Trichosporon mycotoxinivorans sp. nov., a new yeast species useful in biological detoxification of various mycotoxins

A yeast strain isolated from the hindgut of the lower termite Mastotermes darwiniensis (Mastotermitidae) was found to represent a new member of the genus Trichosporon. Trichosporon mycotoxinivorans is closely related to T. loubieri on the basis of the phylogenetic trees based on the D1/D2 region of 26S rDNA, an approx. 600 bp fragment of the 18S rDNA and both ITS regions. However, the two species differ at nine positions in the D1/D2 region of 26S rDNA. The IGS1 region of T. mycotoxinivorans is 401 bp long. T. mycotoxinivorans is distinguished from T. loubieri by its ability to assimilate inulin and galactitol, and its inability to grow at 40 °C. The name of this newly isolated strain refers to an important characteristics of T. mycotoxinivorans to detoxify mycotoxins such as ochratoxin A and zearalenone. Therefore this strain can be used for the deactivation of the respective mycotoxins in animal feeds.     

Inheritance patterns of new genetic markers and occurrence of spontaneous mosaicism in the monogenic blowfly Chrysomya rufifacies (Diptera: Calliphoridae)

 Four new genetic markers for Chrysomya rufifacies, a fly with maternal sex determination, were characterized. The markers include one body colour mutant, black body (bl), and three eye colour mutants, brown eye (br), apricot eye (ap), and red eye (w ^r ). Two of the latter, br and w ^r , turn out to be sex linked, the others behave as autosomal genes belonging to different linkage groups. w ^r is a hypomorphic and w an apomorphic mutation of the white gene, w/w is epistatic to br/br and to ap/ap. A preliminary genetic linkage map with the sex realizer F′/f  and the loci br and w residing in homomorphic sex chromosomes is established. Evidence is presented that crossing over is absent in the male sex. The possible causes of the spontaneous appearance of mosaics for eye colour observed among individuals heterozygous for recessive genes are discussed. Received: 18 March 1996/Accepted: 9 August 1996     

Inheritance patterns of new genetic markers and occurrence of spontaneous mosaicism in the monogenic blowfly Chrysomya rufifacies(Diptera: Calliphoridae)

Four new genetic markers for Chrysomya rufifacies, a fly with maternal sex determination, were characterized. The markers include one body colour mutant, black body (bl), and three eye colour mutants, brown eye (br), apricot eye (ap), and red eye (w ^r ). Two of the latter, br and w ^r , turn out to be sex linked, the others behave as autosomal genes belonging to different linkage groups. w ^r is a hypomorphic and w an apomorphic mutation of the white gene, w/w is epistatic to br/br and to ap/ap. A preliminary genetic linkage map with the sex realizer F′/f? and the loci br and w residing in homomorphic sex chromosomes is established. Evidence is presented that crossing over is absent in the male sex. The possible causes of the spontaneous appearance of mosaics for eye colour observed among individuals heterozygous for recessive genes are discussed.     

Analysis of the predetermining effect of a sex realizer by ovary transplantations in the monogenic flyChrysomya rufifacies

Summary In the heterozygousF/f female-producing females of the strictly monogenic blowflyChrysomya rufifacies the gene product of the dominant or epistatic female sex realizerF which causes sexpredetermination is thought to be synthesized either by cells of the germ line (oocytes, nurse cells or oogonia) or by somatic cells and then transferred into the oocytes. To determine the possible site of synthesis, reciprocal transplantations were made of prepupal ovaries between female-producing (thelygenic; t) and male-producing (arrhenogenic; a) females ofChrysomya rufifacies. In another series of experiments prepupal host females of the wild t-type and a-type were each provided with one additional ovary either from a0type (f/f) or a t-type (F/f) prepupa (neither were distinguishable by their phenotypes). In all these experiments the donor females were marked by the recessive sex-linked mutation white (w/w); white eyes, white Malpighian tubules). In a considerable number of cases the implanted ovaries were in contact with the host's own oviduct and grew normally, but the rate of hatched adults was somewhat reduced. Crosses between such host females andw/w males (f/f) produced female or male offspring with white eyes from the eggs of the implantedw/w ovary, as well as flies with wild-type eyes (+/w) which had developed in the host's own ovaries. In all cases so far examined, the genetically thelygenic (or arrhenogenic) host females with an additional ovary implanted from an arrhenogenic (thelygenic) donor, produced progeny of both sexes: sons (daughters) from the eggs of the donor's ovary and daugthers (sons) from the eggs of the host's own gonads.These results demonstrate that the ovaries of the t-females ofChrysomya rufifacies at least from the early prepupal stage, are autonomous for the product of theF gene. Transplantations of the premordial germ cells (pole cells) are planned to find out whether the predeterminingF gene product is synthesized before the prepupal stage, by somatic cells outside the ovary or by somatic (follicle) cells of the ovary itself.Dedicated to Professor Dr. Hans Bauer with gratitude in commemoration of his 75th birthday     

Analysis of sex determination in the monogenic blowfly Chrysomya rufifacies by pole cell transplantation

Summary Sex determination in the monogenic blowfly Chrysomya rufifacies is controlled by a dominant or epistatic female sex realizer (F) having sex predetermining properties (F/f=female-producing female; f/f=male-producing female or male, respectively). To determine (1) the cell type in which the maternal effect gene F is expressed. and (2) the autonomous or nonautonomous sexual differentiation of the germ cells germ-line mosaics were constructed in C. rufifacies by pole-cell transplantations. The production of bisexual progeny by germ-line mosaics generated by transplanting pole cells between both types of female embryos shows that the F gene product is synthesized by germ-line cells themselves, not by maternal (intra- or extraovarian) somatic cells. Pole cell transplantations between male and female embryos yielded completely fertile heterosexual germ-line mosaics thus demonstrating phenotypic sex reversal of donor germ cells in a host of the opposite sex. Consequently, the sexual differentiation of a germ cell in C. rufifacies is not determined by its own genotypic constitution but is induced by the surrounding somatic cells.The male sex of F/f individuals generated by fertilization with F-bearing sperm from a heterosexual germ-line mosaic indicates that the F gene is either not expressed during spermatogenesis and early embryogenesis or is expressed too late or in not sufficient amounts to direct differentiation into the female sex. This finding is consistent with the assumption that progamic expression of F is found exclusively during oogenesis in F/f females.     

Identifizierung der genetischen Geschlechtschromosomen bei der monogenen Schmeißfliege Chrysomya rufifacies (Calliphoridae,Diptera)

Previous investigations have shown the sex determination in the monogenic blowfly Chrysomya rufifacies to be controlled by a cytologically not discernible homogamety-heterogamety mechanism in the female. Female-producing (thelygenic) females are assumed to be heterozygous for a dominant female sex realizer (F′) with sex-predetermining properties, while male-producing (arrhenogenic) females as well as males are supposed to be homozygous for the recessive allele (f). In order to identify the genetic sex chromosomes of C. rufifacies among its five pairs of long euchromatic chromosomes (nos.1–5) plus one pair of small heterochromatic ones (no. 6), all chromosomes were marked by reciprocal translocations induced by X-ray treatment of adult males. The inheritance of thirteen different heterozygous translocations has been analyzed. All of the translocations (eleven) between two of the four longer chromosomes did not show sex-linked inheritance, thus demonstrating the autosomal character of the chromosomes nos 1, 2, 3 and 4. The same is true for the translocation T6 (2/6). Therefore the small heterochromatic chromosome no. 6, corresponding to the morphologically differentiated sex chromosomes within the amphogenic calliphorid species, remains without sex determining function in the monogenic fly. This could be confirmed by the analysis of monosomic (monosomy-6) and trisomic (trisomy-6) individuals, which resulted from meiotic non-disjunction in T6/+ translocation heterozygotes. Contrary to these translocations, the heterozygous 5/2 translocation (T14) exhibited sex-linked inheritance: There was but a very low frequency (0,76 per cent) of recombinants resulting from crossing-over between F′/f and the translocation breakage point in thelygenic F₁ T14/+ females. The sex-linked inheritance of T14 was confirmed by the progeny of a thelygenic F₁ T14/+ female crossed to a homozygous T14/T14 translocation male. Among the offspring of that F₁ T14/+ female, which had received the translocation from its father, all of the F₂ T14/+ females were thelygenic compared to their arrhenogenic T14/T14 sisters. These results prove that the chromosomes of pair no. 5 genetically act as X′X-XX sex chromosomes in C. rufifacies.