Microalga <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis> as a potential source for biodiesel production

Biodiesel from microalgae seems to be the only renewable biofuel that has the potential to completely replace the petroleum-derived transport fuels. Therefore, improving lipid content of microalgal strains could be a cost-effective second generation feedstock for biodiesel production. Lipid accumulation in Scenedesmus obliquus was studied under various culture conditions. The most significant increase in lipid reached 43% of dry cell weight (dcw), which was recorded under N-deficiency (against 12.7% under control condition). Under P-deficiency and thiosulphate supplementation the lipid content also increased up to 30% (dcw). Application of response surface methodology in combination with central composite rotary design (CCRD) resulted in a lipid yield of 61.3% (against 58.3% obtained experimentally) at 0.04, 0.03, and 1.0 g l⁻¹ of nitrate, phosphate, and sodium thiosulphate, respectively for time culture of 8 days. Scenedesmus cells pre-grown in glucose (1.5%)-supplemented N 11 medium when subjected to the above optimized condition, the lipid accumulation was boosted up to 2.16 g l⁻¹, the value ~40-fold higher with respect to the control condition. The presence of palmitate and oleate as the major constituents makes S. obliquus biomass a suitable feedstock for biodiesel production.     

SCL-LCL-PHA copolymer production by a local isolate,Pseudomonas aeruginosa MTCC 7925

A five-level-four-factor central composite rotary design (CCRD) was employed in combination with response surface methodology (RSM) to optimize the process variables for the production of a novel copolymer consisting of short-chain-length (SCL) and long-chain-length (LCL) PHA units, i.e., P(3HB-3HV-3HHD-3HOD) copolymer in Pseudomonas aeruginosa MTCC 7925. The four variables involved in this study were ethanol, glucose, ammonium nitrate (NH₄NO₃), and potassium dihydrogen phosphate (KH₂PO₄). A second-order polynomial equation was obtained by multiple regression analysis using RSM. The statistical analyses of the results showed that all the four variables had significant impact on the copolymer yield. The model predicted a maximum yield of 81.1% of dry cell weight (dcw) on setting the concentrations of ethanol and glucose at 1.5 and 1.1%, and KH₂PO₄ and NH₄NO₃ at 2.79 and 1.86 g/L, respectively. Verification of the predicted value resulted into a yield of 77.6% (dcw). This novel copolymer exhibited comparable material properties with polypropylene (PP) and low density polyethylene (LDPE), thus advocating its potential applications in various fields.     

Seedling survival in a northern temperate forest understory is increased by elevated atmospheric carbon dioxide and atmospheric nitrogen deposition

We tested the main and interactive effects of elevated carbon dioxide concentration ([CO₂]), nitrogen (N), and light availability on leaf photosynthesis, and plant growth and survival in understory seedlings grown in an N‐limited northern hardwood forest. For two growing seasons, we exposed six species of tree seedlings (Betula papyrifera, Populus tremuloides, Acer saccharum, Fagus grandifolia, Pinus strobus, and Prunus serotina) to a factorial combination of atmospheric CO₂ (ambient, and elevated CO₂ at 658 μmol CO₂ mol⁻¹) and N deposition (ambient and ambient +30 kg N ha⁻¹ yr⁻¹) in open‐top chambers placed in an understory light gradient. Elevated CO₂ exposure significantly increased apparent quantum efficiency of electron transport by 41% (P<0.0001), light‐limited photosynthesis by 47% (P<0.0001), and light‐saturated photosynthesis by 60% (P<0.003) compared with seedlings grown in ambient [CO₂]. Experimental N deposition significantly increased light‐limited photosynthesis as light availability increased (P<0.037). Species differed in the magnitude of light‐saturated photosynthetic response to elevated N and light treatments (P<0.016). Elevated CO₂ exposure and high N availability did not affect seedling growth; however, growth increased slightly with light availability (R²=0.26, P<0.0001). Experimental N deposition significantly increased average survival of all species by 48% (P<0.012). However, seedling survival was greatest (85%) under conditions of both high [CO₂] and N deposition (P<0.009). Path analysis determined that the greatest predictor for seedling survival in the understory was total biomass (R²=0.39, P<0.001), and that carboxylation capacity (V_cmax) was a better predictor for seedling growth and survival than maximum photosynthetic rate (A_max). Our results suggest that increasing [CO₂] and N deposition from fossil fuel combustion could alter understory tree species recruitment dynamics through changes in seedling survival, and this has the potential to alter future forest species composition.     

Exploitation of inexpensive substrates for production of a novel SCL–LCL-PHA co-polymer by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> MTCC 7925

Studies conducted with various inexpensive carbon sources such as whey, vegetable oils (palm, mustard, soybean and coconut), a low-cost source of glucose-D, rice and wheat bran, and mustard and palm oil cakes demonstrated palm oil as the best substrate for accumulation of a novel short-chain-length–long-chain-length polyhydroxyalkanoate (SCL–LCL-PHA) co-polymer containing SCL 3HAs [3-hydroxybutyric acid (3HB) and 3-hydroxyvaleric acid (3HV)] and LCL 3HAs of 3-hydroxyhexadecanoic acid (3HHD) and 3-hydroxyoctadecanoic acid (3HOD) units as constituents by a sludge-isolated Pseudomonas aeruginosa MTCC 7925. The co-polymer content reached up to 60% of dry cell weight (dcw) at 48 h of incubation in 0.5% (v/v) palm oil and the extract of 0.5% (v/v) palm oil cake supplemented vessels. The PHAs pool was further enhanced up to 69 and 75% (dcw), when the above culture was subjected to P- and N-limitation, respectively. The mol fraction of 3HB:3HV:3HHD:3HOD units were, respectively, 83.1:7.7:3.8:5.4 and 87.3:5.1:3.6:4.0 in P- and N-limited cultures. Consequently, a co-polymer yield of 5 g l⁻¹ (approx.) was achieved, which was about 80-fold higher as compared to 69 mg l⁻¹ of the control culture. On substrate basis, the accumulation reached up to 0.62 g PHAs per g substrate, which was significantly higher as compared to the yield obtained from starch by Haloferax mediterranei and Azotobacter chroococum, from molasses by A. vinelandii UWD, and from lactose and xylose by Pseudomonas cepacia. This novel P(3HB-co-3HV-co-3HHD-co-3HOD) co-polymer exhibited better thermal and mechanical properties as revealed from the differential scanning calorimetry and mechanical property studies, thus opens up new possibilities for various industrial applications.     

Soil and rhizosphere as habitats for Pseudomonas inoculants: new knowledge on distribution,activity and physiological state derived from micro-scale and single-cell studies

Pseudomonas spp. comprise an important group of bacteria used for biological control of microfungi in the plant rhizosphere. Successful performance of microbial inoculants requires both establishment, proliferation and activity under in situ conditions. To identify the factors controlling fate and performance of the inoculants, small-scale analyses are needed due to the heterogeneity characterizing the complex soil and rhizosphere environments. Direct staining techniques and advanced microscopy have provided the first detailed single-cell images of root colonization by these bacteria using fluorescent antibodies, fluorescent in situ hybridization and marker gene technology. These tracking methods have, in conjunction with activity assays, provided high-resolution data on the metabolic activity and growth of the inoculants. Finally, Pseudomonas reporter bacteria constructed to sense phosphorus, nitrogen, iron, and oxygen limitations have provided new insight into the significance of growth-limiting factors in the soil and along the root. The present work reviews the current knowledge on Pseudomonas inoculants in soil and rhizosphere based on these modern techniques. Finally, some perspectives for future studies are discussed.     

CHARACTERISTICS OF SEXUAL AND ASEXUAL RESTING CYST (STATOSPORE) FORMATION IN DINOBRYON CYLINDRICUM IMHOF (CHRYSOPHYTA)1

The reproductive significance of siliceous cysts (statospores) produced by the common vernal chrysophyte Dinobryon cylindricum Imhof has been investigated under defined culture conditions. Three types of statospores have thus far been induced in culture: 1) uninucleate, asexual; 2) binucleate, asexual (potentially autogamic); 3) binucleate, sexual (zygotic). The production of each type of cyst responds differently to an array of nutrient deficiencies (P, N, vitamins, micrometals). An individual clone may be capable of participating in the production of all or only a subset of these types of resting cysts. All D. cylindricum statospores are morphologically identical regardless of their reproductive significance. Sexual reproduction leading to zygotic statospore formation is anisogamous, heterothallic, and involves a gametogenic hormone (erogen) that is apparently continuously released from female clones. Only a single bipolar mating group is documented here and clonal compatibility varies considerably within the mating group. The dynamics of encystment for each type of statospore has been determined relative to the growth of the vegetative cell population. Statospores may be produced either during the exponential phase (intrinsic encystment) or stationary phase (extrinsic encystment) of culture growth depending on the clones involved. The effect of both asexual and sexual resting cyst production on the net growth rate and dynamics of natural chrysophyte populations is discussed. Statospores appear to represent a more flexible reproductive strategy than the resistant zygospores produced by the other common groups of planktonic microalgae.