Growth, nutrient removal, and lipid productivity promotion of Chlorella sorokiniana by phosphate solubilizing bacteria Bacillus megatherium in swine wastewater: Performances and mechanisms

Effects of a phosphorus-solubilizing bacteria (PSB) Bacillus megatherium on growth and lipid production of Chlorella sorokiniana were investigated in synthesized swine wastewater with dissolved inorganic phosphorus (DIP), insoluble inorganic phosphorus (IIP), and organic phosphorus (OP). The results showed that the PSB significantly promoted the algal growth in OP and IIP, by 1.10 and 1.78-fold, respectively. The algal lipid accumulation was also greatly triggered, respectively by 4.39, 1.68, and 1.38-fold in DIP, IIP, and OP. Moreover, compared with DIP, OP improved the oxidation stability of algal lipid by increasing the proportion of saturated fatty acids (43.8 % vs 27.9 %), while the PSB tended to adjust it to moderate ranges (30.2-41.6 %). Further, the transcriptome analysis verified the OP and/or PSB-induced up-regulated genes involving photosynthesis, lipid metabolism, signal transduction, etc. This study provided novel insights to enhance microalgae-based nutrient removal combined with biofuel production in practical wastewater, especially with complex forms of phosphorus.

Tomato domestication rather than subsequent breeding events reduces microbial associations related to phosphorus recovery

Legacy phosphorus (P) is a reservoir of sparingly available P, and its recovery could enhance sustainable use of nonrenewable mineral fertilizers. Domestication has affected P acquisition, but it is unknown if subsequent breeding efforts, like the Green Revolution (GR), had a similar effect. We examined how domestication and breeding events altered P acquisition by growing wild, traditional (pre-GR), and modern (post-GR) tomato in soil with legacy P but low bioavailable P. Wild tomatoes, particularly accession LA0716 (Solanum pennellii), heavily cultured rhizosphere P solubilizers, suggesting reliance on microbial associations to acquire P. Wild tomato also had a greater abundance of other putatively beneficial bacteria, including those that produce chelating agents and antibiotic compounds. Although wild tomatoes had a high abundance of these P solubilizers, they had lower relative biomass and greater P stress factor than traditional or modern tomato. Compared to wild tomato, domesticated tomato was more tolerant to P deficiency, and both cultivated groups had a similar rhizosphere bacterial community composition. Ultimately, this study suggests that while domestication changed tomato P recovery by reducing microbial associations, subsequent breeding processes have not further impacted microbial P acquisition mechanisms. Selecting microbial P-related traits that diminished with domestication may therefore increase legacy P solubilization.

Residual effects of biochar and phosphorus on growth and nutrient accumulation by maize (Zea mays L.) amended with microbes in texturally different soils

The purpose of study was to examine the residual effects of two types of biochar amendments, two phosphorus (P) fertilizer levels, phosphorus solubilizing bacteria (PSB) and arbuscular mycorrhizal fungs (AMF) on plant growth, nutrients absorption and root architecture of Zea mays L. in texturally different soils. Biochar signficantly increased nutrients absorption and plant biomass production with P-fertilization and microbial inoculantion. Texturally different soils enhanced the plant biomass and nutrients absorption in their independent capacity on addition of biochar, microbial inoculants and P-fertilization. It was shown that mycorrhizal inoculation had positive influence on plant root and shoot biomass in both soils irrespective to the biochar type used. Root colonization was notably increased in biochar + mycorrhizae (B + M) inocultaed plants. It was shown that mycorrhizal inoculation had positive influence on nutrients absorption by plant roots and it had high content of P, potassium, calcium and magnesium in plants at all biochar and P levels. Without P fertilization, biochar amendments significantly promoted shoot P content and root colonization. The P application significantly influenced soil microbial activity in terms of nutrient concentration and plant growth. Root attributes were significantly inclined by microbial inoculation. Residual effects of biochar and P significantly enhanced the nutreints absorption and maize plant growth. Thus, we concluded that residual biochar and P fertilizer showed positive effects on nutrients absorption and maize plant growth promotion in differently textured soils. Microbial inoculants further stimulated the plant biomass production and nutrients absorption due to effective root colonization.

Different pathways of nitrogen and phosphorus regeneration mediated by extracellular enzymes in temperate lakes under various trophic state

Several Italian and Chinese temperate lakes with soluble reactive phosphorus concentrations < 0.015 mg L^-1 were studied to estimate nitrogen and phosphorus regeneration mediated by microbial decomposition and possible different mechanisms driven by prevailing oligo- or eutrophic conditions. Leucine aminopeptidase (LAP), beta-glucosidase (GLU) and alkaline phosphatase (AP), algal, and bacterial biomass were related to trophic and environmental variables. In the eutrophic lakes, high algal and particulate organic carbon concentrations stimulated bacterial respiration (> 20 μg C L^-1 h^-1) and could favor the release of inorganic phosphorus. High extracellular enzyme activities and phosphorus solubilizing bacteria abundance in sediments accelerated nutrient regeneration. In these conditions, the positive GLU-AP relationship suggested the coupling of carbon and phosphorus regeneration; an efficient phosphorus regeneration and high nitrogen levels (up to 0.067 and 0.059 mg L^-1 NH₄ and NO₃ in Italy; 0.631 and 1.496 mg L^-1 NH₄ and NO₃ in China) led to chlorophyll a peaks of 14.9 and 258.4 μg L^-1 in Italy and China, respectively, and a typical algal composition. Conversely, in the oligo-mesotrophic lakes, very low nitrogen levels (in Italy, 0.001 and 0.005 mg L^-1 NH₄ and NO₃, respectively, versus 0.053 and 0.371 mg L^-1 in China) induced high LAP, while low phosphorus (33.6 and 46.3 μg L^-1 total P in Italy and China, respectively) led to high AP. In these lakes, nitrogen and phosphorus regeneration were coupled, as shown by positive LAP-AP relationship; however, the nutrient demand could not be completely met without the supply from sediments, due to low enzymatic activity and phosphorus solubilizing bacteria found in this compartment.

Negative effects of artemisinin on phosphorus solubilizing bacteria in vitro

The anti-malarial drug artemisinin is extracted from the leaves of Artemisia annua L. Due to toxicity to some microorganisms, the release of artemisinin from this medicinal plant in commercial cultivation might produce a potential risk for phosphorus (P) solubilizing bacteria (PSB). Therefore, the growth, P mobilization, and proton and organic acid efflux by two PSB isolates, Bacillus subtilis and Pseudomonas fluorescens, obtained from the soil without growing A. annua L. in history in the region for growing A. annua L., Chongqing, China, were studied through soil and solution incubations with different nominal concentrations of artemisinin (0, 2.5, 5.0, and 10.0 mg/kg or mg/L). Addition of artemisinin into soil and culture solutions decreased significantly the number of PSB except P. fluorescens at a low artemisinin concentration (2.5 mg/L) in culture solution which remained unchanged in comparison with the control (without artemisinin). This suggests high artemisinin inhibited the cell division or led to the death of PSB, and the different species responded differently to artemisinin. Compared with original soil, PSB inoculation significantly increased Olsen P, whilst the addition of artemisinin decreased this P form in soil. There was a positive correlation between the number of PSB and Olsen P content in soils (r² = 0.824, n = 8), indicating the involvement of PSB in P mobilization of insoluble minerals. Oxalate and acetate were commonly found in the bacterial culture solutions, which accounted for 73.6-84.4% of all organic acids in the culture medium without artemisinin. Malate was detected in the culture solution of B. subtilis, and citrate and succinate in P. fluorescens. The percentage of tricalcium phosphate solubilization (PTPS) positively correlated to the concentrations of protons and all organic acids (r²_proton＝0.901, n＝8, P＜0.01; r²_{organic acids}＝0.923, n＝8, P＜0.01). The concentrations of protons, organic acids and soluble inorganic P in culture solutions, and PTPS were decreased simultaneously as nominal artemisinin concentrations increased. For these decreases it implies the metabolic inhibition and the death of PSB caused by artemisinin could be the main reasons for the less efflux of protons and organic acids, presumably resulting in the decreased ability of PSB to mobilize inorganic P. Therefore, artemisinin released from A. annua L. in commercial and continual cultivation could adversely affect the community structure and inorganic P mobilization of PSB in soils.