This study deals with two adjacent terrestrial oil spills, with similar properties, located in a hyper-arid region in Israel, one from 1975 and the other from 2014. It tests the effect of biostimulation on crude oil degradation in both spills and whether biostimulated sediments from the 1975 spill can bioaugment crude oil degradation in the 2014 spill. Soil hydrophobicity, expressed as Water Drop Penetration Time (WDPT), and Gasoline Range Organics (GRO) and Diesel Range Organics (DRO) content in sediments were measured in one-month ex-situ experiments. No significant reduction in hydrophobicity and GRO + DRO content was observed in non-biostimulated controls. A combined treatment of mineral fertilization at t₀ and maintaining 50% water saturation, significantly accelerated the decrease in hydrophobicity and GRO + DRO content in sediments of both spills. The addition of biostimulated sediments from the 1975 spill failed to accelerate the reduction of GRO + DRO content and hydrophobicity in the 2014 spill. Surprisingly, the GRO + DRO degradation rate in biostimulated sediments from the 2014 spill was 36% higher than in biostimulated sediments from the 1975 spill. Crude oil composition in both spills changes during its degradation and is characterized by an increase in the GRO fraction. To a certain range, WDPT was found to serve as a reliable indicator for oil content in the soil. We conclude that even in a hyper-arid region, oil bio-degradation capabilities develop in a relatively short time. Moreover, while biostimulation was effective in accelerating biodegradation, bioaugmentation with biostimulated sediments from a nearby older spill was found ineffective.

Because of their high lipid content, microalgae are regarded as a potentially competitive source for biofuels. However, one of the main biotechnological challenges in algae-based biofuels is that cell division is arrested under conditions which promote lipid accumulation, resulting in reduced overall lipid yield. In this study, sethoxydim-resistant mutants of the promising thermotolerant green microalga Micractinium sp., which has a relatively fast growth rate and tolerance to outdoor high temperatures, were generated by UV-C mutagenesis for increased cellular triacylglycerol (TAG) without compromising on growth rate. Two Micractinium mutants were isolated (designated as Mut 3 and Mut 4) that displayed significant increase in TAG cell content up to 71% and 84%, with decreased chlorophyll content by 37% and 38%, respectively, compared with the wild-type cells. Final TAG culture productivity of Mut 3 and Mut 4 were also greater, reaching up to 0.61 ± 0.01 and 0.62 ± 0.02 g L⁻¹, respectively, compared with the wild-type culture of 0.40 ± 0.03 g L⁻¹. The mutants were stable without using antibiotics or any other chemicals during the experiments and preservation. These results highly nominate the mutants of Micractinium sp. isolated in this work as potential microalgae candidates to serve as a feedstock for sustainable and cost-effective biofuel production.

Bioaugmentation is a bioremediation option based on increasing the natural in-situ microbial population that possesses the ability to degrade the contaminating pollutant. In this study, a diesel-degrading consortium was obtained from an oil-contaminated soil. The diesel-degrading consortium was grown on wood waste that was plasma-pretreated. This plasma treatment led to an increase of bacterial attachment and diesel degradation rates. On the 7th day the biofilm viability on the plasma-treated wood waste reached 0.53 ± 0.02 OD 540 nm, compared to the non-treated wood waste which was only 0.34 ± 0.02. Biofilm attached to plasma-treated and untreated wood waste which was inoculated into artificially diesel-contaminated soil (0.15% g/g) achieved a degradation rate of 9.3 mg day⁻¹ and 7.8 mg day⁻¹, respectively. While, in the soil that was inoculated with planktonic bacteria, degradation was only 5.7 mg day⁻¹. Exposing the soil sample to high temperature (50 °C) or to different soil acidity did not influence the degradation rate of the biofilm attached to the plasma-treated wood waste. The two most abundant bacterial distributions at the family level were Xanthomonadaceae and Sphingomonadaceae. To our knowledge, this is the first study that showed the advantages of biofilm attached to plasma-pretreated wood waste for diesel biodegradation in soil.

The aim of this work was to examine the potential of the thermophilic green microalga Micractinium sp. to accumulate triacylglycerols (TAGs) and to develop a light strategy to increase TAG productivity in this alga. To this end, dense cultures of Micractinium sp. were grown at 37 °C under nitrogen (N) starvation and exposed to a light intensity of 1000 µmol photons m⁻² s⁻¹ of different light regimes. The highest per-biomass TAG-content and maximal volumetric productivities of TAG were displayed by the cultures grown under flashing light of 5 Hz with 50% duty cycle. Based on the results, a sufficiently high-starting culture density should be combined with a high irradiance delivered by an appropriate light regime to enhance the production of biomass enriched TAGs.

Two algal cultures, TvB and SH, were isolated from extreme habitats along the Syrian-African rift Valley (Israel). These cultures were initially identified as Chlorella spp. according to their morphology and lack of bristles, but following molecular phylogenetic analyses, re-identified as Micractinium spp. closely related to Chlorella. The strains were subjected to a bi-factorial study in the search for algae that grow well at elevated temperatures and salinities for future biotechnological uses. Cell density (CD) and optical density (OD) were measured for each strain at three temperatures: 35, 40 and 45ºC, and five salinities of seawater (SW): 34.8 ppt (100% SW), 26.5 ppt (75% SW), 18.3 ppt (50% SW) 10 ppt (25% SW) and 1.8 ppt (0% SW). Both strains grew best at 35–40ºC and at 0–50% SW. Increased salinity enhanced temperature tolerance to 45ºC, particularly for strain TvB. At 45ºC, following a short initial growth spurt, cultures underwent a lag period of c. 7 days, followed by a significant growth phase. During the lag period, algae underwent a substantial increase in average cell diameter (ACD). These enlarged or gigantic cells with diameters of up to ~20 μm, produced and eventually released multiple autospores. By day 13, original size distribution was almost restored. The observed morphological alterations appear to enable these strains to survive and grow autotrophically at supra-optimal temperatures (SOT). These natural adjustments may be exploited for reducing costs associated with both cooling and desalination in future cultivation.

 Like higher plants, unicellular green algae of the genus Dunaliella respond to light stress by enhanced de-epoxidation of violaxanthin and accumulation of Cbr, a protein homologous to early light-inducible proteins (Elips) in plants. Earlier studies indicated that Cbr was associated with the light-harvesting complex of photosystem II (LHCII) and suggested it acted as a zeaxanthin-binding protein and fulfilled a photo-protective function (Levy et al. 1993, J. Biol. Chem. 268: 20892–20896). To characterize the protein-pigment subcomplexes containing Cbr in greater detail than attained so far, thylakoid membranes from Dunaliella salina grown in high light or normal light were solubilized with dodecyl maltoside and fractionated by isoelectric-focusing. Analysis of the resolved LHCII subcomplexes indicated preferred associations among the four LHCIIb polypeptides and between them and Cbr: subcomplexes including Cbr contained one or two of the more acidic of the four LHCIIb polypeptides as well as large amounts of lutein and zeaxanthin relative to chlorophyll a/b. After sucrose gradient centrifugation, Cbr free of LHCIIb polypeptides was detected together with released pigments; this Cbr possibly originated in subcomplexes dissociated in the course of the analysis. These results agree with the conclusion that Cbr is part of the network of LHCIIb protein-pigment complexes and suggest that the role played by Cbr involves the organization and/or stabilization of assemblies highly enriched in zeaxanthin and lutein. Such assemblies may function to protect PSII from photodamage due to overexcitation.

Unicellular green algae of the genus Dunaliella, similar to higher plants, respond to light stress by enhanced de-epoxidation of violaxanthin and accumulation of Cbr, a protein homologous to early light inducible proteins (Elips) in plants. These proteins belong to the superfamily of chlorophyll a/b binding proteins. Two Dunaliella strains, D. bardawil and D. salina, were compared for these two responses under light in the UVA, blue, green and red spectral ranges. In D. bardawil, the two stress responses were similarly induced under UVA, blue or red light and to a lesser extent under green light. In D. salina, a similar spectral range dependence was exhibited for violaxanthin de-epoxidation. However, Cbr accumulated only under UVA or blue light but not under green or red light. A strong synergistic effect of a low dose of blue light superimposed on red light resulted in Cbr accumulation. These results reveal strain-specific differences in spectral range requirements of the two light-stress responses. In the two strains, violaxanthin de-epoxidation is triggered under photosynthetically-active spectral ranges but at least in D. salina, Cbr accumulation appears to require a specific light signal additionally to a signal(s) generated by light stress.

The unicellular green alga Dunaliella bardawil exhibits typical responses to excessive light when starved for sulfate under normal light (60 [mu]E m-2 s-1) but not under low light (14 [mu]E m-2 s-1). Algae were analyzed during several days of sulfate starvation for nonphotochemical quenching of chlorophyll fluorescence in the absence or presence of the uncouplers SF-6847 (SF) or carbonyl cyanide p- trifluoromethoxyphenyl hydrazone. Parallel analyses followed two light-stress responses: (a) violaxanthin conversion to zeaxanthin and (b) accumulation of Cbr, a protein analogous to plant early-light-induced proteins and implicated in zeaxanthin binding. In cells starved under normal light SF inhibited nonphotochemical quenching during the first 24 h, but not from 40 h onward. In cells starved under low light SF inhibited nonphotochemical quenching throughout the starvation period. Under normal light accumulation of zeaxanthin was nearly maximal by 24 h, but Cbr was fully induced only by 40h. Under low light zeaxanthin accumulated slowly but no Cbr was evident. These results suggest that during exposure to excessive light, the initial pH gradient-dependent, Cbr-independent mode of nonphotochemical quenching is modified to become less dependent on pH gradient and requires Cbr.