simpler. All names taining eight combinations as shown in published prior to 1980and not included in Table 1. Combination No. 8 can be taken as the Approved Lists are nomenclaturally indefining B.cereus and No. 1 as defining valid. This means that in the present time B.thuringiensis; others can be regarded as the only valid name for these bacteria is sets of intermediate strains. However, Bacillus thuringiensis nom. approb. and the when one presumes that an absence of an other names of species and subspecies are attribute in the set of characters under con- without standing in nomenclature. Further sideration may be regarded as a negative mutant, the tinal taxonomic position of this particular strain depends upon the a priori TABLE 2 OCCURRENCE UF STRAINS OF Bacillus definition of the taxon. This stipulation thlrringiensis AND B. cereus IN SAMPLES FROM should be taken into consideration, when o Taxonomic attributes determiningB. rhurirtgiensis: CR, crystals: P, pathogenicity for insects: Ha, specific H antigens. Explanation in text. h WU, biovar wuhanensis: FO, Fowler’s strain: FI, serovarfinitimus: CR-, does not form crystals.
REARING
PLACES OF MCWQUITOES
AND BLACKFLIES
GUEST EDITORIAL subdivisions of B.thuringiensis (sensu lato) LObiovars, serovars, pathovars, or “crystovars” are not covered by the rules of the Bacteriological code. Infrasubspecific taxa can be based on different overlapping sets of properties, which is the case of B.thuringiensis; e.g., one serovar may contain strains belonging to different pathovat-s. This arrangement has enough spaceto cover all the needs of insect pathologists. Overlooking the development of the idea of a specialized taxonomy of entomogenous strains belonging to the group of B.cereus one can ask “Was splitting of this species necessary? Is it normal, after 20 years of
evolution, for an idea to come back to where it started”? I guess that this can happen to any taxonomic idea which is closely bound to a narrow criterion and does not respect general taxonomic experience. The circle of development of B.thuringiensis taxonomy seems to be closed and let us hope it will not continue as a circullus viciosus. ACKNOWLEDGMENTS A part of this research has been supported by a grant from the UNDP World Bank WHO Special Programme for Research and Training in Tropical Diseases.
JOURNAL OF INVERTEBRATE PATHOLOGY
GUEST Bacillus
thuringiensis:
EDITORIAL
Evolution
of a Taxonomic
Conception
OLEG LYSENKO Insect
Pathology,
Institute of Entomology, Czechoslovak 166 09 Prague 6, Czechoslovakia
Academy
of Sciences,
Received November 5, 1982
Invertebrate pathology can be defined by the subject it examines rather than by the methods applied. In this branch there work people with different scientific and educational backgrounds. From time to time this heterogeneous scientific community behaves as a system with a tendency to separate itself from other systems, even when it uses the same methods and deals with similar problems. This would imply that analogous problems that had been solved elsewhere could be solved smoothly in this system. But time and time again it is not so because under specific conditions, analogous algorithms produce the same errors. This is not due to an absence of relevant information, but to overestimating the exclusivity of particular problems and ignoring a common experience of analogous
dencies and to demonstrate where and why what has happened has occurred. The name Bacillus thuringiensis was introduced by Berliner who validly described this bacterium in 1915. The interest in this bacillus has been proportional to attempts to use it in biological control of insects. In the classical taxonomic scheme of the genus Bacillus (N. R. Smith, R. E. Gordon, and F. E. Clark, USDA Agric. Monogr. 16, l-148, 1952), because of its pathogenicity to insects, this organism was classified as a variety of Bacillus cereus. Later, when some former varieties of this species were elevated in rank to species, the original combination, B. thuringiensis (sensu lacto), was used again to name insect pathogenic strains of B.cereus in taxonomic schemes of the genus Bacillus.
296
GUEST EDITORIAL
able, in our experience this is not the case with crystal-forming bacteria pathogenic for Lepidoptera.” Despite experience in other fields of microbiology these criteria were accepted by insect pathologists and they have been used for over 20 years. In 1962, A. Bonefoi and H. de Barjac (Entomophaga 8, 223-229, 1963) showed that strains of B.thuringiensis can be distinguished by their flagellar antigens and they proposed a taxonomic scheme based on serotypes. J. R. Norris (J. Appl. Bacterial. 27, 439-447, 1964) showed that different serotypes have different esterase patterns. Thus two separate specialized taxonomic schemes were proposed: one based on specific toxicity and toxins, the other on serotypes. Each scheme had its pros and cons. The first operated with properties (specific toxicity and toxins), which in practice were difficult to define and standardize. The second one gave clear-cut results when only serotyping was involved, but required specific sera and a specialized laboratory. When it was believed that serotypes were in correlation with specific pathogenicities, an improved scheme was widely accepted by insect pathologists. From the nomenclatural point of view, descriptions as given by A. M. Heimpel and T. A. Angus were validly published and had standing in nomenclature. This could not be
venient even for a specialized purpose, because specific pathogenicity could not be fully correlated with serotypes and should be used only as one of several taxonomic criteria. Also an experience from medical microbiology implied possible trouble if a subgeneric subdivision was based on serotypes. These arguments were later supported by A. Krieg (J. Invertebr. Parhol. 12, 366-378, 1968) and from the view point of general bacteriological taxonomy reviewed by R. E. Gordon (1975, in “Biological Regulation of Vectors,” J. D. Briggs, ed., US DHEW Publ. No. NIH-77-1180, pp. 67-82). This kind of critique, however, had no chance of being accepted by the majority of insect pathologists because it made a unity between specific pathogenicity and serotypes (or any other simple phenotypic marker) problematic. Within the last 5 years it was demonstrated that (1) besides flagellar antigens. strains can also be grouped according to crystal antigens; (2) within a given H serovar, different crystovars can occur; (3) there is no strict correlation between H antigenicity and specific pathogenicity. For further details see H. T. Dulmage (1981, in “Microbial Control of Pests and Plant Diseases, 1970-1980,” H. D. Burges, ed., Academic Press, New York/London, pp. 193-222). The discoverv of a relatinnhin
291
GUEST EDITORIAL
ON SOME
TAXONOMIC
ATTRISUTES
Combination Attributesu Determinationb NO.
1
CR P Ha
2b 3
+ + ? + + + - -
4 5 6 7 8
t - + - -t --
2a
+
t+
t + + -
Bath. typical strain Bath, new serovar Bath, not motile, WU Bath, not motile, new serovar ?, FO Bath, unknown host. Fl Bath, CR- mutant Bath, CR- mutant Bate?, Bath Cr- not motile Bate. typical strain
mosiuitoes and blackfliesc.oILAxI ;II Nigeria, it was found that approximately 50% of isolated strains can be classified as B.cereus, and 30% as B.thuringiensis. The summary of this examination is presented in Table 2 (0, Lysenko, unpubl.). If the same set of strains were to be routinely examined, i.e., all strains for CR, and those CR+ for P and/or Ha, only strains in combination Nos. 1-4 could be taken as l?.thuringiensis.
As was mentioned above, from the nomenclatural point of view several names of crystaliferous bacteria were not validly published and this would require some action. The last edition of Bacteriological Code and the Approved Lists of Bacterial Names (Int. J. Syst. Bacterial. 30,225-420, bined and a table can be constructed con- 1980) has made things simpler. All names taining eight combinations as shown in published prior to 1980and not included in Table 1. Combination No. 8 can be taken as the Approved Lists are nomenclaturally indefining B.cereus and No. 1 as defining valid. This means that in the present time B.thuringiensis; others can be regarded as the only valid name for these bacteria is sets of intermediate strains. However, Bacillus thuringiensis nom. approb. and the when one presumes that an absence of an other names of species and subspecies are attribute in the set of characters under con- without standing in nomenclature. Further sideration may be regarded as a negative mutant, the tinal taxonomic position of this particular strain depends upon the a priori TABLE 2 OCCURRENCE UF STRAINS OF Bacillus definition of the taxon. This stipulation thlrringiensis AND B. cereus IN SAMPLES FROM should be taken into consideration, when o Taxonomic attributes determiningB. rhurirtgiensis: CR, crystals: P, pathogenicity for insects: Ha, specific H antigens. Explanation in text. h WU, biovar wuhanensis: FO, Fowler’s strain: FI, serovarfinitimus: CR-, does not form crystals.
REARING
PLACES OF MCWQUITOES
AND BLACKFLIES
GUEST EDITORIAL subdivisions of B.thuringiensis (sensu lato) LObiovars, serovars, pathovars, or “crystovars” are not covered by the rules of the Bacteriological code. Infrasubspecific taxa can be based on different overlapping sets of properties, which is the case of B.thuringiensis; e.g., one serovar may contain strains belonging to different pathovat-s. This arrangement has enough spaceto cover all the needs of insect pathologists. Overlooking the development of the idea of a specialized taxonomy of entomogenous strains belonging to the group of B.cereus one can ask “Was splitting of this species necessary? Is it normal, after 20 years of
evolution, for an idea to come back to where it started”? I guess that this can happen to any taxonomic idea which is closely bound to a narrow criterion and does not respect general taxonomic experience. The circle of development of B.thuringiensis taxonomy seems to be closed and let us hope it will not continue as a circullus viciosus. ACKNOWLEDGMENTS A part of this research has been supported by a grant from the UNDP World Bank WHO Special Programme for Research and Training in Tropical Diseases.