Dimorphism inBenjaminiella poitrasii: cell wall chemistry of parent and two stable yeast mutants

In the dimorphic zygomycetous fungusBenjaminiella poitrasii, the cell wall compositions of mycelial phase (M), yeast phase (Y) and its yeast form mutants (Y-2 and Y-5) were studied. Chitosan was abundant in M-phase (26.6%) whereas lesser amounts were present in Y-phase (17.3%) and in mutants Y-2 (19.6%) or Y-5 (17.3%). Although chitin was present as a smaller fraction of the total glucosaminoglycan in each of different cell wall preparations, it was almost 3 times more prevalent in M-phase than the Y-phase cells. Cross-linking studies among the various cell wall components inB. poitrasii, suggest linkages among mannans and proteins and glucans and glucosaminoglycans.NCL Communication No. 5111.     

Intergeneric hybridization between Pleurotus ostreatus and Schizophyllum commune by PEG-induced protoplast fusion

Intergeneric hybridization between Pleurotus ostreatus and Schizophyllum commune was studied using PEG-induced fusion. The fusion of protoplasts from auxotrophic mutant strains resulted in the formation of fusion hybrids in the frequencies of 3.6 to 7.3×10^–5. Most of these fusion hybrids were monokaryotic and sterile and no heterokaryosis occurred. Most fusants showed a significantly higher nuclear DNA content when compared to parental strains and no diploids (parent 1 genome plus parent 2 genome) were found. Some fusion hybrids revealed both parental fragments in nuclear and mitochondrial rDNA PCR profiles. AP-PCR (Arbitrarily-primed Polymerase Chain Reaction) fingerprints also indicated that most of the fusion products were recombinant hybrids.     

Characterization of heat resistant mutant strains of Rhizobium sp. [Cajanus] for growth, survival and symbiotic properties

Fourteen heat resistant mutant strains were isolated from a wild-type strain (PP201, Nod⁺ Fix⁺) of Rhizobium sp. (Cajanus) by giving it a heat shock of 43°C. These mutant strains showed a greater increase in optical density (O.D.) and a higher viable cell count in both rhizospheric and non-rhizospheric soil at high temperature. Symbiotic studies showed that pigeon pea plants inoculated with a few mutant strains had ineffective nodules (Nod⁺ Fix⁻) under controlled temperature (43°C) conditions, but under natural high temperature (40–45°C) conditions, the host plants infected with all the mutant strains showed higher total shoot nitrogen than the plants inoculated with the parent strain. Four mutant strains (HR-3, HR-6, HR-10 and HR-12) were found to be highly efficient for all the symbiotic parameters, and thus have the potential to be used as bioinoculants in the North-Western regions of India during the summer season.     

Double Mutants of Cellulomonas biazotea for Production of Cellulases and Hemicellulases following Growth on Straw of a Perennial Grass

Summary Deoxyglucose-resistant mutants of Cellulomonas biazotea secreted elevated levels of cellulases and xylanases. The production of β-glucosidase in the constitutive mutant was increased 5-fold over its parent strain. This mutant showed an approximately 1.6-fold enhanced productivity of extracellular endo-glucanase following growth on Leptochloa fusca over the mutant parent. Extracellular production of xylanase, filter-paper cellulase (FPase) and endo-glucanase (CMCase) were also altered in the mutant. Maximum volumetric productivities for xylanase, β-xylosidase, FPase, β-glucosidase and endo-glucosidase were 451, 98, 80, 95, and 143 IU l⁻¹ h⁻¹ which were significantly more than their respective values from the parental strains. The enzyme preparation of the mutants exhibited improved saccharification of kallar grass straw.     

Pullulanases of alkaline and broad pH range from a newly isolated alkalophilicBacillus sp. S-1 and aMicrococcus sp. Y-1

Summary Two highly alkalophilic bacteria, and potent producers of alkaline pullulanase, were isolated from Korean soils. The two isolates, identified asBacillus sp. S-1 andMicrococcus sp. Y-1, grow on starch under alkaline conditions and effectively secrete extracellular pullulanases. The two isolates were extremely alkalophilic since bacterial growth and enzyme production occurred at pH values ranging from pH 6.0 to 12.0 forMicrococcus sp. Y-1 and pH 6.0 to 10.0 forBacillus sp. S-1. Both strains secrete enzymes that possess amylolytic and pullulanolytic acitivities. Extracellular crude enzymes of both isolates gave maltotriose as the major product formed from soluble starch and pullulan hydrolysis. Compared to other alkalophilic microbes such asMicrococcus sp. (0.57 units ml^–1),Bacillus sp. KSM-1876 (0.56 units ml^–1) andBacillus No. 202-1 (1.89 units ml^–1) these isolates secreted extremely high concentrations (7.0 units ml^–1 forBacillus sp. S-1 and 7.6 units ml^–1 forMicrococcus sp. Y-1) of pullulanases in batch culture. The pullulanase activities from both strains were mostly found in the culture medium (85–90%). The extracellular enzymes of both bacteria were alkalophilic and moderately thermoactive; optimal activity was detected at pH 8.0–10.0 and between 50 and 60°C. Even at pH 12.0, 65% of original Y-1 pullulanase activity and 10% of S-1 pullulanase activity remained. The two newly isolated strains had broad pH ranges and moderate thermostability for their enzyme activities. These result strongly indicate that these new bacterial isolates have potential as producers of pullulanases for use in the starch industry.     

Establishment of phosphate-solubilizing strains of Azotobacter chroococcum in the rhizosphere and their effect on wheat cultivars under green house conditions

A pot experiment was conducted in the green house to investigate the establishment of phosphate solubilizing strains of Azotobacter chroococcum, including soil isolates and their mutants, in the rhizosphere and their effect on growth parameters and root biomass of three genetically divergent wheat cultivars (Triticum aestivum L.). Five fertilizer treatments were performed: Control, 90 kg N ha^—1, 90 kg N + 60 kg P₂O₅ ha^—1, 120 kg N ha^—1 and 120 kg N + 60 kg P₂O₅ ha^—1. Phosphate solubilizing and phytohormone producing parent soil isolates and mutant strains of A. chroococcum were isolated and selected by an enrichment method. In vitro phosphate solubilization and growth hormone production by mutant strains was increased compared with soil isolates. Seed inoculation of wheat varieties with P solubilizing and phytohormone producing A. chroococcum showed better response compared with controls. Mutant strains of A. chroococcum showed higher increase in grain (12.6%) and straw (11.4%) yield over control and their survival (12—14%) in the rhizosphere as compared to their parent soil isolate (P4). Mutant strain M37 performed better in all three varieties in terms of increase in grain yield (14.0%) and root biomass (11.4%) over control.     

Nitrate and nitrite reductase negative mutants of N2-fixingAzospirillum spp.

Chlorate resistant spontaneous mutants ofAzospirillum spp. (syn.Spirillum lipoferum) were selected in oxygen limited, deep agar tubes with chlorate. Among 20 mutants fromA. brasilense and 13 fromA. lipoferum all retained their functional nitrogenase and 11 from each species were nitrate reductase negative (nr^–). Most of the mutants were also nitrite reductase negative (nir^–), only 3 remaining nir⁺. Two mutants from nr⁺ nir⁺ parent strains lost only nir and became like the nr⁺ nir^– parent strain ofA. brasilense. No parent strain or nr⁺ mutant showed any nitrogenase activity with 10 mM NO ₃ ^– . In all nr^– mutants, nitrogenase was unaffected by 10 mM NO ₃ ^– . Nitrite inhibited nitrogenase activity of all parent strains and mutants including those which were nir^–. It seems therefore, that inhibition of nitrogenase by nitrate is dependent on nitrate reduction. Under aerobic conditions, where nitrogenase activity is inhibited by oxygen, nitrate could be used as sole nitrogen source for growth of the parent strains and one mutant (nr^– nir^–) and nitritite of the parent strains and 10 mutants (all types). This indicates the loss of both assimilatory and dissimilatory nitrate reduction but only dissimilatory nitrite reduction in the mutants selected with chlorate.     

Hyper-Production of Insecticidal Crystal Protein (δ-Endotoxin)by Bacillus thuringiensis var. israelensis Is Not Related toSporulation-Specific Biochemical Functions

Hypertoxic mutant strains of Bacillus thuringiensis var. israelensis were isolated by mutagenesis of the parent strain. The correlation, if any, between hyper-production of insecticidal crystal protein (δ-endotoxin) by hypertoxic mutant strains of Bacillus thuringiensis var. israelensis and sporulation-specific biochemical functions was studied. No increase in sporulation-specific biochemical markers was observed in the hypertoxic mutant strains. Asporogenous mutants of hypertoxic mutant strains blocked at different stages of sporulation were isolated, and larvicidal activity was studied. The hypertoxic parent strains and the sporulation-deficient, hypertoxic mutant strains showed almost identical larvicidal activity. Therefore, the increased production of toxin is not related to sporulation-specific biochemical changes. Received: 14 February 2000 / Accepted: 21 March 2000     

Physical and genetic characterization of linear DNA plasmids from the heterothallic yeastSaccharomycopsis crataegensis

Five strains of the heterothallic yeastSaccharomycopsis crataegensis have been previously shown to contain DNA and/or RNA plasmidlike molecules (Shepherd et al. 1987). Three DNA plasmids, designated pScrl-1,-2 and -3, were found in strain NRRL Y-5902, while two were identified in each of NRRL strains Y-5903 and Y-5904. DNA plasmids were not identified inS. crataegensis strains Y-5910 or YB-192. FourS. crataegensis strains (Y-5903, Y-5904, Y-5910 and YB-192) were also shown to possess double-stranded RNA (dsRNA) molecules not found in strain Y-5902 (Shepherd et al. 1987). Hybridization studies now demonstrate the DNA plasmids in Y-5903 and Y-5904 to be highly homologous to their respective size counterparts (pScrl-1 and pScrl-2) in Y-5902 and to show some homology to pScrl-3. Restriction endonuclease mapping studies confirm the linear nature of each plasmid and establish identical restriction maps for a 1.4 kilobase (kb) region in pScrl-2 and -3. This 1.4 kb region accounts for the hybridization homology of pScrl-2 and pScrl-3 noted by Shepherd et al. (1987) and for homology of the plasmids of Y-5903 and Y-5904 to pScrl-3 of Y-5902. The pScrl plasmids show no homology to the dsRNA molecules ofS. crataegensis, the 2 M circular DNA ofStaccharomyces cerevisiae, the killer plasmids ofKluyveromyces lactis, or the linear DNA plasmids ofPichia inositovora.In crosses between linear DNA plasmid-containing and dsRNA-containing strains, only progeny containing the pScrl plasmids were recovered. Poor spore viability and a lack of complete tetrad recovery limited the extent of the analysis, but the findings suggest a cytoplasmic mode of inheritance for these linear DNAs.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Investigation of Lipopolysaccharides from Sinorhizobium meliloti SKHM1-188 and Two of Its Mutants with Decreased Nodulation Competitiveness

A comparative study of the lipopolysaccharides (LPS) isolated from Sinorhizobium meliloti SKHM1-188 and two of its LPS mutants (Tb29 and Ts22) with sharply decreased nodulation competitiveness was conducted. Polyacrylamide gel electrophoresis with sodium dodecyl sulfate revealed two forms of LPS in all three strains: a higher molecular weight LPS1, containing O-polysaccharide (O-PS), and a lower molecular weight LPS2, without O-PS. However, the LPS1 content in mutants was significantly smaller than in the parent strain. The LPS of the strains studied contained glucose, galactose, mannose, xylose, three nonidentified sugars (X ₁ (TGlc 0.53), X ₂ (TGlc 0.47), and X ₃ (TGlc 0.43)), glucosamine, and ethanolamine, while the LPS of S. meliloti SKHM1-188 additionally contained galactosamine, glucuronic and galacturonic acids, and 2-keto-3-deoxyoctulosonic acid (KDO), as well as such fatty acids as 3-OH C14:0, 3-OH C15:0, 3-OH C16:0, 3-OH C18:0, nonidentified hydroxy X (T_{3-OH C14:0} 1.33), C18:0, and unsaturated C18:1 fatty acids. The LPS of both mutants were similar in the component composition but differed from the LPS of the parent strain by lower X ₂, X ₃, and 3-OH C14:0 contents and higher KDO, C18:0, and hydroxy X contents. The LPS of all the strains were subjected to mild hydrolysis with 1% acetic acid and fractionated on a column with Sephadex G-25. The higher molecular weight fractions (2500–4000 Da) contained a set of sugars typical of intact LPS and, supposedly, corresponded to the LPS polysaccharide portion (PS1). In the lower molecular weight fractions (600–770 Da, PS2), glucose and uronic acids were the major components; galactose, mannose, and X ₁ were present in smaller amounts. The PS1/PS2 ratio for the two mutants was significantly lower than for strain SKHM1-188. The data obtained show that the amount of O-PS–containing molecules (LPS1) in the heterogeneous lipopolysaccharide complex of the mutants was smaller than in the SKHM1-188 LPS; this increases the hydrophobicity of the cell surface of the mutant bacteria, which supposedly contributes to their nonspecific adhesion to the roots of the host plant, thus decreasing their nodulation competitiveness.     

Isolation of quizalofop-resistant mutants of Nannochloropsis oculata (Eustigmatophyceae) with high eicosapentaenoic acid following N-methyl-N-nitrosourea-induced random mutagenesis

Nannochloropsis oculata was subjected to N-methyl-N-nitrosourea-induced mutagenesis under the selection pressure of quizalofop, a known inhibitor of acetyl-CoA carboxylase (ACCase) activity with the objective of generating genetically tractable mutants with altered fatty acid metabolism. Two mutants, QUIZ1 and QUIZ2, with stable resistance to quizalofop were isolated and partially characterized. The growth properties and morphology of the mutants appeared identical with the parent strain. However thermo-tolerance was observed in the mutants. Enhanced resistance to quizalofop suggested the presence of herbicide resistant isoforms of ACCase. In vitro assays for ACCase activity showed that ACCase in the wild strains was much more sensitive to quizalofop than the mutant strains. Gas chromatographic analysis of fatty acids revealed that the mutant strains were rich in polyunsaturated fatty acids (n– 3PUFAs), as well as total fatty acid contents; this was accompanied by a concomitant increase in triacylglycerol (TAG) followed by linoleic acid (18:2), arachidonic acid (20:4 n– 6) and EPA (20:5 n– 3). These results suggest that an increased substrate pool (malonyl-CoA) (due to increased specific activity of ACCase) in the mutant strains in vivo and in vitro may have led to the increased TAG accumulation. Random mutagenesis was shown to be a good tool to manipulate PUFAs and EPA in Nannochloropsis. The strains developed will be useful in understanding fatty acid metabolism using genetic and biochemical approaches and also for their direct use in mariculture.     

Nitrate effects on the nodulation of legumes inoculated with nitrate-reductase-deficient mutants of Rhizobium

The effect of nitrate on the symbiotic properties of nitrate-reductase-deficient mutants of a strain of cowpea rhizobia (32H1), and of a strain of Rhizobium trifolii (TA1), were examined; the host species were Macroptilium atropurpureum (DC.) Urb. and Trifolium subterraneum L. Nitrate retarded initial nodulation by the mutant strains to an extent similar to that found with the parent strains. It is therefore unlikely that nitrite produced from nitrate by the rhizobia, plays a significant role in the inhibition of nodulation by nitrate. Nitrite is an inhibitor of nitrogenase, and its possible production in the nodule tissue by the action of nitrate reductase could be responsible for the observed inhibition of nitrogen fixation when nodulated plants are exposed to nitrate. However, the results of this investigation show that nitrogen fixation by the plants nodulated by parent or mutant strains was depressed by similar amounts in the presence of nitrate. No nitrite was detected in the nodules. Nodule growth, and to a lesser extent, the nitrogenase specific activity of the nodules (mol C₂H₄g^–1 nodule fr. wt. h^–1), were both affected by the added nitrate.     

Th1-type immune response to infection by pYV-cured <Emphasis Type="Italic">phoP-phoQ</Emphasis> null mutant of <Emphasis Type="Italic">Yersinia pseudotuberculosis</Emphasis> is defective in mouse model

The PhoP-PhoQ two-component system of Yersinia pseudotuberculosis, a Gram-negative enteric pathogen which causes a variety of gastrointestinal and extraintestinal infections in humans, has been shown to be necessary for virulence. A phoP-phoQ null mutant of a strain of Y. pseudotuberculosis cured of its native plasmid pYV was obtained and studied for generation of immune response in mouse model following intravenous inoculation. The phoP-phoQ null mutant elicited much weaker IgG antibody response to whole cell sonicated (WCS) antigen, in particular that of IgG2a isotype. Interferon-γ levels were also significantly reduced in cultured splenocytes of mice immunized with phoP-phoQ null mutant. The null mutant was found to be about 72-fold less virulent than the parent isogenic strain of Y. pseudotuberculosis. Average counts in spleen of mice inoculated with the null mutant were observed to reduce by at least four logs when compared with the counts in the spleen of mice inoculated with parent isogenic strain. We can thus suggest that the Th1-type immune response of the phoP-phoQ null mutant of Y. pseudotuberculosis is diminished in mice.     

Metabolism associated with raised metabolic flux to sugar nucleotide precursors of exopolysaccharides in Lactobacillus delbrueckii subsp. bulgaricus

Exopolysaccharide (EPS) metabolism was studied in a galactose-negative strain of Lactobacillus delbrueckii subsp. bulgaricus, using two different approaches. Firstly, using both the parent strain and a chemically induced mutant with higher yield and specific productivity of EPS than the parent, comparative information was obtained relating to enzyme activities and metabolite levels associated with EPS formation when grown on lactose. Under continuous culture conditions (D=0.10 h⁻¹), the higher metabolic flux towards EPS formation in the mutant strain relative to the parent appeared to be mediated by raised levels of UDP-glucose pyrophosphorylase (UGP). Marginally raised UDP-galactose 4-epimerase (UGE) activity in the mutant strain suggested that this enzyme could also play a role in EPS overproduction. The second approach involved investigating the effect of growth rate on sugar nucleotide metabolism in the parent, as it is known that EPS production is growth-associated in this strain. UGE activity in the parent strain appeared to increase when the growth rate was elevated from 0.05 to 0.10 h⁻¹, and further to 0.35 h⁻¹, conditions that can be associated with higher levels of metabolic flux to EPS formation. Concurrent with these increments, intracellular ATP levels in the cell were raised. In both investigations glucose-6-phosphate accumulated pointing to a constriction at this branch-point, and a limitation in the flow of carbon towards fructose-6-phosphate or glucose-1-phosphate. The changes in metabolism associated with enhanced flux to EPS provide guidance as to how the yield of Lactobacillus delbrueckii subsp. bulgaricus EPS can be improved.     

Endopolyploidy in Chlorella

A mutant of Dunaliella tertiolecta produced by treatment with methyl nitrosoguanidine and designated HL25/8, grew more slowly than the parent strain under all experimental conditions and was conspicuously less tolerant of NaCl. Total photosynthetic activity (C-fixation and O₂ evolution) was less in HL25/8 than in the parent strain and was affected differently by [NaCl] in the two strains. Various growth characteristics indicated that the mutant had a greater need than the parent strain for CO₂ as distinct from HCO ₃ ^– as a source of carbon. Gaseous CO₂ extended the range of salt tolerance of the mutant. For example, HL25/8 could not sustain growth at 1.02 M NaCl in a conventional buffered medium containing bicarbonate as the sole carbon source but could do so if the medium were sparged with a CO₂/air mixture. The mutant strain has a lower activity of carbonic anhydrase on the cell surface than the parent D. tertiolecta. Moreover, the two strains differ sharply in the responses of their surface carbonic anhydrase activity to salinity of the growth medium. Increasing sodium chloride concentration above 0.17 M raised activity of the enzyme in the parent strain but decreased it in HL25/8. We conclude that the low activity of carbonic anhydrase and its response to salinity can largely, but perhaps not fully, explain the diminished salt tolerance of the mutant. A plate counting method applicable to Dunaliella is described.     

Phenotypic Features of Ferroplasma acidiphilum Strains YT and Y-2

Earlier, we described a new family of mesophilic, strictly autotrophic Fe²⁺-oxidizing archaebacteria, Ferroplasmaceae, which belongs to the order Thermoplasmales and includes the genus Ferroplasma and the species F. acidiphilum (strain Y^T) [1]. The present work is concerned with a comparative study of phenotypic characteristics of the type strain Y and a new strain, F. acidiphilum Y-2, isolated from dense pulps during oxidation of gold-containing arsenopyrite/pyrite concentrates from the Bakyrchikskoe (Kazakhstan) and Olimpiadinskoe (Krasnoyarsk krai) ore deposits, respectively. The G+C content of DNA from strains Y^T and Y-2 comprised 35.1 and 35.2 mol %, respectively; the level of DNA–DNA homology between the strains was 84%. Restriction profiles of chromosomal DNA from both strains exhibited a similarity coefficient of 0.87. Genotypic characteristics of these strains indicate their affiliation to the same species. The cells of both strains are polymorphic and lack cell walls. Strains of F. acidiphilum oxidized ferrous iron and pyrite as the sole source of energy and fixed carbon dioxide as the sole carbon source. The strains required yeast extract as a growth factor. Optimum pH for cell growth ranged from 1.7 to 1.8; the temperature optima for the growth of strains Y^T and Y-2 were 34–36 and 40–42°, respectively. Comparative analysis of the total lipids revealed their close similarity in the strains; two glycophospholipids comprised 90% of the total lipids: lipid I, -D-glucopyranosylcaldarchaetidylglycerol (about 55%), and lipid II, trihexosylcaldarchaetidylglycerol (26%), whose isopranyl chains contained no cyclopentane rings. The carbohydrate fraction of lipid I hydrolysate contained only D-glucose, whereas hydrolysate of lipid II contained both D-glucose and D-galactose in a molar ratio of 2 : 1. Thus, it was established that the intraspecies phylogenetic divergence within F. acidiphilum is manifested in the two strains by different temperature optima against a background of similarity in other phenotypic properties.     

New species and a new combination in the <Emphasis Type="Italic">Hyphopichia</Emphasis> and <Emphasis Type="Italic">Yarrowia</Emphasis> yeast clades

Three new species of Candida and a new combination in the genus Hyphopichia are proposed from phylogenetic analysis of nucleotide divergence in domains D1/D2 of the large subunit (26S) rDNA. The new taxa and their type strains are the following: Candida bentonensis sp. nov. (NRRL YB-2364, CBS 9994), Candida hispaniensis sp. nov. (NRRL Y-5580, CBS 9996), Candida pseudorhagii sp. nov. (NRRL YB-2076, CBS 9998) and Hyphopichia heimii comb. nov. (NRRL Y-7502, CBS 6139), basionym Pichia heimii Pignal. Phylogenetic analysis placed C. pseudorhagii and H. heimii in the Hyphopichia clade whereas C. bentonensis and C. hispaniensis are members of the Yarrowia clade.     

Restriction site variation,length polymorphism and changes in gene order in the mitochondrial DNA of the yeast Kluyveromyces lactics

The purpose of this work was to compare mitochondrial DNA restriction endonuclease patterns in strains of the yeast Kluyveromyces lactis, from different sources, to see how conserved is the organization of this organellar genome. The mitochondrial DNA of five independently-isolated strains and one of unknown origin were compared. Strains NRRL Y-1205, NRRL Y-8279 and NRRL Y-1140 gave identical patterns. Strain NRRL Y-1564 showed an insertion, with respect to the other three, of approximately 1250 bp. Strain W600B had also an insertion with extra restriction sites for EcoRI, HpaI, HaeIII, HincII and XbaI. On the other hand, strain Y-123 showed a restriction pattern quite different from the others.Sequences putatively encoding apocytochrome b, ATPase subunit 9 and ribosomal RNA large subunit, were localized on the physical maps of three strains. Results demonstrated that the order of these three genes shows a common feature in strains W600B and WM37 (auxotroph of Y-1140) but a different distribution in WM27 (auxotroph derived from Y-123). All these facts explain the extensive intraspecific polymorphism observed in the mtDNA of this yeast.     

Isolation and characterization of a Chlorella mutant producing high amounts of chlorophyll and carotenoids

Mutants of Chlorella that form dark green colonies under heterotrophic conditions were generated from the parental Chlorella regularisS-88 by MNNG mutagenesis. The mutant Y-21 was the highest in chlorophyll and carotenoids contents among these isolates. Y-21 grew a little slower than its parental S-88 under heterotrophic and photoautotrophic conditions. Although chloroplasts were generated in both S-88 and Y-21 during glucose starvation and under illumination, the chlorophyll and carotenoid contents of Y-21 were approximately 1.5–1.8 times those of S-88 under both growth conditions, suggesting that relative size of chloroplast is larger in Y-21 than in S-88. Consistent with these results, photosynthesis genes on chloroplast DNA were more highly up-regulated in Y-21 than in S-88 during glucose starvation and under illumination. These results lead us a model in which chloroplast generation is sugar-repressed and photoinduced in Chlorella. Y-21 appears to be a mutant in which sugar repression of chloroplast generation is weak.