Identification, mapping and characterization of two genes ofEscherichia coli K-12 regulating growth and resistance to streptomycin in cold

Escherichia coli MD1157, a routine isolate of AB1157 maintained in our laboratory, was noticed to have spontaneously acquired two conditional cold-dependent phenotypes: C^s (cold sensitivity) and Sm^sc (streptomycin sensitivity in cold). C^s involved delayed appearance of visible colonies on solid (LB or minimal) medium in cold (22° C or below) without any loss of viability, and an extended lag period and longer doubling time following a temperature downshift in liquid medium. Sm^sc involved conditional suppression of therpsL31 -mediated streptomycin (Sm) resistance in cold, resulting in reduced colony forming ability in the presence of Sm. This phenotype was seen only on LB plates and weakly on minimal-medium plates containing some LB, but not on minimal medium alone. Genetic mapping traced these two phenotypes to mutations in two genes mapping to the 14-15 min region of the standardE. coli map, which have been namedgicA (growth in cold) andgicB respectively. Comparison of MD1157 with transductants which had lost either one or both of these mutations showed that whilegicBl contributes only to Sm^sc,gicAl is associated with both C^s and Sm^sc. Comparison of these strains with AB1157 suggested the involvement of a third, as yet unidentified gene in causing these phenotypes.     

Growth and survival of cowpea rhizobia in bauxitic silt loam and sandy clay loam soils

Survival of 4 cowpea Rhizobium strains, IRC291, MI-50A, JRW3 and JRC29, in two soil types (bauxitic silt loam and sandy clay loam) undergoing drying at 30°C and 37°C was examined. While all strains except JRW3 showed a general pattern of increase in their numbers during the first 3 weeks in sterile soils, none of the strains showed any increase in their population in non-sterile soils. Cowpea rhizobia showed better survival in non-sterile bauxitic silt loam than in clay loam soils at 30°C. However, the long-term survival (examined up to 6 months) of rhizobia in both soils was poor at 37°C as compared to 30°C. We also found that cowpea rhizobia survived better in soils undergoing drying than in moist soils at 30°C. Our results suggest that (a) cowpea rhizobia survived better in bauxitic silt loam than in clay loam soil and (b) the low indigenous cowpea rhizobial population in Jamaican soils may be due to their poor long-term survival and weak saprophytic competence.     

How do combinations of rpsL- and miaA- generate streptomycin dependence?

Summary Petrullo et al. (1983) have studied the consequences of combining a mutation (rpsL ^–) that normally generates streptomycin resistant (Sm^r) ribosomes with a mutation (miaA ^–) that leads to loss of a tRNA hypermodification. They found surprisingly that such doubly mutant bacteria become streptomycin dependent (Sm^d). Here, we show in vitro that ribosomes purified from an Sm^r mutant behave very like Sm^d ribosomes when they are combined with tRNA from an miaA ^– mutant. Our analysis suggests that proofreading becomes excessively intense when the mutant components are combined, and that this reduces the efficiency of translation to the very low levels characteristic of Sm^d ribosomes. We show that Sm increases the efficiency of translation in vitro by suppressing the proofreading flows. We suggest that this will explain the growth stimulatory effect of Sm on the rpsL ^–, miaA ^–double mutants.     

Phenotypic suppression by streptomycin of amber mutants in the ribonucleic Acid bacteriophage coat protein cistron

After mutagenesis with nitrosoguanidine or ultraviolet light, 298 streptomycin high-resistant and 98 streptomycin high-dependent mutants were isolated from HfrC Su⁻. They were tested for their ability to phenotypically suppress five different amber ribonucleic acid (RNA) bacteriophage mutants in the presence of streptomycin. The phage mutants are all in the coat protein, which is 129 amino acids long; the uracil-adenine-guanine codons were at the following positions: sus3 and amB2, 6; amB11, 50; amB21, 54; sus11, 70. Only sus3 and amB2 could be phenotypically suppressed by streptomycin; this was clearly demonstrated in nine mutant strains, seven str-HR and two str-HD. The suppression was always dependent upon added streptomycin and was dose-dependent in all cases. None of the mutants showed measurable suppression in absence of the drug. Among revertants to streptomycin independence from streptomycin-dependent strains that could show phenotypic suppression, most of those that were still resistant to streptomycin (10 μg or more) retained the capacity to show phenotypic suppression; whereas among those revertants sensitive to 10 μg of streptomycin or less, none retained the capacity. Eight different amber polar mutants (strong and weak) in gene 34 of phage T4 were also tested for pleiotypic suppression by streptomycin in all the streptomycin-resistant and -dependent strains isolated. No suppression was found in any of the 396 strains tested.     

Role of thiol redox systems in <Emphasis Type="Italic">Escherichia coli</Emphasis> response to thermal and antibiotic stresses

Isogenic knockout mutants of Escherichia coli deficient in components of the glutathione and thioredoxin redox systems and growing at various temperatures (20–46°C) exhibited considerable differences in growth rate and survival, as well as in expression of the antioxidant genes. In the parental strain E. coli BW25113 (wt) treated with ciprofloxacin, ampicillin, or streptomycin, dependence of survival on growth temperature was a V-shaped curve with the maximum sensitivity within the range corresponding to high growth rates (40–44°C). Significant inverse correlation was observed between log CFU at different temperatures and specific growth rate prior to antibiotic addition. This applied to most of the mutants, which exhibited higher resistance to the three antibiotics tested at nonoptimal temperatures (20 and 46°C) than at 37 and 40°C. No correlation was found between resistance to stress and antibiotics and expression of the antioxidant genes. The role of global regulators ppGpp and σ^s in E. coli resistance to antibiotics and nonoptimal temperatures was shown.     

The rpsL gene and streptomycin resistance in single and multiple drug-resistant strains of Mycobacterium tuberculosis

The recent emergence of indolent and rapidly fatal drug-resistant strains of Mycobacterium tuberculosis has renewed interest in defining the molecular mechanisms of drug resistance in the tubercle bacilli. In this report, we have examined the mechanism of resistance to streptomycin (Sm) in M. tuberculosis through the cloning and nucleotide sequence analysis of the gene encoding the ribosomal S^R protein (rpsL gene) from streptomycin-resistant strains and their streptomycin-sensitive parental strains. We have demonstrated that five singly Sm^RM. tuberculosis strains and an Sm^R isolate that has reduced sensitivity to multiple antibiotics have identical point mutations at codon 43 of the rpsL gene. Mutations at this same site confer Sm^R in Escherichia coli. In contrast, two other multiple drug-resistant M. tuberculosis strains that are resistant to Sm have rpsL genes that have the same nucleotide sequence as their drug-sensitive parent strains, suggesting that different resistance mechanisms are involved in these strains.     

Subject index vol. 70 (1980)

Antibiotic-resistant (either to erythromycin or chloramphenicol) temperature-sensitive mutants were isolated with about the same frequency in 2 strains of the petite negative yeast K. lactis.The ery^R and cap^R mutants isolated in the strain K. lactis CBS 2359 showed with high frequency both a lethal-conditioned (lc) or a petite temperature-sensitive (pts) phenotype, whereas amongst the many ery^R and cap^R mutants isolated in the strain K. lactis CBS 2360 only lc phenotypes appeared. In the mutants isolated from K. lactis CBS 2360, one growth cycle in the presence of ethidium bromide irreversibly blocked the transmission of antibiotic resistance and temperature sensitivity (lc and pts), whereas at least 2 growth cycles were required to give the same results for the mutants isolated in K. lactis CBS 2359.The spontaneous reversion frequencies for the temperature sensitivity were about the same for the lc mutants isolated in the 2 strains, but the frequencies of co-reversion of the antibiotic resistance were higher in ery^Rlc and cap^Rlc mutants isolated from K. lactis CBS 2360.The analysis of the effect of the exposure to erythromycin or to the temperature of 36°C on protein synthesis carried out by isolated mitochondria of 2 ery^Rlc mutants of K. lactis CBS 2360 and CBS 2359 showed that, in these mutants, mitochondrial protein synthesis became resistant to the drug and sensitive to temperature. The exposure at 36°C, before protein synthesis was inactived, determined in these mutants a condition of sensitivity to the antibiotic, suggesting that even though the 2 K. lactis strains differ in some aspects concerning the behaviour of their mitochondrial information they might depend, as to their petite-negative character, on the role that mitochondrial protein synthesis has in cell division.     

The growth of four species of Azolla as affected by temperature

The growth of 22 strains of Azolla pinnata R. Br., 3 strains of A. filiculoides Lam. and one strain each of A. mexicana Presl and A. caroliniana Willd. was tested separately in liquid culture media kept in controlled, artificial light (30 klux) growth cabinets. Three temperature levels were used: 33°C (37/29°C day/night), 29°C (33/25°C) and 22°C (26/18°C)/ Photoperiod was 12 h a day.For most A. pinnata strains (except three) and an A. mexicana strain the maximum weekly relative growth rate was higher at 33°C than at 22°C, but not for A. filiculoides and A. caroliniana. The highest value of maximum relative growth rate corresponded to 1.9 doubling days and in most strains this occurred in the first week. As the plants grew, the growth rate slowed down more severely at higher temperatures. The maximum biomass was higher at 22°C than at 33°C in all strains. At 22°C, it took 30–50 days to attain maximum biomass and the highest value was 14 g N m^?2 or 320 g dry m^?2 by A. caroliniana, followed by 12 g N m^?2 or 290 g dry wt. m^?2 by one strain of A. filiculoides. At 29°C, the maximum biomass was attained in 20–35 days. The highest value was 6.3 g N m^?2 or 154 g dry wt. m^?2 by A. caroliniana. At 33°C, most A. pinnata strains gave a maximum biomass of less than 4 g N m^?2 after 13–23 days, while some strains grew up to 30 days, resulting in a higher maximum biomass. The highest maximum biomass at 33°C was 5.5 g N m^?2 or 140 g m^?2 dry wt. by A. pinnata from Cheng Mai while the maximum biomass of A. filiculoides and A. caroliniana was much less. Azolla filiculoides requires lower temperature than other species for its growth. Azolla pinnata has the best tolerance to high temperatures among the four species. Azolla mexicana could not be discriminated from A. pinnata in its response to temperature. Azolla caroliniana may keep an intermediate position between A. filiculoides and A. pinnata in temperature response.The formation of ammonia in the medium was examined and it occurred mostly under stationary growth conditions, but, at 33°C, some strains of A. pinnata and A. mexicana released or formed ammonia at 0.3–0.8 μg N ml^?1 per week during their initial exponential growth stage.     

A cold-sensitive mutant ofNeurospora crassa obtained using tritium-suicide enrichment that is conditionally defective in the biosynthesis of cytoplasmic ribosomes

The purpose of this investigation was to use tritium-suicide enrichment with a mutagenized population of wild-typeNeurospora crassa to isolate cold-sensitive mutants with conditional defects in the production of cytoplasmic ribosomes. Eighty-six cold-sensitive mutant strains were obtained following tritium-suicide enrichment using [5-³H]uridine. Zone sedimentation analysis of cytoplasmic ribosomes produced by the strains at 10°C (the nonpermissive temperature) indicated that one strain,PJ31562, is defective in the accumulation of ribosomal subunits at that temperature. The properties of strainPJ31562 are: (1) At 10°C the growth rate is 28 times slower than at 25°C, whereas the factor for the wild type is 5.1. At 25°C the mutant's growth rate is 90% that of the wild type. (2) At 10°C the mutant accumulates the two ribosomal subunits, 60 and 37 S, in markedly disproportionate amounts apparently as a result of the underproduction of, or an instability of, the 17 S ribosomal RNA component of the small ribosomal subunit. At 25°C the mutant strain still exhibits a disproportionality in ribosomal subunit accumulation but to a much lesser degree than at 10°C. (3) Genetic studies have shown that a single nuclear gene is responsible for both the cold sensitivity and ribosome biosynthesis defect of strainPJ31562. The mutation involved is located in linkage group IV and appears to be closely linked to, and not allelic with, the cold-sensitive mutation carried by strainPJ30201 which has been shown previously to exhibit a similar phenotype with respect to ribosomal subunit accumulation, and which defines thecrib-1 locus. Thus tritium-suicide enrichment can be used to isolate cold-sensitive mutants ofNeurospora among which a relatively low frequency have conditional defects in ribosome production.     

A Suitable Streptomycin-Resistant Mutant for Constructing Unmarked In-Frame Gene Deletions Using rpsL as a Counter-Selection Marker

The streptomycin counter-selection system is a useful tool for constructing unmarked in-frame gene deletions, which is a fundamental approach to study bacteria and their pathogenicity at the molecular level. A prerequisite for this system is acquiring a streptomycin-resistant strain due to rpsL mutations, which encodes the ribosomal protein S12. However, in this study no streptomycin resistance was found to be caused by rpsL mutations in all 127 clinical strains of Klebsiella pneumoniae isolated from liver abscess patients. By screening 107 spontaneous mutants of streptomycin resistance from a clinical strain of K. pneumoniae, nucleotide substitution or insertion located within the rpsL was detected in each of these strains. Thirteen different mutants with varied S12 proteins were obtained, including nine streptomycin-dependent mutants. The virulence of all four streptomycin-resistant mutants was further evaluated. Compared with the parental strain, the K42N, K42T and K87R mutants showed a reduction in growth rate, and the K42N and K42T mutants became susceptible to normal human serum. In the mice LD₅₀ (the bacterial dose that caused 50% death) assay, the K42N and K42T mutants were ∼1,000-fold less lethal (∼2×10⁵ CFU) and the K87R mutant was ∼50-fold less lethal (∼1×10⁴ CFU) than the parental strain (∼2×10² CFU). A K42R mutant showed non-observable effects on the above assays, while this mutant exhibited a small cost (P<0.01) in an in vitro growth competition experiment. In summary, most of the K. pneumoniae strains with streptomycin resistance caused by rpsL mutations are less virulent than their parental strain in the absence of streptomycin. The K42R mutant showed similar pathogenicity to its parental strain and should be one of the best choices when using rpsL as a counter-selection marker.     

Production of microsclerotia by Brazilian strains of Metarhizium spp. using submerged liquid culture fermentation

We investigated the potential production and desiccation tolerance of microsclerotia (MS) by Brazilian strains of Metarhizium anisopliae (Ma), M. acridum (Mc) and M. robertsii (Mr). These fungi were grown in a liquid medium containing 16 g carbon l^?1 with a carbon:nitrogen ratio of 50:1. One hundred milliliters cultures were grown in 250 ml Erlenmeyer flasks in a rotary incubator shaker at 28 °C and 200 rpm for 5 days. Five-day-old MS were harvested, mixed with diatomaceous earth (DE) and air-dried for 2 days at 30 °C. The air-dried MS–DE granular preparations were milled by mortar + pestle and stored in centrifuged tubes at either 26 or ?20 °C. Desiccation tolerance and conidia production were assessed for dried MS granules by measuring hyphal germination after incubation for 2 days on water agar plates at 26 °C and for conidia production following 7 days incubation. Yields of MS by all strains of Metarhizium were 6.1–7.3 × 10⁶ l^?1 after 3 days growth with maximum MS yields (0.7–1.1 × 10⁷ l^?1) after 5 days growth. No differences in biomass accumulation were observed after 3 days growth, whereas Ma-CG168 showed the highest biomass accumulation after 5 days growth. Dried MS–DE preparations of all fungal strains were equally tolerant to desiccation (≥93 % germination) and the highest conidia production was obtained by MS granules of Mc-CG423 (4 × 10⁹ conidia g^?1). All MS granules showed similar stability after storage at either 26 or ?20 °C for 3.5 months.     

Studies on Transformations of Hemophilus influenzae : III. The genotypes and phenotypic patterns of three streptomycin-resistant mutants

A general method of determining the nature of the genotypes in mutants of transformable bacteria with similar phenotypes is discussed. The method is used to identify the genotypic patterns of three mutants of Hemophilus influenzae which are resistant to different levels of streptomycin. A mutant resistant to 700 µg per ml of the antibiotic was found to be made up of two unlinked, independent loci—presumably on different molecules of transforming DNA. These loci, when in separate cells, render them resistant to maximum levels of 10 and 100 µg per ml streptomycin respectively and are therefore designated as Sm¹⁰ and Sm¹⁰⁰. When they enter the same cell they produce a resistance up to 700 µg per ml streptomycin, so the cells are noted as Sm⁷⁰⁰. This multiplicative action is more easily visualized as due to two independent processes of combating the antibiotic which enhance each other rather than two identical processes.     

R-Plasmids in Pasteurella multocida.

Multiple drug-resistant strains of Pasteurella multocida were associated with a high incidence of fatal pneumonia in feedlot cattle. A representative strain, CAH160, resistant to tetracycline (Tc), streptomycin (Sm), and sulfonamide (Su) was studied. The minimal inhibitory concentration (MIC) of Tc was 32 μg/ml while Sm had an MIC of 256 μg/ml. Plasmid DNA was isolated from CAH160 by cesium chloride-ethidium bromide centrifugation. Agarose gel electrophoresis showed that at least three distinct species of plasmid DNA were present. DNA isolated from CAH160 was used to transform Escherichia coli K12 strain C600 r_k^?m_k^?. Transformants resistant to Tc; to Sm, Su; and to Tc, Sm, Su were obtained. Contour length measurements of plasmid DNA isolated from transformant cells showed that Tc resistance was associated with a 3-Mdal plasmid (pSR10), while Sm, Su resistance resided on a 2.7-Mdal molecule (pSR11). More than 20% of the transformants were resistant to Tc, Sm, Su and contained both plasmid species. In E. coli the MIC of Tc was 256 μg/ml and that of Sm was 64 μg/ml. The buoyant density of pSR10 was 1.699 g/cm³, while the density of pSR11 was 1.709 g/cm³.     

Targeted Curing of All Lysogenic Bacteriophage from Streptococcus pyogenes Using a Novel Counter-selection Technique

Streptococcus pyogenes is a human commensal and a bacterial pathogen responsible for a wide variety of human diseases differing in symptoms, severity, and tissue tropism. The completed genome sequences of >37 strains of S. pyogenes, representing diverse disease-causing serotypes, have been published. The greatest genetic variation among these strains is attributed to numerous integrated prophage and prophage-like elements, encoding several virulence factors. A comparison of isogenic strains, differing in prophage content, would reveal the effects of these elements on streptococcal pathogenesis. However, curing strains of prophage is often difficult and sometimes unattainable. We have applied a novel counter-selection approach to identify rare S. pyogenes mutants spontaneously cured of select prophage. To accomplish this, we first inserted a two-gene cassette containing a gene for kanamycin resistance (Kan^R) and the rpsL wild-type gene, responsible for dominant streptomycin sensitivity (Sm^S), into a targeted prophage on the chromosome of a streptomycin resistant (Sm^R) mutant of S. pyogenes strain SF370. We then applied antibiotic counter-selection for the re-establishment of the Kan^S/Sm^R phenotype to select for isolates cured of targeted prophage. This methodology allowed for the precise selection of spontaneous phage loss and restoration of the natural phage attB attachment sites for all four prophage-like elements in this S. pyogenes chromosome. Overall, 15 mutants were constructed that encompassed every permutation of phage knockout as well as a mutant strain, named CEM1ΔΦ, completely cured of all bacteriophage elements (a ~10% loss of the genome); the only reported S. pyogenes strain free of prophage-like elements. We compared CEM1ΔΦ to the WT strain by analyzing differences in secreted DNase activity, as well as lytic and lysogenic potential. These mutant strains should allow for the direct examination of bacteriophage relationships within S. pyogenes and further elucidate how the presence of prophage may affect overall streptococcal survival, pathogenicity, and evolution.     

A sequence of dependent stages in the development of Dictyostelium discoideum.

Eleven marker enzymes which accumulate during discrete stages of development in Dictyostelium discoideum were followed in two independent temperature-sensitive mutant strains. Strain TS2 has a temperature-sensitive period during aggregation and remains as a smooth lawn at the nonpermissive temperature (27°C). It develops normally at 22°C. Strain DTS6 has a temperature-sensitive lesion in the post-aggregation stage and fails to form slugs at 27°C. Early enzymes accumulate in these strains at the nonpermissive temperature but late stage-specific enzymes fail to accumulate at 27°C. The pattern of accumulation of specific enzymes in these and other morphological mutants defines a linear dependent pathway of at least eight steps which determines temporal differentiation in this organism. Development in Dictyostelium is also dependent on environmental cues which determine the onset of differentiation and the preparation for culmination.     

Ecophysiological Features of Polar Soil Unicellular Microalgae1

Due to their ecological, physiological, and molecular adaptations to low and varying temperatures, as well as varying seasonal irradiances, polar non-marine eukaryotic microalgae could be suitable for low-temperature biotechnology. Adaptations include the synthesis of compounds from different metabolic pathways that protect them against stress. Production of biological compounds and various biotechnological applications, for instance, water treatment technology, are of interest to humans. To select prospective strains for future low-temperature biotechnology in polar regions, temperature and irradiance of growth requirements (Q₁₀ and Ea of 10 polar soil unicellular strains) were evaluated. In terms of temperature, three groups of strains were recognized: (i) cold-preferring where temperature optima ranged between 10.1 and 18.4°C, growth rate 0.252 and 0.344 · d⁻¹, (ii) cold- and warm-tolerating with optima above 10°C and growth rate 0.162–0.341 · d⁻¹, and (iii) warm-preferring temperatures above 20°C and growth rate 0.249–0.357 · d⁻¹. Their light requirements were low. Mean values Q₁₀ for specific growth rate ranged from 0.7 to 3.1. The lowest Ea values were observed on cold-preferring and the highest in the warm-preferring strains. One strain from each temperature group was selected for P_N and R_D measurements. The P_N:R_D ratio of the warm-preferring strains was less affected by temperature similarly as Q₁₀ and Ea. For future biotechnological applications, the strains with broad temperature tolerance (i.e., the group of cold- and warm-tolerating and warm-preferring strains) will be most useful.     

Isolation and Characterization of Thermotolerant Gluconobacter Strains Catalyzing Oxidative Fermentation at Higher Temperatures

Thermotolerant acetic acid bacteria belonging to the genus Gluconobacter were isolated from various kinds of fruits and flowers from Thailand and Japan. The screening strategy was built up to exclude Acetobacter strains by adding gluconic acid to a culture medium in the presence of 1% D-sorbitol or 1% D-mannitol. Eight strains of thermotolerant Gluconobacter were isolated and screened for D-fructose and L-sorbose production. They grew at wide range of temperatures from 10°C to 37°C and had average optimum growth temperature between 30-33°C. All strains were able to produce L-sorbose and D-fructose at higher temperatures such as 37°C. The 16S rRNA sequences analysis showed that the isolated strains were almost identical to G. frateurii with scores of 99.36-99.79%. Among these eight strains, especially strains CHM16 and CHM54 had high oxidase activity for D-mannitol and D-sorbitol, converting it to D-fructose and L-sorbose at 37°C, respectively. Sugar alcohols oxidation proceeded without a lag time, but Gluconobacter frateurii IFO 3264^T was unable to do such fermentation at 37°C. Fermentation efficiency and fermentation rate of the strains CHM16 and CHM54 were quite high and they rapidly oxidized D-mannitol and D-sorbitol to D-fructose and L-sorbose at almost 100% within 24 h at 30°C. Even oxidative fermentation of D-fructose done at 37°C, the strain CHM16 still accumulated D-fructose at 80% within 24 h. The efficiency of L-sorbose fermentation by the strain CHM54 at 37°C was superior to that observed at 30°C. Thus, the eight strains were finally classified as thermotolerant members of G. frateurii.     

Biochemical studies with bi-resistant mutants (ethambutol plus streptomycin and isoniazid plus streptomycin) ofMycobacterium smegmatis ATCC 607

Biochemical characteristics of bi-resistant mutants (resistant to ethambutol plus streptomycin or isoniazid plus streptomycin) of mycobacteria isolated by replica plating fromMycobacterium smegmatis ATCC were compared with those of the drug-susceptible strains. Reduced incorporation of [¹⁴C]uracil, [³H]lysine and [¹⁴C]acetate into RNA, protein and phospholipids respectively was seen in the resistant mutants. Total phosphorlipids were enhanced in ethambutol plus streptomycin resistant mutant and decreased in isoniazid plus streptomycin resistant mutant. There were similar changes in levels of individual phospholipids. The resistant mutants revealed an accumulation of phospholipids in the cell wall, and a marked decrease of phospholipids in the cell membrane in comparison to the susceptible strain. Several qualitative alterations in the polypeptide profile (with respect to number and molecular weight) of the crude protein extract and of different subcellular compartments were seen in the resistant mutants.     

The combined effect of salinity and temperature on the growth and toxin content of four Chilean strains of Alexandrium catenella (Whedon and Kofoid) Balech 1985 (Dinophyceae) isolated from an outbreak occurring in southern Chile in 2009

The toxic dinoflagellate Alexandrium catenella has been detected in the southern Chile since 1972, causing severe negative impacts on public health and aquaculture activities. Several environmental factors have been determined to affect growth and toxin production in Alexandrium strains. The aim of this study was to determine the effect of four combined conditions of two temperatures (10 and 15 °C) and two salinities (15 and 35 psu) on the growth and the Paralytic Shellfish Poisoning (PSP) toxin content and composition in four Chilean strains of A. catenella (PFB41, PFB42, PFB37 and PFB38), isolated during a summer outbreak occurred in southern Chile in 2009. The growth curves showed a higher effect of the salinity in strains PFB41 and PFB42 than in strains PFB37 and PFB38. The values of growth rates and maximum cell densities ranged from 0.25 to 0.73 div day⁻¹ and 1.1 × 10⁴ to 5.2 × 10⁴ cells mL⁻¹, respectively. All of the strains showed the highest values for both growth parameters at 15 °C and 35 psu. In general, growth parameters were higher at 35 psu independently of the temperature. On the other hand, the total PSP toxin content ranged widely from 3.99 to 239 fmol cell⁻¹. The highest values of PSP toxin content were attained at 10 °C and 35 psu for all of the strains, at both stages of growth. All of the strains displayed different toxin compositions, with neoSTX, GTX4-1, GTX3-2 and GTX5 being the main toxins detected. The results showed significant differences in the absolute values of growth and toxin production parameters among the strains grown under the same culture conditions, and for each strain grown under different combined conditions of temperature and salinity. These findings demonstrate that abiotic factors can differentially affect the population dynamics of the A. catenella toxic genotypes, thus making it extremely difficult to predict the ecological behavior of this species in the field in terms of the intensity of a potential outbreak.     

Study of trivalent samarium ion embedded lithium‐based borate glass for high‐density optical memory devices

Sm³⁺ ions doped strontium lithium lead borate glasses (SLLB:Sm) were prepared using a conventional melt‐quenching technique. The glasses were analyzed using X‐ray diffractometry and Fourier transform infrared spectroscopy, optical absorption, fluorescence spectral analysis, and fluorescence lifetime decay. The Judd–Ofelt (J–O) parameters and radiative parameters of the SLLB:Sm10 glass (1.0 mol% Sm³⁺ ion‐doped glass) were calculated using J–O theory. From the emission spectra, among all the synthesized glass, SLLB:Sm10 glass had the highest emission intensity for ⁴G_5/2→⁶H_11/2 transition (610 nm). Emission parameters, such as stimulated emission cross‐section and optical gain bandwidth, were calculated. For all concentrations of Sm³⁺ ions, the decay profile showed an exponential nature and decreased when the Sm³⁺ ion concentration was increased due to a concentration quenching effect. This result suggests that the synthesized SLLB:Sm10 glass could be used for application in high‐density optical memory devices.