Phosphorus transformation behavior and phosphorus cycling genes expression in food waste composting with hydroxyapatite enhanced by phosphate-solubilizing bacteria

The potential bioavailability of phosphorus and the microbial community involved in agro-industrial composts as organic amendments or growing media

Harnessing agro-industrial residues through composting is gaining importance as a means of phosphorus recovery, as is its reutilization as plant available phosphorus. This research seeks to analyze various combinations of agroindustrial waste and observe the microbial communities contributing to the availability of this element for plants. Six composts were used with different proportions of agroindustrial waste. Phosphorus fractionation was carried out, and the available phosphorus was determined. The molecules involved in phosphorus mineralization and solubilization, alkaline phosphatase activity, organic acids, and microbial communities were also determined. Finally, the potential phosphorus genes (Inorganic P solubilization genes (gcd, ppx, ppqC), and Organic P mineralization genes (phoA, phoD, phnL, phnl, phnJ, phnP, phnH, and phnG)) present in the analyzed composts were established. Compost X2B, composed of vineyard and tomato residues, demonstrated superior performance in providing available phosphorus compared to other composts. This was determined by microbial communities harboring genes involved in the phosphorus cycle, facilitating phosphorus availability.

Differential contributions of microbial necromass to humic acid during composting of organic wastes

Microbial necromass is a crucial source of stable organic matter in composting, yet its role in the humification process remains poorly understood. This study aims to explore the contribution of microbial necromass carbon (MNC) to humic acid (HA) formation during the composting of sewage sludge (SS), kitchen waste (KW), and pig manure (PM), and to examine the involvement of fungal communities in microbial necromass humification. The results show that fungal necromass carbon (FNC) consistently contributes more to MNC than bacterial necromass carbon (BNC), with FNC accounting for over 60% of MNC across all treatments. KW exhibited the highest accumulation of FNC (4.09-98.92 g/kg), and its MNC contribution to total organic carbon was 23.63%, significantly higher than sewage sludge (5.57%) and pig manure (7.47%). The carbon-to-nitrogen (C/N) ratio was found to be a critical factor influencing microbial growth, necromass accumulation, and HA formation, with a lower C/N ratio promoting faster microbial turnover and enhancing MNC contribution to HA. The analysis also revealed that Ascomycota dominated the maturation phase, with a significant role in driving humification, especially in KW. Structural equation modeling confirmed that FNC and BNC are directly influenced by the C/N ratio, which in turn affects HA formation This study enhances our understanding of microbial necromass dynamics and its contribution to humic substance formation, providing valuable insights for improving compost quality and optimizing composting strategies for enhanced carbon sequestration.

Harnessing phosphate-solubilizing microorganisms for mitigation of nutritional and environmental stresses, and sustainable crop production

MAIN CONCLUSION

Phosphate-solubilizing microorganisms enhance nutrients availability, mitigate environmental stresses, and increase plant growth. The bioengineering of phosphate-solubilizing microbes and host plants may further improve their efficacy for increasing crop yield. Unsustainable agricultural practices are followed in current crop production systems worldwide for resolving food demand issues of ever-increasing human population. In addition, global food crop production is further affected due to continuous climatic change, erratic rains, and environmental stresses during the recent past causing threat to microbial as well as plant biodiversity. The application of plant beneficial microorganisms into agricultural practices has emerged recently as an innovative and sustainable approach to increase crop yield with limited resources and in vulnerable environment. These beneficial microbes improve crop productivity by enhancing nutrients' availability and mitigation of abiotic stresses along with suppression of plant diseases. However, there have been limited studies on the stress ameliorative role of phosphate-solubilizing microorganisms (PSMs), and there is still a need to elucidate the contribution of PSMs in improving plant health and crop productivity under harsh environmental conditions. This review summarizes the role of PSMs in improving phosphorus availability in soil through solubilization or mineralization of organic phosphate, and by assisting plants in amelioration of environmental stresses. Other beneficial activities of PSMs, such as release of phytohormones, production of ACC deaminase, strengthening of antioxidant system, and induction of systemic resistance, also contribute toward stress mitigation and plant growth promotion under stressful environments. Improvement in efficacy of PSMs and host plants using genetic engineering techniques has been discussed leading to increases in crop yields. However, further research is needed to develop sustainable climate-resilient approach by improving plant growth-promoting activities of PSMs even under environmental stresses to increase soil fertility and crop production in different agroecosystems.

Diversity, characterization, and biotechnological potential of plant growth-promoting bacteria from Bryophyllum pinnatum (Lam.) (Crassulaceae) roots and rhizosphere soil

Cultivable microbial communities associated with plants inhabiting extreme environments have great potential in biotechnological applications. However, there is a lack of knowledge about these microorganisms from Bryophyllum pinnatum (which survives in severely barren soil) and their ability to promote plant growth. The present study focused on the isolation, identification, biochemical characterization, and potential applications of root endophytic bacteria and rhizosphere bacteria. A total of 73 bacterial isolates were obtained, with 50 derived from rhizospheric soil and 23 from root tissue. The identified strains were categorized into 16 genera, with Bacillus, Priestia, Pseudarthrobacter, Neobacillus, Mesobacillus, and Arthrobacter being the most species-rich genera. Heat stress experiments indicated that almost half (50.7%) of the selected isolates were tolerant to heat stress. Furthermore, most strains present diverse capabilities for biotechnological applications, including the potential for indole-3-acetic acid (IAA) production, organic phosphorus solubilization, inorganic phosphorus solubilization, and nitrogen fixation. Some isolates (21.92%) exhibited broad-spectrum antagonistic activity against various phytopathogenic fungi, including Fusarium spp. Agar plate assays revealed that the Cellulomonas hominis strain LS43 and Bacillus inaquosorum strain LS77 significantly increased the total fresh weight of Arabidopsis (P < 0.05), yet these strains did not significantly affect the primary root length or the number of leaves. Notably, a subset of the strains tested did not significantly increase the growth of Arabidopsis and, in fact, had inhibitory effects on certain growth parameters. This is the first investigation highlighting the potential of root endophytic bacteria and rhizosphere bacteria in association with B. pinnatum in barren soils. Thus, these isolated strains positively influence plant nutrient uptake, stress resilience, and biocontrol to reduce chemical inputs in conventional agricultural practices, highlighting the importance of their development as biofertilizers for improving the quality of barren soil.

Water-logged composting with sealed system enhances phosphorus availability and changes ecological attributes of bacterial community

Deciphering effects of sealed environment on phosphorus (P) availability and microbial community during water-logged composting is an essential but underestimated theme. Research targets are to unveil divergences in P fractions and bacterial landscapes between breathable and sealed systems using molecular and statistical tools. Water-logged composting with sealed system enhanced P availability, with soluble reactive P in overlying water notably increasing from 1.20 to 1.92 mg L-1 and available P in composting substrate significantly arising from 1.61 to 2.28 g kg-1. Higher abundances of organic P (Po)-mineralizing genes, including β-propeller phytase-encoding gene of bpp, acid phosphatase-encoding gene of phoC, alkaline phosphatase-encoding gene of phoD, and phosphonoacetaldehyde hydrolase-encoding gene of phnX, were found in sealed system than in breathable system. Bacterial community composition varied notably between sealed and breathable systems, with dominant bacterial phyla of Proteobacteria and Actinobacteriota in overlying water were notably more abundant in sealed and breathable systems, respectively. Bacteria in sealed system rather than breathable system displayed higher community complexity and stability, stronger migration potential and phylogenetic signal, and were affected more by determinism. Our findings highlight ecological consequences of water-logged composting with sealed system, and these findings might guide composting in a water-logged way to obtain P fertilizer.

Demonstrating the key role of Bacillus in poly lactic acid film degradation through statistical analysis and strain screening

Plastic films are extensively utilized in agriculture, construction, and manufacturing, with their annual production reaching staggering figures. Addressing the global plastic pollution crisis is imperative. One promising approach is the augmentation of plastic films degradation through microbial agents. Consequently, we undertook composting experiments employing various plastics, including Polyethylene (PE), Poly lactic acid (PLA), and a treatment without plastic films addition (CK), mixed with kitchen waste. Employing bipartite association networks and difference significance analysis methods, we scrutinized the impact of different plastics on the microbial community within the compost piles. There were significant disparities in the microbial community composition among three composting piles. To pinpoint the key microorganisms responsible for PLA degradation, we conducted a comparative analysis of microbial species present on PLA compost piles and PLA film surfaces (PLAS), utilizing variance analysis, co-occurrence network analysis, and Spearman's correlation analysis. Our findings identified Bacillus as the pivotal microorganism involved in PLA degradation. Furthermore, employing function prediction by PICRUSt 2, we identified K00016 as the crucial gene facilitating PLA degradation by Bacillus. Subsequently, employing strain screening techniques, we isolated a highly effective PLA-degrading bacterium, Bacillus amyloliquefaciens strain ML274. The PLA films degradation rate of ML274 reached 3.18%. and other strains was lower than 3.0%. Thus, Bacillus emerges as the primary microorganism driving PLA degradation, emphasizing the significance of focusing on Bacillus genus microorganisms in the development of plastic-degrading bacterial agents for future endeavors.

Effects of volcanic environment on Setaria viridis rhizospheric soil microbial keystone taxa and ecosystem multifunctionality

Keystone taxa are significant within ecosystem multifunctionality, as certain species fulfil essential functions such as recycling soil nutrients, promoting plant growth, influencing biogeochemical processes, and contributing to human health maintenance. However, there are still gaps regarding the relationship between microbial communities in volcanic rhizospheric soil and ecosystem multifunctionality. As a result, in this research, we employed Illumina MiSeq high-throughput sequencing to analyse the microbial community composition of rhizospheric soil from volcanic S. viridis. Compared with non-volcanic areas, volcanic soils have higher fungal alpha diversity and the absolute abundance of bacteria (16S gene copies) showed significant variation between the two successions (P < 0.0001). The network analysis further demonstrated that the microbial diversity in non-volcanic regions surpassed that of the volcanic area. The volcanic fungi network has more nodes and edges, is more complex than non-volcanic areas (Nodes: 425 vs. 770; Edges: 21844 vs. 74532), and more rhizosphere growth-promoting bacteria are enriched. Regression analysis and correlation networks showed that fungal communities were more closely associated with ecosystem multifunctionality than bacteria. This study lays the groundwork for examining the microbial keystone taxa in the rhizosphere of volcanic plants and offers valuable insights into the multifaceted functions of plant rhizospheric soil ecosystems.

Redistribution of phosphorus fraction driven by organic carbon and microbial community during composting

Available information on the coupling relationship between phosphorus fraction and organic carbon during composting remains limited. Thus, this research investigated the changes of phosphorus fraction, dissolved organic carbon fluorescent components and microbial community in swine manure composting with different carbon sources including the maize straw (MS), garden waste (GW) and distillers' grains (DG), in order to investigate whether the distribution and availability of phosphorus are influenced by different carbon sources used in the composting of swine manure. The result showed that different carbon sources changed phosphorus availability variously mainly by altering the succession of fungal communities and phosphorus functional genes. The dissolved organic material including tyrosine and tryptophan facilitate the mineralization of organic phosphorus (Org-P) into water-soluble phosphorus, thereby improving phosphorus availability. However, humic acid-like carbon components promote the conversion of inorganic-phosphorus to Org-P, which is the direct cause of the reduced phosphorus availability during composting. The results of this study provide support for the development of phosphorus-rich, stable, and clean compost products.

Effects of calcium phosphate and phosphorus-dissolving bacteria on microbial structure and function during Torreya Grandis branch waste composting

BACKGROUND BURKHOLDERIA: is a phosphorus solubilizing microorganism discovered in recent years, which can dissolve insoluble phosphorus compounds into soluble phosphorus. To investigate the effects of Burkholderia and calcium phosphate on the composting of Torreya grandis branches and leaves, as well as to explain the nutritional and metabolic markers related to the composting process.

METHODS

In this study, we employed amplicon sequencing and untargeted metabolomics analysis to examine the interplay among phosphorus (P) components, microbial communities, and metabolites during T. grandis branch and leaf waste composting that underwent treatment with calcium phosphate and phosphate-solubilizing bacteria (Burkholderia). There were four composting treatments, 10% calcium phosphate (CaP) or 5 ml/kg (1 × 108/ml Burkholderia) microbial inoculum (WJP) or both (CaP + WJP), and the control group (CK).

RESULTS

The results indicated that Burkholderia inoculation and calcium phosphate treatment affected the phosphorus composition, pH, EC, and nitrogen content. Furthermore, these treatments significantly affected the diversity and structure of bacterial and fungal communities, altering microbial and metabolite interactions. The differential metabolites associated with lipids and organic acids and derivatives treated with calcium phosphate treatment are twice as high as those treated with Burkholderia in both 21d and 42d. The results suggest that calcium phosphate treatment alters the formation of some biological macromolecules.

CONCLUSION

Both Burkholderia inoculation and calcium phosphate treatment affected the phosphorus composition, nitrogen content and metabolites of T. grandis branch and leaf waste compost.These results extend our comprehension of the coupling of matter transformation and community succession in composting with the addition of calcium phosphate and phosphate-solubilizing bacteria.

Enhancing simultaneous nitrogen and phosphorus availability through biochar addition during Chinese medicinal herbal residues composting: Synergism of microbes and humus

The disposal of Chinese medicinal herbal residues (CMHRs) derived from Chinese medicine extraction poses a significant environmental challenge. Aerobic composting presents a sustainable treatment method, yet optimizing nutrient conversion remains a critical concern. This study investigated the effect and mechanism of biochar addition on nitrogen and phosphorus transformation to enhance the efficacy and quality of compost products. The findings reveal that incorporating biochar considerably enhanced the process of nutrient conversion. Specifically, biochar addition promoted the retention of bioavailable organic nitrogen and reduced nitrogen loss by 28.1 %. Meanwhile, adding biochar inhibited the conversion of available phosphorus to non-available phosphorus while enhancing its conversion to moderately available phosphorus, thereby preserving phosphorus availability post-composting. Furthermore, the inclusion of biochar altered microbial community structure and fostered organic matter retention and humus formation, ultimately affecting the modification of nitrogen and phosphorus forms. Structural equation modeling revealed that microbial community had a more pronounced impact on bioavailable organic nitrogen, while humic acid exerted a more significant effect on phosphorus availability. This research provides a viable approach and foundation for regulating the levels of nitrogen and phosphorus nutrients during composting, serving as a valuable reference for the development of sustainable utilization technologies pertaining to CMHRs.

Response of phosphorus fractions transformation and microbial community to carbon-to-phosphorus ratios during sludge composting

Phosphorus (P) is one of the essential nutrient elements for plant growth and development. Sludge compost products can be used as an important source of soil P to solve the shortage of soil P. The difference in the initial carbon-to-phosphorus ratio (C/P) will lead to difference in the bacterial community, which would affect the biological pathway of P conversion in composting. However, few studies have been reported on adjusting the initial C/P of composting to explore P conversion. Therefore, this study investigated the response of P component transformations, bacterial community and P availability to C/P during sludge composting by adjusting initial C/P. The results showed that increasing C/P promoted the mineralization of organic P and significantly increased the content of the labile P. High C/P also increased the relative content of available P, especially when the C/P was at 45 and 60, it reached 60.51% and 60.47%. High C/P caused differences in the community structure, and improved the binding ability of microbial network modules and the competitiveness of microbial communities. Additionally, high C/P strengthened the effect of microbial communities on the transformation of P components. Finally, the study showed that C/P was the main contributor to P content variation (64.7%) and indirectly affected P component conversion by affecting the microbial community. Therefore, adjusting the C/P is crucial to improve the P utilization rate of composting products.

Modifying humus-phosphorus-arsenic interactions in sludge composting: The strengthening of phosphorus availability and arsenic efflux detoxification mechanisms

Arsenic (As) in sewage sludge poses a significant threat to environmental and human health, which has attracted widespread attention. This study investigated the value of adding sodium percarbonate (SP) on phosphorus (P) availability and As efflux detoxification through HS-P-As interactions. Due to the unique structure of humus (HS) and the similar chemical properties of P and As, the conditions for HS-P-As interaction are provided. This study discussed the content, morphology and microbial communities of HS, P and As by using metagenomic and correlation analysis. The results showed that the humification index in the experiment group (SPC) was 2.34 times higher than that in the control group (CK). The available phosphorus (AP) content of SPC increased from 71.09 mg/kg to 126.14 mg/kg, and SPC was 1.11 times that of CK. The relative abundance of ACR3/ArsB increased. Pst, Actinomyces and Bacillus commonly participated in P and As conversion. The correlation analysis revealed that the humification process was enhanced, the AP was strengthened, and the As was efflux detoxified after SP amendment. All in all, this study elucidated the key mechanism of HS-P-As interaction and put forward a new strategy for sewage sludge resource utilization and detoxification.

Effects of Bacillus-based inoculum on odor emissions co-regulation, nutrient element transformations and microbial community tropological structures during chicken manure and sawdust composting

This study aims to evaluate whether different doses of Bacillus-based inoculum inoculated in chicken manure and sawdust composting will provide distinct effects on the co-regulation of ammonia (NH3) and hydrogen sulfide (H2S), nutrient conversions and microbial topological structures. Results indicate that the Bacillus-based inoculum inhibits NH3 emissions mainly by regulating bacterial communities, while promotes H2S emissions by regulating both bacterial and fungal communities. The inoculum only has a little effect on total organic carbon (TOC) and inhibits total sulfur (TS) and total phosphorus (TP) accumulations. Low dose inoculation inhibits total potassium (TK) accumulation, while high dose inoculation promotes TK accumulation and the opposite is true for total nitrogen (TN). The inoculation slightly affects the bacterial compositions, significantly alters the fungal compositions and increases the microbial cooperation, thus influencing the compost substances transformations. The microbial communities promote ammonium nitrogen (NH4+-N), TN, available phosphorus (AP), total potassium (TK) and TS, but inhibit nitrate nitrogen (NO3--N), TP and TK. Additionally, the bacterial communities promote, while the fungal communities inhibit the nitrite nitrogen (NO2--N) production. The core bacterial and fungal genera regulate NH3 and H2S emissions through the secretions of metabolic enzymes and the promoting or inhibiting effects on NH3 and H2S emissions are always opposite. Hence, Bacillus-based inoculum cannot regulate the NH3 and H2S emissions simultaneously.

Ultrahigh-porosity Ranunculus-like MgO adsorbent coupled with predictive deep belief networks: A transformative method for phosphorus treatment

Phosphorus is a nonrenewable material with a finite supply on Earth; however, due to the rapid growth of the manufacturing industry, phosphorus contamination has become a global concern. Therefore, this study highlights the remarkable potential of ranunculus-like MgO (MO4-MO6) as superior adsorbents for phosphate removal and recovery. Furthermore, MO6 stands out with an impressive adsorption capacity of 596.88 mg/g and a high efficacy across a wide pH range (2-10) under varying coexisting ion concentrations. MO6 outperforms the top current adsorbents for phosphate removal. The process follows Pseudo-second-order and Langmuir models, indicating chemical interactions between the phosphate species and homogeneous MO6 monolayer. MO6 maintains 80 % removal and 96 % recovery after five cycles and adheres to the WHO and EUWFD regulations for residual elements in water. FT-IR and XPS analyses further reveal the underlying mechanisms, including ion exchange, electrostatic, and acid-base interactions. Ten machine learning (ML) models were applied to simultaneously predict multi-criteria (sorption capacity, removal efficiency, final pH, and Mg leakage) affected by 15 diverse environmental conditions. Traditional ML models and deep neural networks have poor accuracy, particularly for removal efficiency. However, a breakthrough was achieved by the developed deep belief network (DBN) with unparalleled performance (MAE = 1.3289, RMSE = 5.2552, R2 = 0.9926) across all output features, surpassing all current studies using thousands of data points for only one output factor. These captivating MO6 and DBN models also have immense potential for effectively applying in the real water test with error < 5 %, opening immense horizons for transformative methods, particularly in phosphate removal and recovery.

Soil microbial community composition and co-occurrence network responses to mild and severe disturbances in volcanic areas

Soil physicochemical properties and vegetation types are the main factors affecting soil microorganisms, but there are few studies on the effects of the disturbance following volcanic eruption. To make up for this lack of knowledge, we used Illumina Miseq high-throughput sequencing to study the characteristics of soil microorganisms on both shores of a volcanically disturbed lake. Soil microorganisms in the two sites were subjected to different degrees of volcanic disturbance and showed significant heterogeneity. Mild volcanic disturbance area had higher enrichment of prokaryotic community. Co-occurrence network analysis showed that a total of 12 keystone taxa (9 prokaryotes and 3 fungi) were identified, suggesting that soil prokaryote may play a more significant role than fungi in overall community structure and function. Compared with severe volcanic disturbance area, the soil microbial community in mild volcanic disturbance area had the higher modular network (0.327 vs 0.291). The competition was stronger (positive/negative link ratio, P/N: 1.422 vs 1.159). Random forest analysis showed that soil superoxide dismutase was the most significant variable associated with soil microbial community. Structural equation model (SEM) results showed that keystone had a directly positive effect on prokaryotic (λ = 0.867, P < 0.001) and fungal (λ = 0.990, P < 0.001) multifunctionality while had also a directly positive effect on fungal diversity (λ = 0.553, P < 0.001), suggesting that keystone taxa played a key role in maintaining ecosystem stability. These results were important for understanding the effects of different levels of volcanic disturbance on soil ecosystems.

Regulating method of microbial driving the phosphorus bioavailability in factory composting

Phosphorus bioavailability is essential for assessing compost quality. However, the effects of microbial and environmental factors on potentially active phosphorus (H2O-P + NaHCO3-Pi) in factory compost have not been investigated. The findings indicated that chicken manure had significantly higher available phosphorus (AP) and H2O-P + NaHCO3-Pi throughout the composting process than kitchen waste (P < 0.05). Chicken manure compost also exhibited higher α-microbial diversity. Novibacillus, Marinococcaceae and Bacillales were the core bacteria involved in bioavailable phosphorus conversion in both composts. The core bacteria in kitchen waste compost had a broader range of phosphorus metabolism functions. Moreover, moisture and pH were the key environmental factors that significantly influenced the bioavailable phosphorus (P < 0.05). These findings provide a scientific foundation for regulating the composting process and improving phosphorus utilization efficiency.

Nutrient-cycling functional gene diversity mirrors phosphorus transformation during chicken manure composting

Elucidating ecological mechanism underlying phosphorus transformation mediated by phosphate-solubilizing bacteria (PSB) during manure composting is an important but rarely investigated subject. The research objective is to disentangle ecological functions of the inoculation of PSB Pseudomonas sp. WWJ-22 during chicken manure composting based on gene quantification and amplicon sequencing. There are large dynamic changes in phosphorus fractions, gene abundances, and bacterial community structure. The PSB addition notably increased available phosphorus from 0.29-0.89 g kg-1 to 0.49-1.39 g kg-1 and significantly affected phosphorus fractionation. The PSB inoculation significantly affected composition of nutrient-cycling functional genes (NCFGs), and notably influenced bacterial community composition and function. Compost bacteria showed significant phylogenetic signals in response to phosphorus fractions, and stochastic processes dominated bacterial community assembly. Results emphasized that PSB addition increased functional redundancy, phylogenetic conservatism, and stochasticity-dominated assembly of bacterial community. Overall, findings highlight NCFG diversity can be a bio-indicator to mirror phosphorus transformation.

Regulating pH and Phanerochaete chrysosporium inoculation improved the humification and succession of fungal community at the cooling stage of composting

This study aimed to explore the effect of regulating pH and Phanerochaete chrysosporium inoculation at the cooling stage of composting on the lignocellulose degradation, humification process and related precursors as well as fungal community for secondary fermentation. Results showed that composting with P. chrysosporium inoculation and pH regulation (T4) had 58% cellulose decomposition, 73% lignin degradation and improved enzyme activities for lignin decomposition. There was 81.98% increase of humic substance content and more transformation of polyphenols and amino acids in T4 compared to control. Inoculating P. chrysosporium affected the fungal community diversity, and regulating pH helped to increase the colonization of P. chrysosporium. Network analysis showed that the network complexity and synergy between microorganisms was improved in T4. Correlation and Random Forest analysis suggested that enriched Phanerochaete and Thermomyces in the mature stage of T4 were key taxa for lignocellulose degradation, and humic acid formation by accumulating precursors.