The 18S ribosomal DNA (rDNA) sequences were determined for two anamorphic basidiomycetous yeasts, Rhodotorula lactosa and R. minuta. A phylogenetic tree was constructed by the neighbor-joining method using ascomycetous yeasts as an outgroup. The p-aminobenzoic acid (PABA) requiring species, R. lactosa, R. minuta, Erythrobasidium hasegawianum, and Rhodosporidium dacryoidum formed an independent lineage with 100% bootstrap confidence level in the basidiomycetous yeasts lacking xylose. In contrast, R. glutinis, the type species of Rhodotorula, showed a close relationship to Rhodosporidium toruloides and other non-PABA requiring basidiomycetous yeasts that lack xylose in the cell. The molecular phylogeny from this study showed the heterogeneity of the genus Rhodotorula, and suggested the taxonomic importance of PABA requirement in Rhodotorula and related taxa.
Seven strains of cellulolytic anamorphic basidiomycetous yeasts isolated from natural materials collected in Japan were identified as three species in the genus Cryptococcus; Cryptococcus flavus (1 strain), Cryptococcuscellulolyticus sp. nov. (5 strains) and Cryptococcus sp. (1 strain). Cr. cellulolyticus resembles Cr. flavus in the taxonomic criteria traditionally employed for yeasts but is differentiated from this species in DNA-DNA reassociation experiments. Practically, Cr. cellulolyticus is discriminated from Cr. flavus in the assimilation of erythritol and the lack of assimilation of ethanol. A strain assigned to Cryptococcus sp. produces septated mycelium and has Q-9 as the major ubiquinone. These characteristics resemble those of Q-9-equipped strains of Cryptococcus humicolus. However, differences are found in the lack of assimilation of melezitose and in growth without vitamins. We retained it as unidentified because Cr. humicolus itself is assumed to be a heterogeneous species and a revision of the species concept is required.
In an attempt to investigate the origin of the intracellular symbiont of the aphid (Buchnera), aphid gut aerobic bacteria were isolated, and their phylogenetic relations to other prokaryotes were examined based on nucleotide sequences of 16S rDNA. It turned out that there are seven aerobic bacterial groups which constitute major flora of the aphid's gut. As three of the isolated bacteria were identified as members of the family Enterobacteriaceae, and share the common ancestor with the intracellular symbiont, the nucleotide sequences of 16S rDNA were determined for 15 representative strains of the family Enterobacteriaceae. One of the gut microbes belonging to the family Enterobacteriaceae was identified as Erwinia herbicola that is found mainly on plant surfaces. This fact may suggest that the intracellular symbiont of aphid is derived from a habitant of plant on which host insects feed.
The gamma radiation response of diploid yeast Saccharomyces cerevisiae was studied under the condition of nitrogen starvation. An increase in radioresistance was observed when the cells were grown either on solid or in liquid media containing low nitrogen supply. Most of the induced resistance was obtained in the first 1h of incubation in the stress medium. Cells incubated in synthetic liquid medium with limited nitrogen source showed an increase in radioresistance with time as the nitrogen supply in the medium became depleted. Diploid strains carrying a mutation at the RAD52 locus did not show increased radioresistance in synthetic low nitrogen medium. The frequencies of gene conversion at a tryptophan locus and reverse mutation at an isoleucine locus were studied for the strain D7 under nitrogen stress. Our results suggest that nitrogen starvation induces DNA repair which is essentially error free and is mediated through activated recombination pathways.
An antifoaming agent was produced by strains of Xenorhabdus nematophilus independent of the type of medium and lipid supplementation. The antifoam was heat stable and susceptible to inactivation at moderately acidic (pH 4-6) and alkaline (pH 7.5-8.0) values. The agent was soluble in chloroform and chloroform-methanol suspensions, resistant to proteolytic digestion, negatively-charged and hydrophobic and may be a lipopeptide. The level of antifoam varied with the bacterial strain and was not correlated with the onset of the stationary phase of strain OP1-7 but it peaked during the early stationary phase for strain 19061. Antifoam release into broth required metabolizing cells and was associated with whole bacterial cells. Nematode growth, reproduction and infective juvenile production was enhanced by the antifoam. Because surfactants conducive to the dispersal of lipids produced similar effects, it is possible that the bacterial antifoam enhanced nematode nutrition directly by increasing the availability of lipids to the animals or indirectly by increasing bacterial activity.
The fermentation activities of three new anaerobic rumen fungi, viz, Neocallimastix variabilis, Piromyces spiralis and P. minutus, and a Caecomycescommunis isolate grown on straw and filter paper media were studied. N. variabilis, P. spiralis and P. minutus produced carboxymethylcellulase (CMCase), FPase (filter paper activity) and xylanases when grown on straw and filter paper media. C. communis produced only xylanases. The maximum production of all the enzymes was at 72h of fungal incubation. On both media, N. variabilis showed the highest enzyme activities, followed by P. spiralis and P. minutus. Specific enzyme activities of the three fungal isolates in descending order of production were: Xylanase>CMCase>FPase when grown on straw medium; and CMCase>Xylanase>FPase> cellobiase when grown on filter paper medium. The major end-products of fermentation by the three new fungal isolates were acetate and formate. Ethanol and succinate were produced in low amounts and lactate was not detected. The absence of lactate in the end-products of fermentation observed in this study is the first such report.
We have partially characterized, purified, and N-terminal amino acid sequenced a protein of approximately 80kDa from Cryptococcus neoformans. Of the 15N-terminal amino acids sequenced, 12 are identical to those found in ovotransferrin. Polyclonal antisera raised against ovotransferrin crossreacted with the 80kDa protein. In addition, incorporation of 55Fe indicated the presence of iron binding by the 80 kDa protein. Because Cryptococcus neoformans does not possess an iron-scavenging ligand, siderophore, we suggest that an alternative transferrin-like molecule (the 80kDa protein) may play a role in iron uptake by this organism.