In Aspergillus several types of test systems have been developed for detection of chemicals which induce aneuploidy and/or malsegregation of chromosomes. Results from 23 papers were reviewed in which numerical data for 42 chemicals had been reported. The test systems fall into two groups. One group includes all purely genetic tests that detect euploid mitotic segregants from heterozygous diploids and identify these either as products of malsegregation of chromosomes or as products of crossing-over (13 papers, several reviewed in detail previously; Käfer et al. (1982) and Scott et al. (1982)). The other group includes tests that treat haploid or diploid strains and detect aneuploids as unstable abnormally growing segregants which can be identified as specific disomics or trisomics by their characteristic phenotypes. In addition, such tests characterize abnormal segregants from heterozygous diploids by correlating phenotypes with patterns of genetic segregation in spontaneous euploid sectors. This analysis makes it possible to distinguish between induced primary aneuploidy of whole chromosomes and partial tri- or monosomy resulting from chromosome breakage and secondary spontaneous malsegregation (10 papers). Based on results of both types of tests, it is postulated that chemicals which cause increases of euploid malsegregants, but not of crossovers, normally induce aneuploids as primary products (as shown for 7 of the 14 cases). These include compounds which damage spindles or membranes (especially the well-known haploidizing agents) and generally are effective only when growing cells are exposed. (8 chemicals that may belong in this category could not be classified for certain, because information was insufficient.) On the other hand, chemicals which cause increases of all types of euploid segregants (11 cases), mostly induce drastic mutations and aberrations as primary effects and cause spontaneous malsegregation or crossing-over only as secondary events (as demonstrated for radiation-induced abnormals). In addition, a few chemicals were negative, because they increased only crossing-over or showed no increased segregation at all at concentrations which reduced survival or growth rate (9 cases). Recommendations are made for standardization of methods and protocols. New tester strains and specific procedures are outlined which should be useful for conclusive tests of chemicals that may induce aneuploidy.

This review represents a critical summary of results from published investigations which analyse effects of chemicals on mitotic segregation in Aspergillus nidulans (covering mainly references of the period 1965–1978). On the basis of the test systems employed the evaluated publications fall into three groups. The first and largest group uses tests which identify effects of chemicals on the frequencies of homo- or hemizygous segregants in heterozygous diploids (14 papers). Such “segregants” arise from increased segregation, usually either by mitotic crossing-over, non-disjunction, malsegregation, or from semi-dominant mutations of various types, including lethals and chromosomal aberrations. The second group includes a few investigations which test for increases in the frequencies of recessive lethals or balanced translocations in treated diploids that are revealed by effects on the recovery of haploid second-order segregants (3 papers). The third group investigates effects on the frequencies of haploid sectors from duplication strains, that are affected by some chemicals and may be due to site-specific recombination or chromosome breakage (4 papers).

The status of the Aspergillus systems, with respect to their usefulness in screening chemicals for genotoxic effects, was evaluated using information available in the open literature. A total of 179 references were evaluated; 58 contained relevant information for the purpose of determining the genotoxic status of a chemical. To simplify presentation, these papers were divided into two groups. The first group of papers analyzed the effect of chemicals on mitotic segregation in Aspergillus (reported in Käfer et al., this issue). The second group of papers, reporting on the response of the haploid Aspergillus systems to various agents, are reviewed in this paper which also contains an overall summary of the responses of an Aspergillus system and compares these results with those obtained from in vivo carcinogenicity studies.

A strain of Aspergillus nidulans has been used to study the inactivating and mutagenic effect of 60Cogamma-rays in the presence of oxygen or nitrogen. Mutation was studied by the 2-thioxanthine system which selectively detects forward mutation at a number of gene loci (at least 16). Mutants resistant to conidial pigmentation effects of 2-thioxanthine can be divided into four main classes (2TxR, hx, uaY and cnx) and three of these classes (hx, uaY and cnx) can be further characterized at the gene level. The results demonstrate the existence of a marked differential forward mutational response of gene loci in Aspergillus conidia which is dependent upon whether gamma-irradiation in aqueous suspension was carried out in the presence of oxygen or of nitrogen: this effect is independent of the dose of radiation exposure. The specificity for mutation is altered by the presence of the self-inhibitor of germination for the anoxic treatment but not the oxic irradiation. The implication of different oer's (oxygen enhancement ratios) for mutation induction in different classes or genes for the mechanism and type of damage induced by the two radiation conditions are discussed.

UV treated conidia of a strain of Aspergillus nidulans (meth Gl. biAl) depleted of germination inhibitory substances have been examined for inactivation and mutation induction at groups of suppressor gene loci defining three classes of methionine revertants. An exponential decline in the colony forming ability and quadratic increase in mutation frequency (for each class of revertant) as the incident dose increased were observed. The induced mutation frequency for each class and the loss of colony forming ability of the conidia are greater in the absence than in the presence of these self-inhibitors of germination. However, the relative frequencies of the individual classes of revertants did not differ whether the inhibitory substances were present or not.

The phototoxic potential of a number of furocoumarins is well established. On the other hand, studies have shown that bergamottin, a furocoumarin containing a bulky, hydrophobic side chain, has significantly less or is even absent of phototoxicity potential. The OECD Test Guideline 432 3T3/Neutral Red Uptake (NRU) in vitro phototoxicity test has shown to be a highly predictive test for identifying compounds that exhibit no phototoxicological potential. In this study using OECD 432, the established phototoxic furocoumarin 5-methoxypsoralen (5-MOP), 8-methoxypsoralen (8-MOP) and psoralen were phototoxic, whereas bergamottin showed no phototoxic potential. When compared to 5-MOP, 8-MOP and psoralen, bergamottin was clearly negative at molar-adjusted concentrations that were more than 9 times higher than those that produced phototoxicity in 8-MOP; nearly 16 times than those for psoralen and more than 36 times higher than those for 5-MOP. These data using in vitro 3T3 NRU Phototoxicity Test (OECD 432) are supportive of earlier studies showing bergamottin does not exhibit phototoxicological properties. The detection and quantification of bergamottin should therefore not contribute to the potential marker furocoumarins for risk management interventions intended to reduce the phototoxicity of natural furocoumarin containing preparations.

The cytotoxic and mutagenic specificity of two therapeutically employed psoralens was examined in several Ames Salmonella typhimurium strains with near ultraviolet light (UVA, 320–400 nm) activation. Photomutagenic activity of 8-methoxypsoralen (8MOP) and 4,5′,8-trimethylpsoralen (TMP) was found to be sequence-specific, and additionally was dependent on the level of DNA-repair proficiency. Base-pair substitution photomutagenesis in hisG46 appeared to require plasmid pKM101-mediated “error-prone” repair. Frameshift photomutagenesis was observed in all hisC3076 strains but not in hisD3052 strains. Frameshift mutagenic activity in hisC3076 was enhanced in the absence of uvrB excision repair and increased further by plasmid pKM101. Phototoxicity was essentially identical in hisC3076, hisD3052 and hisG46 strains; uvrB− excision-repair-deficient bacteria were considerably more susceptible to lethal effects than wild-type parental strains, while the presence of pKM101 had no apparent effect on survival. Finally, the data show that psoralens are potent frameshift photomutagens in Salmonella hisC3076 strains and demonstrate the potential utility of these strains in evaluating photomutagenic and phototoxic activity of new furocoumarin derivatives.