Sympatric natural Saccharomyces cerevisiae and S. paradoxus populations have different thermal growth profiles

Saccharomyces cerevisiae and its close congener S. paradoxus are typically indistinguishable by the phenotypic criteria of classical yeast taxonomy, but they are evolutionarily distinct as indicated by hybrid spore inviability and genomic sequence divergence. Previous work has shown that these two species coexist in oak-associated microhabitats at natural woodland sites in North America. Here, we show that sympatric populations of S. cerevisiae and S. paradoxus from a single natural site are phenotypically differentiated in their growth rate responses to temperature. Our main finding is that the S. cerevisiae population exhibits a markedly higher growth rate at 37 degrees C than the S. paradoxus population; we also find possible differences in growth rate between these populations at two lower temperatures. We discuss the implications of our results for the coexistence of these yeasts in natural environments, and we suggest that thermal growth response may be an evolutionarily labile feature of these organisms that could be analyzed using genomic approaches.     

Flow calorimetry and dielectric spectroscopy to control the bacterial conversion of toxic substrates into polyhydroxyalcanoates

The microbial conversion of toxic substrates into valuable products in continuous culture requires the equivalent of a tight rope walk between formation of the desired product and intoxication of the microbial catalyst. The condition of the latter is reflected immediately by changes in heat flow rate and beta-dispersion in an electrical RF field. Therefore, these were applied to the example of the continuous growth-associated synthesis of polyhydroxyalcanoates (PHA) from phenol by the bacterial strain Variovorax paradoxus DSM 4065. By controlling the supply of phenol to the chemostat, the rates of degradation, biomass formation, and synthesis of target product, respectively, were increasingly elevated until the onset of poisoning the organisms. The boundary between the maximum rates and the initiation of intoxication coincided with a sudden change in the heat flux. Using this occurrence, it was possible to develop a control strategy and test it successfully for a time period of 80 h. After 40 h the process stabilized at mean values, i.e., at rates of 92% phenol degradation, 100% biomass formation, and 70 - 75% of PHA formation compared with the situation shortly before poisoning the organisms. Using a moving-average technique to filter the raw dielectric spectroscope data, changes were followed in biomass concentration of approximately 100 mg/L. However, this technique was not sensitive or rapid enough to control the process.     

从白蚁中分离到具有纤维素酶活的贪噬菌

以黄胸散白蚁Reticulitermes flaviceps后肠为材料,分离培养具有降解纤维素能力的微生物,以进一步了解白蚁后肠微生物的种类。通过以羧甲基纤维素钠(CMC-Na)为唯一碳源的富集及选择培养基培养、筛选,获得一株具有纤维素酶活的菌株R3063。形态学鉴定、革兰氏染色观察及16S rDNA基因序列分析表明该菌株属于贪噬菌(Variovorax sp.)。目前尚未见贪噬菌具有纤维素酶活的报道。     

Generation of a large set of genetically tractable haploid and diploid Saccharomyces strains

Saccharomyces cerevisiae has proved to be an invaluable model in classical and molecular genetics studies. Despite several hundreds of isolates already available, the scientific community relies on the use of only a handful of unrelated strains. The lack of sequence information, haploid derivatives and genetic markers has prevented novel strains from being used. Here, we release a set of 55 S. cerevisiae and Saccharomyces paradoxus genetically tractable strains, previously sequenced in the Saccharomyces Genome Resequencing Project. These strains are stable haploid derivatives and ura3 auxotrophs tagged with a 6-bp barcode, recognized by a restriction enzyme to allow easy identification. We show that the specific barcode can be used to accurately measure the prevalence of different strains during competition experiments. These strains are now amenable to a wide variety of genetic experiments and can be easily crossed with each other to create hybrids and segregants, providing a valuable resource for breeding programmes and quantitative genetic studies. Three versions of each strain (haploid Mat a and Mat α and diploid Mat a /α all as ura3 ∷ KanMX-Barcode ) are available through the National Culture Yeast Collection.     

Mitochondrial DNA phylogeography of Acrossocheilus paradoxus (Cyprinidae) in Taiwan

Nucleotide sequences of 3' end of the cytochrome b gene, tRNA genes, D-loop control region, and the 5' end of the 12S rRNA of mitochondrial DNA (mtDNA) were used to assess the genetic and phylogeographic structure of Acrossocheilus paradoxus populations, a Cyprinidae fish of Taiwan. A hierarchical examination of populations in 12 major streams from three geographical regions using an analysis of molecular variance (AMOVA) indicates high genetic differentiation both among populations (PhiST = 0.511, P < 0.001) and among regions (PhiCT = 0.368, P < 0.001). Limited migration largely contributed to the genetic differentiation. High nucleotide diversity (1.13%) and haplotype diversity (0.80%) were detected among populations. The degree of genetic differentiation was correlated with geographical distance between populations, a result consistent with the one-dimensional stepping stone models. A neighbour-joining tree recovered by (DAMBE) supports the pattern of isolation by distance and reveals a closer relationship between populations of the central and southern regions. A minimum spanning network based on nucleotide substitutions reflected migration routes from populations of the central region to the northern and southern regions, respectively. Postglacial colonization and expansion can explain the phylogeographical pattern. Single and ancient migration events may have allowed the northern region to attain the monophyly of mtDNA alleles. In contrast, most populations within geographical regions are either paraphyletic or polyphyletic due to the relatively shorter time period for coalescence. Both low haplotype number and genetic variability suggest a bottleneck event in the Chingmei population of northern Taiwan. Based on coalescence theory, the monophyly of the Tungkang population of the southern region may be associated with a founder event.     

Strain conformation controls the specificity of cross-species prion transmission in the yeast model

Transmissible self-assembled fibrous cross-β polymer infectious proteins (prions) cause neurodegenerative diseases in mammals and control non-Mendelian heritable traits in yeast. Cross-species prion transmission is frequently impaired, due to sequence differences in prion-forming proteins. Recent studies of prion species barrier on the model of closely related yeast species show that colocalization of divergent proteins is not sufficient for the cross-species prion transmission, and that an identity of specific amino acid sequences and a type of prion conformational variant (strain) play a major role in the control of transmission specificity. In contrast, chemical compounds primarily influence transmission specificity via favoring certain strain conformations, while the species origin of the host cell has only a relatively minor input. Strain alterations may occur during cross-species prion conversion in some combinations. The model is discussed which suggests that different recipient proteins can acquire different spectra of prion strain conformations, which could be either compatible or incompatible with a particular donor strain.     

Biological control of phytophagous ladybird beetles Epilachna vigintioctopunctata (Col., Coccinellidae) by chitinolytic phylloplane bacteria Alcaligenes paradoxus entrapped in alginate beads

The chitinase secreting strain KPM‐012A of Alcaligenes paradoxus was isolated from tomato leaves and vitally entrapped in sodium alginate gel beads to provide a new method for biocontrol of phytophagous ladybird beetles Epilachna vigintioctopunctata. First, the peritrophic membrane was dissected from the adult ladybird beetles that ingested the suspension of KPM‐012A after starvation to observe degradation of the midgut surface by the bacteria under electron microscopy. The peritrophic membrane around the bacteria was degraded, suggesting the release of chitinase from the ingested bacteria. Large amounts of chitinase were successfully released from KPM‐012A‐entrapped calcium alginate beads. This chitinase release from the microbial beads was sustained for 1 week and was sufficient to digest the peritrophic membrane. Daily supply of tomato leaves treated with the microbial beads caused considerable suppression of leaf feeding and oviposition by the adult ladybird beetles, indicating that this method is effective for decreasing population of insect pests in the subsequent generation. Thus, the present study provided an experimental basis for the biocontrol measures of herbivorous insect pests by the chitinolytic bacteria entrapped in alginate beads.     

Degradation of homovanillate by a strain of Variovorax paradoxus via ring hydroxylation

Abstract A newly isolated strain of Variovorax paradoxus could grow on homovanillate and several monohydroxylated phenylacetic acids. During growth on homovanillate, the organism formed separate NAD(P)H-dependent hydroxylases with activity towards 4-hydroxyphenylacetic acid and homovanillate. Homovanillate hydroxylase catalysed a typical monooxygenase reaction and had little activity towards 4-hydroxyphenylacetic acid. GC-MS and TLC analysis suggested that homovanillate was 1-hydroxylated to yield a dihydroxymonomethoxyphenylacetic acid which served as a substrate for homogentisate 1,2-dioxygenase. Methanol, but not formaldehyde, was released either during ring-cleavage or subsequent metabolism of the ring-cleavage product.