Ore improver additions alter livestock manure compost ecosystem C:N:P stoichiometry.

Deciphering the pivotal components of nutrient metabolism in compost is of paramount importance. To this end, ecoenzymatic stoichiometry, enzyme vector modeling, and statistical analysis were employed to explore the impact of exogenous ore improver on nutrient changes throughout the livestock composting process. The total phosphorus increased from 12.86 to 18.72 g kg-1, accompanied by a marked neutralized pH with ore improver, resulting in the Carbon-, nitrogen-, and phosphorus-related enzyme activities decreases. However, the potential C:P and N:P acquisition activities represented by ln(ßG + CB): ln(ALP) and ln(NAG): ln(ALP), were increased with ore improver addition. Based on the ecoenzymatic stoiometry theory, these changes reflect a decreasing trend in the relative P/N limitation, with pH and total phosphorus as the decisive factors. Our study showed that the practical employment of eco stoichiometry could benefit the manure composting process. Moreover, we should also consider the ecological effects from pH for the waste material utilization in sustainable agriculture.

Core Species Derived from Multispecies Interactions Facilitate the Immobilization of Cadmium.

Microbial consortia have opened new avenues for heavy-metal remediation. However, the limited understanding of the overall effect of interspecific interactions on remediation efficacy hinders its application. Here, the effects of multispecies growth and biofilm formation on Cd immobilization were explored from direct and multiple interactions through random combinations of two or three rhizosphere bacteria. In monocultures, Cd stress resulted in an average decrease in planktonic biomass of 26%, but through cooperation, the decrease was attenuated in dual (21%) and triple cultures (13%), possibly involving an increase in surface polysaccharides. More than 65% of the co-cultures exhibited induction of biofilm formation under Cd stress, which further enhanced the role of biofilms in Cd immobilization. Notably, excellent biofilm-forming ability or extensive social induction makes Pseudomonas putida and Brevundimonas diminuta stand out in multispecies biofilm formation and Cd immobilization. These two core species significantly increase the colonization of soil microorganisms on rice roots compared to the control, resulting in a 40% decrease in Cd uptake by rice. Our study enhances the understanding of bacterial interactions under Cd stress and provides a novel strategy for adjusting beneficial soil consortia for heavy-metal remediation.

Effective immobilization of heavy metals via reactive barrier by rhizosphere bacteria and their biofilms.

As the portal of plants, rhizosphere microorganisms play an essential role in controlling the species, transformation, and bioavailability of heavy metals, yet the potential passivation mechanism is still unclear. In this study, two heavy metal resistant and growth-promoting rhizosphere bacteria were screened, and their mechanisms in dealing with external stress and immobilizing heavy metal were explored. The results showed that heavy metals inhibited the ability of Pseudomonas sp. H13 and Brevundomonas sp. H16 to promote plant growth, but stimulated the production of extracellular polysaccharides and inorganic labile sulfide, and enhanced biofilm formation, thereby significantly improved the removal efficiency of Cu2+, Zn2+, Cd2+, and Pb2+. Compared with H16, the biofilm of H13 disintegrated rapidly in the later stage, so more metal ions were adsorbed on the planktonic cells. The C-OH and PO groups related to polysaccharides play a crucial role in heavy metal adsorption, and the immobilization mechanism of the planktonic cell is mainly ion exchange and group complex, but for H16, intracellular enrichment cannot be ignored. Functional group complexes played a dominant role in biofilm, and the immobilized heavy metals were more difficult to release into the environment. This study highlighted the potential application prospects of biofilm bacteria in heavy metal remediation and explained the reactive barrier of rhizosphere bacteria to heavy metals.

Linking rare and abundant phoD-harboring bacteria with ecosystem multifunctionality in subtropical forests: From community diversity to environmental adaptation.

Environmental factor-driven bacterial diversity could be an indicator for evaluating ecosystem multifunctionality (EMF). However, little is known about interconnections between EMF and the community diversity of rare and abundant phoD-harboring bacteria responsible for organic phosphorus mineralization. Illumina MiSeq sequencing and multiple statistical analyses were used to evaluate diversity maintenance of rare and abundant phoD-harboring bacteria at both taxonomic and phylogenetic levels and their contributions to soil EMF in the subtropical Shennongjia primeval forest. We found that rare phoD-harboring bacteria exhibited higher community diversity and broader environmental breadths than abundant ones, while abundant phoD-harboring bacteria showed closer phylogenetic clustering and stronger phylogenetic signals of ecological preferences than rare ones. Stochastic processes dominated community assemblies of rare and abundant phoD-harboring bacteria, and temperature was an important environmental variable adjusting the balance between stochastic and deterministic processes. The taxonomic α-diversity of rare phoD-harboring bacteria showed larger contribution to soil EMF than that of abundant ones, while the phylogenetic α-diversity of abundant phoD-harboring bacteria contributed significantly more than that of rare ones. Our findings enrich knowledge of the environmental adaptation of rare and abundant phoD-harboring bacteria, and highlight linkages between soil EMF and the diversity of rare and abundant phoD-harboring bacteria at both the taxonomic and phylogenetic levels.

Bridging Rare and Abundant Bacteria with Ecosystem Multifunctionality in Salinized Agricultural Soils: from Community Diversity to Environmental Adaptation.

Bacterial diversity and ecosystem multifunctionality (EMF) vary along environmental gradients. However, little is known about interconnections between EMF and taxonomic and phylogenetic diversities of rare and abundant bacteria. Using MiSeq sequencing and multiple statistical analyses, we evaluated the maintenance of taxonomic and phylogenetic diversities of rare and abundant bacteria and their contributions to EMF in salinized agricultural soils (0.09 to 19.91 dS/m). Rare bacteria exhibited closer phylogenetic clustering and broader environmental breadths than abundant ones, while abundant bacteria showed higher functional redundancies and stronger phylogenetic signals of ecological preferences than rare ones. Variable selection (86.7%) dominated rare bacterial community assembly, and dispersal limitation (54.7%) and variable selection (24.5%) determined abundant bacterial community assembly. Salinity played a decisive role in mediating the balance between stochastic and deterministic processes and showed significant effects on functions and diversities of both rare and abundant bacteria. Rare bacterial taxonomic α-diversity and abundant bacterial phylogenetic α-diversity contributed significantly to EMF, while abundant bacterial taxonomic α-diversity and rare bacterial phylogenetic α-diversity did not. Additionally, abundant rather than rare bacterial community function had a significant effect on soil EMF. These findings extend our knowledge of environmental adaptation of rare and abundant bacteria and highlight different contributions of taxonomic and phylogenetic α-diversities of rare and abundant bacteria to soil EMF.IMPORTANCE Soil salinization is a worldwide environmental problem and threatens plant productivity and microbial diversity. Understanding the generation and maintenance of microbial diversity is essential to estimate soil tillage potential via investigating ecosystem multifunctionality. Our sequence-based data showed differences in environmental adaptations of rare and abundant bacteria at taxonomic and phylogenetic levels, which led to different contributions of taxonomic and phylogenetic α-diversities of rare and abundant bacteria to soil EMF. Studying the diversity of rare and abundant bacteria and their contributions to EMF in salinized soils is critical for guiding soil restoration.

Dispersal limitation driving phoD-harboring bacterial community assembly: A potential indicator for ecosystem multifunctionality in long-term fertilized soils.

Elucidating the association between the phoD-harboring bacterial community and soil ecosystem multifunctionality, which is crucial for the comprehension of the phoD-harboring bacterial role and contribution in agro-ecosystems, is an essential but rarely investigated subject. Here, we explored the phoD-harboring bacterial community in long-term fertilized soils using amplicon sequencing and multiple analysis methods including the null, neutral, and niche breadth models. We found distance-decay relationships of community similarities against geographical distance on a large spatial scale. Community dissimilarity was significantly lower in the organic fertilization treatment (M) than that in the no (CK) and mineral (NPK) fertilizer treatments. Dispersal limitation governed community assembly in CK, M, NPK, and whole samples, with corresponding relative contributions of 58.2%, 58.3%, 52.8%, and 54.4%, respectively. Electrical conductivity, total carbon, total nitrogen, total phosphorus, organic phosphorus, and available phosphorus were responsible for the community assembly of phoD-harboring bacteria. Multiple model analysis revealed that the phoD-harboring bacterial community was less constrained by the environment and presented flexible metabolism in soils with the M fertilization treatment. phoD-harboring bacteria presented more conflicting interaction and exhibited significantly higher ecosystem multifunctionality in soils with the M fertilization treatment than that in the CK and NPK fertilization treatments. To our knowledge, this is the first study to report a less environment-constrained phoD-harboring bacterial community might lead to a larger difference in ecosystem multifunctionality in fertilized soils. Therefore, we suggest phoD-harboring bacterial community assembly could be a biotic indicator for evaluating soil ecosystem multifunctionality.

Synergistic effect of biofilm growth and cadmium adsorption via compositional changes of extracellular matrix in montmorillonite system.

The interaction of bacterial biofilm and clay minerals provides great potential for heavy metal remediation in contaminated soil, yet, little is known about how heavy metal, clay minerals and their combinations affect the bacterial biofilm performance and heavy metal adsorption. In this study, the response of biofilm development as well as Cd2+ adsorption in the presence of Cd2+ and montmorillonite has been deciphered. Low concentrations of Cd2+ and montmorillonite or their combinations enhanced biofilm formation by increasing polysaccharides proportion in the biofilm matrix, and the maximum adsorption capacity of Cd2+ by biofilm was increased by 1.5 times. Furthermore, the immobilization of Cd2+ by soil was significantly improved when S14-biofilm was introduced. Such results could gain deeper insight into bacterial survival tactics in the complex systems which makes major contribution to microbial remediation of heavy metal polluted environments.

A manganese-oxidizing bacterial consortium and its biogenic Mn oxides for dye decolorization and heavy metal adsorption.

Manganese (Mn) contamination is a common environmental problem in the world and manganese oxidizing bacteria (MOB) play important roles in bioremediation of heavy metal and organic pollution. In this study, a novel MOB consortium AS containing core microbes of Sphingobacterium and Bacillus was acclimated from Mn-contaminated rivulet sediments. The MOB consortium AS presented good Mn(II) removal performance under 500-10,000 mg/L Mn(II), with Mn(II) removal capacities ranging from 481 to 3478 mg/L. In coexistence systems of Mn(II) and Fe(II), Ni(II), Cu(II), and Zn(II), the MOB consortium AS removed 98%, 91%, 99%, and 76% of Mn(II), respectively. Additionally, the MOB consortium AS could utilize multiple carbon sources (e.g., Chitosan, ß-Cyclodextrin, and Phenanthrene) to remove Mn(II), with Mn(II) removal efficiencies ranging from 11% to 97%. Meanwhile, XRD, XPS, FTIR, SEM, and EDS analyses reflected that biogenic Mn oxides (bio-MnOx-C) contained C, O, Mn (Mn(II) and Mn(IV)) and embodied in rhodochrosite and birnessite. The bio-MnOx-C exhibited second-order kinetic reaction for removal of dye, with corresponding decolorization capacities of 22.0 mg/g for methylene blue and 23.8 mg/g for crystal violet. In addition, bio-MnOx-C showed adsorption capacities of 159.0 mg/g for Cu(II), 130.7 mg/g for Zn(II), and 123.3 mg/g for Pb(II). Overall, this study illustrates consortium AS and bio-MnOx-C have great potentials in remediation of pollution caused by heavy metals and organic pollutants.

Co-effect of minerals and Cd(II) promoted the formation of bacterial biofilm and consequently enhanced the sorption of Cd(II).

Heavy metal pollution is very common in soils. Soils are complex systems including minerals, bacteria, and various other substances. In Cd(II) contaminated soil, the combined effects of clay minerals and heavy metals on bacterial biofilm and Cd(II) adsorption are unappreciated. Our study showed that the combination of clay minerals (goethite, kaolinite, and montmorillonite) and heavy metals promoted Serratia marcescens S14 biofilm development significantly more than clay minerals or Cd(II) alone. The amount of biofilm after binary treatment with clay minerals and Cd(II) was 2.3-7.3 times than that in control. Mineral-induced cell death and the expression of the fimA, bsmA, and eps were key players in biofilm formation. Binary treatment with montmorillonite and Cd(II) significantly enhanced biofilm development and consequently increased the adsorption of Cd(II). Cd(II) removal is the result of co-adsorption of bacteria and minerals. Bacterial biofilm played an important role in Cd(II) adsorption. FTIR spectroscopy showed the components of biofilm were not affected by minerals and revealed the functional groups -OH, -NH, -CH2, -SH, -COO participated in Cd(II) immobilization. Our findings are of fundamental significance for understanding how minerals and Cd(II) affect biofilms and thereby enhance Cd(II) adsorption and predicting the mobility and fate of heavy metals in heavy metal-contaminated soil.

Characterization of Cd2+ biosorption by Pseudomonas sp. strain 375, a novel biosorbent isolated from soil polluted with heavy metals in Southern China.

Water pollution with heavy metals is a global problem. Using microbial adsorbents to remediate water bodies contaminated with heavy metals has been garnering considerable attention. In this study, a cadmium (Cd2+)-resistant bacterium, isolated from soil polluted with heavy metals, was characterized as Pseudomonas sp. 375 based on its biochemical characteristics and 16S rRNA gene. The minimum inhibitory concentration (MIC) of Cd2+ for strain 375 was 6 mM. We evaluated the effects of different parameters, such as initial pH, contact time, and initial Cd2+ concentration, on Cd2+ uptake. The data acquired using nonliving biomass were fitted to a Langmuir isotherm model; however, the Freundlich isotherm model showed better fit for data acquired using living biomass. The maximum biosorption capacities were 92.59 mg g-1 and 63.29 mg g-1 for living and nonliving cells, respectively. The kinetics of biosorption was described using a pseudo-second order kinetic model. The tightly bound Cd on the cell wall played a major role in Cd2+ adsorption for both biosorbents. SEM-EDX analysis also showed that Cd2+ was bound to the cell wall. FTIR spectral analysis showed that -CH2, -OH, -SO3, CO, N-H, C-N, phosphate, or sulfate functional groups were the main functional sites for the binding of Cd2+ ions. Effectively Cd2+ removal from Cd2+ contaminated water suggested Pseudomonas sp. 375 was an (a) inexpensive, effective, and promising biosorbent that can be used for bioremediation Cd2+-contaminated wastewater.

Complete genome sequence of Raoultella sp. strain X13, a promising cell factory for the synthesis of CdS quantum dots.

A novel cadmium-resistant bacterium, Raoultella sp. strain X13, recently isolated from heavy metal-contaminated soil, and this strain can synthesize CdS quantum dots using cadmium nitrate [Cd(NO4)2] and l-cysteine. Biomineralization of CdS by strain X13 can efficiently remove cadmium from aqueous solution. To illuminate the molecular mechanisms for the biosynthesis of CdS nanoparticle, the complete genome of Raoultella sp. strain X13 was sequenced. The whole genome sequence comprises a circular chromosome and a circular plasmid. Cysteine desulfhydrase smCSE has been previously found to be associated with the synthesis of CdS quantum dots. Bioinformatics analysis indicated that the genome of Raoultella sp. strain X13 encodes five putative cysteine desulfhydrases and all of them are located in the chromosome. The genome information may help us to determine the molecular mechanisms of the synthesis of CdS quantum dots and potentially enable us to engineer this microorganism for applications in biotechnology.

Role of novel bacterial Raoultella sp. strain X13 in plant growth promotion and cadmium bioremediation in soil.

Heavy metal pollution in agricultural soils has become a widespread serious problem with the rapid industrialization and urbanization in the past two decades. Cadmium (Cd2+) is of the most concern in soils due to its high toxicity. It is necessary to develop remediation strategies to remove or neutralize its toxic effects in Cd-contaminated soil. Microbial bioremediation is a promising technology to treat heavy metal-contaminated soils. In this study, Cd-resistant bacterium, isolated from heavy metal-polluted soil in Southern China, was characterized as Raoultella sp. strain X13 on the basis of its biochemical profile and 16S rRNA. We investigated the characterization of Cd2+ distribution in different cellular compartments after Cd2+ uptake. Cd2+ uptake by strain X13 was mainly by ion exchange and chelation binding tightly to the cell wall. In addition, X13 plant growth-promoting characteristics suggested that X13 could solubilize phosphate and produce indole acetic acid. Pot experiments for the remediation of Cd-contaminated soil in situ by X13 inoculation demonstrated that X13 application to Cd-contaminated soils significantly promoted pak choi growth and improved production. We also found that X13 substantially reduced the Cd2+ bioavailability for pak choi. Therefore, strain X13 is an effective treatment for potential application in Cd2+ remediation as well as for sustainable agronomic production programs in Cd-contaminated soils.