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Showa Denko’s genetically modified bacteria

On December 14, 1982, Showa Denko received a U.S. patent (#4,363,875) for its L-tryptophan production process using a novel mutant microorganism, Bacillus amyloliquefaciens strain IAM 1521, obtained from the Institute of Applied Microbiology, University of Tokyo.5 A mutant of this parent strain was developed by Showa Denko as Strain I, and was used from the start of production on December 16, 1982 to October 22, 1984, when Strain II was introduced.5

Strain II was the first of several genetically engineered—recombinant DNA—strains of the parent bacterium used by the company to bolster L-tryptophan yields (see table of genetic modifications).6 Strain III was used in commercial production from February 23, 1986 to November 21, 1988; Strain IV from November 22 to December 25, 1988 and Strain V from December 26, 1988 until November 21, 1989,7 when production ceased following news of the L-tryptophan-linked epidemic in America.

Showa Denko, like most Japanese manufacturers of L-tryptophan at that time, used a fermentation process, where a selected bacterial strain was grown from specific precursors under specific conditions.8 Showa Denko’s bacteria were fed intermittently with sterilized glucose (sugar) and anthranilic acid to produce a broth containing L-tryptophan and impurities. The liquid broth was then heat treated and sent to a cell separator. From there it was sent to the purification process, including ion exchange resin columns, a membrane for removal of high molecular weight substances, and towers with activated and granulated carbon powder to remove trace impurities.9

In the summer of 1988, a German company, A.S. Biologische, tested Showa Denko L-tryptophan and found impurities, one of which was called Peak D. According to internal Showa Denko documents, when Showa Denko was questioned about the Peak D impurity, they admitted that they couldn’t determine a lack of toxicity of the impurity because they couldn’t figure out what the impurity was.10,11

However, all L-tryptophan preparations contain various minor impurities, which vary with different manufacturing processes. The high performance liquid chromatography (HPLC) “fingerprint” profiles of impurities13 are relatively consistent from lot to lot for each manufacturer. The chromatograms from EMS patient-related L-tryptophan (i.e., Showa Denko’s product) showed many more small peaks of impurities and much higher levels of several impurities than other manufacturers’ products.14

“There is no evidence to suspect that any external materials got into the production process and ‘contaminated’ the product. The manufacturing process was carefully controlled to assure, among other things, that contaminants did not get into the process. All fermentation products contain a number of impurities. For example, beer contains numerous impurities, most of which I believe have never been identified or isolated.”5

If the contaminants did not get into the product externally, where did they come from?

One of the world’s leading authorities on the biosynthesis of L-tryptophan, Charles Yanofsky, PhD, with the Department of Biological Sciences at Stanford University, said that impurities could be created in several ways:

“If you significantly overproduce a natural substance, such as tryptophan, it is likely that one or more enzymes of the bacterium will modify tryptophan and produce an unnatural product or products [during fermentation]. Furthermore, tryptophan is unstable at extreme pH’s and therefore during purification it is possible that under the conditions used some other compounds produced by the bacterium, or that are used during purification, modify the tryptophan at some step in purification.

“Thus depending upon the organism used for overproduction, the level of expression, and the conditions of growth, some fraction of the synthesized tryptophan could be modified. In addition, during purification modification is also possible. In fact there is also a third possibility, namely that a modified form of tryptophan produced during bacterial growth is further altered during purification, i.e., toxic forms of tryptophan could be generated by a two-stage process. It should be possible to determine exactly what happened from analysis of a typical bacterial preparation of tryptophan, before purification, and what contaminants are present before and at different stages of purification.”18

Yanofsky raises a key point, which suggests that if contaminant(s) are formed at some stage of purification, it doesn’t necessarily eliminate what happened during bacterial fermentation as a possible cause or contributing factor.

In an article in the Medical Post in 1990, Yanofsky explained that the more L-tryptophan that is produced in the fermentation cell, the greater the chance that some side reaction will occur at a greater rate, producing more of some contaminant: “It’s possible that one purification scheme may be quite adequate when producing low levels of tryptophan, but at higher levels, it might not be good enough.”19

Showa Denko’s genetically modified strains (II-V) were used to increase the biosynthesis of L-tryptophan through bacterial fermentation. Interestingly, the introduction of these higher yielding GE strains over several years prior to the EMS epidemic appears, on the surface, to correspond directly to the gradual increase in the incidence of EMScases reported by researchers.20

Regarding overproduction of L-tryptophan through bacterial fermentation, Yanofsky said (emphasis added):

“If Showa Denko engineered the bacterium to overproduce tryptophan [which Showa Denko did], then there are many unknowns that would be associated with its overproduction. They probably engineered the strain to overproduce chorismate [which they did], the common aromatic precursor of tryptophan, as well as overproduce all the enzymes of the tryptophan biosynthetic pathway. Overall this would mean that the bacterium is producing large amounts of about 10-15 metabolites that are not normally produced in excess. The accumulation of these metabolites would, in some cases, lead to the modification by other enzymes, to give products that normally are never produced by the bacterium. One or more of these products could be a compound toxic to man.

“Similarly the production of enzymes of the aromatic and tryptophan biosynthetic pathways could lead to the synthesis of unnatural products by side reactions that normally do not occur. Again, toxic products could be produced….”21

In fact, in an unpublished study7 Showa Denko scientists reported that in Strain V, genetic engineering was used to increase and amplify genes for two enzymes used in the biosynthesis of L-tryptophan:

“The principal difference between strains III and V is that the prs and serA genes for two enzymes required for the biosynthesis of tryptophan PRPP [5-phosphoribosyl-1-pyrophosphate] and serine were increased and their expression amplified in Strain V by standard genetic engineering techniques.”

Dr. Yanofsky continued:

“Genetic engineering results in the formation of higher than normal concentrations of certain enzymes and products; these could provide the basis for the synthesis of higher levels of toxic substances.”21

Thus, from a theoretical perspective, genetic engineering could have played a role in creating metabolites, enzymes and other compounds during fermentation that directly or indirectly caused increased toxins in Showa Denko’s product.

Is there any evidence to support this view? Unfortunately, there’s very little, because researchers have not been able to study samples of the genetically engineered (GE) bacteria used in Showa Denko’s fermentation.

The manufacturer eventually destroyed the cultures in 1996.

In the absence of the GE cultures, researchers have studied how the case-associated contaminants could have been formed during the purification process.

One case-associated contaminant that has received significant attention is 3-phenylamino-L-alanine (3-PAA, 25 also referred to as Peak I or UV-5 26,15). 3-PAA is remarkably similar to 3-PAP (3-phenylamino-1, 2-propanediol), an impurity implicated in the 1981 toxic oil syndrome (TOS) that seriously injured 20,000 people (causing 839 deaths) in Spain with an EMS-like disease.17,6 Both 3-PAA and 3-PAP are aniline derivatives.6

Showa Denko used anthranilic acid in the biosynthetic pathway during fermentation to create L-tryptophan:9 Anthranilic acid + 5-phosphoribosyl-1-pyrophosphate (PRPP) + serine = LT.

According to an Asahi News Service report (1992), Showa Denko said that it “did not use any aniline compounds anywhere in the manufacturing process.”27 But an article in the Journal of the American Medical Association (JAMA) reported that the chemical structures of anthranilic acid and aniline are similar.20 Could anthranilic acid, which has a similar structure to aniline, get modified to form an aniline-derived compound, 3-PAA?

The Asahi News Service article states, “Showa Denko genetically altered the Bacilli to increase the bacteria’s production of the serine used to manufacturer L-tryptophan.”27 Serine is a non-toxic, natural amino acid, but its overproduction via the genetically engineered bacteria could have created the contaminant 3-PAA, according to Yanofsky:

“It is conceivable that by overproducing serine the manufacturer [Showa Denko] caused, or increased, the production of [3-] PAA.”28

So, theoretically, Showa Denko’s genetically engineered bacteria, which were used to overproduce serine in the biosynthesis of L-tryptophan, could quite feasibly have created the toxic aniline derivative 3-PAA by modifying anthranilic acid during fermentation.

However, a study by Toyoda, et al., found that 3-PAA could be formed under the purification conditions used by Showa Denko from anthranilic acid and serine through a 2-step process: Aniline was made first by the heat degradation of anthranilic acid under acidic conditions, and this aniline subsequently reacted with L-serine under basic conditions to produce 3-PAA. The authors stated that formation of 3-PAA from anthranilic acid and serine had not yet been investigated (i.e., during fermentation) and cautioned, “more precise experiments are needed before any quantitative statements can be made regarding the formation of PAA under fermentation and purification conditions.”29

Interestingly, in the paper’s abstract, it states, “These results suggest that PAA could be formed under the fermentation and purification conditions used to produce L-tryptophan on an industrial scale.”(emphasis added). Why did the authors include “fermentation” in the abstract, if the conditions of their experiment pertained to Showa Denko’s purification procedures?

This appears confusing, but a description of Showa Denko’s manufacturing process may offer clarification. It states that the fermentation broth—containing anthranilic acid, serine, L-TRP, glucose, anti-foaming agent and impurities—underwent “heat treatment” immediately following fermentation, while the broth was still in the vat, and before it went to the cell separator and onto the filtration system.9 Technically, the results of the study would suggest that aniline and case-associated contaminant 3-PAP were formed between fermentation and filtration.

Is there evidence of other steps in the process where the case-associated contaminants may have been formed?

A study by Thomas Simat and colleagues at the University of Hamburg, Germany, reported that two case-associated contaminants, IMT and HIT, were 2-tryptophan derivatives formed by the reaction of excess L-tryptophan during purification.30

Showa Denko used GE bacteria specifically to produce excess L-tryptophan, i.e., to amplify the biosynthetic pathway of tryptophan to increase yields. This suggests that the GE bacteria did, in fact, play a role in creating case-associated contaminants IMT and HIT, because if excess L-tryptophan had not been produced during fermentation in the first place, then IMT and HIT would not have been formed, or at least not to the same extent, in the downstream processing (filtration).

From the foregoing discussion it is apparent that the formation of these and other contaminants associated with EMS (i.e., EBT and PIC) were the result of specific features of Showa Denko’s manufacturing process—both during fermentation and purification.

Simat and his colleagues reported, “All results indicate that the purification process, not the fermentation, governs the pattern of contaminants in biotechnologically derived Trp.”16 But this claim is contrary to findings of a CDC priority case lot study, which showed “peaks predictive of case status reflected principally the differences in trace components between the bacterial strain V (and IV2) fermentation processes and bacterial strain III fermentation processes.”15

This contradiction in reports is clarified by Yanofsky’s earlier point, that contaminants in SDK product could have formed in two-step processes, where the overproduction or excess of L-tryptophan produced from the GE bacteria during fermentation subsequently reacted to some condition during purification. At first glance, some researchers may fault Showa Denko’s purification process. But the two aspects of the manufacturing process—fermentation and purification—are not as separate as some have suggested. Contaminants formed during purification could have been directly influenced by what happened during the GE-enhanced fermentation, which created the initial conditions for the reactions.

parsy, who says this looks like science to him

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