A PRELIMINARY NOTE ON YEASTS ASSOCIATED WITH FECAL PELLETS OF RODENTS AND MARSUPIALS OF ATLANTIC FOREST FRAGMENTS IN RIO DE JANEIRO, BRAZIL

 

Jacqueline Abranches¹; Hilda N. Nóbrega¹; Patrícia Valente^1,2; Leda C. Mendonça-Hagler¹; Allen N. Hagler¹ *
¹Instituto de Microbiologia Prof. Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil; ² Escola Técnica Federal de Química, Rio de Janeiro, RJ, Brasil

Submitted: March 03, 1997; Returned to authors for corrections: October 28, 1997;
Approved: July 23, 1998

 

SHORT COMMUNICATION

 

 

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ABSTRACT

Yeasts had mean counts of above 10⁶ CFU/g in the fecal pellets of small mammals from tropical forest fragments. Most of the 55 species isolated were fermentative ascomycetes, with the most frequent being Debaryomyces hansenii, Pichia membranifaciens and Issatchenkia orientalis, whereas Rhodotorula mucilaginosa was the most frequent yeast of basidiomycetous affinity.

Key words: Small mammals, yeast diversity, yeast vectors

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In nature yeast dispersion is done mainly by animal vectors (especially insects) and air currents (4, 15). The most studied yeast vectors are the Drosophila fruit flies, which often have specific relationships with the substrates used for breeding and feeding. They influence the yeast composition of these substrates by carrying specific yeasts from one site to another and the yeasts isolated from their surface and crop reflect their habitats (3, 11, 12, 13).

Small mammals like rodents and marsupials feed on a wide variety of substrates found on the ground such as ripe and rotting fruits, fallen leaves, insects and mushrooms (2, 14). Some of the animals have been reported as vectors of mycorrhizal fungi in Australia and North America (2, 7, 8, 9, 10). Since they have a more generalist diet than drosophilids, these animals could be used as a tool for more random sampling of the yeast diversity from a given habitat. If these animals actually function as yeast vectors, the yeast flora present in their fecal pellets should include many transient organisms. Some opportunist pathogenic yeasts should also be expected as residents of their intestinal tract. In the present work we studied the ocurrence of different yeast species in the fecal pellets of small mammals from forest fragments of Rio de Janeiro, Brazil.

Fecal pellets from the marsupials Didelphis marsupialis (common opossum) and Philander frenata (grey four-eyed opossum) and from the rodents Akodon sp. (South American field mouse), Oryzomys sp. (rice rat) and Nectomys squamipes (water rat) were studied. These animals were trapped in small tropical forest fragments in Sumidouro county of Rio de Janeiro, Brazil. Fecal pellets were collected asseptically from the traps in which the animals were caught during the previous night. The traps consisted of cages with the bottoms covered with sterile surgical caps where the fecal pellets were retained. Fecal pellets were transported on ice to the laboratory, stored in the refrigerator, and then 0.5g portions were suspended in 4.5ml of sterile distilled water by agitation with a vortex mixer. 0.1ml of serial dilutions were spread in triplicate on AYM (acidified Yeast Extract - Malt Extract) agar (1% glucose, 0.3% malt extract, 0.3% yeast extract, 0.5% peptone, 2% agar, pH4.5) with 400mg/l of chloranphenicol and acidified Yeast Nitrogen Base (YNB) agar with 0.5% of glucose, pH4.5 + 400mg/l of chloranphenicol and incubated at 22^oC for 3 days. The colonies growing on these plates were counted to estimate the yeast population (CFU/g) and representatives of each type of colony morphology were isolated. Identification procedures were done according to standard methods described in Kreger van-Rij, 1984 (6) and Barnett et al., 1990 (1). Species names followed by the suffix -like indicate that the organism is similar to this species but is sufficiently different to be considered a probable new species.

159 different yeast cultures were isolated from the fecal pellets. The yeasts were identified to 55 species mostly of ascomycetous affinity (130 isolates representing 46 species), many of which were fermentative. Basidiomycetous yeasts were represented by 29 isolates including 9 species (Table 1). Geometric means of plate counts from D. marsupialis fecal samples on YNB + glucose were 1.1x10⁶ CFU/g and 2.8x10⁶ CFU/g on AYM, and from P. opossum were 5.8x10⁶ CFU/g on YNB + glucose and 1.32x10⁶ CFU/g on YM. We found the mean counts from rodents to be 1.3x10⁶ CFU/g on YNB + glucose and 3.2x10⁶ CFU/g on YM agar.

 

Table 1 - Frequency of yeasts species in fecal pellets from marsupials^a and rodents^b.

n= number of samples.
a= Didelphis marsupialis and Philander frenata.
b= Akodon sp., Nectomys squamipes and Oryzomys sp.

 

Debaryomyces hansenii, Pichia membranifaciens and Issatchenkia orientalis were the most frequent ascomycetous yeasts, and Rhodotorula mucilaginosa was the most frequent basidiomycetous yeast. Opportunistic pathogenic yeasts like Candida albicans, Candida parapsilosis and Candida tropicalis were mainly found associated with marsupials. The dermatophyte Trichosporon beigelii was also found but in low frequency.

Yeasts reported from tropical fruits in Brazil have been mostly species with low assimilation profiles and with counts on ripe fruits often in the range of 10⁵ to 10⁷ CFU/g as noted for amapa, cashew, mango, caja and umbu (5, 11, 17). These results are similar to those obtained here for small mammals and are consistent with these animals having diets that include large proportions of fruit (14). The presence of basidiomycetous yeasts may be explained by the fact that these animals eat the fruit skin and also some leaves that they find on soil. The high yeast diversity found probably reflected the diversity of foods eaten, suggesting that small mammals could be used as a tool for habitat sampling. Yeasts serve as protein and vitamin sources for insects and other animals (16), and although small mammals do not eat yeasts specifically, they could receive nutritional benefits from eating a substrate rich in these microorganisms.

Small mammals are often reported as natural reservoirs of pathogenic microorganisms, and some human diseases are related with them. Although opportunistic pathogenic yeasts were in low frequency, our data suggests that these animals could disperse some opportunistic pathogenic yeasts, including C. albicans, in the environment. The presence of a diverse yeast flora associated with the fecal pellets of small mammals is consistent with these animals using a wide variety of food items and allows them to act as vectors of yeasts in nature.

 

ACKNOWLEDGMENTS

We thank to Dr. F.A.S. Fernandez for his cooperation in collecting samples and identifying the animals, and D. Pimentel, F.V. Araújo and G.A. Lemos for their technical assistance. This work was funded by a European Economic Community fixed contribution contract (n^o C11*-CT93-0054), Pronex, CAPES and CNPq.

 

 

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RESUMO

Uma nota preliminar sobre leveduras associadas a pelotas fecais de roedores e marsupiais de fragmentos de Mata Atlântica do Rio de Janeiro, Brasil.

Leveduras em pelotas fecais de pequenos mamíferos provenientes de fragmentos de Mata Atlântica tiveram contagem média acima de 10⁶ UFC/g. A maioria das 55 espécies isoladas foi de ascomicetos fermentativos, com as mais freqüentes sendo Debaryomyces hansenii, Pichia membranifaciens e Issatchenkia orientalis, enquanto Rhodotorula mucilaginosa foi a levedura mais freqüente de afinidade basidiomicética.

Palavras-chave: Pequenos mamíferos, diversidade de leveduras, vetores de leveduras.

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* Corresponding author. Mailing address: Instituto de Microbiologia Prof. Paulo de Góes, Bloco I, CCS, Universidade Federal do Rio de Janeiro, Ilha do Fundão, CEP 21941-590, Rio de Janeiro, RJ, Brasil.