A synthetic C4 shuttle via the β-hydroxyaspartate cycle in C3 plants

Plants depend on the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) for CO2 fixation. However, especially in C3 plants, photosynthetic yield is reduced by formation of 2-phosphoglycolate, a toxic oxygenation product of Rubisco, which needs to be recycled in a high-flux–demanding metabolic process called photorespiration. Canonical photorespiration dissipates energy and causes carbon and nitrogen losses. Reducing photorespiration through carbon-concentrating mechanisms, such as C4 photosynthesis, or bypassing photorespiration through metabolic engineering is expected to improve plant growth and yield. The β-hydroxyaspartate cycle (BHAC) is a recently described microbial pathway that converts glyoxylate, a metabolite of plant photorespiration, into oxaloacetate in a highly efficient carbon-, nitrogen-, and energy-conserving manner. Here, we engineered a functional BHAC in plant peroxisomes to create a photorespiratory bypass that is independent of 3-phosphoglycerate regeneration or decarboxylation of photorespiratory precursors. While efficient oxaloacetate conversion in Arabidopsis thaliana still masks the full potential of the BHAC, nitrogen conservation and accumulation of signature C4 metabolites demonstrate the proof of principle, opening the door to engineering a photorespiration-dependent synthetic carbon–concentrating mechanism in C3 plants.

Little evidence the standard genetic code is optimized for resource conservation

Shenhav & Zeevi (Science, 2020, 370:683-687) propose nitrogen and carbon conservation as optimization principles in the standard genetic code that are not confounded by the established optimizations for polar requirement and hydropathy. We show their results for nitrogen conservation are highly sensitive to their choice of null model and their results for carbon conservation are confounded by molecular volume.

Effects of urease inhibitors on enzymatic activities and fungal communities during the biosolids composting

Adding UI was effective for nitrogen conservation and the increase of enzyme activity during biosolid composting.

Study of the Nutritional Increase in Organic Composts Obtained by Aerobic Biostabilization in the Management of Food Wastes

Composting is a sustainable alternative regarding an environmentally appropriate management of the organic fraction contained in the municipal solid wastes. To minimize nitrogen losses during the biostabilization process, due to ammonia volatilization, the present study aimed to evaluate the composting technique combined with the possible precipitation of struvite (MgNH4PO4.6H2O). A mixture containing food wastes was subjected to different experimental composting conditions with synthetic chemicals of magnesium and phosphorus—0.020 mol kg-1 (EXPI) and 1.8 mol kg-1 (EXPII), in addition to the control treatment (CONT). Experiments were carried out in closed systems, under forced aeration, over a period time of 56 days. In general, the addition of synthetic chemicals provided a nutritional increase in the organic composts obtained at the end of the experimental period in both conditions (EXPI and EXPII) compared to the treatment CONT. It was observed a total nitrogen conservation of about 21% and 122% in samples of composts obtained under the conditions EXPI and EXPII, respectively. Germination tests of lettuce seeds (Lactuca sativa) were also carried out to evaluate the agricultural applicability of the composts obtained in comparison with a commercial substrate (COM). A germination index with an average value of 87% was reached with the use of 100% of the compost obtained under the condition of greater conservation of total nitrogen (EXPII). Finally, the strategy considered for the conservation of nutrients in organic composts showed technical feasibility, indicating the formation of struvite and/or its analogues in the products obtained.

Impacts of peat on nitrogen conservation and fungal community composition dynamics during food waste composting

Peat, as a heterogeneous mixture of decaying plant debris and microbial residues, has been widely used in many fields. However, little research focused on the impact of peat addition on food waste composting. To fill this gap, a composting experiment of food waste mixed with five varying percent peat 0, 5, 10, 15, and 20% (w/w, dry weight) was designed to investigate the effect of different dosages of peat on nitrogen conservation, physiochemical parameters, and fungal community dynamics during composting. The results showed that adding peat elevated the peak temperature of composting, lowered final pH, reduced ammonia emissions and increased the final total nitrogen content. Compared to control, adding 5, 10, 15, and 20% peat decreased ammonia emissions by 1.91, 10.79, 23.73, and 18.26%, respectively, during 42 days of composting. Moreover, peat addition increased fungal community diversity especially during maturation phase. The most two abundant phyla were Basidiomycota and Ascomycota in all treatments throughout the composting process. At the end of composting, in treatments with adding 10 and 15% peat, the richest fungi were Scedosporium spp. and Coprinopsis spp., respectively. Simultaneously, canonical correlation analyses showed that pH, moisture content, and seed germination index had significant association with fungal community composition. The study also showed that fungal community and nitrogen conservation had no direct obvious relation during composting. Overall, the results suggest that the addition of peat could efficiently enhance nitrogen conservation through reduction of ammonia emissions and 15% peat addition is the optimal formula for food waste composting.