Production of Fumonisin Analogs by Fusarium Species

The fumonisins, a family of food-borne carcinogenic mycotoxins, were first isolated in 1988 (21) from cultures of Fusarium verticillioides (Sacc.) Nirenberg (previously known as Fusarium moniliforme Sheldon). During the same year, the structures of the fumonisins were elucidated (6) and fumonisin B₁ was shown to cause equine leukoencephalomalacia (34). There have been numerous publications dealing with this group of novel, carcinogenic mycotoxins, and comprehensive reviews of different aspects of the fumonisins are available (20, 22, 23, 24, 35, 36, 37, 41, 43, 46, 52, 55, 60, 61, 66). Due to the widespread occurrence of the fumonisins in maize, a dietary staple in many countries, the carcinogenic risk of fumonisins to humans was evaluated by the International Agency for Research on Cancer in 1993, and the toxins produced by F. moniliforme were evaluated as “Group 2B carcinogens,” i.e., probably carcinogenic to humans (24). This review focuses on the Fusarium species that produce fumonisins and the fumonisin analogs produced by each of these species.

FUMONISIN ANALOGS

The 28 fumonisin analogs that have been characterized since 1988 can be separated into four main groups, identified as the fumonisin A, B, C, and P series (Fig. 1 and Table 1). The fumonisin B (FB) analogs, comprising toxicologically important FB₁, FB₂, and FB₃, are the most abundant naturally occurring fumonisins, with FB₁ predominating and usually being found at the highest levels (36). FB₁ typically accounts for 70 to 80% of the total fumonisins produced, while FB₂ usually makes up 15 to 25% and FB₃ usually makes up from 3 to 8% when cultured on corn or rice or in liquid medium (7, 39, 40). Apart from the FB series, some of the other analogs may occur in naturally contaminated maize at relatively low levels (<5% of the total fumonisins present) (48). These lesser-known fumonisin analogs are not detected with most analytical techniques due to the derivatization process, but they can be detected with the use of liquid chromatography-mass spectrometry with electrospray ionization (49).

FIG. 1.

Basic structure of fumonisin (see Table 1 for a list of known fumonisin analogs and the positions of R side chains).

TABLE 1.

Fumonisin analogs

Analog	Side chains to fumonisin backbonea							Referenceb
	R1	R2	R3	R4	R5	R6	R7
FA1	TCA	TCA	OH	OH	H	NHCOCH3	CH3	6
FA2	TCA	TCA	H	OH	H	NHCOCH3	CH3	6
FA3	TCA	TCA	OH	H	H	NHCOCH3	CH3	49
PHFA3a	TCA	OH	OH	H	H	NHCOCH3	CH3	59
PHFA3b	OH	TCA	OH	H	H	NHCOCH3	CH3	59
HFA3	OH	OH	OH	H	H	NHCOCH3	CH3	59
FAK1	O	TCA	OH	OH	H	NHCOCH3	CH3	47
FBK1	O	TCA	OH	OH	H	NH2	CH3	49
FB1	TCA	TCA	OH	OH	H	NH2	CH3	21
Iso-FB1	TCA	TCA	OH	H	OH	NH2	CH3	31
PHFB1a	TCA	OH	OH	OH	H	NH2	CH3	68
PHFB1b	OH	TCA	OH	OH	H	NH2	CH3	68
HFB1	OH	OH	OH	OH	H	NH2	CH3	59
FB2	TCA	TCA	H	OH	H	NH2	CH3	21
FB3	TCA	TCA	OH	H	H	NH2	CH3	11
FB4	TCA	TCA	H	H	H	NH2	CH3	11
FB5c								49
FC1	TCA	TCA	OH	OH	H	NH2	H	8
N-acetyl-FC1	TCA	TCA	OH	OH	H	NHCOCH3	H	65
Iso-FC1	TCA	TCA	OH	H	OH	NH2	H	65
N-acetyl-iso-FC1	TCA	TCA	OH	H	OH	NHCOCH3	H	65
OH-FC1	TCA	TCA	OH	OH	OH	NH2	H	64
N-acetyl-OH-FC1	TCA	TCA	OH	OH	OH	NHCOCH3	H	65
FC3	TCA	TCA	OH	H	H	NH2	H	64
FC4	TCA	TCA	H	H	H	NH2	H	58
FP1	TCA	TCA	OH	OH	H	3HP	CH3	48
FP2	TCA	TCA	H	OH	H	3HP	CH3	48
FP3	TCA	TCA	OH	H	H	3HP	CH3	48

^aSee Fig. 1 for the structure of the fumonisin backbone and the positions of the R side chains. TCA, tricarballylic acid.

^bCited references are the first publications dealing with the analogs in question.

^cHexahydroxyalkyl backbone; exact structure unknown at present.

FUMONISIN PRODUCERS

Fifteen Fusarium species have been reported to produce fumonisins (Table 2). Eight of these are in the Section Liseola, i.e., F. verticillioides, mating population A (MP-A) in the Gibberella fujikuroi species complex (6, 8, 9, 10, 11, 14, 15, 17, 18, 21, 25, 28, 29, 30, 31, 32, 45, 46, 48, 49, 50, 57, 58, 62, 68, 70); F. sacchari (Butler) W. Gams MP-B (29); F. fujikuroi Nirenberg MP-C (16); F. proliferatum (Matsushima) Nirenberg MP-D (4, 10, 14, 16, 25, 29, 32, 47, 49, 51, 53, 62, 70, 72); F. subglutinans (Wollenw. et Reinking) Nelson, Toussoun, et Marasas MP-E (29); F. subglutinans sensu lato, isolated from teosinte seed, representing a potentially new biological species within the G. fujikuroi species complex (19); F. thapsinum Klittich, Leslie, Nelson, et Marasas MP-F (26, 30, 45); F. anthophilum (A. Braun) Wollenw. (12, 51); and F. globosum Rheeder, Marasas, et Nelson (69). Another five species fall within the proposed Section Dlaminia (27) (closely related to Section Liseola), i.e., F. nygamai Burgess et Trimboli MP-G (32, 48, 49, 51, 70); F. dlamini Marasas, Nelson, et Toussoun (51); and F. napiforme Marasas, Nelson, et Rabie (51). Trace amounts of fumonisin were detected in culture material of two newly described species, i.e., F. andiyazi Marasas, Rheeder, Lamprecht, Zeller, et Leslie; and F. pseudonygamai Nirenberg et O'Donnell (J. F. Leslie, unpublished data). The remaining two fumonisin-producing Fusarium species are one species in Section Elegans, i.e., F. oxysporum Schlecht. emend. Snyd. et Hans. (2, 64, 65) and one in Section Arthrosporiella, i.e., F. polyphialidicum Marasas, Nelson, Toussoun, et Van Wyk (1). Reports that certain strains of F. oxysporum var. redolens (2) and F. polyphialidicum (1) produce fumonisins need to be confirmed by taxonomic verification of the strains in question as well as by verification of the fumonisins produced.

TABLE 2.

Fumonisin-producing Fusarium species, analogs produced, and the maximum yields of FB₁, FB₂, and FB₃ reported for each species

Fusarium sp.	Fumonisin analog(s)	Reference(s)a	Maximum fumonisin level (mg kg−1) for:			Reference(s)b
			FB1	FB2	FB3
Section Liseola
F. verticillioides MP-A	FA1-3, FB1-5, iso-FB1, FAK1, FBK1, FC1,4, FP1-3, PH1a-b	5, 6, 8, 9, 10, 11, 15, 17, 21, 25, 30, 31, 32, 45, 48, 49, 57, 58, 68, 70	17,900	3,000	2,300	5, 30, 70
F. sacchari MP-B	FB1	29	21	NTc	NT	29
F. fujikuroi MP-C	FB1	16	7	NT	NT	16
F. proliferatum MP-D	FA1-3, FB1-5, FAK1, FBK1, FC1, FP1-3, PH1a-b	10, 14, 16, 25, 32, 47, 49, 51, 53, 62, 70	31,000	17,000	5,700	10, 53
F. subglutinans MP-E	FB1	29	150	NT	NT	29
F. subglutinans MP-?d	FB1	19	230	NT	NT	19
F. thapsinum MP-F	FB1-3	26, 30, 45	30	5	5	30
F. anthophilum	FB1-2	12, 51	610	35	NT	12, 51
F. globosum	FB1-3	69	330	4	24	69
Section Dlaminia
F. nygamai MP-G	FA1-3, FB1-5, FAK1, FBK1, FC1, FP1, PH1a-b	32, 48, 49, 51, 70	7,200	530	140	51, 70
F. dlamini	FB1	51	82	NT	NT	51
F. napiforme	FB1	51	480	NT	NT	51
F. pseudonygamai	FB1-2	31	Tre	Tr	NT	31
F. andiyazi	FB1	31	Tr	NDf	NT	31
Section Elegans
F. oxysporum	FC1,3-4, N-acetyl-FC1, iso-FC1, N-acetyl-iso-FC1, OH-FC1, N-acetyl-OH-FC1	64, 65	NT	NT	NT
F. oxysporum var. redolens	FB1-3	2	300	6	0.9	2
Section Arthrosporiella
F. polyphialidicum	FB1	1	500	NT	NT	1

^aReferences to the analogs produced by each Fusarium species.

^bReferences to the maximum FB₁, FB₂, and FB₃ yields in culture. Where more than one reference is cited, the maximum levels for FB₁, FB₂, and FB₃ are summarized from multiple reports.

^cNT, not tested.

^dF. subglutinans senso lato. These strains were nonfertile with tester strains of mating populations B, E, and H within the G. fujikuroi species complex (19).

^eTr, trace amounts (1 to 4 ng g⁻¹) were detected.

^fND, not detected (<1 ng g⁻¹).

The only fungus that does not belong to the genus Fusarium that has been reported to produce fumonisins (FB₁, FB₂, and FB₃) in culture is Alternaria alternata (Fr.) Keissler f. sp. lycopersici (3, 13, 44).

The relative production of FB₁, FB₂, and FB₃ by different Fusarium species is briefly summarized in Table 2. The most important producers of fumonisins are F. verticillioides and F. proliferatum because of their overall high levels of production, wide geographical distribution, frequent occurrence on maize, and association with known animal mycotoxicoses (62, 63). With the exception of F. verticillioides and F. proliferatum, less than 50% of isolates of other fumonisin-producing Fusarium species may produce fumonisins at various levels (51).

NON-FUMONISIN PRODUCERS

Several Fusarium species have been reported as non-fumonisin producers, but in most cases only a few isolates per species have been analyzed. These Fusarium species are F. acuminatum Ell. et Ev. (25, 70); F. annulatum Bugnicourt (51); F. avenaceum (Fr.) Sacc. (70); F. beomiforme Nelson, Toussoun, et Burgess (51); F. camptoceras (Wollenw. et Reinking) emend. Marasas et Logrieco (25, 70); F. circinatum Nirenberg et O'Donnell (= F. subglutinans f. sp. pini) MP-H (19); F. compactum (Wollenw.) Gordon (70); F. concolor Reinking (56); F. crookwellense Burgess, Nelson, et Toussoun (= F. cerealis [Cooke] Sacc.) (56); F. culmorum (W. G. Smith) Sacc. (56); F. decemcellulare Brick (70); F. dimerum Penzig (25); F. equiseti (Corda) Sacc. (25, 70); F. graminearum Schwabe (teleomorph: G. zeae [Schwabe] Petch) (56, 70); F. lateritium Nees (70); F. longipes Wollenw. et Reinking (70); F. poae (Peck) Wollenw. (70); F. pseudograminearum O'Donnell et Aoki (= F. graminearum Group 1) (56, 70); F. reticulatum Mont. (70); F. sambucinum Fuckel (56, 70); F. scirpi Lambotte et Fautr. (70); F. semitectum Berk. et Rav. (= F. pallidoroseum [Cooke] Sacc.) (25, 56, 70); F. solani (Mart.) Appel et Wollenw. emend. Snyder et Hansen (25, 70); F. sporotrichioides Sherb. (70); F. succisae (Schröter) Sacc. (51); and F. tricinctum (Corda) Sacc. (70).

FUMONISIN PRODUCTION BY F. VERTICILLIOIDES

Most isolates of F. verticillioides have the ability to produce fumonisins. Some of the highest FB₁ levels produced by this species have been reported with isolates from South Africa (17,900 mg kg⁻¹) (5), China (10,200 mg kg⁻¹) (72), and Argentina (8,160 mg kg⁻¹) (67). Although a few F. verticillioides isolates from Nepal (50) do not produce any fumonisin, other isolates from the same region have been reported to produce FB₁ at levels of up to 6,400 mg kg⁻¹ (16, 50). Several isolates of this species from Southeast Asia (42) produce fumonisins at low levels, with a maximum of 147 mg kg⁻¹, whereas some isolates from Australia (50) produced only trace quantities of FB₁.

F. verticillioides strain MRC 826 (= FRC M-1325, accession number at the Fusarium Research Center, Pennsylvania State University, Pa.), which was isolated in 1975 from maize in an area of high incidence of human esophageal cancer in the Transkei region of the Eastern Cape Province, South Africa (33), and from which the fumonisins were first isolated and characterized (21), has been used to produce fumonisins in numerous studies all over the world. “It has been the most thoroughly studied strain of F. moniliforme and consequently much of our knowledge of F. moniliforme toxicity is attributable to experiments using MRC 826 as a model” (71).

The highest yield of FB₁ (17,900 mg kg⁻¹) by F. verticillioides was obtained from whole maize kernels as culture material, with F. verticillioides MRC 826 as inoculum, incubated at 20°C in the dark for 13 weeks (5). The highest yield of FB₁ that has been reported for a Fusarium species was obtained with a maize isolate of F. proliferatum (no accession number given) from Spain cultured on whole maize (31,000 mg kg⁻¹) (10). This isolate also produced the highest published yield of FB₂ (17,000 mg kg⁻¹). F. proliferatum M-6284, cultured on whole yellow maize, produced the highest reported yield of FB₃ (5,700 mg kg⁻¹) (53).

CONCLUSION

Numerous studies have provided valuable data on the toxicology of purified fumonisins of the FB series, yet the search continues for other toxic fumonisin analogs which may also pose a health risk to humans and animals. Maize and maize-based products have been the main focus of fumonisin research due to the widespread contamination of this food source by relatively high levels of FB₁, FB₂, and FB₃. As additional and new Fusarium species with various fumonisin-producing capabilities are described from other agriculturally important crops, such as sorghum (38) and millet (54), it becomes necessary to determine whether fumonisins also occur in these crops and, if so, to determine which analogs occur and at what levels.