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As crude glycerol comprises a potential substrate for microalga fermentation and value added products' biosynthesis

With the aim to recommend an integrated alternative for the combined treatment of olive mill wastewater (OMW) and cotton residues (CR), and the production of high value and environmentally friendly products, two compost piles were set up. The first pile (control, pile 1) consisted of ginned CR, whereas the second (pile 2) was made of CR with the addition of OMW. A series of physicochemical parameters and the culturable microbial diversity in both piles were assessed. Co-composting (pile 2) displayed higher temperatures during the whole process, a prolonged second thermophilic phase and temperature values higher than 40 °C even after the thermophilic stage. Comparing the physicochemical parameters of the pile 2 with those of the pile 1, it was deduced that pH in the former was more acidic during the onset of the process; the EC values were higher throughout the process, while the levels of ammonium and nitrate nitrogen, as well as the NH4+/NO3− ratios, were lower at most of the sampling dates. By evaluating the abovementioned results, it was estimated that the co-composting process headed sooner toward stability and maturity, Isolated microorganisms from both piles were identified as members of the genera Brevibacillus, Serratia, Klebsiella, and Aspergillus, whereas active thermotolerant diazotrophs were detected in both piles at the 2nd thermophilic phase emerging a promising prospect upon further evaluation for enhancing the end-product quality. Our findings indicate that co-composting is an interesting approach for the exploitation of large quantities of agro-industrial residues with a final product suitable for improving soil fertility and health.

This study examined the effects of monochromatic illumination (blue, red, green and yellow) employing light-emitting diodes (LEDs), trophic conditions (photoautotrophic and mixotrophic), and nitrogen availability (high and low peptone concentration) on the growth and biochemical composition of Auxenochlorella protothecoides. The results revealed that mixotrophic conditions did not favor A. protothecoides, giving lower growth rates compared to heterotrophy (dark conditions). However, mixotrophy gave significantly higher growth rates compared to photoautotrophy. The best light wavelengths for mixotrophic cultivation were that of white and red. In all cases investigated in this study, high peptone concentration (4 g/L) resulted in decreased growth rates. Regarding the biochemical composition of A. protothecoides, the strongest effect, irrespective of trophic conditions, was caused by nitrogen availability (peptone concentration). Specifically, at nitrogen replete conditions (4 g/L peptone), biomass was rich in proteins (32–67%), whereas under deplete conditions (0.5 g/L peptone), A. protothecoides accumulated mainly carbohydrates (up to 56%). Mixotrophic conditions generally favored higher carbohydrate content, whereas photoautotrophic conditions favored higher protein content. The different illumination spectra did not have any clear effect on the biochemical composition (metabolites content), except that, in all trophic conditions, the use of the green spectrum resulted in higher chlorophyll b content. Chlorophyll a fluorescence studies revealed that the trophic conditions and the high peptone concentrations impacted the photosystem II (PSII) performance, and also affected plastoquinone re-oxidation kinetics and the heterogeneity of the PSII reaction centers.

The strategy of alternative prey (switching), regulated by a catabolic repression control-like (CRCL) mode, in which the desirable prey acts as repressor on the predator's attack on the alternative prey, was studied in a two-prey–one-predator chemostat system. In this system, alternative prey has to survive predation and competition for nutrients from the desirable prey. Therefore, when the alternative prey has no competitive advantage for the common substrate over the desirable prey, its survival depends on the protection offered by the desirable prey via CRCL. In this case, CRCL allows the coexistence of both desirable and alternative prey and predator populations. However, when the alternative prey has the competitive advantage over the desirable prey, CRCL negatively affects both the state of survival of the desirable prey and the coexistence state.

Since many predators can live under certain circumstances as saprophytes or consume more than one prey, and different enzymes are generally required for each prey or nutrient digestion, the predator must be sufficiently adaptive for effective utilization of the prey mass. Control modes as induction and repression, however, act at the level of genes and cause changes in the biosynthesis rate of these enzymes. In this work, an extension of the catabolic repression control mode from the level of genes to the level of the behavior of the predator is proposed, in order to model the balanced attack of the predator on the prey. It is demonstrated that, when the prey population has the competitive advantage over the predator (in using the common substrate), the catabolic repression mechanism favors the prey population, which dominates over the predator even at low specific dilution rate values, whereas, the stable steady or periodic coexistence state is not favored. When the predator has the competitive advantage at low substrate concentrations and the prey at high substrate concentrations, the introduction of the catabolic repression mechanism in the model again favors the stable steady state of the prey, while the coexistence region is dramatically reduced. Conversely, when the prey population has the competitive advantage at low and the predator at high substrate concentrations, dominance of prey and coexistence steady state could be favored by the catabolic repression mechanism. It is concluded that the catabolic repression control favors dominance of the prey population and, under certain circumstances, coexistence of both prey and predator populations.

Newly isolated bacterial strains belonging to Bacillaceae (Bacillus sp.), Micrococcaceae and three unidentified strains were tested for their pathogenicity against the mite, Varroa destructor. The Bacillus sp. strain and two of the strains belonging to the Micrococcaceae family significantly decreased the time for 50% mortality of the mite population (up to 57%) and hence may be potential control agents. In in vitro bioassay whole cells, extracellular broth and cellular extract of the Bacillus sp. strain effectively killed the mites, suggesting that both endotoxins and exotoxins contributed to the killing.

Pleurotus ostreatus grown in bioreactor batch cultures in a model phenolic wastewater (diluted and sterilized olive oil mill wastewater-OMW), caused significant phenolic removal. Laccase, the sole ligninolytic enzyme detected in the growth environment, was produced during primary metabolic growth. The bioprocess was simulated with the aid of a mathematical model and the parameters of growth were determined. When the fungal biomass was increased in the reactor (during repeated batch experiments) the rate of reducing sugars consumption progressively increased, but a phenolic fraction seemed of being strongly resistant to oxidation. The toxicity of OMW against the seeds of Lepidium sativum and the marine Branchiopoda Artemia sp. was significantly decreased after biotreatment. On the contrary, the toxicity against the freshwater Branchiopoda Daphnia magna was not affected by the treatment, whereas on the soil and freshwater sediments Ostracoda Heterocypris incongruens was slightly decreased. Both treated and untreated OMWs, used as water for irrigation of lettuce and tomato plants, did not significantly affect the uptake of several nutrients by the cultivated plants, but resulted in a decrease in the plant yields, which was minimized when high OMW dilutions were used. As a conclusion, P. ostreatus is able to reduce phenolic content and toxicity of sterilized OMW, in bioreactor cultures. However, high OMW dilutions should be used, and/or additional treatment should be applied before use of the OMW in the environment, e.g. as water for irrigation. Further research should be done in order to transfer this technology under industrial conditions (e.g. by using unsterilized OMW).

The utilization of some agro-industrial wastes as soil conditioners to provide free-living nitrogen-fixing bacterial populations (e.g. Azospirillum spp.) with carbon and energy sources, may be an interesting perspective for agriculture. However, the presence of ammonium nitrogen in cultivated soils and/or various wastes could inhibit the growth of the nitrogen-fixing populations. The present investigation shows that growth of Azospirillum lipoferum was restricted at a dissolved oxygen (DO) concentration equal to 135 microM, when the initial NH4Cl concentration increased from 0.5 to 0.9 g/l. The activities of both citrate synthase (CS) and isocitrate dehydrogenase were significantly decreased in the presence of 0.9 g/l NH4Cl (e.g., 40% and 66%, respectively, in cells incubated for 95 h), while ammonium assimilation occurred via the glutamate dehydrogenase reaction. Furthermore, growth limitation occurred even in the presence of 0.5 g/l NH4Cl, when the DO concentration decreased from 135 to 30 microM. The activities of both CS and succinate dehydrogenase were dramatically decreased in cells grown at the lower DO concentration (e.g., 90% and 93% respectively, in a 95 h incubation), while ammonium assimilation was limited due to the low activities of both glutamate dehydrogenase and glutamate synthase. It is concluded that the threshold of ammonium concentration at which growth of A. lipoferum is limited, depends on the DO concentration in the medium.