Efficient regeneration for enhanced steviol glycosides production in Stevia rebaudiana (Bertoni)

An efficient method of regeneration for antidiabetic plant (Stevia rebaudiana) has been established for healthy biomass and main steviol glycosides (SGs) production, using different PGRs and agar concentrations. Higher callus induction (93.3%) was recorded when leaf explants were placed on an MS medium supplemented with 3.5 gL⁻¹ agar and 2.0 mgL⁻¹ 2,4-D. The addition of 7.0 gL⁻¹ agar and BA (1.0, 2.0 and 4.0 mgL⁻¹) significantly (P < 0.01) influences shooting response (100%). A maximum mean shoot length (13.03 cm) and 28 shoots per explant were observed on a medium containing 1.0 mgL⁻¹ BA. However, the maximum number of leaves (132.67) was encouraged by the addition of BA (1.0 mgL⁻¹) and Kin (1.0 mgL⁻¹). Lower agar (3.5 gL⁻¹), IAA (2.0 mgL⁻¹), and NAA (2.0 mgL⁻¹) concentrations significantly influence the rooting percent (100%), the mean root length (2.9 cm), and the number of roots per plantlet (26.3). These plantlets were successfully acclimatized in the soil. The BA (3.0 mgL⁻¹) in combination with Kin (3.0 mgL⁻¹) and 3.5 gL⁻¹ agar increases dulcoside-A content (Dul-A; 71.8 μg/g-DW) in shoots compared to control (50.81 μg/g-DW). Similar PGRs with 7.0 gL⁻¹ significantly increases the production of steviosides (Stev. 82.48 μg/g-DW). A higher rebaudioside-A content (Reb-A; 12.35 μg/g-DW) was observed in shoots that underwent the addition of BA (1.0 mgL⁻¹) and 7.0 gL⁻¹ agar than in control (07.39 μg/g-DW). Hereby, we developed an efficient and cost-effective method for regeneration and major SGs production, which could be helpful for future studies on this species.     

In silico optimization and low structured kinetic model of poly[(R)-3-hydroxybutyrate] synthesis by Cupriavidus necator DSM 545 by fed-batch cultivation on glycerol

Glycerol was utilized by Cupriavidus necator DSM 545 for production of poly-3-hydroxybutyrate (PHB) in fed-batch fermentation. Maximal specific growth rates (0.12 and 0.3 h⁻¹) and maximal specific non-growth PHB production rate (0.16 g g⁻¹ h⁻¹) were determined from two experiments (inocula from exponential and stationary phase). Saturation constants for nitrogen (0.107 and 0.016 g L⁻¹), glycerol (0.05 g L⁻¹), non-growth related PHB synthesis (0.011 g L⁻¹) and nitrogen/PHB related inhibition constant (0.405 g L⁻¹), were estimated. Five relations for specific growth rate were tested using mathematical models. In silico performed optimization procedures (varied glycerol/nitrogen ratio and feeding) has resulted in a PHB content of 70.9%, shorter cultivation time (23 h) and better PHB yield (0.347 g g⁻¹). Initial concentration of biomass 16.8 g L⁻¹ and glycerol concentration in broth between 3 and 5 g L⁻¹ were decisive factors for increasing of productivity.     

Ecology of aquatic Ranunculus communities under the Mediterranean climate

The Iberian Peninsula encompasses more than 80% of the species richness of European aquatic ranunculi. The floristic diversity of the phytocoenosis characterised by aquatic Ranunculus and the main physical–chemical factors of the water were studied in 43 localities of the central Iberian Peninsula. Four aquatic Ranunculus communities are found in most of the aquatic environments. These are species-poor and have an uneven distribution: three species of Batrachium are heterophyllous and their communities are distributed in different aquatic ecosystems on silicated substrates; one species is homophyllous and its community occurs in various aquatic ecosystems with carbonated waters. In the Mediterranean climate, Ranunculus species are present in different habitats, as shown by the results of all the statistical analyses. Ranunculus trichophyllus communities occur in base-rich waters with a high buffering capacity (2273.44 ± 794.57 mg CaCO₃ L⁻¹) and a high concentration of cations (Ca²⁺, 121 ± 33.12 mg L⁻¹; Mg²⁺, 71.64 ± 82.77 mg L⁻¹), nitrates (2.89 ± 4.80 mg L⁻¹), ammonium (2.19 ± 1.36 mg L⁻¹) and sulphates (216.25 ± 218.54 mg L⁻¹). Ranunculus penicillatus communities are found in flowing waters with a high concentration of phosphates (0.48 ± 0.6 mg L⁻¹) and intermediate buffering capacity (683.66 ± 446.76 mg CaCO₃ L⁻¹). Both Ranunculus pseudofluitans and Ranunculus peltatus communities grow in waters with low buffering capacity (R. pseudofluitans, 385.91 ± 209.2 mg CaCO₃ L⁻¹; R. peltatus, 263.3 ± 180.36 mg CaCO₃ L⁻¹), and a low concentration of cations (R. pseudofluitans: Ca²⁺, 12.57 ± 9.42 mg L⁻¹; Mg²⁺, 3.42 ± 1.67 mg L⁻¹; R. peltatus: Ca²⁺, 15 ± 18.26 mg L⁻¹; Mg²⁺, 6.26 ± 8.89 mg L⁻¹) and nutrients (R. pseudofluitans: nitrates, 0.23 ± 0.2 mg L⁻¹; phosphates, 0.09 ± 0.1 mg L⁻¹; R. peltatus: nitrates, 0.19 ± 0.21 mg L⁻¹; phosphates, 0.09 ± 0.12 mg L⁻¹); the first in flowing waters, the latter in still waters.     

Evaluation of selenite bioremoval from liquid culture by Enterococcus species

The genus Enterococcus belong to the genera of bacteria that produce lactic acid and can confer health benefits to living organisms. Selenium (Se) is an essential micronutrient for humans and animals. Thirty-six Enterococcus species isolated from dairy products were screened for Se(IV) sorption capacity for use as a probiotics in animal nutrition. Several isolates grew luxuriantly and significantly removed Se(IV) from Se(IV) amended medium. Two isolates, LAB 14 and LAB 18, identified by 16S rRNA gene sequence analysis as Enterococcus faecalis (98% nucleotide sequence similarity) and Enterococcus faecium (97% nucleotide sequence similarity), respectively, were selected for further studies. The two isolates grew optimally and removed selenium at initial pH 7.0. Optimum removal of Se(IV) from the medium was recorded at 25 °C. Time course studies showed that after 8 h of incubation LAB 14 and LAB 18 cultures displayed the highest biomass production and Se(IV) bioremoval and most selenite in culture depleted in 24 h. At initial concentrations of 10 mg L⁻¹ and 60 mg L⁻¹, E. faecium (LAB 18) removed 9.91 mg L⁻¹ and 59.70 mg L⁻¹, respectively after 24 h. Similar Se(IV) bioremoval capacity was recorded with E. faecalis (LAB 14). Substantial amount of Se was detected in biomass of E. faecium (0.4599 mg g⁻¹ of dry weight) and E. faecalis (0.4759 mg g⁻¹ of dry weight). The significant uptake and transformation of Se(IV) by the Enterococcus species observed in this study suggest that they can be used to deliver dietary Se through feed augmentation with Se(IV)-enriched Enterococcus biomass.     

Laboratory experiments on the effects of variable suspended sediment concentrations on the ecophysiology of the porcelain crab Petrolisthes elongatus (Milne Edwards, 1837)

The porcelain crab Petrolisthes elongatus is a particulate suspension feeding species common to coastal areas of New Zealand (NZ). Consistent with the responses of other suspension feeding species, it is likely to be negatively influenced by elevated suspended sediment concentrations. Laboratory experiments were conducted to quantify the effect of temperature (12 °C, 15 °C and 18 °C) and suspended sediment concentration (total particulate matter (TPM): low < 100 mg L^− 1; medium 100-1000 mg L^− 1; high > 1000 mg L^− 1) on the clearance rate (CR in L h^− 1), oxygen uptake rate (VO₂ in mL h⁻¹), net absorption efficiency (AE), and net energy budget (NEB in J h^− 1) of P. elongatus across a range of sizes. Variation in CR and AE was independent of temperature and of body size, but were significantly different (P < 0.05) at low and medium suspended sediment concentrations compared with high suspended sediment concentrations. CR responded in a non-linear manner to changes in TPM, increasing with TPM up to a maximum value at medium-low concentrations (approximately 250 mg L^− 1) and then decreasing thereafter. CR had almost completely shut down at TPM concentrations of > 1000 mg L^− 1 and at particulate organic matter (POM) concentrations of > 250 mg L^− 1. AE was zero at approximate TPM and POM values of 1200 mg L^− 1 and 300 mg L^− 1, respectively. VO₂ was positively correlated with body size and with temperature, but was independent of TPM. NEB values for P. elongatus were low (approx 110 J g^− 1 h^− 1) at low sediment concentrations, were high (approx 320 J g^− 1 h^− 1) at medium sediment concentrations, and were negative (approx − 114 J g^− 1 h^− 1) at high sediment concentrations. These findings indicate that P. elongatus is likely to be food-limited at sediment concentrations of < 100 mg L^− 1, and severely negatively affected at sediment concentrations of > 1000 mg L^− 1, at least for the duration of such events which may persist for 2-3 days in coastal environments where this crab occurs.     

Hypoxia and sulphide influence gamete production in Ulva sp.

Gamete production after exposure to hypoxia or sulphide was studied in the marine macroalga Ulva sp. collected in the Sacca di Goro, Italy. Experiments were carried out on discs (12 mm diameter) of thalli cultured in artificial sea water in laboratory at 20 ± 1 °C, 152 μmol m⁻² s⁻¹, 16 h photoperiod and 30‰ salinity. Dehydration of thallus was used as inducer of gametogenesis and growth and gamete release during recovery after 10, 20, 30 or 40 min dehydration (20 ± 1 °C, 25% humidity) were analysed. Unlike non-dehydrated thalli the dehydrated ones produced gametes. Thallus discs, non-dehydrated or subjected to 30 min dehydration, were exposed to hypoxia (1.78–4.02 μmol O₂ L⁻¹) or sulphide (1 mM) for 3, 5, or 7 days at 20 °C in the dark. Non-dehydrated and dehydrated thalli maintained in normoxic conditions in the dark were the controls. Gamete density was checked by counting at the end of the incubation period and during the subsequent 7 days of recovery under 16 h photoperiod in normoxic conditions. Non-dehydrated thalli maintained in normoxic conditions in the dark released gametes when returned to light suggesting that dark constitutes a stimulus to gamete production. The presence of gametes at the end of 3 days incubation of dehydrated thalli in normoxia demonstrated that gametogenesis can occur even in the dark. However, gametes were not present at the end of incubation in hypoxic and sulphidic conditions. Actually, during hypoxic incubation oxygen consumption in D-thalli was very low, only 0.117 × 10⁻³ μmol O₂ mg⁻¹ h⁻¹ compared to 5.93 × 10⁻³ μmol O₂ mg⁻¹ h⁻¹ in normoxia, denoting a reduction of the metabolic rate that could not sustain gametogenesis. During recovery after incubation in normoxic, hypoxic or sulphidic conditions densities of gametes from dehydrated thalli showed significant differences and resulted after hypoxia > after normoxia > after sulphide. Differences in non-dehydrated thalli were not significant. Dehydrated thalli, still green at the end of the incubation period, underwent blanching in the course of recovery in parallel to gamete production, while non-dehydrated thalli maintained their green colour even after exposure to sulphide. Our findings suggest that macroalga Ulva sp. can survive exposure to darkness, severe hypoxia and high sulphide levels and can maintain gamete production even when the exposure to these stress conditions is joined to dehydration.     

Treatment of industrial wastewater with two-stage constructed wetlands planted with Typha latifolia and Phragmites australis

Industrial wastewater treatment comprises several processes to fulfill the discharge permits or to enable the reuse of wastewater. For tannery wastewater, constructed wetlands (CWs) may be an interesting treatment option. Two-stage series of horizontal subsurface flow CWs with Phragmites australis (UP series) and Typha latifolia (UT series) provided high removal of organics from tannery wastewater, up to 88% of biochemical oxygen demand (BOD₅) (from an inlet of 420 to 1000 mg L⁻¹) and 92% of chemical oxygen demand (COD) (from an inlet of 808 to 2449 mg L⁻¹), and of other contaminants, such as nitrogen, operating at hydraulic retention times of 2, 5 and 7 days. No significant (P < 0.05) differences in performance were found between both the series. Overall mass removals of up to 1294 kg COD ha⁻¹ d⁻¹ and 529 kg BOD₅ ha⁻¹ d⁻¹ were achieved for a loading ranging from 242 to 1925 kg COD ha⁻¹ d⁻¹ and from 126 to 900 kg BOD₅ ha⁻¹ d⁻¹. Plants were resilient to the conditions imposed, however P. australis exceeded T. latifolia in terms of propagation.     

Near anoxia and sulfide as possible factors influencing the spatial distribution of Acartia tonsa and Acartia clausi: Comparative evaluation of egg tolerance

In many coastal and estuarine areas the planktonic copepods Acartia tonsa and Acartia clausi show a spatial separation with A. tonsa restricted to brackish waters and confined environments and A. clausi inhabiting areas more influenced by sea water. The hatching and viability of A. tonsa and A. clausi eggs exposed to anoxia and anoxia/sulfide (conditions that are frequent in bottom waters of the most confined areas) was evaluated to determine if these stress factors play a role in the distribution of these species. Subitaneous eggs, spawned by laboratory reared organisms, were incubated in near anoxia (< 7.59 × 10^− 3 mmol O₂ L^− 1) or anoxia/sulfide (∼ 1 mmol L^− 1) for different periods (1, 4, 8 and 15 days), then transferred to normoxic conditions. The exposure of the eggs to near anoxia and sulfide appears to induce the same response (quiescence) in both species. Exposure times ≤ 8 days to near anoxia or anoxia/sulfide did not affect egg viability, while 15 day exposure caused significant declines in hatching success of both species. A significant difference between the effects of near anoxia and anoxia/sulfide was observed when incubation lasted 15 days; hatching of eggs exposed to sulfide being higher than that of eggs exposed to near anoxia for both species. No significant differences were observed between the two species in hatching success of eggs exposed to both near anoxia and anoxia/sulfide (with the exception of eggs incubated in near anoxia for 4 days). The results indicate that the impact of anoxia and sulfide on the eggs of the two Acartia species cannot be a factor explaining the spatial distribution in coastal and brackish environments of these copepods.Feeding experiments on A. clausi were also performed. Suitability of different algal species to rear this copepod was evaluated and the results were compared with data previously obtained for A. tonsa. Differences in feeding needs between A. clausi and A. tonsa are discussed.     

Characterization of functional intermediates of endoglucanase from Aspergillus aculeatus during urea and guanidine hydrochloride unfolding

Low concentrations of urea and GuHCl (2 M) enhanced the activity of endoglucanase (EC 3.1.2.4) from Aspergillus aculeatus by 2.3- and 1.9-fold, respectively. The K_m values for controls, in the presence of 2 M urea and GuHCl, were found to be 2.4 ± 0.2 × 10⁻⁸ mol L⁻¹, 1.4 ± 0.2 × 10⁻⁸ mol L⁻¹, and 1.6 ± 0.2 × 10⁻⁸ mol L⁻¹, respectively. The dissociation constant (K_d) showed changes in the affinity of the enzyme for the substrate with increases in the K_cat suggesting an increased turnover number in the presence of urea and GuHCl. Fluorescence studies showed changes in the microenvironment of the protein. The increase in the activity of this intermediate state was due to conformational changes accompanied by increased flexibility at the active site.     

pH-control modes in a 5-L stirred-tank bioreactor for cell biomass and exopolysaccharide production by Tremella fuciformis spore

The effect of pH-control modes on cell growth and exopolysaccharide production by Tremella fuciformis was evaluated in a 5-L bioreactor. The results show that the maximal dry cell weight (DCW) and exopolysaccharide production were 23.57 and 4.48 g L⁻¹ in pH-stat fermentation, where the maximal specific growth rate (μ_max) and specific production rate of exopolysaccharide (P_P/X) were 1.03 and 0.24 d⁻¹, respectively; under pH-shift cultivation, the maximal DCW and exopolysaccharide production were 30.57 and 3.90 g L⁻¹, where the μ_max and P_P/X were 1.21 and 0.06 d⁻¹. Unlike batch fermentation, maximal DCW and exopolysaccharide production merely reached 15.04 and 2.0 g L⁻¹, where the μ_max and P_P/X were 0.86 and 0.05 d⁻¹, respectively. These results suggest that a pH-stat strategy is a more efficient way of performing the fermentation process to increase exopolysaccharide production. Furthermore, this research has also proved that the three-stage pH-control mode is effective for cell growth.     

Understanding the potential effects of water regime and salinity on recruitment of Melaleuca ericifolia Sm.

Although many emergent wetland plants may readily tolerate rapid changes in flooding and drying under freshwater conditions, their tolerance to dynamic water regimes may be compromised by salinity. Melaleuca-dominated woodlands occur naturally in Australia, south-east Asia and New Caledonia. Coastal wetlands dominated by Swamp paperbark (Melaleuca ericifolia) (Myrtaceae), native to south-east Australia, are commonly degraded as a consequence of altered water regime and salinity. This study simulates the release of M. ericifolia seeds from the aerial canopy under a range of water regime and salinity scenarios to determine conditions limiting sexual recruitment. Plant growth and survival were examined following seed release under two static water regimes (moist and flooded sediment) and two dynamic water regimes (simulated drawdown—“flooded-moist” and simulated re-flooding—“moist-flooded”). All water regimes, excluding the continuously flooded regime, were examined at three salinities: 0.1 dS m⁻¹ (fresh), 8 dS m⁻¹ and 16 dS m⁻¹, over a 50-day period commencing 44 days after the seeds were sown. The flooded treatment was examined at 0.1 dS m⁻¹ only, to confirm that flooding prohibits establishment of M. ericifolia. Seed and seedlings were positively buoyant and establishment was limited to moist soil. Flotation of seedlings in the flooded-moist treatment, however, did not inhibit subsequent establishment upon moist soil, even at the highest salinity of 16 dS m⁻¹. Growth, but not survival, was reduced by salinities of 8 dS m⁻¹ and 16 dS m⁻¹ in the moist treatment. Flotation of seedlings in saline water in the flooded-moist treatment did not reduce growth or survival compared with fresh water. Survival of seedlings in the moist-flooded treatment was lower in the freshwater and 16 dS m⁻¹ treatment compared with the moist treatment, but not at 8 dS m⁻¹. These findings suggest that water regime influences establishment of young M. ericifolia plants more strongly than does salinity, at least up to ∼1/3 seawater and in the short term (<2 months). Seedlings are likely to establish during a drawdown where the soil is exposed at salinities of ≤16 dS m⁻¹. In contrast, premature re-flooding of seedlings, even with fresh water, will compromise survival.     

Vertical tubular photobioreactor for semicontinuous culture of Cyanobium sp

We evaluated the kinetic culture characteristics of the microalgae Cyanobium sp. grown in vertical tubular photobioreactor in semicontinuous mode. Cultivation was carried out in vertical tubular photobioreactor for 2 L, in 57 d, at 30 °C, 3200 Lux, and 12 h light/dark photoperiod. The maximum specific growth rate was found as 0.127 d⁻¹, when the culture had blend concentration of 1.0 g L⁻¹, renewal rate of 50%, and sodium bicarbonate concentration of 1.0 g L⁻¹. The maximum values of productivity (0.071 g L⁻¹ d⁻¹) and number of cycles (10) were observed in blend concentration of 1.0 g L⁻¹, renewal rate of 30%, and bicarbonate concentration of 1.0 g L⁻¹. The results showed the potential of semicontinuous cultivation of Cyanobium sp. in closed tubular bioreactor, combining factors such as blend concentration, renewal rate, and sodium bicarbonate concentration.     

Biotic and abiotic regulation of resting spore formation in vivo of obligate aphid pathogen Pandora nouryi: Modeling analysis and biological implication

Entomophthoralean fungus Pandora nouryi is an obligate aphid pathogen that enables to produce resting spores (azygospores) for surviving host absence. To explore possible mechanisms involved in the regulation of resting spore formation in vivo, host cohorts consisting of 40-60 nymphs of green peach aphid Myzus persicae produced within 24 h on cabbage leaf discs in petri dishes were exposed to spore showers of P. nouryi at the concentrations (C) from a very few to nearly 2000 conidia/mm² and then reared for 7-11 days at the regimes of 10-25 °C (T) and 8-16 h daylight (H_L) or ambient (17.5 ± 3.1 °C, 13:11 L:D). Aphid mortalities observed from 35-83 cohorts (showered separately) at each regime showed typical sigmoid trend and fit well a general logistic equation (0.79 ? r² ? 0.88), yielding similar LC₅₀ estimates of 1.7-6.1 conidia/mm². The proportions (P) of cadavers forming resting spores in the cohorts also fit the same equation (0.73 ? r² ? 0.85) at all tested regimes except at 10 °C, a low temperature for the host-pathogen interaction. This indicates the dependence of resting spore formation on the spore concentration. The effects of T and H_L on P over C were well elucidated by the fitted modified logistic equations P = 0.578/{1 + exp[1.710 − (0.136 − 0.0053T)C]} and P = 0.534/{1 + exp[1.639 + (0.034 − 0.0053H_L)C]} (both r² = 0.79). Our results highlight that the resting spore formation in vivo of P. nouryi is regulated primarily by the concentration of host-infecting conidia discharged from cadavers and facilitated by lower temperature and longer daylight.     

Accumulation of lead by free and immobilized cyanobacteria with special reference to accumulation factor and recovery

Lead accumulation by free and immobilized cyanobacteria, Lyngbya majuscula and Spirulina subsalsa was studied. Exponentially growing biomass was exposed to 1-20 mg L⁻¹ of Pb(II) solution at pH 6, 7 and 8 for time periods ranging from 10 min to 48 h. L. majuscula accumulated 10 times more Pb (13.5 mg g⁻¹) than S. subsalsa (1.32 mg g⁻¹) at pH 6 within 3 h of exposure to 20 mg L⁻¹ Pb(II) solution and 76% of the Pb could be recovered using 0.1 M EDTA. This chelator (2 μM) did not influence Pb accumulation whereas 100 μM citrate increased that of S. subsalsa 6- to 8-fold. L. majuscula filaments enmeshed in a glass wool packed in a column removed 95.8% of the Pb from a 5 mg L⁻¹ Pb solution compared to free and dead biomass which removed 64 and 33.6% Pb respectively. A 92.5% recovery of accumulated Pb from the immobilized biomass suggests that repeated absorption-desorption is possible.     

Inoculation of Rhizobium (VR-1 and VA-1) induces an increasing growth and metal accumulation potential in Vigna radiata and Vigna angularis L. growing under fly-ash

Fly-ash-tolerant Rhizobium strains were isolated from plants grown in fly-ash-contaminated soil, axenically under laboratory conditions. Saplings of both plants were raised in N₂-free Jenson medium and inoculated with 2.6 × 10⁸ cell ml⁻¹ and 5.2 × 10⁸ cell ml⁻¹ of culture after 10 d of growth. Plants were transferred into 100% fly-ash under natural condition. Rhizobium-inoculated plants grown on 100% fly-ash showed marked increase in relation to root-shoot length, biomass yield, photosynthetic pigment, protein content and nodulation frequency compared to uninoculated plant grown in control (100% fly-ash). Inoculation of fly-ash-tolerant Rhizobium increased the accumulation of Fe, Zn, Cu Cd and Cr in different tissues vis-à-vis enhanced translocation of metals to the aboveground part of plant. Although inoculation of fly-ash-tolerant Rhizobium strains (VR-1 and VA-1) enhanced the translocation of more Fe to shoot parts, nevertheless, the amount of Rhizobium inoculants supplied to the plant was found to be very important since it has a positive role in increasing plant growth through increased N₂ supply via nitrogenase activity. Results suggest that an integrated approach employing biotechnological means and inoculation of plants with host-specific fly-ash-tolerant Rhizobium strain may prove a stimulus to a fly-ash management programme.     

The role of ammonium in photoprotection against high irradiance in the red alga Grateloupia lanceola

Combined and/or interactive effects of inorganic nitrogen (as ammonium) and irradiance on the accumulation of nitrogenous compounds, like UV-absorbing mycosporine-like amino acids (MAAs), chlorophyll a and phycobiliproteins, were examined in the red alga Grateloupia lanceola (J. Agardh) J. Agardh in a high irradiance laboratory exposure and a subsequent recovery period under low light. Also, photosynthetic activity as in vivo chlorophyll fluorescence of photosystem II, i.e. optimum quantum yield (F_v/F_m), electron transport rate (ETR) and quantum efficiency, were examined. Photosynthetic activity, phycobiliproteins and internal nitrogen content declined during the 3-day PAR (photosynthetically active radiation; 600 μmol s⁻¹ m⁻²) and PAR + UVR (ultraviolet radiation; UVB 280–315 nm 0.8 W m⁻², UVA 315–400 nm 16 W m⁻²) exposure. Ammonium supplied in the culture medium (0, 100 and 300 μM NH₄Cl) modified the responses of the alga to high irradiance exposures in a concentration dependent manner, mainly with respect to recovery, as the highest recovery during a 10-day low light period was produced under elevated concentration of ammonium (300 μM). The recovery of photosynthetic activity and phycobiliproteins was enhanced in the algae previously incubated under PAR + UVR as compared to exposure to only PAR, suggesting a beneficial effect of UVR on recovery or photoprotective processes under enriched nitrogen conditions. However, the content of MAAs did not follow the same pattern and thus it could not be concluded as the cause of observed enhanced recovery.     

3-Phenyllactic acid production by substrate feeding and pH-control in fed-batch fermentation of Lactobacillus sp. SK007

3-Phenyllactic acid (PLA), which is produced by some strains of lactic acid bacteria (LAB), is a known antimicrobial agent with a broad spectrum. Batch and fed-batch fermentation by the strain Lactobacillus sp. SK007 for PLA production have been reported. With batch fermentation without pH-control, PLA production yield was 2.42 g L⁻¹. When fed-batch fermentation by Lactobacillus sp. SK007 was conducted in 3 L initial volume with pH-control at 6.0 and intermittent feeding, which was developed after fermentation for 12 h and every 2 h with 120 mL 100 g L⁻¹ PPA phenylpyruvic acid (PPA) and 50 mL 500 g L⁻¹ glucose each time, PLA production yield reached 17.38 g L⁻¹. The final conversion ratio of PPA to PLA was 51.1%, and the PLA production rate was 0.241 g L⁻¹ h⁻¹. This indicated that PPA was the ideal substrate for PLA fermentation production, and fed-batch fermentation with intermittent PPA feeding and pH-control was an effective approach to improve PLA production yield.     

Accumulation, speciation, and coordination of arsenic in an inbred line and a wild type cultivar of the desert plant species Chilopsis linearis (Desert willow)

This study investigated the absorption of arsenic (As), sulfur (S), and phosphorus (P) in the desert plant Chilopsis linearis (Desert willow). A comparison between an inbred line (red flowered) and wild type (white flowered) plants was performed to look for differential responses to As treatment. One month old seedlings were treated for 7 days with arsenate (As₂O₅, As^V) at 0, 20, and 40 mg As^V L⁻¹. Results from the ICP-OES analysis showed that at 20 mg As^V L⁻¹, red flowered plants had 280 ± 11 and 98 ± 7 mg As kg⁻¹ dry wt in roots and stems, respectively, while white flowered plants had 196 ± 30 and 103 ± 13 mg As kg⁻¹ dry wt for roots and stems. At this treatment level, the concentration of As in leaves was below detection limits for both plants. In red flowered plants treated with 40 mg As^V L⁻¹, As was at 290 ± 77 and 151 ± 60 mg As kg⁻¹ in roots and stems, respectively, and not detected in leaves, whereas white flowered plants had 406 ± 36, 213 ± 12, and 177 ± 40 mg As kg⁻¹ in roots, stems, and leaves. The concentration of S increased in all As treated plants, while the concentration of P decreased in roots and stems of both types of plants and in leaves of red flowered plants. X-ray absorption spectroscopy analyses demonstrated partial reduction of arsenate to arsenite in the form of As-(SX)₃ species in both types of plants.     

双色真藓的组织培养和发育研究

对双色真藓(Bryum dichotomum Hedw.)的孢子发育过程及愈伤组织的诱导和培养进行了研究。结果表明,双色真藓孢子萌发和原丝体发育属于典型的真藓型。将双色真藓原丝体接种在含有2.0 mg L-1的硅酸钠和3.0 mg L-1 6-BA的MS固体培养基上,可诱导双色真藓原丝体分化为愈伤组织。愈伤组织在含有2.0 mg L-1的硅酸钠、1.0 mg L-12,4-D和1.0 mg L-1 6-BA的MS固体培养基上可以长期继代培养。而愈伤组织在含有2.0 mg L-1的硅酸钠、1.0 mg L-1 2,4-D和1.0 mg L-1 6-BA的MS液体培养基中可以悬浮培养,且生长迅速,培养28 d达到接种鲜重的9.25倍。