ABSTRACT
BACKGROUND: Some parasites use olfactory cues to detect their hosts and, since bacterial symbionts are partially responsible for animal odours, they could influence host parasitism. By autoclaving nest materials of hoopoe (Upupa epops) nests before reproduction started, we explored the hypothetical links between host-associated bacteria, volatiles and parasitism. During the nestling stage, we (i) estimated the level of ectoparasitism by chewing lice (Suborder Mallophaga) in adult hoopoe females and by Carnus haemapterus flies in nestlings, and (ii) characterized microbial communities and volatile profiles of nest environments (nest material and nest cavity, respectively) and uropygial secretions. RESULTS: Experimental nests had less diverse bacterial communities and more diverse volatile profiles than control nests, while occupants experienced lower intensity of parasitism in experimental than in control nests. The experiment also affected beta diversity of the microbial communities of nest material and of the volatiles of the nestling uropygial secretions. Moreover, microbial communities of uropygial secretions and of nest materials covaried with their volatile profiles, while the volatile profile of the bird secretions explained nest volatile profile. Finally, a subset of the volatiles and bacteria detected in the nest material and uropygial secretions were associated with the ectoparasitism intensity of both adult females and nestlings, and with fledging success. CONCLUSIONS: These results show that a component of animal odours is linked with the microbial communities of the host and its reproductive environment, and emphasize that the associations between bacteria, ectoparasitism and reproductive success are partially mediated by volatiles of bacterial origin. Future work should focus on mechanisms underlying the detected patterns.
ABSTRACT
An integrated process for the indoor production of 13C labeled polyunsaturated fatty acids (PUFAs) from Phaeodactylum tricornutum is presented. The core of the process is a bubble column photobioreactor operating with recirculation of the exhaust gas using a low-pressure compressor. Oxygen accumulation in the system is avoided by bubbling the exhaust gas from the reactor in a sodium sulfite solution before returning to it. To achieve a high 13C enrichment in the biomass obtained, the culture medium is initially stripped of carbon, and labeled 13CO(2) is automatically injected on-demand during operation for pH control and carbon supply. The reactor was operated in both batch and semicontinuous modes. In semicontinuous mode, the reactor was operated at a dilution rate of 0.01 h(-1), resulting in a biomass productivity of 0.1 g l(-1) per day. The elemental analysis of the inlet and outlet flows of the reactor showed that 64.9% of carbon was turned into microalgal biomass, 34.9% remained in the supernatant mainly as inorganic compounds. Only 3.8% of injected carbon was effectively fixed as the target labeled product (EPA). Regarding the isotopic composition of fatty acids, results showed that fatty acids were not labeled in the same proportion, the higher the number of carbons the lower the percentage of 13C. Isotopic composition of EPA ranged from 36.5 to 53.5%, as a function of the methodology used (GC-MS, EA-IRMS or gas chromatography-combustion-isotope ratio mass spectrometry (GC-IRMS)). The low carbon uptake efficiency combined with the high cost of 13CO(2) make necessary to redefine the designed culture system to increase the efficiency of the conversion of 13CO(2) into the target product. Therefore, the possibility of removing 12C from the fresh medium, and recovering and recirculating the inorganic carbon in the supernatant and the organic carbon from the EPA depleted biomass was studied. The inorganic carbon of the fresh medium was removed by acidification and stripping with N(2). The inorganic carbon of the supernatant was recovered also by acidification and subsequent stripping with N(2). The operating conditions of this step were optimized for gas flow rate and type of contactor. A carbon recovery step for the depleted biomass was designed based on the catalytic oxidation to CO(2) using CuO (10 wt.%) as catalyst with an oxygen enriched atmosphere (80% O(2) partial pressure). In this way, the carbon losses reduced an 80.2% and the efficiency of the conversion of carbon in EPA was increased to 19.5%, which is close to the theoretical maximum. Further increase in 13CO(2) use efficiency is only possible by additionally recovering other labeled by-products present in the biomass: proteins, carbohydrates, lipids, and pigments.
