Substrate degradation, biodiesel production, and microbial community of two electro-fermentation systems on treating oleaginous microalgae Nannochloropsis sp

Enhanced biological nitrogen fixation and nodulation in alfalfa through the synergistic interactions between Sinorhizobium meliloti and Priestia aryabhattai

Nitrogen fertilizer is crucial for agricultural output. However, prolonged overuse has resulted in nitrate leaching and potential soil acidification. Research on microbial fertilizer has become essential to enhance soil conditions and minimize nitrogen fertilizer usage. In alfalfa cultivation, research on efficient compound microbial agents remains limited, therefore this study concentrates on the investigation of dual microbial combinations. In the screening process, black soil was utilized with alfalfa plants as samples to identify a strain of rhizobacteria, Sinorhizobium meliloti LMGL3-1, exhibiting nitrogen-fixing capabilities, and Priestia aryabhattai (Bacillus aryabhattai) YJHT21, demonstrating phosphorus-solubilizing abilities. In addition, they were able to produce indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylic acid deaminase (ACCd). The S. meliloti strain was demonstrated to have the ability to symbiotically associate with the alfalfa variety Longmu 806, resulting in the formation of effective nodules containing leghemoglobin, thereby enabling the plants to thrive in the absence of nitrogen fertilizer application. Here, we discovered that the inoculation of phosphorus-solubilizing P. aryabhattai enhanced alfalfa growth and the nitrogenase activity of S. meliloti (P < 0.0001). Comparing with no nitrogen fertilizer control, the two-bacteria complex culture made an extreme increase in chlorophyll (P < 0.0001) of alfalfa. The protein content and dry weight of alfalfa were also increased (P < 0.01 and P < 0.001, respectively). Additionally, it also increased the total nitrogen content of the black soil. Moreover, the incorporation of P. aryabhattai resulted in a significant increase in flavonoid production within the root system of alfalfa plants (P < 0.0001). Consequently, under the influence of the inducer extracted from the root system of quantitatively analyzed plants, the rhizobacteria exhibited enhanced production of metabolites associated with the Nod factor cluster. This study demonstrates that the interaction between S. meliloti and P. aryabhattai significantly enhanced biological nitrogen fixation, providing a theoretical foundation for the development of eco-friendly biofertilizer as an alternative to chemical fertilizer.

Recent advances in electro-fermentation technology: A novel approach towards balanced fermentation

Biotransformation of organic substrates via acidogenic fermentation (AF) to high-value products such as C1-C6 carboxylic acids and alcohol serves as platform chemicals for various industrial applications. However, the AF technology suffers from low product titers due to thermodynamic constraints. Recent studies suggest that augmenting AF redox potential can regulate the metabolic pathway and provide seamless electron flow by lowering the activation energy barrier, thus positively influencing the substrate utilization rate, product yield, and speciation. Hence, the augmented AF system with an exogenous electricity supply is termed as electro-fermentation (EF), which has enormous potential to strengthen the fermentation technology domain. Therefore, this critical review systematically discusses the current understanding of EF with a special focus on the extracellular electron transfer mechanism of electroactive bacteria and provides perspectives and research gaps to further improve the technology for green chemical synthesis, sustainable waste management, and circular bio-economy.

Spatiotemporal changes of bacterial communities during a cyanobacterial bloom in a subtropical water source reservoir ecosystem in China

Cyanobacterial blooms, which not only threaten the health and stability of aquatic ecosystems but also influence the microbial community within, emerges as one of the most concerning problems in China. However, how cyanobacterial blooms affect the spatiotemporal variation of aquatic microbial communities remains relatively unclear. In this study, we used high-throughput sequencing to investigate how the cyanobacterial and bacterial community spatiotemporally vary along with main cyanobacterial bloom phases in upstream rivers of a eutrophicated water source reservoir. Both cyanobacterial and bacterial diversities in each river were significantly lower (P < 0.05) during the bloom outbreak phase, showing the apparent influence of cyanobacterial bloom. Dominant cyanobacterial taxa included Cyanobacteriales and Synechococcales, and dominant bacterial taxa comprised Acinetobacter, CL500-29, hgcI clade, Limnohabitans, Flavobacterium, Rhodoluna, Porphyrobacter, Rhodobacter, Pseudomonas, and Rhizobiales, whose changes of relative abundance along with the bloom indicated distinct community composition. Non-metric multidimensional scaling analysis proved that community composition had significant difference amongst bloom phases. Linear discriminant analysis (LDA) with LDA effect size analysis (LEfSe) identified unique dominant cyanobacterial and bacterial OTUs at different phases in each river, indicating spatiotemporal variations of communities. Canonical correlation analysis or redundancy analysis revealed that at different bloom phases communities of each river had distinct correlation patterns with the environmental parameters (temperature, ammonium, nitrate, and total phosphorus etc.), implying the spatial variations of microbial communities. Overall, these results expand current understanding on the spatiotemporal variations of microbial communities due to cyanobacterial blooms. Microbial interactions during the bloom may shed light on controlling cyanobacterial blooms in the similar aquatic ecosystems.

Water-plasma-enhanced and phase-separation-assisted extraction of microalgal lipid for biodiesel production

Traditional methods for lipid extraction from microalgal biomass usually involve harsh reaction conditions or the use of contaminant reagents, which lead to enormous energy consumption and wastage. Hence, a novel strategy was presented, which combined water-plasma and three-phase partitioning (TPP) techniques. Benefiting from its unique advantages such as rapid and low cost, water-plasma strategy can disrupt microalgal cell wall and can thus greatly affect lipid extraction. As a result, assisted with the TPP method, excellent performance lipid recovery (74.34%) was obtained at 200 W in 10 min. The performance was superior to that achieved through cell disruption via water-plasma pretreatment. Importantly, the whole process of lipid extraction prevented the drying of microalgal biomass, contributing to reduced energy consumption in large-scale biodiesel production. Moreover, the high fatty acids content suggested that the extracted lipids are great potential candidate for biodiesel production.