Pietro Buzzini

Antimicrobial and antiviral activity of hydrolysable tannins.

Hydrolysable tannins (HTs), secondary metabolites widely distributed in the plant kingdom, are generally multiple esters of gallic acid with glucose. HTs have been shown to be effective antagonists against viruses, bacteria and eukaryotic microorganisms. The present review examines the antimicrobial and antiviral activity of HTs, the mechanism(s) of action, and some structure-activity relationships.

Psychrophilic yeasts from worldwide glacial habitats: diversity, adaptation strategies and biotechnological potential

Glacial habitats (cryosphere) include some of the largest unexplored and extreme biospheres on Earth. These habitats harbor a wide diversity of psychrophilic prokaryotic and eukaryotic microorganisms. These highly specialized microorganisms have developed adaptation strategies to overcome the direct and indirect life-endangering influence of low temperatures. For many years Antarctica has been the geographic area preferred by microbiologists for studying the diversity of psychrophilic microorganisms (including yeasts). However, there have been an increasing number of studies on psychrophilic yeasts sharing the non-Antarctic cryosphere. The present paper provides an overview of the distribution and adaptation strategies of psychrophilic yeasts worldwide. Attention is also focused on their biotechnological potential, especially on their exploitation as a source of cold-active enzymes and for bioremediation purposes.

Production of carotenoids by strains of Rhodotorula glutinis cultured in raw materials of agro-industrial origin

The production of carotenoids by strains of Rhodotorula glutinis on different raw materials of agro-industrial origin (grape must, glucose syrup, beet molasses, soybean flour extract, maize flour extract) was investigated. Maximum yield (5.95 mg/l of total carotenoids culture fluid, 630 μg/g dry cell weight) was obtained with a particular strain of Rhodotorula glutinis after a batch culture of 120 h in a substrate containing concentrated rectified grape must as the sole carbohydrate source. In all experiments, the major pigments forming carotenoids (β-carotene, torulene, torularhodin) were quantified.

Extracellular enzymatic activities of basidiomycetous yeasts isolated from glacial and subglacial waters of northwest Patagonia (Argentina).

As part of a project aimed at the selection of cold-adapted yeasts expressing biotechnologically interesting features, the extracellular enzymatic activity (EEA) of basidiomycetous yeasts isolated from glacial and subglacial waters of northwest Patagonia (Argentina) was investigated. Ninety-one basidiomycetous yeasts (belonging to the genera Cryptococcus, Leucosporidiella, Dioszegia, Mrakia, Rhodotorula, Rhodosporidium, Sporobolomyces, Sporidiobolus, Cystofilobasidium, and Udeniomyces) were screened for extracellular amylolytic, proteolytic, lipolytic, esterasic, pectinolytic, chitinolytic, and cellulolytic activities. Over 15% of the strains exhibited three or more different EEAs at 4 degrees C and more than 63% had at least two EEAs at the same temperature. No chitinolytic or cellulolytic activities were detected at 4 and 20 degrees C. Cell-free supernatants exhibited significantly higher (P < 0.01) protease and lipase activities at < or = 10 degrees C, or even at 4 degrees C. In light of these findings, cold environments of Patagonia (Argentina) may be considered a potential source of cold-adapted yeasts producing industrially relevant cold-active enzymes.

Yeast and yeast-like diversity in the southernmost glacier of Europe (Calderone Glacier, Apennines, Italy)

The present study reports the characterization of psychrophilic yeast and yeast-like diversity in cold habitats (superficial and deep sediments, ice cores and meltwaters) of the Calderone Glacier (Italy), which is the southernmost glacier in Europe. After incubation at 4 and 20 degrees C, sediments contained about 10(2)-10(3) CFU of yeasts g(-1). The number of viable yeast cells in ice and meltwaters was several orders of magnitude lower. The concomitant presence of viable bacteria and filamentous fungi has also been observed. In all, 257 yeast strains were isolated and identified by 26S rRNA gene D1/D2 and internal transcribed spacers (1 and 2) sequencing as belonging to 28 ascomycetous and basidiomycetous species of 11 genera (Candida, Cystofilobasidium, Cryptococcus, Dioszegia, Erythrobasidium, Guehomyces, Mastigobasidium, Mrakia, Mrakiella, Rhodotorula and Sporobolomyces). Among them, the species Cryptococcus gastricus accounted for almost 40% of the total isolates. In addition, 12 strains were identified as belonging to the yeast-like species Aureobasidium pullulans and Exophiala dermatitidis, whereas 15 strains, presumably belonging to new species, yet to be described, were also isolated. Results herein reported indicate that the Calderone Glacier, although currently considered a vanishing ice body due to the ongoing global-warming phenomenon, still harbors viable psychrophilic yeast populations. Differences of yeast and yeast-like diversity between the glacier under study and other worldwide cold habitats are also discussed.

Carotenoid profiles of yeasts belonging to the genera Rhodotorula, Rhodosporidium, Sporobolomyces, and Sporidiobolus

Eighteen yeast species of the genera Rhodotorula, Rhodosporidium, Sporobolomyces, and Sporidiobolus, each one represented by its type strain, were investigated with the objective of evaluating their carotenoid composition. The pigments were extracted from yeast cells, quantified by high pressure liquid chromatography diode array detector and the main compounds were confirmed by atmospheric pressure chemical ionization quadrupole mass spectrometry. Significant (P < 0.01) differences among several species and (or) genera were observed. Thirteen strains were seen to be able to produce carotenoids, from 16.4 to 184 microg/g cell dry mass and from 6.0 to 1993.4 microg/L culture. The main carotenoids produced were identified as torularhodin, torulene, gamma-carotene, and beta-carotene. The correlation matrix calculated on the basis of the carotenoid composition data matrix indicated significant (P < 0.01) relationships between torulene and torularhodin (r = 0.81), gamma-carotene and torulene (r = 0.49), beta-carotene and torulene (r = -0.72), as well as beta-carotene and gamma-carotene (r = 0.64). These significant correlation coefficients may suggest that species belonging to the genera Rhodosporidium, Sporobolomyces, and Sporidiobolus possess a carotenoid biosynthetic pathway analogous to that elsewhere postulated for Rhodotorula species.

Cold-adapted yeasts from Antarctica and the Italian Alps—description of three novel species: Mrakia robertii sp. nov., Mrakia blollopis sp. nov. and Mrakiella niccombsii sp. nov.

Worldwide glaciers are annually retreating due to global overheating and this phenomenon determines the potential lost of microbial diversity represented by psychrophilic microbial population sharing these peculiar habitats. In this context, yeast strains, all unable to grow above 20°C, consisting of 42 strains from Antarctic soil and 14 strains isolated from Alpine Glacier, were isolated and grouped together based on similar morphological and physiological characteristics. Sequences of the D1/D2 and ITS regions of the ribosomal DNA confirmed the previous analyses and demonstrated that the strains belong to unknown species. Three new species are proposed: Mrakia robertii sp. nov. (type strain CBS 8912), Mrakia blollopis sp. nov. (type strain CBS 8921) and a related anamorphic species Mrakiella niccombsii sp. nov. (type strain CBS 8917). Phylogenetic analysis of the ITS region revealed that the new proposed species were closely related to each other within the Mrakia clade in the order Cystofilobasidiales, class Tremellomycetes. The Mrakia clade now contains 8 sub-clades. Teliospores were observed in all strains except CBS 8918 and for the Mrakiella niccombsii strains.

An optimization study of carotenoid production by Rhodotorula glutinis DBVPG 3853 from substrates containing concentrated rectified grape must as the sole carbohydrate source

A multivariate statistical approach was employed for the optimization of conditions for carotenoid production by Rhodotorula glutinis DBVPG 3853 from a substrate containing concentrated rectified grape must as the sole carbohydrate source. Several experimental parameters (carbohydrate, yeast autolysate and salt concentrations, and pH) were tested at two levels by following a fractional factorial design. Carotenogenesis was most sensitive to both initial pH and yeast autolysate concentration. A Central Composite Design experiment was then performed by obtaining both second-order polynomial models and isoresponse diagrams where initial pH and yeast autolysate concentration were considered as variables. In this way it was possible to determine the conditions (pH = 5.78, yeast autolysate = 4.67 g L−1) which maximize both the concentration of total carotenoids and that of β-carotene (6.9 mg L−1 and 1100 μg L−1 of culture fluid, respectively, after 120 h of fermentation). Journal of Industrial Microbiology & Biotechnology (2000) 24, 41–45.

Bacteria and yeast microbiota in milk kefir grains from different Italian regions

Kefir grains are a unique symbiotic association of different microrganisms, mainly lactic acid bacteria, yeasts and occasionally acetic acid bacteria, cohabiting in a natural polysaccharide and a protein matrix. The microbial composition of kefir grains can be considered as extremely variable since it is strongly influenced by the geographical origin of the grains and by the sub-culturing method used. The aim of this study was to elucidate the bacteria and yeast species occurring in milk kefir grains collected in some Italian regions by combining the results of scanning electron microscopy analysis, viable counts on selective culture media, PCR-DGGE and pyrosequencing. The main bacterial species found was Lactobacillus kefiranofaciens while Dekkera anomala was the predominant yeast. The presence of sub-dominant species ascribed to Streptococcus thermophilus, Lactococcus lactis and Acetobacter genera was also highlighted. In addition, Lc. lactis, Enterococcus sp., Bacillus sp., Acetobacter fabarum, Acetobacter lovaniensis and Acetobacter orientalis were identified as part of the cultivable community. This work further confirms both the importance of combining culture-independent and culture-dependent approaches to study microbial diversity in food and how the combination of multiple 16S rRNA gene targets strengthens taxonomic identification using sequence-based identification approaches.

Growth, lipid accumulation, and fatty acid composition in obligate psychrophilic, facultative psychrophilic, and mesophilic yeasts

Obligate psychrophilic, facultative psychrophilic, and mesophilic yeasts were cultured in a carbon-rich medium at different temperatures to investigate whether growth parameters, lipid accumulation, and fatty acid (FA) composition were adaptive and/or acclimatory responses. Acclimation of facultative psychrophiles and mesophiles to a lower temperature decreased their specific growth rate, but did not affect their biomass yield (Y(X/S)). Obligate and facultative psychrophiles exhibited the highest Y(X/S). Acclimation to lower temperature decreased the lipid yield (Y(L/X)) in mesophilic yeasts, but did not affect Y(L/X) in facultative psychrophilic ones. Similar Y(L/X) were found in both groups of psychrophiles, suggesting that lipid accumulation is not a distinctive characteristic of adaptation to permanently cold environments. The unsaturation of FAs was one major adaptive feature of the yeasts colonizing permanently cold ecosystems. Remarkable amounts of alpha-linolenic acid were found in obligate psychrophiles at the expense of linoleic acid, whereas it was scarce or absent in all the other strains. Increased unsaturation of FAs was also a general acclimatory response of facultative psychrophiles to a lower temperature. These results improve the knowledge of the responses enabling psychrophilic yeasts to cope with the cold and may be of support for potential biotechnological exploitation of these strains.