Paula B. Morais

Trehalose accumulation by tropical yeast strains submitted to stress conditions.

Trehalose, a non-reducing disaccharide that accumulates in Saccharomyces cerevisiae, has been implicated in survival under various stress conditions by acting as membrane protectant, as a supplementary compatible solute or as a reserve carbohydrate which may be mobilized during stress. However, most of these studies have been done with strains isolated from European or Asian habitats of temperate climate. In this study, yeasts living in tropical environments, isolated from different microhabitats in Southeastern Brazil, were used to evaluate whether trehalose contributes to survival under osmotic, ethanol and heat stress. The survival under severe stress was compared to a well-characterized laboratorial wild-type strain (D273-10B). Most of the Saccharomyces cerevisiae strains isolated from Drosophila in Tropical Rain Forest were able to accumulate trehalose after a preconditioning treatment at 40 °C for 1 h. The amount of intracellular trehalose levels was better correlated with survival during a challenging heat shock at 50.5 °C for 8 min. Saccharomyces cerevisiae and Candida guilliermondii were observed to be thermotolerant as well as osmotolerant. No clear correlation between intracellular trehalose levels and survival could be derived during ethanol stress. In some cases, the amount of trehalose accumulated before the ethanol stress seemed to play an important role for the survival of these strains.

Screening of Yeasts from Brazilian Amazon Rain Forest for Extracellular Proteinases Production

Eighty seven yeast strains representing 34 species isolated from Parahancornia amapa fruit and associated Drosophila flies collected in the Brazilian Amazon rain forest, were screened for proteinase production. Proteolytic activity was tested through casein hydrolysis in solid medium supplemented with 0.5% casein and glucose. Among 23 strains, 18 from genus Candida and 5 from Pichia were caseinolytic and produced proteinases in yeast carbon base liquid medium supplemented with casein 0.01%. The proteolytic activity was tested on pH ranging from 2.0 to 9.0 in correspondence to the pH of the cultures media in which the yeasts were grown. Six highly proteolytic strains: Candida parapsilosis AP153A, C. krusei AP176, C. sorbosa DR215, C. sorbosa AP259, C. valida AP209A and C. sorboxylosa AP287 were selected and the pH optima of production and the proteolytic activity were determined. In general the secretion of proteinase was maximum throughout the exponential and the stationary phases. Greater production occurred in acidic culture and high activity was observed at pH 3.0, 4.0 and 5.0.

Hannaella pagnoccae sp. nov., a tremellaceous yeast species isolated from plants and soil.

Several independent surveys of yeasts associated with different plant materials and soil led to the proposal of a novel yeast species belonging to the Tremellales clade (Agaricomycotina, Basidiomycota). Analysis of the sequences of the D1/D2 domains and internal transcribed spacer region of the large subunit of the rRNA gene suggested affinity to a phylogenetic lineage that includes Hannaella coprosmaensis, Hannaella oryzae and Hannaella sinensis. Thirty-two isolates were obtained from different sources, including bromeliads, nectar of Heliconia psittacorum (Heliconiaceae), flowers of Pimenta dioica (Myrtaceae), roots and leaves of sugar cane (Saccharum spp.) in Brazil, leaves of Cratoxylum maingayi, Arundinaria pusilla and Vitis vinifera in Thailand, soil samples in Taiwan, and prairie soil in the USA. Sequence analysis of the D1/D2 domains of the large subunit of the rRNA gene showed that the novel species differs from Hannaella coprosmaensis and Hannaella oryzae by 36 and 46 nt substitutions, respectively. A novel species is suggested to accommodate these isolates, for which the name Hannaella pagnoccae sp. nov. is proposed. The type strain is BI118(T) ( = CBS 11142(T) = ATCC MYA-4530(T)).

Evidence of Natural Hybridization in Brazilian Wild Lineages of Saccharomyces cerevisiae.

The natural biology of Saccharomyces cerevisiae, the best known unicellular model eukaryote, remains poorly documented and understood although recent progress has started to change this situation. Studies carried out recently in the Northern Hemisphere revealed the existence of wild populations associated with oak trees in North America, Asia, and in the Mediterranean region. However, in spite of these advances, the global distribution of natural populations of S. cerevisiae, especially in regions were oaks and other members of the Fagaceae are absent, is not well understood. Here we investigate the occurrence of S. cerevisiae in Brazil, a tropical region where oaks and other Fagaceae are absent. We report a candidate natural habitat of S. cerevisiae in South America and, using whole-genome data, we uncover new lineages that appear to have as closest relatives the wild populations found in North America and Japan. A population structure analysis revealed the penetration of the wine genotype into the wild Brazilian population, a first observation of the impact of domesticated microbe lineages on the genetic structure of wild populations. Unexpectedly, the Brazilian population shows conspicuous evidence of hybridization with an American population of Saccharomyces paradoxus. Introgressions from S. paradoxus were significantly enriched in genes encoding secondary active transmembrane transporters. We hypothesize that hybridization in tropical wild lineages may have facilitated the habitat transition accompanying the colonization of the tropical ecosystem.

Yeasts Occurring in Surface and Mouth Cavity of Two Chelonian Species, Podocnemis expansa Schweigger and P. unifilis Troschel (Reptilia: Chelonia: Pelomedusidae), in the Javaés River Border of Araguaia National Park in Brazil.

Thirty-eight specimens of free-ranging Podocnemis expansa (Amazon turtle) and 22 of P. unifilis (Tracajá) were screened for yeast isolation from surface (plastron, skin, and nails), eye, and mouth cavity. A hundred and eighteen yeast isolates belonging to 39 species were obtained. Debaryomyces hansenii, Candida galli, C. sake, and Rhodotorula mucilaginosa were the most frequent species isolated from these chelonians. Species diversity measured by Shannons index was shown to be low and a degree of dominance could be detected as species known as potential pathogens were commonly isolated. The effective number of species in plastron of P. expansa was higher than in mouth samples, but not in P. unifilis probably due to dietary factors. P. expansa animals were captured on the beaches, and the superficial yeast populations may include terrestrial species. P. unifilis animals were captured in the water and the yeasts from superficial sites may represent species from river water.

Synonymy of the yeast genera Moniliella and Trichosporonoides and proposal of Moniliella fonsecae sp. nov. and five new species combinations

Analyses of nucleotide sequences from the D1/D2 domains of the large-subunit rDNA and phenotypic characteristics showed that the genera Moniliella and Trichosporonoides are members of a single, monophyletic clade that would be best represented by a single anamorphic genus. On the basis of taxonomic priority, we propose the transfer of the five species of the genus Trichosporonoides to the genus Moniliella. The description of the genus Moniliella is emended and the following new combinations are proposed: Moniliella madida comb. nov., Moniliella megachiliensis comb. nov., Moniliella nigrescens comb. nov., Moniliella oedocephalis comb. nov. and Moniliella spathulata comb. nov. In addition, ten strains representing a novel yeast species belonging to the Moniliella clade were isolated from flowers in Thailand, Cuba and Brazil. Analysis of the internal transcribed spacer and D1/D2 large-subunit rDNA sequences indicated that the isolates represent a single species that was distinct from other species of the Moniliella clade. The name Moniliella fonsecae sp. nov. is proposed to accommodate these strains. The type strain is BCC 7726(T) (=CBS 10551(T)).

Integrated control of Penicillium digitatum by the predacious yeast Saccharomycopsis crataegensis and sodium bicarbonate on oranges

Our investigation of integrated biological control (IBC) started with an assay testing activity of the predacious yeast Saccharomycopsis crataegensis UFMG-DC19.2 against Penicillium digitatum LCP 4354, a very aggressive fungus that causes postharvest decay in oranges. Under unfavourable environmental conditions, the yeast showed a high potential for control (39.9% disease severity reduction) of this fungus. This result was decisive for the next step, in which S. crataegensis was tested in association with sodium bicarbonate salt, a generally regarded as safe (GRAS) substance. The yeast was able to survive at different concentrations of the salt (1%, 2% and 5%), and continued to grow for a week at the wound site, remaining viable at high population for 14 days on the fruit surface. The yeast alone reduced the severity of decay by 41.7% and sodium bicarbonate alone reduced severity of decay by 19.8%, whereas the application of both led to a delay in the development of symptoms from 2 to 10 days. Ingredients of the formulations were not aggressive to fruits since no lesions were produced in control experiments.

Yeast Communities in Tropical Rain Forests in Brazil and other South American Ecosystems

Yeast ecology has a strong emphasis on the description of novel taxa of yeasts colonizing a substrate. Studies on the structure and functioning of yeast communities are rare and based on a multitude of methodological approaches and different strategies of collection used by different researchers. Among fungi, yeasts are immotile, predominantly unicellular organisms that are functionally heterotrophic colonizers of sugary substrates. Yeasts are known as specialized organisms with limited physiological characteristics (Lachance and Starmer 1986; Phaff and Starmer 1987). Ecological studies aim to understand colonization and distribution of yeasts in different ecosystems and substrates (Phaff 1990), and have shown that the majority of yeast species and groups have specialized habitats. It is possible to isolate yeasts typical of different natural substrates in the geographical areas where they occur (Phaff and Starmer 1987). The commonest difficulty in studies of yeast ecology in natural ecosystems is to define a yeast community. Möbius (1877) made the first attempts to describe an ecological community when describing oyster banks in marine ecosystems, which he called biocenosis. According to Odum (1994) communities are defined as groups of different species living together in a geographic area, or else to say in space and time defined altogether. Brewer (1988) describes communities as systems composed of species populations bound by coactions. Guilds are defined as groups of species that share a resource in a community. Lachance and Starmer (1986) consider a yeast community as a multidimensional array, the elements of which are its component species or the characteristics of these species. Differing from bacterial communities, Chapter 18

Starmerella aceti f.a., sp. nov., an ascomycetous yeast species isolated from fungus garden of the leafcutter ant Acromyrmex balzani

A novel yeast species was recovered from the fungus garden of the leaf-cutting ant Acromyrmex balzani (Hymenoptera: Formicidae). The growth of the novel yeast species is limited by its ability to metabolize only a few carbon and nitrogenous compounds. A remarkable characteristic of this strain is the vigorous growth in 1 % acetic acid. Sequence analysis of the D1/D2 domains of the LSU rRNA gene showed that the novel species belongs to the Starmerella clade and is phenotypically and genetically divergent from currently recognized species in this clade. Described here as Starmerella aceti f.a., sp. nov., it differs by 37 nucleotide substitutions in the D1/D2 region from Starmerella jinningensis CBS 11864(T), the most closely related species. The type strain of Starmerella aceti sp. nov. is TO 125(T) ( = CBMAI 1594(T) = CBS 13086(T)).

Wickerhamiella pagnoccae sp. nov. and Candida tocantinsensis sp. nov., two ascomycetous yeasts from flower bracts of Heliconia psittacorum (Heliconiaceae)

Two novel yeast species were isolated from nectar of flower bracts of Heliconia psittacorum (Heliconiaceae) collected in a Cerrado ecosystem in the state of Tocantins, northern Brazil. Wickerhamiella pagnoccae sp. nov., which is closely related to Candida jalapaonensis, is heterothallic and produces one spheroid ascospore per ascus. Candida tocantinsensis sp. nov. belongs to the Metschnikowiaceae clade and its nearest relative is Candida ubatubensis, but the sequence identity (%) in the D1/D2 domains of the rRNA gene is low. The type strain of W. pagnoccae is UFMG-F18C1(T) ( = CBS 12178(T) = NRRL Y-48735(T)) and the type strain of C. tocantinsensis is UFMG-F16D1(T) ( = CBS 12177(T) = NRRL Y-48734(T)).