Comparison between mouse bioassay and HILIC-MS/MS for quantification of paralytic shellfish toxin in Japanese basket clams and mussels caught off coastal Osaka Bay in Japan.

The content and composition of paralytic shellfish toxins (PSTs) in Japanese basket clam (Corbicula japonica) and mussels (Mytilus galloprovincialis) from Osaka Bay, Japan, were investigated using a mouse bioassay (MBA) and hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS), and the association between toxicity values of MBA and HILIC-MS/MS was verified based on research data. The overall toxicity in Japanese basket clam was lower than that in the mussel. The PSTs of Japanese basket clam and mussel consisted mainly of C1, C2, and gonyautoxins 1-4 (GTX1-4) taking toxins compositional differences as mol%. When multiplying the content of different toxins by the toxic equivalent factor (TEF), C2 and GTX1-4 accounted for more than 90% of total toxicity (MU TEF/g) based on the MU TEF score converted by TEF for the two species. The total content of C2 and GTX1-4 converted to toxicity was significantly correlated with the toxicity determined by MBA for the two species (r2 > 0.983). This study provides a suitable and ethical monitoring method to investigate toxicity in bivalves contaminated with A. tamarense by analysis of only predominant toxins, along with reducing use of MBA.

PCR-Based Method for the Detection of Toxic Mushrooms Causing Food-Poisoning Incidents.

In this study, species-specific identification of five toxic mushrooms, Chlorophyllum molybdites, Gymnopilus junonius, Hypholoma fasciculare, Pleurocybella porrigens, and Tricholoma ustale, which have been involved in food-poisoning incidents in Japan, was investigated. Specific primer pairs targeting internal transcribed spacer (ITS) regions were designed for PCR detection. The specific amplicons were obtained from fresh, cooked, and simulated gastric fluid (SGF)-treated samples. No amplicons were detected from other mushrooms with similar morphology. Our method using one-step extraction of mushrooms allows rapid detection within 2.5 hr. It could be utilized for rapid identification or screening of toxic mushrooms.

Detection of Histamine in Fish and Fishery Products in Osaka Prefecture (Fiscal 2015 Report).

Histamine food poisoning is caused by ingestion of spoiled fish containing high levels of histamine. This paper reports cases in which histamine was detected in Osaka prefecture in fiscal year 2015 in a survey of fish and fishery products on the market and the food poisoning. A suspected case of histamine food poisoning was also evaluated to investigate the cause and minimize further problems. Histamine in food was separated on SPE cartridge columns, and analyzed after derivatization with fluorescamine by means of HPLC-FL. Histamine was detected in some fishery products on the market and in food that had caused poisoning. The samples in which histamine was detected were semi-dried whole round herring (Urumeiwashi-maruboshi), mackerel (Saba) and sardine dumpling (Iwashi-tsumire). These foods were the main causes of histamine food poisoning according to the report of the Ministry of Health, Labour and Welfare, Government of Japan.

Discrimination of mushrooms causing food-poisoning incidents by using DNA sequence analysis.

In this study, the identification of mushrooms by using DNA analysis was investigated. Our analysis of internal transcribed spacer (ITS) regions revealed that a DNA-based method could be applicable for samples that are difficult to distinguish in terms of the morphological characteristics. PCR amplification using templates extracted from cooked samples gave sufficient fragments to analyze the sequence. However, treatment with simulated gastric fluid (SGF) for more than 30 min affected the analysis of the ITS region. Application to samples of vomit is also discussed.

DNA-based identification of fish species implicated in Puffer fish poisoning.

A method for identification of fish species using three different mitochondrial DNA regions, 16S rRNA, cytochrome b and cytochrome c gene fragments, was investigated. The combined use of all three regions enabled reliable species identification in not only raw fish, but also dried, seasoned and boiled fish, products. Furthermore, the method was applicable even to vomitus from a patient involved in a puffer fish poisoning incident. However, further improvement is necessary to discriminate between closely related species such as Takifugu rubripes and T. chinensis, because they showed close similarity in the nucleotide sequences in the three gene fragments analyzed in this study.

Synthesis of phosphatidylinositols having various inositol stereoisomers by engineered phospholipase D.

Phospholipase D-mediated synthesis of phosphatidylinositols having various inositol stereoisomers was studied. Seven inositol stereoisomers were tested, all of which were found to be substrates of the enzyme, generating the corresponding phosphatidylinositols. Based on the substrate specificity, models for the recognition of inositol by the enzyme were proposed.

Bacillus subtilis spore coat protein LipC is a phospholipase B.

In Bacillus subtilis, the germination-related lipase LipC is located in the spore coat, and mutant spores are defective in L-alanine-stimulated germination. To determine the physiological role of LipC, the recombinant LipC expressed in Escherichia coli was purified and characterized. The enzyme hydrolyzes p-nitrophenyl ester substrates with various acyl-chain lengths. Thin-layer chromatography and gas chromatography-mass spectrometry analysis indicated that LipC cleaves the fatty acids at the sn-1 and sn-2 positions of phospholipids as phospholipase B, and that the enzyme shows no selectivity for the polar head groups of lipid molecules. When the amounts of free fatty acids in dormant wild-type and lipC mutant (YCSKd) spores were measured, the amount of free fatty acids in the YCSKd spores was about 35% less than in the wild-type spores. These results suggest the possibility that Bacillus subtilis LipC plays an important role in the degradation of the outer spore membrane during sporulation.

Physiological role of carbon dioxide in spore germination of Clostridium perfringens S40.

Germination of Clostridium perfringens is known to be triggered by nutrients such as l-alanine and inosine, and facilitated by CO2, however the role of CO2 has not been fully understood. During the studies of the germination-specific protease GSP, we found that CO2 could be replaced by bicarbonate or weakly acidic pH (pH 6.0-6.5). We also found that the spores obtained from the C. perfringens S40 overproducing GSP could germinate without CO2. Moreover, the spores could germinate in the absence of nutrients, when the spores were incubated with bicarbonate or under weakly acidic pH. GSP, which might consist of three homologous proteases, CspA, CspB, and CspC, is one of the key enzymes involved in the spore germination, and converts the pre-mature form of the spore cortex-lytic enzyme, SleC, to the mature form. Maturation of SleC in the spores obtained from the mother strain of C. perfringens S40 requires nutrients plus bicarbonate or weakly acidic pH. In contrast, mature SleC was found in the spores obtained from the cells overpoducing GSP, when the spores were treated by nutrients, bicarbonate or weakly acidic pH. Each nutrients, bicarbonate and weakly acidic pH can trigger the germination of the spores obtained from C. perfringens cells overproducing GSP.

Composition analysis of positional isomers of phosphatidylinositol by high-performance liquid chromatography.

An HPLC-based method has been developed for composition analysis of six positional isomers of phosphatidylinositol (PI), of which the phosphatidyl group was connected to different positions of the myo-inositol moiety. The method employed a combination of two types of HPLC analyses. One was direct separation of the six PI isomers into four peaks of 1(3)-PI, 2-PI, 4(6)-PI and 5-PI on a normal-phase silica gel column. The second method was for the separations of 1-PI from 3-PI and 4-PI from 6-PI, which were not separable on the normal-phase column. This method involved conversion of PI isomers into pentakis-(R)-1-phenylethylcarbamate (PEC) derivatives, which were separated on a reversed-phase column. Using the established method, positional specificity of several engineered phospholipases D in enzymatic synthesis of PI from myo-inositol and phosphatidylcholine was investigated. This was performed by analyzing the isomeric composition of PIs synthesized by the mutant enzymes. Among five mutant enzymes tested, two showed strong specificity to 1-OH, one showed moderate preference to 1-OH, one preferred 3-OH, and one showed broad specificity towards 1-, 3-, 4- and 6-OH.

Isolation of phospholipase D mutants having phosphatidylinositol-synthesizing activity with positional specificity on myo-inositol.

ENZYME-MEDIATED SYNTHESIS OF PHOSPHATIDYLINOSITOL: Engineered phospholipase D enzymes enable the synthesis of phosphatidylinositol by transphosphatidylation. The 1- or 3-hydroxy group of myo-inositol is selectively reacted. Phospholipase D (PLD) mutants that have phosphatidylinositol (PI)-synthesizing activity with positional selectivity towards 1- or 3-OH groups of myo-inositol have been isolated. A mutant PLD library, in which site-directed saturation mutations were introduced in vitro at positions 187, 191, and 385 of the wild-type PLD of Streptomyces antibioticus, was screened for PI-synthesizing mutants. TLC and HPLC analyses of the PI synthesized by the isolated mutant PLDs revealed that three mutants, namely 187D/191Y/385R (DYR), 187A/191Y/385R (AYR), and 187M/191Y/385R (MYR), selectively generated 1- or 3-PI among the other possible PI positional isomers. Taking into account the consensus sequence of the three mutants, a series of mutants, 187X/191Y/385R (XYR), was constructed and analyzed. Almost all the XYR mutants generated 1(3)-PI selectively, thus suggesting that the Y385R mutation contributed to the selectivity for the 1(3)-PI synthesis. The XYR mutants showed similar phosphatidylcholine-hydrolyzing activity among the mutants, but the PI-synthesizing activities were different depending on the amino acid at position 187. In particular, aromatic amino acids at position 187 greatly reduced the PI-synthesizing activity. The ratios of 1-PI versus 3-PI in the PIs synthesized with the XYR mutants were analyzed by selective hydrolysis with PI-specific phospholipase C. It was found that 187H/191Y/385R (HYR) generated 1-PI more than 3-PI (ratio=7:3), whereas 187T/191Y/385R (TYR) generated 1-PI less than 3-PI (ratio=2:8). This confirmed that the amino acid at position 187 determined the selectivity between 1-PI and 3-PI formation.

Streptomyces phospholipase D mutants with altered substrate specificity capable of phosphatidylinositol synthesis.

The substrate specificity of a phospholipase D (PLD) from Streptomyces antibioticus was altered by site-directed saturation mutagenesis, so that it was able to synthesize phosphatidylinositol (PI). Mutations were introduced in the pld gene at the positions corresponding to three amino acid residues that might be involved in substrate recognition, and the mutated genes were expressed in Escherichia coli BL21 (DE3). High-throughput screening of approximately 10,000 colonies for PI-synthesizing activity identified 25 PI-synthesizing mutant PLDs. One of these mutant enzymes was chosen for further analysis. The structure of the PI synthesized with the mutant enzyme was analyzed by HPLC-MS and NMR. It was found that the mutant enzyme generated a mixture of structural isomers of PIs with the phosphatidyl groups connected at different positions of the inositol ring. The phosphatidylcholine-hydrolyzing activity of the mutant PLD was much lower than that of the wild-type enzyme. The mutant enzyme was able to transphosphatidylate various cyclohexanols with a preference for bulkier compounds. This is the first example of alteration of the substrate specificity of PLD and of PI synthesis by Streptomyces PLD.

Mode of action of a germination-specific cortex-lytic enzyme, SleC, of Clostridium perfringens S40.

The hydrolysis of the bacterial spore peptidoglycan (cortex) is a crucial event in spore germination. It has been suggested that SleC and SleM, which are conserved among clostridia, are to be considered putative cortex-lytic enzymes in Clostridium perfringens. However, little is known about the details of the hydrolytic process by these enzymes during germination, except that SleM functions as a muramidase. Muropeptides derived from SleC-digested decoated spores of a Bacillus subtilis mutant that lacks the enzymes, SleB, YaaH and CwlJ, related to cortex hydrolysis were identified by amino acid analysis and mass spectrometry. The results suggest that SleC is most likely a bifunctional enzyme possessing lytic transglycosylase activity and N-acetylmuramoyl-L-alanine amidase activity confined to cross-linked tetrapeptide-tetrapeptide moieties of the cortex structure. Furthermore, it appears that during germination of Clostridium perfringens spores, SleC causes merely small and local changes in the cortex structure, which are necessary before SleM can function.

A novel lipolytic enzyme, YcsK (LipC), located in the spore coat of Bacillus subtilis, is involved in spore germination.

The predicted amino acid sequence of Bacillus subtilis ycsK exhibits similarity to the GDSL family of lipolytic enzymes. Northern blot analysis showed that ycsK mRNA was first detected from 4 h after the onset of sporulation and that transcription of ycsK was dependent on SigK and GerE. The fluorescence of the YcsK-green fluorescent protein fusion protein produced in sporulating cells was detectable in the mother cell but not in the forespore compartment under fluorescence microscopy, and the fusion protein was localized around the developing spores dependent on CotE, SafA, and SpoVID. Inactivation of the ycsK gene by insertion of an erythromycin resistance gene did not affect vegetative growth or spore resistance to heat, lysozyme, or chloroform. The germination of ycsK spores in a mixture of L-asparagine, D-glucose, D-fructose, and potassium chloride and LB medium was also the same as that of wild-type spores, but the mutant spores were defective in L-alanine-stimulated germination. In addition, zymogram analysis demonstrated that the YcsK protein heterologously expressed in Escherichia coli showed lipolytic activity. We therefore propose that ycsK should be renamed lipC. This is the first study of a bacterial spore germination-related lipase.

Expression of germination-related enzymes, CspA, CspB, CspC, SleC, and SleM, of Clostridium perfringens S40 in the mother cell compartment of sporulating cells.

In Clostridium perfringens S40, spore germination-specific enzymes are synthesized during sporulation. Previous reports have demonstrated that two cortex-lytic enzymes, SleC and SleM, and a component of germination-specific protease, CspC, are located outside the cortex as an integral part of the dormant spore. In the present study, we examined the time and compartment of these enzymes' gene expression using reverse transcription-PCR (RT-PCR) and fluorescence microscopy on green fluorescence protein (GFP)-fused proteins. These results suggested that CspABC, SleC, and SleM are synthesized in the mother cell compartment of sporulating cells, probably at stages II approximately III of sporulation, and that the expression of cspABC genes is tricistronic.

Subcellular localization of a germiantion-specific cortex-lytic enzyme, SleB, of Bacilli during sporulation.

The subcellular localization of a germination-specific cortex-lytic enzyme, SleB, of Bacillus subtilis during sporulation was observed by using fusions of N-terminal region of SleB to the green fluorescent protein (GFP). A fusion with a putative peptidoglycan-binding motif (SleB1-108-GFP) formed a fluorescent ring around the forespore of the wild type strain, as expected from the known location of the intact SleB in the dormant spore. SleB1-108-GFP formed a similar fluorescent ring around the forespore of the gerE mutant which has a severe defect in the coat structure, and of the cwlD mutant which lacks a muramic delta-lactam unique to the spore peptidoglycan (cortex), whereas the fusion could not attach to the spore of the cwlDgerE mutant. By contrast, a fusion without the motif (SleB1-45-GFP) could not be recruited around the forespore of the gerE mutant though it appeared to be accumulated on the outside of the spore of the wild type strain. Since SleB was shown to degrade only the cortex with muramic delta-lactam, these results suggested that a proper localization of SleB requires a strict interaction between the motif of the enzyme and the delta-lactam structure of the cortex, not the formation of normal coat layer.