Pichia Guillermondii Research Articles

Selection of Microbial Targets for Treatments to Preserve Fresh Carrot Juice

Fresh carrot juice presents nutritional and organoleptic qualities which have to be preserved. However, it is a fast perishable beverage, and its low-acidic pH promotes the development of foodborne pathogens and spoilage microorganisms. This study aims to assess the modification and variability of physicochemical and microbial indicators during storage of carrot juice, and to isolate and select microorganisms to be used as promoters of spoilage to quantify the effect of preservation treatments. To achieve that, 10 batches of carrot Daucus carota cv. Maestro juice were prepared independently, stored up to 14 days at 4 °C and analyzed. Volatile compound composition differed mainly according to the analyzed batch. During storage, an increase of the content of ethanol, ethyl acetate or 2-methoxyphenol, which are produced by different microorganisms, was noticed. Isolation of bacteria revealed Pseudomonas, lactic acid bacteria, and enterobacteria, some of them provoking odor modification of carrot juice at 4 °C. Assays in carrot juice with isolated yeasts and molds showed the ability of Meyerozyma guillermondii to induce texture modification and some isolates, e.g., Pichia guillermondii, resulted in gas production. Selected isolates able to induce spoilage are useful to test preservative treatments of fresh carrot juice under controlled conditions.

Isolation and identification of microbial species found in cocoa fermentation as microbial starter culture candidates for cocoa bean fermentation in Colombia.

Microbial activity involved in the cocoa beans fermentation process is essential to maintain and improve the organoleptic and nutritional qualities of chocolate; therefore, the aim of this investigation was to search and select microbial isolates with the potential to improve the quality of cocoa beans. Fermentation experimentswere conducted on farms located in Maceo (Antioquia), San Vicente de Chucurí (Santander), and Rivera and Algeciras (Huila), Colombia. Yeast, lactic acid bacteria (LAB), acetic acid bacteria (AAB), and mesophilic aerobic microorganisms were obtained from different fermentation batches. The growth of these microorganismswas tested in six treatments as follows: 50% cocoa pulp agar (CPA), high concentrations of glucose (10%), ethanol (5%), and acetic acid (7%), an acidic pH of 3.0, and a high temperature of 50oC for 24 h. The isolates with the highest growth were identified by 18S and 16S rRNA gene analysis, revealing a high diversity ofspecies associated with cocoa fermentation, including eight species of yeasts (Debaryomyces hansenii, Meyerozyma guillermondii, Wickerhanomyces anomalus, Pichia guillermondii, Pichia kudriavzevii, Trichosporon asahii, Candida parapsilosis, and Pichia manshurica), six species of LAB (Pediococcus acidilactici, Lactobacillus brevis, Lactobacillus plantarum, Lactobacillus farraginis, Lactobacillus rhamnosus, and Leuconostoc mesenteroides), four species of AAB (Gluconobacter japonicus, Acetobacter tropicalis, Acetobacter pasteurianus, and Acetobacter malorum/tropicalis), and three species of Bacillus spp. (Bacillusaryabhattai /megaterium, Bacillus subtilis, and Bacillus coagulans). In general, microbial populations increased in cocoa batches after 12 h of fermentation and decreased after 84-96 h. All the yeast isolates grew in 10% glucose and CPA, 85.7% in 5% ethanol, and 95% at a pH of 3.0. All the yeast isolates were affectedby 7% acetic acid and incubation at 50oC for 24 h. Eighty-five percent of the LAB grew in 10% glucose, 100% in 5% ethanol, 42.8% in CPA, 64% at a pH of 3.0, and 35.7% grew after being exposed to 50oC for 24 h; all were affected by 7% acetic acid. As for the AAB, 100% grew in 10% glucose, 71% in 7% ethanol, 100% grew in CPA, in 7% acetic acid, and at a pH of 3.0, while 100% were affected by incubation at 50oC. Three yeast isolates, W. anomalus, D. hansenii and M. guillermondii, three LAB isolates, P. acidilactici, L. brevis, and L. plantarum, and three AAB isolates, A. tropicalis, A. pasteurianus and G. japonicus, were selected as promising strains to be used in a microbial starter culture for cocoa bean fermentation to improve the organoleptic quality of cocoa.

Bio-efficacy of different biological control agents for the management of chilli fruit rot/anthracnose disease

Chilli (Capsicum annum L.) an important economic crop worldwide is severely infected by fruit rot disease which may cause yield losses of up to 100%. Although different chemical fungicides are being recommended and used for the management of the disease, biocontrol-based strategy attracts considerable attention and offers great potential of novel biocontrol agents. Further, biological control methods for chilli fruit rot/anthracnose disease have not received much attention. Therefore, an investigation was carried out to assess the efficacy of different biological control agents against chilli fruit rot/anthracnose disease. Antagonistic yeast isolates Pichia guillermondii (Y-12), Hanseniaspora uvarum (Y-73) and Trichoderma asperellum (Th-3), Pseudomonas fluorescens (Pf-1) were tested through seed treatment, seedling dip and foliar spray at concentration of 2 í— 108 cfu/g. The pathogens viz., Colletotrichum capsici, Alternaria alternata and Periconia byssoides were found associated with fruit rot during the study. Lowest mean disease intensity (MDI), highest disease control (DC) over untreated control was recorded in the treatment <i>P. guillermondii</i> (Y-12) (5.39% MDI, 64.72% DC) and this was found at par with the treatment <i>P. fluorescens</i> (Pf-1) (5.92% MDI, 65.52% DC). However, <i>T. asperellum</i> (Th-3) showed satisfactory results. The present study highlights the efficacy of antagonistic yeast species against chilli fruit rot pathogens and these findings serve as base for further exploration and exploitation of yeast species for eco-friendly management of crop diseases.

Bio-efficacy of different biological control agents for the management of chilli fruit rot/anthracnose disease

Chilli ( Capsicum annu m L.) an important economic crop worldwide is severely infected by fruit rot disease which may cause yield losses of up to 100%. Although different chemical fungicides are being recommended and used for the management of the disease, biocontrol-based strategy attracts considerable attention and offers great potential of novel biocontrol agents. Further, biological control methods for chilli fruit rot/anthracnose disease have not received much attention. Therefore, an investigation was carried out to assess the efficacy of different biological control agents against chilli fruit rot/anthracnose disease. Antagonistic yeast isolates Pichia guillermondii (Y-12), Hanseniaspora uvarum (Y-73) and Trichoderma asperellum (Th-3), Pseudomonas fluorescens (Pf-1) were tested through seed treatment, seedling dip and foliar spray at concentration of 2 A— 10 8 cfu/g. The pathogens viz., Colletotrichum capsici , Alternaria alternata and Periconia byssoides were found associated with fruit rot during the study. Lowest mean disease intensity (MDI), highest disease control (DC) over untreated control was recorded in the treatment P. guillermondii (Y-12) (5.39% MDI, 64.72% DC) and this was found at par with the treatment P. fluorescens (Pf-1) (5.92% MDI, 65.52% DC). However, T. asperellum (Th-3) showed satisfactory results. The present study highlights the efficacy of antagonistic yeast species against chilli fruit rot pathogens and these findings serve as base for further exploration and exploitation of yeast species for eco-friendly management of crop diseases.

Biodegradation of Ammonium Ions and Formate During Ammonium Formate Metabolism by Yarrowia lipolytica and Pichia guilliermondii in a Batch Reactor

The use of microorganisms for the biodegradation of pollutants is increasingly being studied. But at high concentrations, these pollutants become rather inhibitors for the metabolism of microorganisms. In this study, the biodegradation of ammonium formate at various concentrations (1.59–7.94 mM) by Yarrowia Lipolytica and Pichia guilliermondii isolated from the rubber effluent is studied by following the variation of ammonium ions and formate. A fitting of eight models of substrate inhibition was performed and the parameters were determined by nonlinear regression using MATLAB 8.5 ©. The R2 and the RSME allow to choose the best model. The results show that ammonium ions (3.17 mM ammonium formate) are used as substrate; no inhibition is observed. But beyond this concentration, the inhibition effect begins to be observed with the specific rates of ammonium biodegradation which decrease. Formate monitoring reveals that is used as the main source of energy and does not inhibit the growth of yeasts. The models of Luong and Webb seem to be more appropriate for predicting the observed phenomena of inhibition. For Yarrowia lipolytica, R2 = 0.958 and 0.998 with RSME = 0.005342 and 0.003433, for Pichia guillermondii, R2 = 0.999 and 0.992 with RSME = 0.0005121 and 0.001212.

Tolerance of pentose utilising yeast to hydrogen peroxide-induced oxidative stress

BackgroundBioethanol fermentations follow traditional beverage fermentations where the yeast is exposed to adverse conditions such as oxidative stress. Lignocellulosic bioethanol fermentations involve the conversion of pentose and hexose sugars into ethanol. Environmental stress conditions such as osmotic stress and ethanol stress may affect the fermentation performance; however, oxidative stress as a consequence of metabolic output can also occur. However, the effect of oxidative stress on yeast with pentose utilising capabilities has yet to be investigated.ResultsAssaying for the effect of hydrogen peroxide-induced oxidative stress on Candida, Pichia and Scheffersomyces spp. has demonstrated that these yeast tolerate hydrogen peroxide-induced oxidative stress in a manner consistent with that demonstrated by Saccharomyces cerevisiae. Pichia guillermondii appears to be more tolerant to hydrogen peroxide-induced oxidative stress when compared to Candida shehatae, Candida succiphila or Scheffersomyces stipitis.ConclusionsSensitivity to hydrogen peroxide-induced oxidative stress increased in the presence of minimal media; however, addition of amino acids and nucleobases was observed to increase tolerance. In particular adenine increased tolerance and methionine reduced tolerance to hydrogen peroxide-induced oxidative stress.

Identification and characterization of non-saccharomyces spoilage yeasts isolated from Brazilian wines

The industry of fine wines and also locally consumed table wines is emerging in Brazil with an increasing volume and economic impact. Enologists in this region currently lack information about the prevalence and characteristics of spoilage yeasts, which may contaminate and potentially undervalue Brazilian wines. Herein, we analyzed 50 local red wines including 27 fine wines (V. vinifera) and 23 table wines (V. labrusca). Presumptive spoilage yeasts were isolated on differential medium, and classified by RFLP-PCR and sequencing of the ITS1-5.8S-ITS2 and D1/D2 26S rDNA loci. The prevalence of spoilage yeasts in fine wines (11%) was comparable to that reported in European and US wines, and significantly lower than that observed for local table wines (70%). The majority of isolates belonged to Brettanomyces bruxelliensis, followed by Pichia guillermondii, and more rarely Candida wickerhamii and Trigonopsis cantarelli. The Brettanomyces isolates varied greatly in off-flavor production, displayed ethanol tolerance (>10% by volume), tolerated sulfite (≥0.68mg/l mSO2), and 39% of them grew on ethanol as sole carbon source. We discuss the causes and consequences of spoilage yeasts in relation to the Brazilian wine industry.

Comparison of media formulations used to selectively cultivate Dekkera/Brettanomyces

The objectives of this research were to (i) optimize the concentration of cycloheximide for use in WL media used in the wine industry and (ii) evaluate Dekkera/Brettanomyces differential medium (DBDM) as a means to detect Dekkera. Dekkera bruxellensis and other yeasts were transferred into WL broths containing 0, 10, 50 or 100 mg l(-1) of cycloheximide. While several grew in 10 mg l(-1) , only Hanseniaspora uvarum, Pichia guillermondii, Schizosaccharomyces pombe and D. bruxellensis tolerated ≥50 mg l(-1) of the antibiotic. On solidified WL media after 8-days incubation, colony sizes of two strains of D. bruxellensis (B1b and ATCC 52905) decreased with increased concentrations of cycloheximide, while others (F3 and P2) were unaffected. Although D. bruxellensis B1b did not grow well on another selective medium, DBDM, colony development was improved by the addition of sterilized red wine. Of the concentrations tested, 50 mg l(-1) cycloheximide inhibited many grape/wine yeasts yet generally yielded countable colonies of Dekkera (1-2.5 mm diameter). Several strains of Dekkera did not grow well on DBDM, probably due to the lack of an unidentified nutrient(s). Better media formulations will improve the detection of Dekkera, thereby increasing microbiological control during winemaking.

Development and application of a real-time PCR-based assay to enumerate total yeasts and Pichia anomala, Pichia guillermondii and Pichia kluyveri in fermented table olives

The objective of this work was to develop a real-time quantitative PCR (qPCR) assay to directly detect and quantify the total number of yeasts besides three species (Pichia anomala, Pichia guillermondii and Pichia kluyveri) associated to table olives. For this purpose, a real-time PCR protocol targeted to the region of the internal transcribed spacers ITS (rDNA) and the conserved sequences of the variable D1/D2 domains of the 26S rRNA gene, respectively, was developed. This assay allowed to unequivocally distinguish the three species from other yeasts and lactic acid bacteria generally associated to table olives fermentation. qPCR performed well both with purified DNA and DNA extracted from olive brines. A reverse transcription-qPCR (RT-qPCR) assay from rRNA aimed to viable yeast quantification was also performed. To evaluate the effectiveness of the technique, the qPCR results were compared with those obtained by a plate count approach in synthetic medium. The small standard errors provided this assay reproducible and robust. qPCR efficiently enumerated cells at concentrations of as low as 102 CFU ml−1 when standard curve was derived both from cells growing in a syntetic medium and in brines. The quantification method for total yeasts and P. anomala, P. guillermondii, P. kluyveri in table olive brines applied in this work was specific, reproducible, sensitive and fast.

Characterization of microbial traits involved with the elaboration of the Cotija cheese

Physicochemical and microbial analyses were conducted for artisanal and semi-industrial manufacturing processes of the Cotija cheese. Differences between manufacturing processes in Cotija cheese affect the microbial composition in the final product. Lactic acid bacteria are important microorganisms in the artisanal Cotija cheese manufacturing. Thirty-one different microorganisms were isolated and identified by ribosomal sequencing analysis during the production of this artisanal cheese. The yeast isolates comprised the following species: Kluyveromyces lactis, Kluyveromyces marxianus, Pichia guillermondii, Rhodotorula mucilaginosa, Galactomyces reessii, and Galactomyces geotrichum. Bacterial isolates were members of the Lactobacillaceae family with the follow species: Pediococcus pentosaceus, Lactobacillus brevis, Lactobacillus plantarum, and Lactobacillus casei. The possible role of these microorganisms in the final flavor and taste, and their utility in the control of undesirable microorganisms in artisanal Cotija cheese is discussed.

Relative Incidence of Ascomycetous Yeasts in Arctic Coastal Environments

Previous studies of fungi in polar environments have revealed a prevalence of basidiomycetous yeasts in soil and in subglacial environments of polythermal glaciers. Ascomycetous yeasts have rarely been reported from extremely cold natural environments, even though they are known contaminants of frozen foods. Using media with low water activity, we have isolated various yeast species from the subglacial ice of four glaciers from the coastal Arctic environment of Kongsfjorden, Spitzbergen, including Debaryomyces hansenii and Pichia guillermondii, with counts reaching 10(4)CFUL(-1). Together with the basidiomycetes Cryptococcus liquefaciens and Rhodotorula mucilaginosa, these yeasts represent the stable core of the subglacial yeast communities. Other glacial ascomycetous species isolated included Candida parapsilosis and a putative new species that resembles Candida pseudorugosa. The archiascomycete Protomyces inouyei has seldom been detected anywhere in the world but was here recovered from ice in a glacier cave. The glacier meltwater contained only D. hansenii, whereas the seawater contained D. hansenii, Debaryomyces maramus, Pichia guilliermondii, what appears to represent a novel species resembling Candida galli and Metschnikowia bicuspidata. Only P. guilliermondii was isolated from sea ice, while snow/ice in the fjord tidal zone included C. parapsilosis, D. hansenii, P. guilliermondii and Metschnikowia zobellii. All of these isolated strains were characterized as psychrotolerant and xero/halotolerant, with the exception of P. inouyei.

Antimicrobial Metabolites from the Endophytic Fungus Pichia guilliermondii Isolated from Paris polyphylla var. yunnanensis

Three steroids and one nordammarane triterpenoid were isolated for the first time from the endophytic fungus Pichia guilliermondii Ppf9 derived from the medicinal plant Paris polyphylla var. yunnanensis. By means of physicochemical and spectrometric analysis, they were identified as ergosta-5,7,22-trienol (1), 5α,8α-epidioxyergosta-6,22-dien-3β-ol (2), ergosta-7,22-dien-3β,5α,6β-triol (3), and helvolic acid (4). Both micro-dilution-colorimetric and spore germination assays were employed to evaluate their antimicrobial activity. Among them, helvolic acid (4) exhibited the strongest antibacterial activity against all test bacteria, with MIC values ranging from 1.56 µg/mL to 50 µg/mL, and IC50 values from 0.98 µg/mL to 33.19 µg/mL. It also showed strong inhibitory activity on the spore germination of Magnaporthe oryzae with an IC50 value of 7.20 µg/mL. Among the three steroids, 5α,8α-epidioxyergosta-6,22-dien-3β-ol (2) exhibited relatively strong antimicrobial activity. The results suggest that the endophytic fungus Pichia guillermondii Ppf9 could be a candidate for producing helvolic acid, and the metabolites from this fungus could be potentially developed as antimicrobial agents in the future.

Soil-borne antagonists for biological control of bacterial wilt disease caused by Ralstonia solanacearum in tomato and pepper.

Bacterial wilt is an important disease of tomatoes and peppers, causing plant death and significant yield losses. Control methods include use of resistant varieties, crop rotation, etc. Biological control is desirable because control with other methods gives variable results. This paper describes the effectiveness of microbial antagonists isolated from soils. Of 73 isolated antagonists, eight were screened and evaluated in vitro and in vivo against Ralstonia solanacearum. They all significantly reduced disease symptoms. The effects of carbon and nitrogen source, incubation temperature and broth culture pH were evaluated for production of inhibitory substances. Results indicated that the optima were sucrose 2.5% (w/v), peptone 2% (w/v), temperature 28°C, and initial medium pH of 7. Three antagonists isolated from soil (Bacillus megaterium, Enterobacter cloacae, Pichia guillermondii) and Candida ethanolica showed high potential for disease suppression and also increased fruit weight, biomass and plant height. These results provide encouragement for continued research on biological control of bacterial wilt by antagonistic isolates from soil.

Formation of vinylphenolic pyranoanthocyanins by Saccharomyces cerevisiae and Pichia guillermondii in red wines produced following different fermentation strategies

The strains of two species of yeast, Saccharomyces cerevisiae and Pichia guillermondii, both with high hydroxycinnamate decarboxylase (HCDC) activity (56% and 90% respectively), were used in the fermentation of musts enriched with grape anthocyanins, to favour the formation of highly stable vinylphenolic pyranoanthocyanin pigments. The different strains were used to ferment the must separately, simultaneously, or sequentially, the latter involving an initial period using the yeast with the greatest HCDC activity ( P. guillermondii). The must was made from concentrated grape juice diluted to 220 g/l of sugar, and enriched with grape anthocyanins to 100 mg/l and with p-coumaric acid to 120 mg/l. The pH was fixed to 3.5. All 50 ml micro-fermentations were done in triplicate. The development of anthocyanin-3- O-glucoside precursors, the decarboxylation of p-coumaric acid, and the formation of 4-vinylphenol and vinylphenolic pyranoanthocyanin derivatives were studied during the fermentation. The fermentation strategy used and the yeast HCDC activity significantly influenced the formation of vinylphenolic pyranoanthocyanins. The latter molecules were separated, identified, and quantified using high performance liquid chromatograph with diode array detection and electrospray-mass spectrometry (HPLC-DAD-ESI/MS). The volatile compounds profile was screened during fermentation using gas cromatogrphy-flame ionisation detection (GC-FID), in order to detect and quantify the main molecules. The best results were reached with the sequential fermentation (3.74 mg/l of malvidin-3- O-glucoside-4-vinylphenol). This work shows that during mixed or sequential fermentations carried out with non- Saccharomyces or highly fermentative Saccharomyces strains, with high HCDC activity, the content of stable pigments can be increased without sensorial modifications.

Evaluation of chitosans and Pichia guillermondii as growth inhibitors of Penicillium digitatum

Chitosans were obtained by room-temperature-homogeneous-deacetylation (RTHD) and freeze-pump-out-thaw-heterogeneous-deacetylation (FPT) from chitins purified from fermentations. Commercial chitosan was deacetylated by three-FPT-cycles. Chitosans and Pichia guillermondii were evaluated on the growth of Penicillium digitatum. Medium molecular weight ( M W) chitosans displayed higher inhibitory activity against the yeast than low M W biopolymers. Chitosans with low degree of acetylation (DA) were inhibitory for yeast and mould. Therefore, a low M W and high DA chitosan was selected for use against moulds combined with yeasts. Biopolymer and yeasts presented an additive effect, since chitosans were effective to delay spore germination, whereas yeast decreased apical fungal growth.

Mold-inhibitory activity of different yeast species during airtight storage of wheat grain

The yeast Pichia anomala J121 inhibits spoilage by Penicillium roqueforti in laboratory and pilot studies with high-moisture wheat in malfunctioning airtight storage. We tested the biocontrol ability of an additional 57 yeast species in a grain mini silo system. Most yeast species grew to CFU levels comparable to that of P. anomala J121 after 14 days of incubation (>10(6) CFU g(-1)). Of the 58 species, 38 (63 strains) had no mold-inhibitory effects (Pen. roqueforti levels >10(5) CFU g(-1)). Among these were 11 species (18 strains) that did not grow on the wheat grain. Several of the non-inhibiting yeast species have previously been reported as biocontrol agents in other postharvest environments. Weak inhibitory activity, reducing Pen. roqueforti levels to between 10(4) and 10(5) CFU g(-1), was observed with 11 species (12 strains). Candida silvicola and Pichia guillermondii reduced Pen. roqueforti to <10(4) CFU g(-1). Candida fennica, Candida pelliculosa, Candida silvicultrix, P. anomala (29 strains), Pichia burtonii, Pichia farinosa and Pichia membranifaciens strongly inhibited Pen. roqueforti (<10(3) CFU g(-1)) in the mini silos, but none had higher biocontrol activity than P. anomala strain J121. This report is the first of biocontrol activity of C. fennica and C. silvicultrix. The ability of 27 yeast species to grow to high CFU values without inhibiting mold growth suggests that nutrient competition may not be the main mode of action of P. anomala J121.

The yeast flora of some decaying mushrooms on trunks of living trees

Several ascomycetous and basidiomycetous yeasts were isolated from rotten mushrooms on the trunks of beech and tamarisk trees. One strain, identified as the novel species Cryptococcus allantoinivorans, assimilated allantoin as the sole carbon source. Phylogenetically it belongs to the C. laurentii complex, Papiliotrema bandonii being the closest relative. Some ascomycetous strains could not be distinguished from Pichia guillermondii, but deviated considerably in rDNA sequences. In addition to these species, both decaying mushrooms were inhabited by more common species, viz. Candida albicans, C. saitoana, Rhodotorula mucilaginosa, Trichosporon asahii, T. multisporum and T. porosum. The basidiomycetous yeasts, except R. mucilaginosa, assimilated some polysaccharides of plant origin.

Characterization of the in vitro antimycotic activity of a novel killer protein from Williopsis saturnus DBVPG 4561 against emerging pathogenic yeasts

A novel killer toxin, labelled as KT4561, secreted by Williopsis saturnus DBVPG 4561, was found to possess a wide antimycotic activity against strains of Candida glabrata, Issatchenkia orientalis and Pichia guillermondii. KT4561 was precipitated by ethanol and purified by ion-exchange chromatography. The active protein migrated as a single band in SDS–PAGE and was characterized by a molecular weight of ∼62 kDa. Purified KT4561 was active across wide ranges of temperature (5–45 °C) and pH (4.5–8.0) and displayed a rapid decrease in viability of yeast cells after 4–8 h. The in vitro activity of KT4561 against 102 yeast isolates (79% of clinical origin) was determined: MIC 50 and MIC 90 of strains were 0.08 and 0.15 μg/ml for C. glabrata, 0.03 and 0.23 μg/ml for I. orientalis and 1.50 and 2.25 μg/ml for P. guilliermondii. Comparative susceptibility tests showed that a high number of strains used in the present study were insensitive to selected azole and polyene antibiotics. The present study demonstrated the potential of KT4561 to be applied as novel control agent against pathogenic yeasts.

Reduction of Inorganic Compounds by Soil Microorganisms

AbstractIsolates of Pichia guillermondii and Micrococcus sp. obtained from soil converted selenate, selenite, tellurate, and tellurite to the elemental forms, vanadate to a vanadyl compound, molybdate and molybdenum trioxide to a molybdenum blue compound, arsenate to arsenite, MnO2 to the manganous ion, nitrate to nitrite, and chlorate to a less oxidized form. Resting cell suspensions and cell‐free extracts of the two organisms also effected the reduction of most of the inorganic compounds and anions. The capacity to reduce selenate, selenite, tellurate, tellurite, vanadate, molybdate, molybdenum trioxide, arsenate, chlorate, and MnO2 was found to be common to soil microrganisms. It is suggested that these microbial reactions may be important in changing the solubility, availability, or toxicity of certain elements in soil.