Limited vegetative compatibility as a cause of somatic recombination in Trichoderma pseudokoningii

With the aim of a better characterization of the somatic recombination process in Trichoderma pseudokoningii, a progeny from crossings between T. pseudokoningii strains contrasting for auxotroph markers was characterized by RAPD markers and PFGE (electrophoretic karyotype). Cytological studies of the conidia, conidiogenesis and heterokaryotic colonies were also performed. The genotypes of the majority of the recombinant strains analyzed were similar to only one of the parental strains and the low frequency of polymorphic RAPD bands suggested that the nuclear fusions may not occur into the heterokaryon. In some heterokaryotic regions the existence of intensely staining hyphae might be related to cell death. We proposed that a mechanism of somatic recombination other than parasexuality might occur, being related to limited vegetative compatibility after postfusion events, as described for other Trichoderma species.

Cytological characterization of an Aspergillus nidulans mutant from a strain with chromosomic duplication

A development mutant, named V103, was obtained spontaneously from the A strain of A. nidulans. The A strain contains a duplicated segment of chromosome I that has undergone translocation to chromosome II (I ¨ II). It is mitotically unstable and generates phenotypically deteriorated types, some with enhanced stability. The deteriorated variants of A. nidulans show abnormal development, exhibiting slower colony growth, variations in colony pigmentation and changes in conidiophore structure. The alterations observed in the conidiophore include fewer metulae and phialides, further elongation and ramification of these structures, delayed nuclear migration and the presence of secondary conidiophores.

Pulsed field gel electrophoresis reveals chromosome length and number differences in Brazilian strains of Metarhizium Anisopliae

Cariótipos de oito linhagens selvagens do fungo entomopatogênico Metarhizium anisopliae var. anisopliae foram obtidos em gel, por eletroforese em campo pulsado. As linhagens foram isoladas de insetos provenientes de seis estados brasileiros. As moléculas de DNA cromossômico de três linhagens foram separadas em sete bandas e, de cinco linhagens, em oito bandas. Polimorfismo de tamanho cromossômico também foi observado. O tamanho do DNA cromossômico de todas as linhagens variou de 7,7 a 0,9 Mb, utilizando-se DNA cromossômico de Aspergillus nidulans como padrão. O tamanho do genoma total foi estimado em pelo menos 29,7 Mb. Algumas correlações entre semelhanças e diferenças no cariótipo eletroforético e a ocorrência do ciclo parassexual como também a especificidade com insetos hospedeiros foram discutidas.

Genetic characterization of somatic recombination in Trichoderma pseudokoningii

Crossing experiments via hyphal anastomosis between two strains contrasting for auxotrophic markers of Trichoderma pseudokoningii were conducted to characterize the somatic recombination process in this specie. Four crossings were made and a total of 1052 colonies obtained from conidial suspensions of the heterokaryotic colonies were analyzed. Sixty-eight recombinant colonies, from four growing generations, were analyzed for the auxotrophic markers. Of the 68 colonies analyzed, 58 were stable after four generations and the remainders were unstable, reverting to one of the parentals. Most of the recombinant colonies were unstable through subculture and after four growing generations they showed the leu ino met markers (auxotrophic for leucin, inositol and metionin respectively). The unstable recombinant colonies showed irregular growing borders, sparse sporulation and frequent sector formation. The results suggest the occurrence of recombination mechanisms in the heterokaryon (somatic recombination), different from those described for the parasexual cycle or parameiosis. Therefore, we proposed the ocurrence of nuclei degradation from one parental (non prevalent parental) in the heterokaryon and that the resulting chromosomal fragments may be incorporated into whole nuclei of the another parental (prevalent parental). However the parameiosis as originally described cannot be excluded.

Isolation of herpotrichiellacious fung from the environment

Herpotrichiellaceous fungi, common agents of chromoblastomycosis and phaeohyphomycosis, were searched in samples of rotten wood, leaf littler, bark and soil of the rhizosphere, collected in the Centro Nacional de Pesquisas de Florestas/EMBRAPA, Colombo, PR, Brazil. Morphological analyses of macro, optic and scanning electron microscopy, as well as the determination of the nutritional pattern of the isolated strains were carried out for a taxonomical study. In a total of 17 colonies, 3 isolates (17.6 per cente) were identified as species of medical relevance: Cladophialophora bantiana (Sacc.) de Hoog et al., Fonsecaea pedrosoi (Brumpt) Negroni and Phialophora verrucosa Medlar. The identifications were based on the results of the analyses and on the comparison with CBS (Centraal Bureau voor Schimmelcultures) reference strains. This investigation revealed the saprophytic existence of species known as agents of chromoblastomycosis and phaeohyphomycosis. These diseases are considered autochthonous in the studied area.(au)

Electrophoretic characterization of Aspergillus nidulans strains with chromosomal duplications

Linhagens de Aspergillus nidulans que apresentam duplicaçäo cromossômica Dp(I-II) foram caracterizadas por eletroforese em campo pulsado. Foram analisados variantes morfologicamente deteriorados e melhorados. O cariótipo eletroforético demonstrou que em ambas as linhagens duplicadas (A e B) a banda de 4,2 Mb, que corresponde ao cromossomo II, näo estava presente e foi encontrada uma nova banda. Foram feitas hibridizaçöes usando os genes uapA (cromossomo I) e wA (cromossomo II), que demonstraram que a nova banda corresponde ao cromossomo II mais o segmento duplicado do cromossomo I. O tamanho da duplicaçäo foi determinado como aproximadamente 1,0 Mb. A análise das bandas cromossômicas da linhagem morfologicamente melhorada mostrou que o segmento duplicado do cromossomo I foi completamente perdido. Os variantes morfologicamente deteriorados V9 e V17 mostraram o mesmo cariótipo eletroforético apresentado pelas linhagens duplicadas. Contudo, o variante deteriorado V5 perdeu parte do cromossomo I e apresentou um rearranjo envolvendo o cromossomo V. Esse rearranjo pode ter resultado do tratamento mutagênico usado para a obtençäo dos marcadores genéticos. Os resultados obtidos nesse trabalho demonstram que a técnica de eletroforese em campo pulsado é uma ferramenta excelente para a localizaçäo de rearranjos cromossômicos.

Recurrent mutation-selection to improve rennet production in Candida tsukubaensis

The yeast Candida tsukubaensis is of industrial importance for the production of microbial milk-clotting enzyme. Milk-clotting enzyme is an enzymatic complex capable of coagulating milk for cheese manufacturing. High clotting activity (CA) and low proteolytic activity (PA) are desirable qualities. To study the genetic nature of the CA and PA traits, we analyzed 179 colonies obtained after mutagenic treatment. Analysis of the data obtained for this populations showed that CA and PA are traits controlled by polygenes and that they are correlated (r = 0.3). The existence of a positive correlation indicates that selection for one trait without considering the other may alter one of the traits in an undesirable direction, since the objective of selection would be an increase in clotting activity and a decrease in proteolytic activity. Three cycles of recurrent mutation-selection were carried out to obtain improved strains. The ultraviolet light dose permitting a 5 per cent rate of cell survival was sufficient to generate genetic variability in the three selection cycles. At the end of the third cycle there was an increase of about 98 per cent in clotting activity and a decrease of about 20 per cent in proteolytic activity. Analysis of variance of the selective cycles showed that the linear effects were significant (P < 0.01) for both traits. Estimates of genetic variances and heritabilities of the three selection cycles are presented.

Genetic recombination after protoplast fusion in Candida sp

O objetivo deste trabalho foi descrever o ciclo parassexual em Candida sp uma levedura que näo apresenta ciclo sexual. As condiçöes para isolamento e regeneraçäo de protoplastos foram estabelecidas para a linhagem selvagem de Candida sp. O polietileno glicol foi utilizado para induzir a fusäo dos protoplastos isolados a partir das linhagens auxotroficas (pab bio e ura arg). As colonias prototróficas originais após fusäo foram selecionadas por complementaçäo em meio mínimo. A partir de um produto de fusäo nuclear selecionado, foram obtidos vários recombinantes monoauxotróficos, os quais tiveram diametro nuclear similar às linhagens parenterais. este fato sugere que os recombinantes auxotróficos se originaram de perdas cromossomicas do produto de fusäo nuclear

Estudo da resistência de amostras de Staphylococcus aureus a diferentes antibióticos / A study of multiple antibiotic resistance in samples of Staphylococcus aureus

Um total de 88 amostras de Staphylococcus aureus, das quais 44 isoladas da narina e pele de estudantes e outras 44 isoladas do ambiente hospitalar, foi testado frente a 11 antibióticos. Os resultados obtidos mostraram níveis de resistência relativamente altos, principalmente com relaçäo à penicilina, nas amostras de estudantes