Adaptation of Pseudomonas helmanticensis to fat hydrolysates and SDS: fatty acid response and aggregate formation

Effect of different diet composition on the fat profile of two different black soldier fly larvae populations

Black soldier fly larvae (Hermetia illucens; BSFL) can transform organic wastes into nutritional biomass useful in animal feeding. The aim of this work was to study the effect of five diets (meat, fruit, vegetable substrates, a mix of them and control) on the profile of fatty acids (FAs) and sterols of BSFL. For a more exhaustive characterization of the nutritional properties, the profile of esterified FAs in the sn-2 position of the triglycerides, the most absorbed lipid component during animal digestion was evaluated. The dietary effect was estimated on two different Hermetia illucens populations (Greek - UTH and Italian - UNIPI). The diet affected all the lipid fractions examined. Regardless of diet, the fat was characterized mainly of lauric acid and other saturated FAs, which were found to be synthesized by the larvae, as it was not present in any of the five substrates. In general, UTH larvae contained a higher level of lipids (7.38 vs 2.48 g/100 g of larvae; P < 0.001) and saturated FAs (49.71 vs 36.10 g/100 g of Total Lipids; P < 0.001) and a lower percentage of monounsaturated FAs (14.74 vs 26.70 g/100 g of Total Lipids), C18:3n-3 (0.67 vs 1.13 g/100 g of Total Lipids; P < 0.001), and C18:2c9t11 (2.02 vs 2.80 g/100 g of Total Lipids; P < 0.001). Irrespective of the populations, BSFL reared on control and fruit substrates showed higher level of lipids (8.06 and 5.61 g/100 g of larvae, respectively), and saturated FA (38.99 and 71.19 g/100 g of Total Lipids, respectively), while the presence of meat increased the level of C20:4n-6, C20:5n-3 and C22:5n-3 (0.70, 0.13 and 0.45 g/100 g of Total Lipids, respectively). The results confirmed that BSFL accumulate phytosterols in their lipid fraction. The sterol profile was strongly influenced by the substrate on which the larvae were reared, with higher levels of cholesterol in the larvae of the meat group (38.55 mg/100 g of Total Lipids) and of stigmasterol and campesterol (9.04 and 15.23 mg/100 g of Total Lipids, respectively) in those of the vegetable group. The sterol content between the two populations was significantly different, with a higher percentage in UTH larvae (113.28 vs 34.03 mg/100 g of Total Lipids; P < 0.001). Finally, BSFLs showed a high plasticity of the lipid profile depending on both the substrate and the metabolism linked to the different populations. This variability allows the nutritional characteristics of the BSFL to be shaped by modifying the substrate, to adapt it to the technological and feeding needs to which the larvae are destined.

Earth to Mars: A Protocol for Characterizing Permafrost in the Context of Climate Change as an Analog for Extraplanetary Exploration

Abstract Permafrost is important from an exobiology and climate change perspective. It serves as an analog for extraplanetary exploration, and it threatens to emit globally significant amounts of greenhouse gases as it thaws due to climate change. Viable microbes survive in Earth's permafrost, slowly metabolizing and transforming organic matter through geologic time. Ancient permafrost microbial communities represent a crucial resource for gaining novel insights into survival strategies adopted by extremotolerant organisms in extraplanetary analogs. We present a proof-of-concept study on ∼22 Kya permafrost to determine the potential for coupling Raman and fluorescence biosignature detection technology from the NASA Mars Perseverance rover with microbial community characterization in frozen soils, which could be expanded to other Earth and off-Earth locations. Besides the well-known utility for biosignature detection and identification, our results indicate that spectral mapping of permafrost could be used to rapidly characterize organic carbon characteristics. Coupled with microbial community analyses, this method has the potential to enhance our understanding of carbon degradation and emissions in thawing permafrost. Further, spectroscopy can be accomplished in situ to mitigate sample transport challenges and in assessing and prioritizing frozen soils for further investigation. This method has broad-range applicability to understanding microbial communities and their associations with biosignatures and soil carbon and mineralogic characteristics relevant to climate science and astrobiology.

Preparation of polyhydroxyalkanoates using <i>Pseudomonas helmanticensis</i> in non-sterile media containing glycerol and sodium dodecyl sulfate

Biosynthetically-produced Pseudomonas poly-3-hydroxyalkanoates (PHAs) are a promising substitute for conventional plastics. Costs involved with the production of PHAs can be reduced by optimizing power consumption, which can be achieved using nutrient media without preliminary steam sterilization. Cultivation of Pseudomonas bacteria resistant to sodium dodecyl sulfate (SDS) on SDS-containing non-sterile media yields a biomass consisting predominantly of a PHA producer. SDS plays the role of an antimicrobial agent that inhibits the growth of foreign microorganisms. In this work, an SDS-resistant culture of Pseudomonas helmanticensis and media containing glycerol and SDS were used. The concentrations of carbon (glycerol) and nitrogen sources were optimized using an experiment performed according to a central composite rotatable design. The concentration of substrate C and the C/N ratio between the glycerol and nitrogen content were varied. The dependence of the degree of substrate conversion in PHA on C and C/N was derived in the R programming environment. The constructed model adequately describes the experimental data at a significance level of 0.05 (adequacy variance of the regression equation 4.1×10-2; R2 =0.98). According to the constructed model, the conversion of glycerol to PHA equals 6.9±0.4%. Under optimized conditions (0.61 g/L nitrogen source; 8.4 g/L glycerol; 96 h), P. helmanticensis converts 7.0% of the substrate to PHA with an average monomer unit length. Using a 16S rRNA metagenomic assay, the proportion of foreign bacteria in P. helmanticensis cultures on non-sterile media containing 0.5 g/L SDS was shown to be 2%.