The incidence of killer activity and extracellular proteases in tropical yeast communities

The presence of killer and proteolytic yeasts was studied among 944 isolates representing 105 species from tropical yeast communities. We found 13 killer toxin producing species, with Pichia kluyveri being the most frequent. Other killer yeast isolates were Candida apis, Candida bombicola, Candida fructus, Candida krusei, Candida sorbosa, Hanseniaspora uvarum, Issatchenkia occidentalis, Kloeckera apis, Kluyveromyces marxianus, Pichia membranaefaciens, Pichia ohmeri-like, and Sporobolomyces roseus. The communities from which killer yeasts were isolated had strains sensitive to them, and there were interspecific and intraspecific differences in the spectra of their killer activities. Pichia kluyveri had the broadest spectra of activity against sensitive isolates, and it apparently produced different toxins. The coexistence of sensitive and killer yeasts using the same substrate suggests that there is spatial separation in microhabitats or temporal separation in different stages of successions. Basidiomycetous yeasts were more frequently proteolytic than ascomycetous yeasts. Extracellular proteases could be important for the yeasts to have access to more nitrogen nutrients and obtain a better balance with available carbon sources.Key words: killer yeasts, extracellular proteases, tropical yeast communities.

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The ecological role of killer yeasts in natural communities of yeasts

Canadian Journal of Microbiology ◽

10.1139/m87-134 ◽

1987 ◽

Vol 33 (9) ◽

pp. 783-796 ◽

Cited By ~ 112

Author(s):

William T. Starmer ◽

Philip F. Ganter ◽

Virginia Aberdeen ◽

Marc-Andre Lachance ◽

Herman J. Phaff

Keyword(s):

Yeast Species ◽

Kluyveromyces Lactis ◽

Killer Toxin ◽

Toxin Production ◽

Killer Activity ◽

Killer Yeast ◽

Killer Toxins ◽

Naturally Occurring ◽

Pichia Kluyveri

The killer phenomenon of yeasts was investigated in naturally occurring yeast communities. Yeast species from communities associated with the decaying stems and fruits of cactus and the slime fluxes of trees were studied for production of killer toxins and sensitivity to killer toxins produced by other yeasts. Yeasts found in decaying fruits showed the highest incidence of killing activity (30/112), while yeasts isolated from cactus necroses and tree fluxes showed lower activity (70/699 and 11/140, respectively). Cross-reaction studies indicated that few killer-sensitive interactions occur within the same habitat at a particular time and locality, but that killer-sensitive reactions occur more frequently among yeasts from different localities and habitats. The conditions that should be optimal for killer activity were found in fruits and young rots of Opuntia cladodes where the pH is low. The fruit habitat appears to favor the establishment of killer species. Killer toxin may affect the natural distribution of the killer yeast Pichia kluyveri and the sensitive yeast Cryptococcus cereanus. Their distributions indicate that the toxin produced by P. kluyveri limits the occurrence of Cr. cereanus in fruit and Opuntia pads. In general most communities have only one killer species. Sensitive strains are more widespread than killer strains and few species appear to be immune to all toxins. Genetic study of the killer yeast P. kluyveri indicates that the mode of inheritance of killer toxin production is nuclear and not cytoplasmic as is found in Saccharomyces cerevisiae and Kluyveromyces lactis.

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Killer toxin of Saccharomyces cerevisiae Y500-4L active against Fleischmann and Itaiquara commercial brands of yeast

Revista de Microbiologia ◽

10.1590/s0001-37141999000300012 ◽

1999 ◽

Vol 30 (3) ◽

pp. 253-257 ◽

Cited By ~ 2

Author(s):

Giselle A.M. Soares ◽

Hélia H. Sato

Keyword(s):

Saccharomyces Cerevisiae ◽

Elevated Temperatures ◽

Killer Toxin ◽

Toxin Production ◽

Chromosomal Dna ◽

Killer Activity ◽

Killer Yeast ◽

Torulopsis Glabrata ◽

Hansenula Anomala ◽

Killer Yeasts

The strain Saccharomyces cerevisiae Y500-4L, previously selected from the must of alcohol producing plants and showing high fermentative and killer capacities, was characterized according to the interactions between the yeasts and examined for curing and detection of dsRNA plasmids, which code for the killer character. The killer yeast S. cerevisiae Y500-4L showed considerable killer activity against the Fleischmann and Itaiquara commercial brands of yeast and also against the standard killer yeasts K2 (S. diastaticus NCYC 713), K4 (Candida glabrata NCYC 388) and K11 (Torulopsis glabrata ATCC 15126). However S. cerevisiae Y500-4L showed sensitivity to the killer toxin produced by the standard killer yeasts K8 (Hansenula anomala NCYC 435), K9 (Hansenula mrakii NCYC 500), K10 (Kluyveromyces drosophilarum NCYC 575) and K11 (Torulopsis glabrata ATCC 15126). No M-dsRNA plasmid was detected in the S. cerevisiae Y500-4L strain and these results suggest that the genetic basis for toxin production is encoded by chromosomal DNA. The strain S. cerevisiae Y500-4L was more resistant to the loss of the phenotype killer with cycloheximide and incubation at elevated temperatures (40oC) than the standard killer yeast S. cerevisiae K1.

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Killer toxin of Pichia membranifaciens and its possible use as a biocontrol agent against grey mould disease of grapevine

Microbiology ◽

10.1099/mic.0.27071-0 ◽

2004 ◽

Vol 150 (8) ◽

pp. 2527-2534 ◽

Cited By ~ 65

Author(s):

A. Santos ◽

D. Marquina

Keyword(s):

Killer Toxin ◽

Grey Mould ◽

Toxin Production ◽

Killer Activity ◽

Pichia Membranifaciens ◽

Sds Page ◽

Toxin Protein ◽

Killing Action ◽

Killer Protein ◽

Potential Use

The use of Pichia membranifaciens CYC 1106 killer toxin against Botrytis cinerea was investigated. This strain exerted a broad-specificity killing action against other yeasts and fungi. At pH 4, optimal killer activity was observed at temperatures up to 20 °C. At 25 °C the toxic effect was reduced to 70 %. The killer activity was higher in acidic medium. Above about pH 4·5 activity decreased sharply and was barely noticeable at pH 6. The killer toxin protein from P. membranifaciens CYC 1106 was purified to electrophoretic homogeneity. SDS-PAGE of the purified killer protein indicated an apparent molecular mass of 18 kDa. Killer toxin production was stimulated in the presence of non-ionic detergents. The toxin concentrations present in the supernatant during optimal production conditions exerted a fungicidal effect on a strain of B. cinerea. The symptoms of infection and grey mould observed in Vitis vinifera plants treated with B. cinerea were prevented in the presence of purified P. membranifaciens killer toxin. The results obtained suggest that P. membranifaciens CYC 1106 killer toxin is of potential use in the biocontrol of B. cinerea.

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Comparison of the Spatial Limits on Direction Selectivity in Visual Areas MT and V1

Journal of Neurophysiology ◽

10.1152/jn.00767.2004 ◽

2005 ◽

Vol 93 (3) ◽

pp. 1235-1245 ◽

Cited By ~ 25

Author(s):

Mark M. Churchland ◽

Nicholas J. Priebe ◽

Stephen G. Lisberger

Keyword(s):

Apparent Motion ◽

Great Majority ◽

Spatial Separation ◽

Direction Selectivity ◽

Temporal Separation ◽

Temporal Area ◽

Mean Values ◽

V1 Neurons ◽

Preferred Direction ◽

The Difference

We recorded responses to apparent motion from directionally selective neurons in primary visual cortex (V1) of anesthetized monkeys and middle temporal area (MT) of awake monkeys. Apparent motion consisted of multiple stationary stimulus flashes presented in sequence, characterized by their temporal separation (Δ t) and spatial separation (Δ x). Stimuli were 8° square patterns of 100% correlated random dots that moved at apparent speeds of 16 or 32°/s. For both V1 and MT, the difference between the response to the preferred and null directions declined with increasing flash separation. For each neuron, we estimated the maximum flash separation for which directionally selective responses were observed. For the range of speeds we used, Δ x provided a better description of the limitation on directional responses than did Δ t. When comparing MT and V1 neurons of similar preferred speed, there was no difference in the maximum Δ x between our samples from the two areas. In both V1 and MT, the great majority of neurons had maximal values of Δ x in the 0.25–1° range. Mean values were almost identical between the two areas. For most neurons, larger flash separations led to both weaker responses to the preferred direction and increased responses to the opposite direction. The former mechanism was slightly more dominant in MT and the latter slightly more dominant in V1. We conclude that V1 and MT neurons lose direction selectivity for similar values of Δ x, supporting the hypothesis that basic direction selectivity in MT is inherited from V1, at least over the range of stimulus speeds represented by both areas.

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Effects of Pichia kluyveri killer toxin on sensitive cells

Antonie van Leeuwenhoek ◽

10.1007/bf00444075 ◽

1980 ◽

Vol 46 (2) ◽

pp. 205-220 ◽

Cited By ~ 18

Author(s):

E. J. Middelbeek ◽

C. Stumm ◽

G. D. Vogels

Keyword(s):

Killer Toxin ◽

Pichia Kluyveri

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PMKT2, a new killer toxin from Pichia membranifaciens, and its promising biotechnological properties for control of the spoilage yeast Brettanomyces bruxellensis

Microbiology ◽

10.1099/mic.0.023663-0 ◽

2009 ◽

Vol 155 (2) ◽

pp. 624-634 ◽

Cited By ~ 78

Author(s):

A. Santos ◽

M. San Mauro ◽

E. Bravo ◽

D. Marquina

Keyword(s):

Biochemical Characterization ◽

Gel Filtration ◽

Chemical Properties ◽

Killer Toxin ◽

Small Scale ◽

Brettanomyces Bruxellensis ◽

Killer Activity ◽

Pichia Membranifaciens ◽

Spoilage Yeast ◽

Spoilage Yeasts

Pichia membranifaciens CYC 1086 secretes a killer toxin (PMKT2) that is inhibitory to a variety of spoilage yeasts and fungi of agronomical interest. The killer toxin in the culture supernatant was concentrated by ultrafiltration and purified to homogeneity by two successive steps, including native electrophoresis and HPLC gel filtration. Biochemical characterization of the toxin showed it to be a protein with an apparent molecular mass of 30 kDa and an isoelectric point of 3.7. At pH 4.5, optimal killer activity was observed at temperatures up to 20 °C. Above approximately this pH, activity decreased sharply and was barely noticeable at pH 6. The toxin concentrations present in the supernatant during optimal production conditions exerted a fungicidal effect on a variety of fungal and yeast strains. The results obtained suggest that PMKT2 has different physico-chemical properties from PMKT as well as different potential uses in the biocontrol of spoilage yeasts. PMKT2 was able to inhibit Brettanomyces bruxellensis while Saccharomyces cerevisiae was fully resistant, indicating that PMKT2 could be used in wine fermentations to avoid the development of the spoilage yeast without deleterious effects on the fermentative strain. In small-scale fermentations, PMKT2, as well as P. membranifaciens CYC 1086, was able to inhibit B. bruxellensis, verifying the biocontrol activity of PMKT2 in simulated winemaking conditions.

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Size Distortions: Space-Time Interaction

Perception ◽

10.1068/v970102 ◽

1997 ◽

Vol 26 (1_suppl) ◽

pp. 114-114

Author(s):

S Chukova ◽

V E Gauzelman

Keyword(s):

Random Order ◽

Spatial Separation ◽

Experimental Session ◽

Reference Stimulus ◽

Temporal Separation ◽

Memory Processing ◽

Modified Method ◽

Time Interaction ◽

Modular Model ◽

Size Distortions

We used a modified method of constant stimuli to measure spatial interval discrimination thresholds. Horizontal intervals were indicated by a pair of dark vertical lines on a bright background. In each experimental session, thresholds were measured for seven reference stimuli, presented in random order. Reference stimulus separations varied from 9.52 to 16.66 min−1 in increments of 1.95 min−1. The interstimulus interval (ISI) was varied (50, 200, 500, and 1000 ms) between experimental sessions. Stimulus duration was constant at 500 ms. For all ISI durations, the point of subjective equality (PSE) for small spatial separation references was less than physical equality, the PSE for larger separations was greater, and the PSE was close to physical equality for reference stimuli in the centre of the range. This result is consistent with the modular model [V D Glezer, 1995 Vision and Mind (Mahwah, NJ: Lawrence Erlbaum)]. However, the magnitude of the PSE shifts was affected by the ISI duration: at 50 and 1000 ms, the small spatial intervals were more underestimated and the large ones were more overestimated than at 200 or 500 ms. The discriminability thresholds based on the slopes of the psychometric functions varied inversely with the ISI duration, but at the ISI of 1000 ms increased again. These findings demonstrate that in the sequential mode of presentation the temporal separation can be as important as the spatial separation distribution in determining the PSE. This suggests that these size distortions result more from memory processing than from spatial processing.

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Divergence Thresholds as Functions of Temporal Separation, Spatial Separation, and Retinal Locus

Perceptual and Motor Skills ◽

10.2466/pms.1983.56.2.459 ◽

1983 ◽

Vol 56 (2) ◽

pp. 459-468 ◽

Cited By ~ 1

Author(s):

Marjorie J. Di Orio ◽

Thomas L. Harrington

Keyword(s):

Spatial Separation ◽

Retinal Locus ◽

Line Density ◽

Information Analysis ◽

Angular Divergence ◽

Temporal Separation ◽

Line Segments ◽

Fast Motion ◽

Straight Lines ◽

Form Information

Human thresholds were measured for the detection of angular divergence between straight lines using pairs of line segments. The dependence of these thresholds on temporal separation between the two lines, spatial separation, and retinal locus was assessed. Results were comparable to prior divergence thresholds obtained by Harrington and Harrington in their study of “blur patterns.” In blur patterns motion parameters may be processed partly or wholly as form information rather than as motion information per se. Harrington and Harrington had used moderate blurring velocities, for which information on both motion and form were present. Observers may have been responding either to motion or to form. The study reported here used briefly presented two-line “blur patterns” with only form information. Analysis suggested that the form components of fast motion-produced blur patterns could be processed by the human visual system. Neither temporal nor spatial separation was a significant determiner of thresholds in accordance with Harrington and Harrington who found no effect of blur-line density in the range studied. Retinal locus was a factor as it was with blur patterns. Some possible mechanisms for the detection of divergence indicated by these results are discussed.

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Identification and susceptibility of clinical isolates of Candida spp. to killer toxins

Brazilian Journal of Biology ◽

10.1590/1519-6984.175635 ◽

2018 ◽

Vol 78 (4) ◽

pp. 742-749

Author(s):

E. Robledo-Leal ◽

L. G. Rivera-Morales ◽

M. P. Sangorrín ◽

G. M. González ◽

G. Ramos-Alfano ◽

...

Keyword(s):

Specific Pattern ◽

Pcr Analysis ◽

Its2 Region ◽

Candida Spp ◽

5.8S Rdna ◽

Killer Toxins ◽

Killer Yeasts ◽

Invasive Infections ◽

Pichia Kluyveri ◽

Species Specific

Abstract Although invasive infections and mortality caused by Candida species are increasing among compromised patients, resistance to common antifungal agents is also an increasing problem. We analyzed 60 yeasts isolated from patients with invasive candidiasis using a PCR/RFLP strategy based on the internal transcribed spacer (ITS2) region to identify different Candida pathogenic species. PCR analysis was performed from genomic DNA with a primer pair of the ITS2-5.8S rDNA region. PCR-positive samples were characterized by RFLP. Restriction resulted in 23 isolates identified as C. albicans using AlwI, 24 isolates as C. parapsilosis using RsaI, and 13 as C. tropicalis using XmaI. Then, a group of all isolates were evaluated for their susceptibility to a panel of previously described killer yeasts, resulting in 75% being susceptible to at least one killer yeast while the remaining were not inhibited by any strain. C. albicans was the most susceptible group while C. tropicalis had the fewest inhibitions. No species-specific pattern of inhibition was obtained with this panel of killer yeasts. Metschnikowia pulcherrima, Pichia kluyveri and Wickerhamomyces anomalus were the strains that inhibited the most isolates of Candida spp.

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Resource partitioning between two species of Ceutorhynchus (Coleoptera: Curculionidae) on Echium plantagineum in a Mediterranean habitat

Bulletin of Entomological Research ◽

10.1017/s0007485300029230 ◽

1993 ◽

Vol 83 (3) ◽

pp. 345-351 ◽

Cited By ~ 9

Author(s):

Guy J. Forrester

Keyword(s):

Biological Control ◽

Resource Partitioning ◽

Spatial Separation ◽

Temporal Separation ◽

Southern France ◽

Early Larval Stage ◽

Tap Root ◽

Mediterranean Habitat ◽

Different Parts ◽

Original Index

AbstractTwo weevil species, Ceutorhynchus geographicus (Goeze) and C. larvatus Schultze, feed on Echium plantagineum (Boraginaceae) in southern France. This paper shows that they do not compete for resources in the host's native environment. Niche overlaps of the two weevils were measured using the proportional overlap measure and Morisita's original index. The two species showed significant overlap in niche requirements during the egg and early larval stage. During the final two larval instars, larvae feed on different parts of the plant, C. geographicus in the tap root and C. larvatus in the root crown. Spatial separation in niche requirements is augmented by a temporal separation, C. larvatus emerging in the field about one month earlier than C. geographicus. In Europe and in Australia, to which E. plantagineum has been introduced and has become a serious weed, the host-plant has an extended germination period during the autumn. The differences in emergence times of the two species mean that their niches are separated both in time and in space. Should the two species be released into Australia they would not compete for resources. They may, however, be able to displace other species of the stemfeeding guild that are also proposed as candidates for the biological control of E. plantagineum.

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