Synthesis, characterization, and antibacterial activity of N,O-quaternary ammonium chitosan

N,N,N-Trimethyl O-(2-hydroxy-3-trimethylammonium propyl) chitosans (TMHTMAPC) with different degrees of O-substitution were synthesized by reacting O-methyl-free N,N,N-trimethyl chitosan (TMC) with 3-chloro-2-hydroxy-propyl trimethyl ammonium chloride (CHPTMAC). The products were characterized by ¹H NMR, FTIR and TGA, and investigated for antibacterial activity against Staphylococcus aureus and Escherichia coli under weakly acidic (pH 5.5) and weakly basic (pH 7.2) conditions. TMHTMAPC exhibited enhanced antibacterial activity compared with TMC, and the activity of TMHTMAPC increased with an increase in the degree of substitution. Divalent cations (Ba²⁺ and Ca²⁺) strongly reduced the antibacterial activity of chitosan, O-carboxymethyl chitosan and N,N,N-trimethyl-O-carboxymethyl chitosan, but the repression on the antibacterial activity of TMC and TMHTMAPC was weaker. This indicates that the free amino group on chitosan backbone is the main functional group interacting with divalent cations. The existence of 100 mM Na⁺ slightly reduced the antibacterial activity of both chitosan and its derivatives.     

In vitro propagation of taro,with spermine,arginine, and ornithine

In vitro growth and multiplication of taro [Colocasia esculenta var. antiquorum cv. Keladi Birah] was improved considerably, when primary shoot apices were cultured on two modifications of Linsmaier and Skoog [1965] medium, containing 5.5 mg 1^–1 naphthaleneacetic acid and 0.2 mg 1^–1 kinetin or 1.85 mg 1^–1 naphthaleneacetic acid and 2 mg 1^–1 kinetin and supplemented with 10^–4 or 10^–3 mol·1^–1 of polyamine spermine or either of the precursors of polyamine putrescine—arginine and ornithine. Plantlets were regenerated directly from primary shoot apices, axillary buds and protocorm-like bodies [PLB]. Frequency of plantlet regeneration, rate of development and growth in height of main plantlets were enhanced by the addition of arginine and ornithine to the media. Secondary plantlet formation from axillary buds and PLB were promoted by spermine and arginine respectively.     

Effect of liquid culture media on morphology,growth, propagule production,and pathogenic activity of the Hyphomycete,Metarhizium flavoviride

Two isolates of Metarhizium spp. were studied for propagule production, because of their pathogenic activity towards locusts and grasshoppers (Mf189 = M. flavoviride (or M. anisopliae var. acridum) strain IMI 330189, and Mf324 = M. flavoviride strain ARSEF324). Both isolates were grown in seven different liquid media, which have been developed for mass production of various Hyphomycetes, considered as candidates for microbial control of noxious insects. Shake-flask experiments were carried out at 28 °C in the dark. Production was quantified for 72 h and the effects of the tested media were evaluated on propagule concentration, morphology and pathogenicity. Based on preliminary experiments, all tested media were supplemented with 0.4% Tween 80 to avoid the formation of pellets and to produce unicellular propagules. Submerged propagule yields were higher withMf189 than with Mf324 in all seven media. While high concentrations of propagules (1.4 to 2.4 × 10⁸ propagules ml^-1 for MF189 and1.4 to 8.3 × 10⁷ propagules ml^-1 for Mf324) were produced in four media (Adamek, Catroux, Jackson, and Jenkins–Prior media), production of propagules was lower in the three other media (Goral, Kondryatiev, and Paris media). Both isolates produced oblong blastospore-like propagules, except in Kondryatiev medium in which they provided ovoid propagules. In this case, Mf189 submerged propagules looked like aerial conidia, but scanning observations did not demonstrate a typical conidiogenesis via phialides. In Kondryatiev medium, Mf324 submerged propagules were significantly smaller than aerial conidia. Infection potential of submerged propagules was assayed on Schistocerca gregaria. Second-instar larvae fed for 48 h on fresh wheat previously contaminated by a spraying suspension of each inoculum titrated at 10⁷ propagules ml^-1. All seven media produced submerged propagules that were highly infectious for S. gregaria larvae. Shake flask culture assays permitted us to select three low-costmedia, Adamek, Jenkins–Prior, and Catroux for improving scale-up of liquid fermentation focused on mass-production of Metarhizium propagules for mycoinsecticides devoted to locust control. This revised version was published online in June 2006 with corrections to the Cover Date.     

Endocrinological investigation into the reproductive cycles of two sympatric skate species, Malacoraja senta and Amblyraja radiata, in the western Gulf of Maine

The smooth skate, Malacoraja senta, and thorny skate, Amblyraja radiata, are two commercially exploited batoids found within the Gulf of Maine. During the past five years, we conducted a large study to accurately describe important biological life history parameters previously lacking for these species. As part of that project, the current study reports our findings on the hormonal profiles associated with the reproductive cycles of M. senta and A. radiata. Blood samples were obtained from mature M. senta and A. radiata of both sexes from all months of the year, and plasma testosterone (T), estradiol (E₂) and progesterone (P₄) concentrations were determined using radioimmunoassay (RIA). In female M. senta and A. radiata, monthly T concentrations ranged from 4,522 pg ml⁻¹ to 1,373 pg ml⁻¹ and 31,940 pg ml⁻¹ to 14,428 pg ml⁻¹, E₂ concentrations from 831 pg ml⁻¹ to 60 pg ml⁻¹ and 8,515 pg ml⁻¹ to 2,902 pg ml⁻¹, and P₄ concentrations from 3,027 pg ml⁻¹ to 20 pg ml⁻¹ and 3,264 pg ml⁻¹ to 331 pg ml⁻¹, respectively. No statistical differences were detected between any months for any hormone. Estradiol concentrations were not correlated with ovary weight, shell gland weight, or diameter of the largest follicles in either species. Monthly T concentrations in male M. senta and A. radiata ranged from 23,146 to 12,660 pg ml⁻¹ and from 57,500pg ml⁻¹ to 24,737 pg ml⁻¹, while E₂ concentrations ranged from 7.5 pg ml⁻¹ to undetectable and 103 to 30 pg ml⁻¹, respectively. No statistical differences were observed between months for either steroid. Testosterone concentrations were weakly correlated with testes weight and percent of stage VI spermatocysts in A. radiata, however, no correlation was detected between T and stage VI spermatocysts in M. senta. Collectively, these data support the previous conclusion that M. senta and A. radiata of both sexes are capable of reproducing year round in the western Gulf of Maine.     

A simple method for mass isolation of protoplasts from species of Monostroma, Enteromorpha and Ulva (Chlorophyta, Ulvales)

A simple enzyme mixture containing 2% Cellulase Onozuka R–10 and1% Macerozyme R–10 prepared in deionised water supplemented with 3% NaCland 1 mM CaCl₂ was developed for isolating rapidlyprotoplasts from different species of Monostroma,Enteromorpha and Ulva. The yield fordifferent species of Monostroma ranged from 9.6 ×10⁶ to 10.2 × 10⁶ cells g^–1f. wt thallus, and forEnteromorpha from 3.48 × 10⁶ to 11.7× 10⁶ cells g^–1 f. wt and forUlva from 4.58 × 10⁶ to 26.8 ×10⁶ cells g^–1 f. wt. The overallregeneration rate of the protoplasts isolated was usually > 90% and showednormal morphogenesis. The method yields rapid mass production of viableprotoplasts with high regeneration rates.     

Expression of klebsiella his and nif genes in serratia marcescens,Erwinia herbicola and Proteus mirabilis

Plasmid pRD1, an R plasmid of the P incompatibility group which carries his and nif genes from Klebsiella pneumoniae in addition to drug resistance markers derived from RP4, was transferred to His^- mutants of Serratia marcescens, Erwinia herbicola and Proteus mirabilis. His⁺ transconjugants were obtained at low but different frequencies according to recipient genus. Transconjugants all acquired the drug resistance, and were Nif⁺ in S. marcescens and E. herbicola, having acetylene-reducing activities of the same order of magnitude as the parent K. pneumoniae and fixing ¹⁵N₂. No evidence for nif expression in P. mirabilis transconjugants was obtained though the nif genes were present.     

Interactions between epsilon, the proofreading subunit of DNA polymerase III, and proteins involved in the SOS response of Escherichia coli

Summary Epsilon, a fidelity subunit of Escherichia coli DNA Polymerase III, is encoded by dnaQ ⁺. dnaQ49 is a recessive allele that confers temperature-sensitive and saltsuppressible phenotypes for both replication fidelity and viability. SOS mutagenesis in E. coli is regulated by LexA and requires activated RecA (RecA^*) and the products of the umuDC operon. dnaQ49 strains with various recA, lexA and umuDC alleles were constructed to determine if activities induced as part of the SOS response influence epsilon activity. We found: (1) both UmuDC and RecA^* independently enhance the dnaQ49 mutator phenotype, and (2) expression of RecA^* activity in the absence of UmuDC function increases the temperature sensitivity for viability of dnaQ49. These results support the hypothesis that RecA and one or both of the UmuDC proteins interact with the replication complex during SOS mutagenesis.     

Suitability of different media for in vitro cultivation of the ruminal protozoa species Entodinium caudatum, Eudiplodinium maggii, and Epidinium ecaudatum

Three protozoal cultivation media were tested to determine the medium which best facilitated growth and viability of key B-type ciliates isolated from the sheep rumen. Entodinium caudatum and Eudiplodinium maggii were grown anaerobically in 50-ml flasks for 32 days in Caudatum-type (C), Kisidayova (K) or Dehority (M) medium. On day 32, in media K and M, E. caudatum cell counts were high with 5.6 × 10³ and 7.8 × 10³ mL⁻¹, respectively, and the proportion of dead cells was low with 0.6 and 1.4%, respectively. E. maggii concentrations when grown in medium M and C were 2.7 × 10³ and 2.4 × 10³ mL⁻¹, respectively, with 3.9 and 14.1% dead cells. Medium M, which favoured growth of both protozoa species, was tested again and Epidinium ecaudatum was included. Protozoa were grown for a 4-month period and samples were taken in the last two months on days 1, 7, 35 and 57. Average cell concentrations were 10.0, 0.8 and 0.5 × 10³ mL⁻¹ for E. caudatum, E. maggii, and E. ecaudatum, respectively. In conclusion, medium M would appear to be the best choice for cultivating these three species in one medium.     

δC, δN, carbon, nitrogen and phosphorus as indicators of plant ecophysiology and organic matter pathways in Everglades deep slough, Florida, USA

Historically, the Florida Everglades was characterized by a corrugated landscape of shorter hydroperiod, elevated sawgrass (Cladium jamaicense) ridges and longer hydroperiod, deep water slough communities. Drainage and compartmentalization of the Everglades have fundamentally altered this pattern, and sawgrass ridge communities have expanded at the expense of deep water slough communities throughout much of the landscape. In this study we provide a simple isotopic and nutrient characterization of major components of the slough ecosystem to elucidate physiological and nutrient differences among species and to suggest pathways for organic matter decomposition that contribute to peat development in deep water sloughs. We examined carbon (C) and nitrogen (N) isotopes and C, N and phosphorus (P) concentrations of the floating-leaved macrophytes Nymphaea odorata and Nymphoides aquatica, the emergent macrophyte Eleocharis elongata, and the submerged species Utricularia foliosa and Utricularia purpurea, as well as soil and flocculent material from the southern Water Conservation Area 3-A. Flocculent material and soils had the highest N content (4.5 ± 0.2%) and U. foliosa and N. odorata had the highest P content (0.13 ± 0.01% to 0.12 ± 0.01%). The range for δ¹⁵N average ± SE values was 5.81 ± 0.29‰ (U. foliosa) to −1.84 ± 0.63‰ (N. odorata), while the range for δ¹³C values was −23.83 ± 0.12‰ (N. odorata) to −29.28 ± 0.34‰ (U. purpurea). Differences of up to 10‰ in C isotopic values of U. foliosa and N. odorata suggest fundamental physiological differences between these species. Along a degradation continuum, enrichment of ¹³C and ¹⁵N and extent of decomposition was negatively related to phosphorus concentrations. A two end-member ¹³C mixing model suggested that Utricularia species were the primary organic source for flocculent materials, whereas organic matter derived from root decomposition of N. odorata contributed to the progressively enriched δ¹³C values found with depth in soils. These results illustrate the fundamentally important roles of Nymphaea and Utricularia species in ecosystem dynamics of deep water sloughs.     

Ethylene-binding characteristics in Phaseolus,Citrus, and Ligustrum plants

A number of plants were tested for their ability to bind ethylene and the number of binding sites present in each was calculated. Primary leaves of laboratory-grown beans (Phaseolus vulgaris) bound 140 dpm/g fwt (1794 dpm/g dry wt) when exposed to 1.0 Ci/1 of [¹⁴C]ethylene (110 ci/mol). Phytotron-grown leaves were less succulent but only bound 90 dpm/g fwt (1046 dpm/g dry wt). Bean roots bound 30 dpm/g fwt. Citrus and Ligustrum bound 207 and 240 dpm/g fwt, respectively. The time required to achieve equilibrium of leaves with the gas phase was 15 min for bean, 30 min for Citrus, and 30–60 min for Ligustrum. The time for 1/2 of the bound ethylene to diffuse out of the leaves was 20 min for bean, 10 min for Citrus, and 30 min for Ligustrum. The amount of ethylene needed to occupy 1/2 of the binding sites was obtained from Scatchard plots. This value (K_d) was 0.2 l/1 for bean, 0.15 for Citrus, and 0.31 for Ligustrum. The quantity of binding sites in the tissues was 2.0×10^-9 mol of binding sites/kg tissue for bean leaves, 5.7×10^-9 for Citrus leaves, and 6.8×10^-9 for Ligustrum. Pretreatment with indoleacetic acid (IAA), ehtylene, and cycloheximide (1 mg/1) had little effect on the level of ethylene-binding sites in Citrus.Contribution from the Department of Biochemistry, School of Agriculture and Life Sciences and School of Physical and Mathematical Sciences, North Carolina State University. Paper No. 8445 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina 27695-7601.North Carolina-Israel exchange Scholar for 1981 at the Department of Biochemistry, North Carolina State University Raleigh, North Carolina, USA     

Uptake of sulphate,taurine, cysteine and methionine by symbiotic and free-living dinoflagellates

Sulphate uptake by Amphidinium carterae, Amphidinium klebsii and Gymnodinium microadriaticum grown on artificial seawater medium with sulphate, cysteine, methionine or taurine as sulphur source occurred via an active transport system which conformed to Michaelis-Menten type saturation kinetics. Values for K _m ranged from 0.18–2.13 mM and V _max ranged from 0.2–24.2 nmol · 10⁵ cells^–1 · h^–1. K _m for symbiotic G. microadriaticum was 0.48 mM and V _max was 0.2 nmol · 10⁵ cells^–1 · h^–1. Sulphate uptake was slightly inhibited by chromate and selenate, but not by tungstate, molybdate, sulphite or thiosulphate. Cysteine and methionine (0.1 mM), but not taurine, inhibited sulphate uptake by symbiotic G. microadriaticum, but not by the two species of Amphidinium. Uptake was inhibited 45–97% under both light and dark conditions by carbonylcyanide 3-chlorophenylhydrazone (CCCP); under dark conditions sulphate uptake was 40–60% of that observed under light conditions and was little affected by 3-(3,4-dichlorophenyl) 1,1-dimethylurea (DCMU).The uptake of taurine, cysteine and methionine by A. carterae, A. klebsii, cultured and symbiotic G. microadriaticum conformed to Michaelis-Menten type saturation kinetics. K _m values of taurine uptake ranged from 1.9–10 mM; for cysteine uptake from 0.6–3.2 mM and methionine from 0.001–0.021 mM. Cysteine induced a taurine uptake system with a K _m of 0.3–0.7 mM. Cysteine and methionine uptake by all organisms was largely unaffected by darkness or by DCMU in light or darkness. CCCP significantly inhibited uptake of these amino acids. Thus energy for cysteine and methionine uptake was supplied mainly by respiration. Taurine uptake by A. carterae was independent of light but was inhibited by CCCP, whereas uptake by A. klebsii and symbiotic G. microadriaticum was partially dependent on photosynthetic energy. Taurine uptake by cultured G. microadriaticum was more dependent on photosynthetic energy and was more sensitive to CCCP. Cysteine inhibited uptake of methionine and taurine by cultured and symbiotic G. microadriaticum to a greater extent than in the Amphidinium species. Methionine did not greatly affect taurine uptake, but did inhibit cysteine uptake. Taurine did not affect the uptake of cysteine or methionine.     

Effect of divalent cations on succinate transport in Rhizobium tropici,R. leguminosarum bv phaseoli and R. loti

Rhizobium tropici, R. leguminosarum bv phaseoli and R. loti each have an active C₄-dicarboxylic acid transport system dependent on an energized membrane. Free thiol groups are probably involved at the active site. Since EDTA inhibited succinate transport in R. leguminosarum bv phaseoli and R. loti, divalent cations may participate in the process; the activity was reconstituted by the addition of Ca²⁺ or Mg²⁺. However, EDTA had no effect on succinate transport in R. tropici, R. meliloti or R. trifolii strains. Ca²⁺ or Mg²⁺ had a similar effect on the growth rates of R. tropici and R. leguminosarum bv phaseoli; R. tropici did not require Ca²⁺ to grow on minimal medium supplemented with succinate but R. leguminosarum bv phaseoli required either or both of the divalent cations Ca²⁺ and Mg²⁺. A R. tropici Mu-dI (lacZ) mutant defective in dicarboxylic acid transport, was isolated and found unable to form effective bean nodules.The authors are with the Division of Biochemistry, Instituto de Investigaciones Biológicas Clemente Estable, Avda, Italia 3318, 11.600 Montevideo, Uruguay     

Community interactions between the filamentous alga Cladophora glomerata (L.) Kuetzing,its epiphytes,and epiphyte grazers

Summary Interactions between epiphytes, epiphyte grazers and the filamentous green alga Cladophora glomerata (L.) Kuetzing were explored with smaples from rivers in Montana. Extracts of C. glomerata lowered photosynthetic rates of Nitzschia fonticola Grunow (an epiphytic diatom). Nutrient enrichment showed that C. glomerata from the Madison River was N deficient and its epiphytes were P deficient on 2 dates and N deficient on one date, while no nutrient deficiencies were detected in samples from 3 other rivers; this implies there was little nutrient competition between the epiphytes and C. glomerata. Epiphytes lowered drag on C. glomerata tufts and current velocity inside the tufts, apparently by decreasing the effective surface area. Lower drag may decrease detachment, but lowering current velocity from 8 to 0 cm s^-1 resulted in a 100 % decrease in photosynthesis. Light absorption by epiphyte pigments may lower photosynthetic rate of C. glomerata when irradiance is below 200–500 E m^-2 s^-1, and protect against photoinhibition above this irradiance range. Invertebrate grazers (predominantly Baetis tricaudatus Dodds, Trycorythodes minutus Traver and Brachycentrus occidentalis Banks) at high densities removed 75% of epiphytes and B. occidentalis grazed on C. glomerata. Invertebrates regenerated a mean of 0.16 mol NH _inf4 ^sup+ individual^-1 d-1 which could have enhanced growth of downstream C. glomerata. Competition and grazing were not the only interactions in the C. glomerata community, positive (mutualistic) interactions were also important.     

Interactions between the fungal pathogen Beauveria bassiana and three species of coccinellid: Harmonia axyridis, Coccinella septempunctata and Adalia bipunctata

Harmonia axyridis is a predatory coccinellid, native to central and eastern Asia. It has been available in many countries for use as a biological control agent of pest aphids and scale insects. In many of these countries, including the USA, H. axyridis has established. It is now considered an invasive alien species for a number of reasons, including its impact on functional biodiversity. Beauveria bassiana is known to be a natural mortality agent of overwintering coccinellids and is a potential candidate for the biological control of H. axyridis. In this paper we compare the susceptibility of three species of coccinellid, H. axyridis (cultures derived from Japan and UK), Coccinella septempunctata and Adalia bipunctata to infection by B. bassiana (commercial strain GHA) after exposure at three doses (10⁵, 10⁷, 10⁹ conidia ml⁻¹). The two subpopulations of H. axyridis (Japan and UK) were more resistant to B. bassiana infection than either A. bipunctata or C. septempunctata. This is exemplified by the median lethal doses at 10 days post-inoculation (LD₅₀) of 10^6.2, 10^6.0, 10^8.3, 10^9.6 conidia ml⁻¹ for A. bipunctata, C. septempunctata, H. axyridis (Japan) and H. axyridis (UK), respectively. Only doses of 10⁹ conidia ml⁻¹ resulted in mortality of H. axyridis, in contrast, 80% of C. septempunctata and 70% of A. bipunctata exposed to 10⁷ conidia ml⁻¹ of B. bassiana succumbed to infection. The fecundity (cumulative mean egg production over 10 days) of A. bipunctata and H. axyridis (UK) was also assessed. The fecundity of C. septempunctata could not be assessed because this species requires diapause prior to the onset of reproduction and these studies were on beetles that had recently eclosed (2–8 weeks). Harmonia axyridis (Japan) produced no eggs in most treatments including the control and so was excluded from analysis. High dose (10⁹ conidia ml⁻¹) inoculation reduced the fecundity of A. bipunctata to zero but egg production was similar for individuals inoculated with doses of 10⁵, 10⁷ conidia ml⁻¹ and control individuals. In contrast, all doses of B. basssiana reduced H. axyridis (UK) egg production dramatically. We discuss these results in relation to the potential for control of H. axyridis using B. bassiana.     

15N-enrichment of plant tissue to mark phytophagous insects, associated parasitoids, and flower-visiting entomophaga

New techniques are presented on the use of ¹⁵N to mark insects. ¹⁵N, a stable isotope of nitrogen, was enriched above natural abundance in plant and insect tissues. Two laboratory studies demonstrated that enriched ¹⁵N-concentrations could be tracked from plant to insect using mass spectrometry. In the first study, adult Cotesia plutellae (Kurdjimov) (Hymenoptera: Braconidae) and Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) were allowed to feed at the flowers of rapid-cycling Chinese cabbage plants that had been fertilized with ¹⁵N-enriched potassium nitrate (KNO₃-¹⁵NO₃). Both insect groups were found to have significantly elevated ¹⁵N levels after visiting the flowers of the ¹⁵N-enriched plants for 48 hours. In the second study, ¹⁵N-enriched bean plant (Phaseolus vulgaris L.) tissue was incorporated into an insect diet and fed to navel orangeworms, Amyelois transitella (Walker) (Lepidoptera: Pyralidae). When the navel orangeworm larvae were 4th instars, they were removed from the diet and exposed to the parasitoid, Goniozus legneri Gordh (Hymenoptera: Bethylidae). Results indicated that the enriched ¹⁵N-concentration of the bean plants was transferred to the navel orangeworms and, subsequently, to the parasitoids. This work may provide useful techniques to help establish whether agriculturally important entomophaga visiting ¹⁵N-enriched flowers or parasitizing enriched sentinel larvae in the field can be effectively marked with ¹⁵N.     

Isolation,Biological Properties,and Spatial Structure of Antibiotic Loloatin A

A peptide antibiotic with cyanolytic activity was isolated from the IGM52 strain of the Brevibacillus laterosporus Gram-positive spore-forming bacteria. By ¹H NMR spectroscopy, this antibiotic was identified as loloatin A, a cyclic decapeptide cyclo(-Asn-Asp-Tyr-Val-Orn-Leu-D-Tyr-Pro-Phe-D-Phe-). The spatial structure of loloatin A in solution was determined.     

Identification, cloning and analysis of theAspergillus niger genepacC, a wide domain regulatory gene responsive to ambient pH

A wide domain regulatory gene implicated in modulating gene expression in response to ambient pH has been cloned and sequenced from the industrially useful filamentous fungusAspergillus niger. This gene,pacC, is able to restore apacC ⁺ phenotype toA. nidulans pacC ^c 11 andpacC ^c 14 mutants with respect to extent of conidiation, conidial pigment intensity and acid phosphatase regulation. ThepacC gene ofA. niger comprises three exons, encodes a three-zinc-finger protein of 677 amino acids, and shows pH-dependent regulation of expression: mRNA levels are elevated under alkaline conditions and considerably reduced under acidic conditions. The occurrence of PacC consensus binding targets within the sequences upstream ofpacC may indicate autoregulation.     

Genetics of selection-induced mutations: I. uvrA,uvrB, uvrC,and uvrD are selection-induced specific mutator loci

Selection-induced mutations, sometimes called directed, adaptive, or Cairnsian mutations, are spontaneous mutations that occur as specific responses to environmental challenges, usually during periods of prolonged stress, and that occur more often when they are selectively advantageous than when they are selectively neutral. In this study I show that lesions in uvrA, uvrB, uvrC, or uvrD increase the mutation rate from trpA46 to trpA ⁺ by 10²– to 10⁴–fold during tryptophan starvation, but those same lesions do not affect random mutation rates in growing cells when tryptophan is present. The increased selection-induced mutation rates remain specific to the gene that is under selection in that no increase in the mutation rate from trpA46 to trpA ⁺ is detected during proline starvation.Evidence is presented showing that proline starvation produces a state of cellular stress which results in a burst of mutations from trpA46 to trpA ⁺ when proline-starved cells are plated onto medium lacking tryptophan but containing proline.These results are consistent with the hypermutable state model for selection-induced mutagenesis.     

Influence of culture temperature on the growth,biochemical composition and fatty acid profiles of six Antarctic microalgae

The growth, biochemical composition and fatty acid profiles of six Antarctic microalgae cultured at different temperatures, ranging from 4, 6, 9, 14, 20 to 30 ^∘C, were compared. The algae were isolated from seawater, freshwater, soil and snow samples collected during our recent expeditions to Casey, Antarctica, and are currently deposited in the University of Malaya Algae Culture Collection (UMACC). The algae chosen for the study were Chlamydomonas UMACC 229, Chlorella UMACC 234, Chlorella UMACC 237, Klebsormidium UMACC 227, Navicula UMACC 231 and Stichococcus UMACC 238. All the isolates could grow at temperatures up to 20 ^∘C; three isolates, namely Navicula UMACC 231 and the two Chlorella isolates (UMACC 234 and UMACC 237) grew even at 30 ^∘C. Both Chlorella UMACC 234 and Stichococcus UMACC 238 had broad optimal temperatures for growth, ranging from 6 to 20 ^∘C (μ = 0.19 – 0.22 day^–1) and 4 to 14 ^∘C (μ = 0.13 – 0.16 day^–1), respectively. In contrast, optimal growth temperatures for NaviculaUMACC 231 and Chlamydomonas UMACC 229 were 4 ^∘C (μ = 0.34 day^–1) and 6–9 ^∘C (μ = 0.39 – 0.40 day^–1), respectively. The protein content of the Antarctic algae was markedly affected by culture temperature. All except Navicula UMACC 231 and Stichococcus UMACC 238 contained higher amount of proteins when grown at low temperatures (6–9 ^∘C). The percentage of PUFA, especially 20:5 in Navicula UMACC 231 decreased with increasing culture temperature. However, the percentages of unsaturated fatty acids did not show consistent trend with culture temperature for the other algae studied.     

北亚热带3种典型森林群落对降水中氮、磷、硫的截留及分配特征

森林群落在净化空气、截留沉降污染物、改善地表水质等方面具有重要作用。本研究以北亚热带地区3种典型森林群落（毛竹林、杉木林、青冈阔叶林）为研究对象,通过分析沉降污染物（NH₄⁺-N、NO₃^--N、NO₂^--N、TP和SO₄^2-）在大气降水、林内穿透雨、树干茎流、枯透水和地表径流中的浓度和通量变化特征,探讨不同森林群落对氮、磷、硫的截留净化作用和分配特征。结果表明,该区域大气降水中NH₄⁺-N、NO₃^--N、NO₂^--N、TP和SO₄^2-年均浓度分别为1.06、0.61、0.04、0.07、1.84 mg/L,其年均pH为5.88;各森林群落林冠层能够调升降雨的pH且全年稳定,对TP和NH₄⁺-N均有吸附作用,截留率分别为79.09%-84.68%和30.88%-69.36%;而枯落物层则是林下氮、磷、硫的主要释放源,对NH₄⁺-N、NO₃^--N、TP和SO₄^2-均具有淋溶作用;此外,由地表径流（输出）与大气降水（输入）的对比分析可知,各林地对沉降污染物中氮、磷、硫的截留率均超过98%;3种森林群落对沉降污染物中氮、磷、硫的截留能力依次为：青冈阔叶林 > 毛竹林 > 杉木林,阔叶林对沉降污染物的净化能力要高于毛竹林及针叶的杉木林。