Indigenous Bacterial Community Research Articles

An evaluation into the biosorption and biodegradation of azo dyes by indigenous siderophores-producing bacteria immobilized in chitosan.

The biodegradation and biosorption efficiency of an indigenous siderophores-producing bacterial community on azo dyes with immobilization in chitosan beads was evaluated in this study. 13 bacterial strains were isolated from textile wastewater streams. The bacterial strains were tested for the production of siderophores as well as their ability to decolorize toxic azo dyes in aqueous solution. Both qualitatively and quantitatively, all of the strains displayed high siderophores productivity. Furthermore, they displayed remarkable decolorization efficiency for azo dyes (Acid Black 1 and Reactive Black 5) in both free and immobilized form. The immobilization process was found not only to enhance the decolorization but also the degradation of azo dyes by the bacterial isolates. In a SEM micrograph, bacterial strains were immobilized, and the pores in chitosan bead to be trapped and adsorbed for dyes from synthetic wastewater. The extent of dye compounds degradation were examined using UV-visible and FTIR spectrophotometers on treated water samples and dye absorbed beads. After 72h of incubation, the UV-visible analysis revealed that the bacterial community could significantly reduce both azo dyes in wastewater by 90% at 300 mgL-1 dyes initial concentration. FTIR study confirmed the bonds of these dyes were broken to form less toxic chemicals via the bacterial community immobilized in chitosan beads. The immobilized bacterial community thus demonstrated effective approach of azo dye biosorption and biodegradation.

Automated flow cytometry as a flexible tool for comparing disinfection characteristics of indigenous bacterial communities and pure cultures

Bacterial inactivation efficiency of chlorine varies with organisms and environmental conditions. The comparability of different samples/studies, especially comparing indigenous bacterial communities with pure cultures, is impeded by inconsistent experimental conditions and analytical methods used in various studies. We tested a novel 96-well plate FCM experimental and automated analytical approach, where bacterial communities and pure cultures were suspended in the same natural water matrix prior to chlorination directly in the plate. We demonstrated the ability to rapidly monitor the efficiency of 32 different combinations of chlorine concentration and time (i.e. chlorine exposure) on bacterial pure cultures and indigenous aquatic communities, which enabled correct comparison of the data from different samples under the exact same experimental conditions. In this study, the 96-well plate automated FCM approach enabled large sets (896) of independent chlorination experiments to be carried out in a short time period. To our knowledge, this is the largest dataset of chlorination experiments which consumed least time (within 18 h after sampling) until now. Staining with SYBR Green I (SG) and SG combined with propidium iodide (SGPI) was used to assess cellular damage during chlorination. The results showed that with the same chlorine exposure, a higher chlorine concentration with a shorter contact time is favorable for inactivation of bacteria. Our research provides a promising framework to compare disinfection characteristics of various microorganism and can be further developed to diagnose effect of antimicrobial products.

Petroleum Hydrocarbon Impacted Aquatic Ecosystem Reveals Methylotenera as the Dominant Genera in the Niger Delta Region of Nigeria

Petroleum pollution of coastal areas such as Nigeria’s Niger Delta is increasingly alarming. After an oil spill, aquatic organisms, including indigenous microbial communities are affected, leading to an increased abundance of oil degraders in the affected environment. During the last decade, microbial ecology research has shifted from cultivation and characterization of individual environmental isolates to metagenomics studies that are focused on the characterization of community dynamics and composition. In this study, we determined the indigenous bacterial community in water bodies polluted with crude oil in Delta State, Nigeria by Next Generation Sequencing (NGS). Oil hydrocarbon composition was determined by Gas Chromatography–Mass Spectrometry analysis (GC–MS) and the physical-chemical dynamics were assessed using standard procedures. Results revealed Proteobacteria (76.9%), Bacteroidetes (8.5%) and Firmicutes (1.1%) as the dominant phyla. GC–MS data revealed different petroleum hydrocarbon concentrations across the seasons and locations sampled. The indigenous bacterial community included the prevalence of oil degrades with Methylotenera as the major genus. This study suggests that Methylotenera could be a useful agent for bioremediation in the Niger Delta.

Plant Growth Promoting Bacterial Consortium Induces Shifts in Indigenous Soil Bacterial Communities and Controls Listeria monocytogenes in Rhizospheres of Cajanus cajan and Festuca arundinacea.

The rhizosphere is a dynamic and complex interface between plant roots and microorganisms. Owing to exudates, a web of interactions establishes among the microbial members of this micro-environment. The present study explored the impact of a bacterial consortium (Azotobacter chroococcum, Bacillus megaterium and Pseudomonas fluorescens, ABP), on the fate of a human pathogen, Listeria monocytogenes EGD-e, in soil and in the rhizospheres of Cajanus cajan and Festuca arundinacea, in addition to its plant growth promoting effect. The study further assessed the impact these bioinoculants exert on the autochthonous soil bacterial communities. Experiments in sterilised soil inoculated with bioinoculants and L. monocytogenes revealed the inhibition of L. monocytogenes by approximately 80-fold compared to that without the consortium. Subsequently, experiments were conducted in non-sterile soil microcosms planted with C. cajan and F. arundinacea, and in bulk soil. The consortium led to a significant increase in plant growth in both plants and prevented growth of L. monocytogenes. However, the presence of resident soil bacterial communities overshadowed this inhibitory effect, and a sharp decline in L. monocytogenes populations (5-6 log reduction) was recorded under non-sterile soil conditions. A shift in the soil resident bacterial communities was observed upon amendment with the bioinoculants. A significant increase of potential Plant Growth Promoting Rhizobacteria (PGPR) and biocontrol agents was observed, while the abundance of potential phytopathogens dropped. The present study opens up new avenues for the application of such a consortium given their dual benefits of plant growth promotion and restricting phytopathogens as well as human pathogen.

The use of indigenous bacterial community as inoculant for plant growth promotion in soybean cultivation

ABSTRACT We characterized the bacterial community in shoot and rhizosphere of healthy adult soybean plants grown in two differentially managed soils. Then, these communities were transplanted to seeds to assess their effect on seedling development. The bacterial communities of inoculated soybean seedlings were assessed through 16S rRNA amplicon sequencing and seedlings’ growth was measured. The diversity in the bacterial consortium inoculum prepared from the rhizosphere was higher than those from the shoot. However, the application of bacterial consortium in seedling had no influence on diversity. The resulting bacterial community of seedlings inoculated with bacterial consortium presented an enrichment of specific plant growth-promoting groups, such as Gammaproteobacteria (Enterobacter, Pseudomonas, and Xanthomonas). The predicted potential functions showed an increased abundance of functions related to plant protection and nutrition. The application of bacterial consortium from the shoot of soybean plants grown in the soil with a previous history of soybean cultivation increased the seedling radicle length, hypocotyl length, and total dry weight by 44%, 30%, and 29%, respectively. Our study showed that selecting a consortium of indigenous microbes as inoculants is a potential approach to enhance the use and impacts of plant beneficial microorganisms on plant growth and possibly productivity.

Inoculation of phosphate-solubilizing bacteria (Bacillus) regulates microbial interaction to improve phosphorus fractions mobilization during kitchen waste composting

Bacillus presents in most composts as core microbial taxa and is widely used as inoculant in composting. However, the role of Bacillus as phosphate-solubilizing bacteria (PSB) inoculant in composting and the response of indigenous bacterial community are unclear. This study used redundancy analysis (RDA), network analysis and structural equation model (SEM) to investigate the dynamics of phosphorus (P) fractions, bacterial community, and microbial interaction in composting with PSB (Bacillus sp. P6) inoculation. Results indicated that Bacillus inoculation increased Olsen P content, organic matter degradation, and bacterial diversity, benefiting P fractions mobilization during composting. RDA showed that pH was the main factor influencing P fractions transformation and bacterial taxa. Network analysis and SEM revealed that Bacillus indirectly improved the contribution of bacterial community on P mobilization by enhancing microbial interactions. Therefore, Bacillus with P solubilizing function may be a potential inoculant to regulate the biotic process of P transformation.

Mycrocystin-LR degradation by indigenous bacterial community of Rybinsk Reservoir

The fate of microcystin-LR (MC-LR) in water samples of Rybinsk Reservoir taken before and during water bloom was assessed. The decrease in the MC-LR concentration in the both samples was due to its biodegradation by indigenous bacterial community. The highest biodegradation rate and shortest half-life of MC-LR in the water sample taken during water bloom were observed. A microcystin degrading bacterium was isolated and shown be 98.92% similar to Sphingopyxis sp. based on a fragment of 16S rRNA gene sequence. The rate of MC-LR biodegradation by Sphingopyxis sp. S7 was strongly dependent on initial concentration of toxin and temperature.

Effective removal of pharmaceutical impurities and nutrients using biocatalyst from the municipal wastewater with moving bed packed reactor

The presence of antibiotics in the wastewater is one of the important issues related to environmental management. In this study, antibiotics-degrading bacteria were screened from the enriched sewage sludge sample. Among the isolated bacterial strains, Bacillus subtilis AQ03 showed maximum antibiotic tolerance (>2000 ppm). The characterized strain B. subtilis AQ03 degraded sulfamethaoxazole and sulfamethoxine and the optimum nutrient and physical-factors were analyzed. B. subtilis AQ03 degraded 99.8 ± 1.3 % sulfamethaoxazole, and 93.3 ± 6.2 % sulfamethoxine. Sodium nitrate and ammonium chloride were improved antibiotics degradation (<90 %). The optimized conditions were maintained in a moving bed bioreactor for the removal of antibiotics and nutrients from the wastewater. The selected strain considerably produced proteases (109.4 U/mL), amylases (55.1 U/mL), cellulase (9.6 U/mL) and laccases (15.2). In moving bed reactor, sulfamethaoxazole degradation was maximum after 8 days (100 ± 1.5 %) and sulfamethoxazole (100 ± 0) was removed completely from wastewater after 10 days. In moving bed reactor, biological oxygen demand (92.1 ± 2.8 %), chemical oxygen demand (79.6 ± 1.2 %), nitrate (89.4 ± 3.9 %) and phosphate (91.8 ± 1.2) were removed from the wastewater along with antibiotics after 10 days of treatment. The findings indicate that the indigenous bacterial communities and the ability to survive in the presence of high antibiotic concentrations and xenobiotics. Moving bed bioreactor is useful for the removal of nutrients and antibiotics from wastewater.

The growth of plants and indigenous bacterial community were significantly affected by cadmium contamination in soil\u2013plant system

Concentrations of heavy metals continue to increase in soil environments as a result of both anthropogenic activities and natural processes. Cadmium (Cd) is one of the most toxic heavy metals and poses health risks to both humans and the ecosystem. Herein, we explore the impacts of Cd on a soil–plant system composed of oilseed rapes (Brassica napus and Brassica juncea) and bacteria. The results showed that Cd accumulation within tissues of two species of oilseed rapes enhanced with increasing concentrations of Cd in soils, and Cd treatment decreased their chlorophyll content and suppressed rapeseeds growth. Meanwhile, Cd stress induced the changes of antioxidative enzymes activities of both B. napus and B. juncea. Response to Cd of bacterial community was similar in soil-two species of oilseed rapes system. The impact of Cd on the bacterial communities of soils was greater than bacterial communities of plants (phyllosphere and endophyte). The α-diversity of bacterial community in soils declined significantly under higher Cd concentration (30 mg/kg). In addition, soil bacterial communities composition and structure were altered in the presence of higher Cd concentration. Meanwhile, the bacterial communities of bulk soils were significantly correlated with Cd, while the variation of rhizosphere soils bacterial communities were markedly correlated with Cd and other environmental factors of both soils and plants. These results suggested that Cd could affect both the growth of plants and the indigenous bacterial community in soil–plant system, which might further change ecosystem functions in soils.

Role of Bacillus inoculation in rice straw composting and bacterial community stability after inoculation: Unite resistance or individual collapse

Bacillus is the classic inoculant in rice straw composting. However, there has been no in-depth study of the mechanism promoting the degradation of lignocellulose and the change of indigenous bacterial communities after Bacillus inoculation. Moreover, the stability of bacterial communities is a significant challenge in achieving the efficacy of inoculation. In this study, the ecological succession and yield-resource acquisition-stress tolerance (Y-A-S) framework were combined with Redundancy analysis (RDA) and changes in relative abundance, Bacillus was found to be a pioneer bacterium that adopts a resource acquisition-stress tolerance strategy. The structural equation model (SEM) revealed that in addition to exerting a degradation effect, Bacillus inoculation could also indirectly affect lignocellulose degradation by changing the bacterial community. Random forest model and network analysis indicated a change in bacterial communities after inoculation, and bacteria with more complex relationships and weaker decomposition ability were key to the stability of bacterial communities.

The Effect of Inoculation of a Diazotrophic Bacterial Consortium on the Indigenous Bacterial Community Structure of Sugarcane Apoplast Fluid.

The extracellular space in plants, termed the apoplast, has a pH and sugar content that enables bacterial growth and represents a possible niche for the establishment of endophytic bacteria. Previous studies have investigated the effects of diazotrophic bacteria inoculation in sugarcane varieties, but it has not yet been analyzed how the microbial community of apoplast fluid of sugarcane is affected. High-throughput next generation sequencing of the 16S rRNA gene was used throughout this study to determine the effect of inoculation with a diazotrophic bacteria consortium, previously isolated from sugarcane, on the native bacterial population of sugarcane variety RB867515 grown in the field. The analyses were carried out 450days after inoculation. The results revealed the presence of 22 phyla, with predominance of Proteobacteria phylum. It was observed that the inoculated consortium changed the indigenous bacterial community structure of sugarcane apoplast fluid by decreasing diversity and evenness, interfering in the composition of rare species. Microbial community composition analysis revealed differences between treatments. The differential abundance test showed there were 43 amplicon sequence variants (ASVs) which were relatively more abundant in the inoculated treatment, with predominance of the Sphingomonas genus. The predicted functions of the most abundant ASVs revealed the presence of genera related to plant growth promotion and protection against phytopathogens. Analysis to evaluate the occurrence of inoculated strains in the recovered data was not conclusive since the ASVs taxonomically close to the inoculated bacteria were observed in low abundance. The present study is the first report to elucidate the bacterial community in sugarcane apoplast fluid using a culture-independent approach. It demonstrated that the diazotrophic bacterial consortium interferes in the natural bacterial community in sugarcane variety RB867515.

Escherichia coli Shiga Toxins and Gut Microbiota Interactions.

Escherichia coli (EHEC) and Shigella dysenteriae serotype 1 are enterohemorrhagic bacteria that induce hemorrhagic colitis. This, in turn, may result in potentially lethal complications, such as hemolytic uremic syndrome (HUS), which is characterized by thrombocytopenia, acute renal failure, and neurological abnormalities. Both species of bacteria produce Shiga toxins (Stxs), a phage-encoded exotoxin inhibiting protein synthesis in host cells that are primarily responsible for bacterial virulence. Although most studies have focused on the pathogenic roles of Stxs as harmful substances capable of inducing cell death and as proinflammatory factors that sensitize the host target organs to damage, less is known about the interface between the commensalism of bacterial communities and the pathogenicity of the toxins. The gut contains more species of bacteria than any other organ, providing pathogenic bacteria that colonize the gut with a greater number of opportunities to encounter other bacterial species. Notably, the presence in the intestines of pathogenic EHEC producing Stxs associated with severe illness may have compounding effects on the diversity of the indigenous bacteria and bacterial communities in the gut. The present review focuses on studies describing the roles of Stxs in the complex interactions between pathogenic Shiga toxin-producing E. coli, the resident microbiome, and host tissues. The determination of these interactions may provide insights into the unresolved issues regarding these pathogens.

Indigenous bacterial community and function in phenanthrene-polluted coastal wetlands: Potential for phenanthrene degradation and relation with soil properties

The Yellow River Delta, adjacent to Shengli Oilfield, has a potential risk of petroleum pollution. In this study, soil samples were collected from phenanthrene (PHE)-polluted (adjacent to abandoned oil well, Zone D) and non-polluted (far away from abandoned oil well, Zone E) coastal wetlands. The influence of PHE pollution on indigenous bacterial community and function, and their relationship with soil characteristics were investigated. The levels of PHE, salinity and NH4+-N were higher in Zone D than in Zone E. PHE-degrading bacteria Achromobacter and Acinetobacter were mainly distributed in Zone E, whereas Halomonas, Marinobacter, and Roseovarius were highly abundant in Zone D. Halomonas and Marinobacter had the potential for denitrification and could achieve PHE degradation through mutual cooperation. PHE pollution could increase the abundance of functional bacteria but reduce the diversity of microbial community. PHE and salinity played key roles in shaping microbial community structure and function. High PHE level inhibited microbial metabolism but stimulated self-protection potential. PHE aerobic degradation associated with the catechol and phthalic acid pathways was found in Zone D, whereas the catechol pathway dominated in Zone E. Interestingly, PHE anaerobic degradation with nitrate reduction also dominated in Zone D, whereas the process coupled with multiple electron acceptors co-existed in Zone E, which was associated with tidal seawater carrying nutrients. This study illustrated the importance of comprehensive consideration of microbial community structure and function under PHE pollution, suggesting indigenous microorganisms as potential microbial consortium for bioremediation in coastal wetlands.

Top-down effects of protists are greater than bottom-up effects of fertilisers on the formation of bacterial communities in a paddy field soil

Communities at any trophic level along the food chain are determined by simultaneous top-down (predators) and bottom-up (nutrients) effects; however, we still lack an understanding of this concept in the soil ecosystem. Here, we aimed to reveal the contributions of the top-down and bottom-up factors on the formation of paddy field bacterial communities. The position of an indigenous bacterial community at the trophic level was centred between soil nutrients (chemical and organic fertilisers [CF and OF, respectively], i.e., bottom-up factors) and bacterial predators (phagotrophic protists, i.e., top-down factors) in a paddy field soil. A 16S rRNA gene amplicon sequencing method was used to evaluate the top-down and bottom-up effects on the bacterial community composition. The results showed that the top-down effects of protists were greater than the bottom-up effects of the applied fertilisers on the formation of bacterial communities. The presence of protists caused the formation of a distinct bacterial community by affecting several bacterial species mainly belonging to Proteobacteria and Bacteroidetes. Among the bottom-up factors, OF significantly affected the bacterial beta diversity, while CF did not. The numbers of bioindicator genera that were associated with the top-down factors were 4.4 and 3.7 times higher than those associated with the bottom effects of CF and OF, respectively. Overall, we provided unique information on the importance of protists in regulating bacterial communities in paddy field soil, which is likely to affect bacterial activities and agricultural productivity.

The Dynamics of Indigenous Epiphytic Bacterial and Fungal Communities of Barley Grains Through the Commercial Malting Process

Microbial activity is present at every step of the malting and brewing process. It is, therefore, critical to managing the grain-associated microbial communities for the production of high-quality malts. Earlier studies and reviews have only focused on the most abundant or culturable microorganisms of the malting environment. Furthermore, fungal-bacterial interactions have not been studied through the barley malting process as had been done for other fermented foods such as cheese and wine. This study used a metabarcoding approach to characterize the barley and the malt-associated epiphytic fungal and bacterial communities and provided the most comprehensive analysis to date of the dynamic shift in diversity, compositional structure, and potential functional roles of the grain-associated microbiome through the commercial malting process. We revealed microbial taxa that have not been identified before in a malting environment and identified functional guilds generating organic acids or degrading the endosperm cell walls and storage proteins that may affect malting efficiency and consistency. Ecological network reconstruction suggested that malting destabilized grain epiphytic microbiome which could be vulnerable to less optimal environmental conditions. This study expanded our knowledge in microbial quality and safety of malt and could help manage microbial-associated problems in the commercial malting industry.

Inoculation of Mimosa Pudica with Paraburkholderia phymatum Results in Changes to the Rhizoplane Microbial Community Structure.

Nitrogen fixing symbiosis between rhizobia and legumes contributes significant amounts of N to agricultural and natural environments. In natural soils, rhizobia compete with indigenous bacterial communities to colonize legume roots, which leads to symbiotic interactions. However, limited information is currently available on the effects of the rhizobial symbiont on the resident microbial community in the legume rhizosphere, rhizoplane, and endosphere, which is partly due to the presence of native nodulating rhizobial strains. In the present study, we used a symbiotic system comprised of Paraburkholderia phymatum and Mimosa pudica to examine the interaction of an inoculant strain with indigenous soil bacteria. The effects of a symbiont inoculation on the native bacterial community was investigated using high throughput sequencing and an analysis of 16S rRNA gene amplicons. The results obtained revealed that the inoculation induced significant alterations in the microbial community present in the rhizoplane+endosphere of the roots, with 13 different taxa showing significant changes in abundance. No significant changes were observed in the rhizospheric soil. The relative abundance of P. phymatum significantly increased in the rhizoplane+endosphere of the root, but significant decreased in the rhizospheric soil. While the rhizosphere, rhizoplane, and root endosphere contained a wide diversity of bacteria, the nodules were predominantly colonized by P. phymatum. A network analysis revealed that the operational taxonomic units of Streptomyces and Phycicoccus were positively associated with P. phymatum as potential keystone taxa. Collectively, these results suggest that the success of an inoculated symbiont depends on its ability to colonize the roots in the face of competition by other soil bacteria. A more detailed understanding of the mechanisms by which an inoculated strain colonizes its plant host is crucial for realizing the full potential of microbial inoculants in sustainable agriculture.

Density and nitrifying potential of indigenous bacterial community in mangrove and seagrass in the north of Vietnam

Density and nitrification potential of indigenous microorganism in mangroves (Tien Yen - Quang Ninh and Bang La - Hai Phong) and seagrass (Ha Coi, Dam Ha - Quang Ninh and Tam Giang - Thua Thien Hue) in the north of Vietnam were evaluated through 4 sampling times in the dry and rainy seasons in the years of 2017-2019. The analytical results showed that the average density of nitrifying bacteria was 4.6 ± 1.8 × 102 MPN/ml, in which the density in mangroves tended to be higher than that in the seagrass beds (P &lt; 0.05) in both the rainy and dry seasons. The average nitrifying rate was 2.7 ± 0.6 µgN/g wet soil/hour, in which the rate in mangroves tended to be higher than that in seagrass beds in the rainy season (P &lt; 0.05). Nitrifying density and rate are not only correlated with substrate concentration but also with other environmental factors such as P-PO4, BOD5, total phosphate in sediment and total bacterial density.

Indigenous microbial strains as bioresource for remediation of chronically polluted Niger Delta soils

An increase in artisanal crude oil refining within the Niger Delta Creeks has led to colossal environmental problems occasioned by spillages and subsequent ecosystem damage. Bacteria have been shown to play key role in biogeochemical cycling and degradation of pollutants from petroleum sources. The present study investigated the degradation efficiency of a bacterial consortia recovered from heavily inundated site in Bie-Ama community, having total petroleum hydrocarbons (TPH) concentration of 22,000 mg/kg, a value higher than Department of Petroleum Resources (DPR)’s 1000 mg/kg intervention limit. Soil samples were collected at 15 cm depth with soil auger while microbial isolation was done using enrichment and vapor phase transfer methods in Bushnell Haas medium. Colorimetric method using 2, 6-dichlorophenol indophenol (DCPIP) redox indicator was employed to determine biodegradation potentials of isolates. Bacterial isolates identified using 16S rRNA gene by Sanger sequencing were further screened for biosurfactant production and aromatic hydrocarbon degradation abilities. A consortium for efficient biodegradation of crude oil was constituted from individual isolates that totally decolorized DCPIP. Total culturable heterotrophic and hydrocarbon utilizing bacterial counts were 2.07 × 106 and 1.71 × 106 CFU/g soil respectively. Bacterial strains from the genera Pseudomonas, Bacillus, Klebsiella, Enterobacter produced biosurfactants while all strains utilized aromatics (benzene and naphthalene). A combination of Pseudomonas, Bacillus, Lysinibacillus and Enterobacter was the most efficient crude oil degrading consortium with significant mean difference (p = 0.05) as evidenced by GC-analysis confirming a more than 25% reduction in total petroleum hydrocarbon (TPH) concentration of 1% crude oil within 48 h. Conclusively, the extant indigenous bacterial community in the impacted site has the natural capability to degrade hydrocarbons and could be further enhanced through biostimulation for in situ remediation.

Application of a microbial consortium improves the growth of Camellia sinensis and influences the indigenous rhizosphere bacterial communities.

To investigate the role of a microbial consortium in influencing of Camellia sinensis growth and rhizosphere bacteria microbial community structure. Based on glasshouse trials, the microbial consortium TCM was selected for a field trial. TCM significantly increased bud density (67·53%), leaf area (31·15%) and hundred-bud weight (22·5%) compared with the control treatment (P<0·01) during 180days. Furthermore, TCM-treated soil showed a significant increase (P<0·05) in organic matter (60·89%), total nitrogen (66·22%), total phosphorus (3·34%), available phosphorus (3·82%), available potassium (9·24%) and 2-3mm water-stable aggregates (77·93%). Molecular ecological network analysis of the rhizobacteria indicated an increase in modularity and the number of community, connection and nodes after TCM application. Several plant growth-promoting bacteria were categorized as hubs or indicators, such as Haliangium, Catenulispora and Gemmatimonas, and showed intensive connections with other bacteria. The TCM consortium enhances the effectiveness of soil mineral nutrition, influences the indigenous rhizobacterial community, alters the rhizobacterial network structure in the rhizosphere and promotes the growth of C. sinensis. The TCM growth-promoting mechanism was closely related to rhizosphere bacterial diversity; therefore, strengthening rhizobacterial interactions may help promote C. sinensis growth, which could be a sustainable approach for improving C. sinensis growth and health in tea plantations.

Effect of protists on rhizobacterial community composition and rice plant growth in a biochar amended soil

The effects of protists on an indigenous soil bacterial community, putative bacterial genes involved in N-cycling, and the rice plant growth were studied in poultry litter biochar (PL) and rice husk biochar (RH) amended (with two application doses: 2% and 4% w/w) paddy field soil. The bacterial community composition, which was evaluated using 16S rRNA gene amplicon sequencing, was significantly and differentially affected by the protists, the PL and the RH. The effects of protists on the bacterial community composition were decreased by the RH and the PL treatments. The number of protist-affected bioindicator bacterial taxa was decreased from 90 to 46, 29, 43, and 21 in the 2% RH-, 4% RH-, 2% PL-, and 4% PL-treated soils, respectively. The presence of the protist significantly increased the abundance of the putative bacterial genes involved in mineralisation, dissimilatory nitrate reduction to ammonium (DNRA), and NO3- assimilation, and the same occurred with PL treatments. The rice plant growth and N uptake were always higher in the presence of protists and PL amendments. Overall our results suggest a new insight into the effects of biochar on the bacterial community via altering the trophic interactions.