Natural Bacterial Communities Research Articles

Trade-off for survival: Microbiome response to chemical exposure combines activation of intrinsic resistances and adapted metabolic activity.

The environmental microbiota is increasingly exposed to chemical pollution. While the emergence of multi-resistant pathogens is recognized as a global challenge, our understanding of antimicrobial resistance (AMR) development from native microbiomes and the risks associated with chemical exposure is limited. By implementing a lichen asa bioindicatororganism and model for a native microbiome, we systematically examined responses towards antimicrobials (colistin, tetracycline, glyphosate, and alkylpyrazine). Despite an unexpectedly high resilience, we identified potential evolutionary consequences of chemical exposure in terms of composition and functioning of native bacterial communities. Major shifts in bacterial composition were observed due to replacement of naturally abundant taxa; e.g. Chthoniobacterales by Pseudomonadales. A general response, which comprised activation of intrinsic resistance and parallel reduction of metabolic activity at RNA and protein levels was deciphered by a multi-omics approach. Targeted analyses of key taxa based on metagenome-assembled genomes reflected these responses but also revealed diversified strategies of their players. Chemical-specific responses were also observed, e.g., glyphosate enriched bacterial r-strategists and activated distinct ARGs. Our work demonstrates that the high resilience of the native microbiota toward antimicrobial exposure is not only explained by the presence of antibiotic resistance genes but also adapted metabolic activity as a trade-off for survival. Moreover, our results highlight the importance of native microbiomes as important but so far neglected AMR reservoirs. We expect that this phenomenon is representative for a wide range of environmental microbiota exposed to chemicals that potentially contribute to the emergence of antibiotic-resistant bacteria from natural environments.

Root exudates and chemotactic strains mediate bacterial community assembly in the rhizosphere soil of Casuarina equisetifolia L.

Rhizosphere bacterial diversity and community structure are important factors involving in plant growth. However, the exact process of how plant rhizosphere bacterial community structures is assembled remains unclear. To investigate the role of bacterial chemotaxis to rhizosphere secretions in the establishment of rhizosphere microbial community in Casuarina equisetifolia, we screened bacteria strains derived from the rhizosphere of Casuarina equisetifolia L. using top three chemicals of the plant root exudates (2,4-di-tert-butylphenol, methyl stearate, and arginine) as chemoattractant. Among 72 bacterial strains, five showed strong chemotaxis to 2,4-di-tert-butylphenol, six to methyl stearate, and eleven to arginine, with the highest bacterial chemotaxis occurring at a concentration of 60 μM. This indicates that arginine is a more important chemoattractant than 2,4-di-tert-butylphenol, methyl stearate in the establishment of rhizosphere microbial community in Casuarina equisetifolia. Bacterial community assembly analysis using different chemoattractants and chemoattractants-plus-bacteria combinations were then performed by burying laboratory prepared bags of sterlized soil into C. equisetifolia forest. Bacteria diversity and enrichment analyses using 16S rDNA sequencing at 7 and 14 days after burying showed that arginine-plus-Ochrobactrum sp. and Pantoea sp. treatment exhibited the greatest similarity to the natural forest bacterial community. Our date provides new insights into how chemoattractants and chemotactic bacteria strains shape the rhizosphere microbial community of C. equisetifolia, which constitutes foundational information for future management of these communities.

Denitrification kinetics during aquifer storage and recovery of drainage water from agricultural land

An aquifer storage transfer and recovery (ASTR) system was studied in which tile drainage water (TDW) was injected with relatively high NO3 (about 14 mg/L) concentrations originating from fertilizers. Here we present the evolution of denitrification kinetics at 6 different depths in the aquifer before, and during ASTR operation. First-order denitrification rate constants increased over time before and during the first days of ASTR operation, likely due to microbial adaptation of the native bacterial community and/or bioaugmentation of the aquifer by denitrifying bacteria present in injected TDW. Push-pull tests were performed in the native aquifer before ASTR operation. Obtained first-order denitrification rate constants were negligible (0.00–0.03 d−1) at the start, but increased to 0.17–0.83 d−1 after a lag-phase of about 6 days. During the first days of ASTR operation in autumn 2019, the arrival of injected TDW was studied at 2.5 m distance from the injection well. First-order denitrification rate constants increased again over time (maximum >1 d−1). Three storage periods without injection were monitored in winter 2019, fall 2020, and spring 2021 during ASTR operation. First-order rate constants ranged between 0.12 and 0.61 d−1. Denitrification coupled to pyrite oxidation occurred at all depths, but other oxidation processes were indicated as well. NO3 concentration trends resembled Monod kinetics but were fitted also to a first-order decay rate model to facilitate comparison. Rate constants during the storage periods were substantially lower than during injection, probably due to a reduction in the exchange rate between aquifer solid phases and injected water during the stagnant conditions. Denitrification rate constants deviated maximally a factor 5 over time and depth for all in-situ measurement approaches after the lag-phase. The combination of these in-situ approaches enabled to obtain more detailed insights in the evolution of denitrification kinetics during AS(T)R.

Ecological and evolutionary solutions to the plasmid paradox

The 'plasmid paradox' arises because, although plasmids are common features of bacterial genomes, theoretically they should not exist: rates of conjugation were believed insufficient to allow plasmids to persist by infectious transmission, whereas the costs of plasmid maintenance meant that plasmids should be purged by negative selection regardless of whether they encoded beneficial accessory traits because these traits should eventually be captured by the chromosome, enabling the loss of the redundant plasmid. In the decade since the plasmid paradox was described, new data and theory show that a range of ecological and evolutionary mechanisms operate in bacterial populations and communities to explain the widespread distribution and stable maintenance of plasmids. We conclude, therefore, that multiple solutions to the plasmid paradox are now well understood. The current challenge for the field, however, is to better understand how these solutions operate in natural bacterial communities to explain and predict the distribution of plasmids and the dynamics of the horizontal gene transfer that they mediate in bacterial (pan)genomes.

Effect of remediation reagents on bacterial composition and ecological function in black-odorous water sediments

Black-odorous urban water bodies and sediments pose a serious environmental problem. In this study, we conducted microcosm batch experiments to investigate the effect of remediation reagents (magnesium hydroxide and calcium nitrate) on native bacterial communities and their ecological functions in the black-odorous sediment of urban water. The dominant phyla (Proteobacteria, Actinobacteria, Chloroflexi, and Planctomycetes) and classes (Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria, Actinobacteria, Anaerolineae, and Planctomycetia) were determined under calcium nitrate and magnesium hydroxide treatments. Functional groups related to aerobic metabolism, including aerobic chemoheterotrophy, dark sulfide oxidation, and correlated dominant genera (Thiobacillus, Lysobacter, Gp16, and Gaiella) became more abundant under calcium nitrate treatment, whereas functional genes potentially involved in dissimilatory sulfate reduction became less abundant. The relative abundance of chloroplasts, fermentation, and correlated genera (Desulfomonile and unclassified Cyanobacteria) decreased under magnesium hydroxide treatment. Overall, these results indicated that calcium nitrate addition improved hypoxia-related reducing conditions in the sediment and promoted aerobic chemoheterotrophy.

Co-culturing of microalgae and bacteria in real wastewaters alters indigenous bacterial communities enhancing effluent bioremediation

Although microalgal–bacterial co-cultures have been largely investigated for nutrient removal, their application in treating real wastewaters is still debatable because effluent systems contain complex bacterial communities that might influence the overall bioremediation. We, therefore, verified the interaction effects of Tetradesmus obliquus IS2–Variovorax paradoxus IS1 co-culture and the native bacterial communities in wastewaters, collected from dairy farm and poultry slaughterhouse, during effluent bioremediation. Co-culturing of the two microbial strains in non-sterile wastewaters alone resulted in significant removal of total N (>92%), PO43−-P (>89%) and COD (>84%) as well as increased production of ROS and neutral lipids, indicating their significant mutualistic interactions with the native bacterial communities for efficient bioremediation of wastewaters. Analysis of 16S rRNA gene-based community data in wastewaters revealed selective enrichment of Firmicutes and Actinobacteria, resulting in enhanced microalgal growth and nutrient removal. The findings of this novel study suggest that microalgal–bacterial co-cultures mediate interspecies interactions for a shift in population dynamics of the indigenous bacteria in wastewaters to facilitate enhanced bioremediation of effluents with sustainable production of biomass and biodiesel.

A Glyphosate-Based Herbicide Cross-Selects for Antibiotic Resistance Genes in Bacterioplankton Communities.

ABSTRACTAgrochemicals often contaminate freshwater bodies, affecting microbial communities that underlie aquatic food webs. For example, the herbicide glyphosate has the potential to indirectly select for antibiotic-resistant bacteria. Such cross-selection could occur if the same genes (encoding efflux pumps, for example) confer resistance to both glyphosate and antibiotics. To test for cross-resistance in natural aquatic bacterial communities, we added a glyphosate-based herbicide (GBH) to 1,000-liter mesocosms filled with water from a pristine lake. Over 57 days, we tracked changes in bacterial communities with shotgun metagenomic sequencing and annotated metagenome-assembled genomes (MAGs) for the presence of known antibiotic resistance genes (ARGs), plasmids, and resistance mutations in the enzyme targeted by glyphosate (enolpyruvyl-shikimate-3-phosphate synthase; EPSPS). We found that high doses of GBH significantly increased ARG frequency and selected for multidrug efflux pumps in particular. The relative abundance of MAGs after a high dose of GBH was predictable based on the number of ARGs in their genomes (17% of variation explained) and, to a lesser extent, by resistance mutations in EPSPS. Together, these results indicate that GBHs can cross-select for antibiotic resistance in natural freshwater bacteria.IMPORTANCE Glyphosate-based herbicides (GBHs) such as Roundup formulations may have the unintended consequence of selecting for antibiotic resistance genes (ARGs), as demonstrated in previous experiments. However, the effects of GBHs on ARGs remain unknown in natural aquatic communities, which are often contaminated with pesticides from agricultural runoff. Moreover, the resistance provided by ARGs compared to canonical mutations in the glyphosate target enzyme, EPSPS, remains unclear. Here, we performed a freshwater mesocosm experiment showing that a GBH strongly selects for ARGs, particularly multidrug efflux pumps. These selective effects were evident after just a few days, and the ability of bacteria to survive and thrive after GBH stress was predictable by the number of ARGs in their genomes and, to a lesser extent, by mutations in EPSPS. Intensive GBH application may therefore have the unintended consequence of selecting for ARGs in natural freshwater communities.

Morphological and physiological response of sour orange (Citrus aurantium L.) seedlings to the inoculation of taxonomically characterized bacterial endophytes

Entophytic bacteria (EBs) are very diverse and found in virtually all plant species studied. These natural EBs live insides the host plant and can be used to maximize crop and fruit yield by exploiting their potential. In this paper, EBs characterization from various citrus genotypes andtheir influence on the morphological and physiological functioning of sour orange (Citrus aurantium) seedlings are described. To assess the influence of 10 distinct EBs, three different techniques (injection, soil mix, and spray) were applied for single and mixed inoculation on sour orange (C. aurantium) seedlings. The selected strains were identified as firmicutes (Enterococcus faecalis, Bacillus safensis, Bacillus cereus, Bacillus megaterium, Brevibacillus borstelensis &Staphylococcus haemolyticus), and gamma Proteobacteria (Enterobacter hormachaei, Proteus mirabilis, Pseudomonas aeruginosa, &Pseudomonas sp.) by 16S rRNA gene sequencing. To investigate the influence of these EBs on host plant morphology, different parameters (morphometric) were recorded after five WOI (weeks of inoculation), including shoot/root length, shoot/root fresh and dry biomass, and biophysical analyses i.e., relative water content (RLWC). Physiological markers such as chlorophyll & carotenoid content, protein content, proline content, phenolics, and flavonoids were also analyzed to determine the influence of endophytes on sour orange seedlings. Five strains such as SM-34, SM-20, SM-36, SM-68, and SM-56 significantly improved the development and physiology of sour orange seedlings. Bacillus cereus and Pseudomonas aeruginosa produced the best outcomes in terms of plant growth. The relative quantification of bacterial inoculums was determined using real-time PCR. A rise in the number of bacterial cells in inoculated treatment suggests that bacterial strains survived and colonized successfully, and also shown their competitiveness with native bacterial community structure. As per the results of inoculation methods,soil mixing, and injection methods were determined to be effective for bacterial inoculation to plants but a variable trend was found for different parameters with test bacterial strains. After testing their impact on field conditions, these strains can be applied as fertilizers as an alternative to conventional chemical fertilizer, although in the context of mixed inoculation of bacterial strains, 5 M and 6 M performed best andenhancedplant growth-promoting activity.

Assessment of the effectiveness of muck-digesting bacterial pellets

Kindervater E, Oudsema M, Hassett MC, Partridge CG, Steinman AD. 2022. Assessment of the effectiveness of muck-digesting bacterial pellets. Lake Reserv Manage. XX:XX–XX. We assessed the ability of Mukk Busster bacterial pellets to decrease organic matter (OM) in lake sediments, as well as their impact on overlying water quality and the native bacterial community composition. Sediment and water from 3 lakes in Newaygo County, Michigan, were incubated for 8 weeks in enclosed tubes with 3 treatments: (1) temperature (ambient or ambient plus 3 C); (2) oxygen level (oxic or anoxic); and (3) pellets (present or absent). We found no statistically significant differences in change in OM between pelleted and control treatments. Sediments were also tested with or without pellets in open bins to include more sediment volume and surface area; again, there was no treatment effect of pellets. OM responses differed among lakes: Irrespective of pellet treatment, there was a slight increase in Hess Lake OM, a significant increase in Brooks Lake OM, and a significant decline in Pickerel Lake OM. We have no definitive explanation for the increases in OM, but because they occurred in both types of experimental containers, we believe the increases were not an artifact. The dominant genera in the bacterial community differed only among lakes, not among the pellet vs. control treatments. Our doses exceeded recommendations (due to the small sediment area used), which the manufacturer claims can change the bacterial composition, but our genetic analysis showed no differences in the flora. We conclude that these pellets are not an effective treatment to reduce sediment OM in these lakes. Supplemental data for this article is available online at https://doi.org/10.1080/10402381.2022.2029635.

Substrate diversity affects carbon utilization rate and threshold concentration for uptake by natural bacterioplankton communities

Persistence of dissolved organic matter (DOM) in aquatic environments may in part be explained by high diversity and low concentrations of carbon substrates. However, changes in dissolved substrate quality can modify aquatic bacterial community composition and rate of carbon uptake. The aim of this study was to test if the presence of multiple simple substrates affects the turnover of organic carbon. Natural bacterial communities were grown in continuous cultures supplied with either individual carbon substrates—salicylic acid (SA), tryptophan (Trp) or tyrosine (Tyr)—or a combination of the 3 substrates. Concentrations were tracked using fluorescence spectroscopy, and steady-state concentrations of a few nanomolar were reached. Bacterial growth efficiency was dependent on which carbon sources were present and reached an intermediate level in the combined treatment. The bacterial community maintained steady-state concentrations of Trp that were lower in the combined treatment than in the individual substrate treatment. In addition, steady-state concentrations were reached faster during growth on combined carbon substrates, although the maximum utilization rate of each individual compound was lower. However, the steady-state concentration of total carbon (sum of carbon content of SA, Trp and Tyr) was higher in the combined culture than in the individual substrate treatments, and seemed to be determined by the carbon substate for which the bacteria had the lowest affinity. The results from this study indicate that persistence of dissolved organic carbon can in part be explained by vast substrate diversity, which raises the threshold concentration for utilization by natural bacterial communities.

Bacterial communities from vagina of dairy healthy heifers and cows with impaired reproductive performance

Vaginal microenvironment plays a significant role in bovine fertility since its resident microorganisms interact with the host mucosa and constitutes the first barrier against ascending pathogens in the reproductive tract. In this study, the vaginal microbiome of healthy heifers (H) and cows with impaired reproductive performance, metritis complex (MT) or repeat breeders (RB), was assessed using a 16S rRNA gene sequencing approach. Analysis revealed that even though a vaginal microbiological guild (Firmicutes, Bacteroidetes, Proteobacteria, Tenericutes, Fusobacteria and Actinobacteria) was shared among healthy heifers and cows with uterine disease; further analysis at genus level showed significant differences depending on the reproductive health status. The relative abundances of recognized uterine pathogens such as Bacteroidetes, Fusobacterium and Helcococcus were higher in MT when compared with H and RB; therefore, their presence in vagina can be considered as a risk factor for fertility. The present study describes for the first time, the composition of native bacterial communities in the vagina of cows undergoing the repeat breeding syndrome (RBS), and reports an association between this disease and the presence of Porphyromonas and unassigned genera of the Pasteurellaceae family. In addition, this work highlights the bacteria associated with a healthy vagina: genera from the families Lachnospiraceae, Rikenellaceae and the genera Acinetobacter, Bacillus, Oscillospira, CF231 and 5-7NS. Results highlighted herein, signify the potential of the evaluation of the bovine vaginal microbiome to future design therapeutic interventions to improve pregnancy rates however, further research is needed to elucidate the balance of bacterial species resulting in an optimal reproductive health.

Bacterial inoculants improved the growth and nitrogen use efficiency of Pyrus betulifolia under nitrogen-limited conditions by affecting the native soil bacterial communities

Increases in crop yield are traditionally supported by the application of high doses of chemical fertilizers, which can have negative environmental impacts on ecosystems. Plant growth-promoting rhizobacteria (PGPR) are increasingly of interest due to their diverse agricultural benefits, but their effects on native soil bacterial communities and their related ecological roles are poorly understood. Currently, high-throughput sequencing provides an opportunity to gain insight into these aspects. The aim of this study was to assess the effects of three PGPR strains (Paenibacillus sp. RF2, Bacillus sp. RC25 and RC3) on the growth of Pyrus betulifolia seedlings under nitrogen (N)-limited conditions and to reveal whether they promote the succession of native soil bacterial communities involved in N supply. Our data showed that all strains significantly enhanced multiple growth parameters of P. betulifolia seedlings, and the strains were ranked in the order RC3 > RF2 > RC25 based on these effects. A similar pattern was also observed for soil urease activity and root vitality. As expected, bacterial inoculants changed the bacterial communities, and increases in the relative abundances of Ideonella, Pseudomonas, Pseudoduganella, Lactococcus and unclassified genera in Rhodocyclaceae and Comamonadaceae were observed with all or two of the inoculation treatments. The predicted results based on PICRUSt2 showed that all inoculation treatments significantly increased the relative abundances of nitrogenase. Furthermore, Ideonella and one unclassified genus in Rhodocyclaceae were mainly associated with nitrogenase and urease, and urease was also related to one unclassified genus in Comamonadaceae and Micropepsis. These results show that the tested strains could change native bacterial communities that take part in the N cycle and improve the N use efficiency of P. betulifolia seedlings under N-limited conditions. The information obtained in this study improves our understanding of the ecological roles of bacterial inoculants and identifies a potential strategy for enhancing the growth of P. betulifolia seedlings and reducing the use of chemical N fertilizer in breeding processes.

Reconstructing large interaction networks from empirical time series data.

Reconstructing interactions from observational data is a critical need for investigating natural biological networks, wherein network dimensionality is usually high. However, these pose a challenge to existing methods that can quantify only small interaction networks. Here, we proposed a novel approach to reconstruct high-dimensional interaction Jacobian networks using empirical time series without specific model assumptions. This method, named "multiview distance regularised S-map," generalised the state space reconstruction to accommodate high dimensionality and overcome difficulties in quantifying massive interactions with limited data. When evaluating this method using time series generated from theoretical models involving hundreds of interacting species, estimated strengths of interaction Jacobians were in good agreement with theoretical expectations. Applying this method to a natural bacterial community helped identify important species from the interaction network and revealed mechanisms governing the dynamical stability of a bacterial community. The proposed method overcame the challenge of high dimensionality in large natural dynamical systems.

Microbial transfers from permanent grassland ecosystems to milk in dairy farms in the Comt\xe9 cheese area

The specificity of dairy Protected Designation of Origin (PDO) products is related to their “terroir” of production. This relationship needs better understanding for efficient and sustainable productions preserving the agroecological equilibrium of agroecosystems, especially grasslands. Specificity of PDO Comté cheese was related to the diversity of natural raw milk bacterial communities, but their sources need to be determined. It is hypothesized that raw milk indigenous microbial communities may originate from permanent grazed grasslands by the intermediate of dairy cows according to the sequence soil–phyllosphere–teat–milk. This hypothesis was evaluated on a 44 dairy farms network across PDO Comté cheese area by characterizing prokaryotic and fungal communities of these compartments by metabarcoding analysis (16S rRNA gene: V3–V4 region, 18S rRNA gene: V7–V8 region). Strong and significant links were highlighted between the four compartments through a network analysis (0.34 < r < 0.58), and were modulated by soil pH, plant diversity and elevation; but also by farming practices: organic fertilization levels, cattle intensity and cow-teat care. This causal relationship suggests that microbial diversity of agroecosystems is a key player in relating a PDO product to its “terroir”; this under the dependency of farming practices. Altogether, this makes the “terroir” even more local and needs to be considered for production sustainability.

Impact of Soil-Applied Microbial Inoculant and Fertilizer on Fungal and Bacterial Communities in the Rhizosphere of Robinia sp. and Populus sp. Plantations

The impact of chemical fertilization on rhizosphere soil communities is a growing concern due to the changes they cause on microbes in soil ecosystems. The present study aims to compare mycorrhizal inoculation and fertilizer applications on bacterial and fungal communities in rhizosphere soil of intensively cultivated Robinia pseudoacacia and Populus × euramericana plantations using the Illumina Miseq sequencing platform. Our results revealed that the different host plants and applied treatments did not significantly affect soil bacterial diversity, but interfered with native rhizosphere bacterial communities in plantation sites. In contrast, host plants and inorganic fertilizer had a strong effect at the family and genus level on the composition of soil fungal communities. In conclusion, our findings suggest that the structure and composition of the fungal community are more sensitive to the nutrient sources in soil than bacteria.

Biodegradation of Ultra-violet Irradiated Waste Polyethylene Bags by Bacterial Community from Soil around Coal -fired Thermal Power Plant

The current study focused on biotic degradation of waste polyethylene bags using bacterial community from hydrocarbon contaminated soil near coal fired thermal power plant and also the effect of UV irradiation on its biodegradation.The predominant groups in the bacterial community in the hydrocarbon contaminated soil near coal fired thermal power plant were identified by 16s DNA sequencing were Steroidobacter, Flavisolibacter, Planctomyces, Balneimonas, Gemmata, Alicyclobacillus, Lactobacillus, Mycobacterium, Geodermatophilus, Prevotella, Virgisporangium and Adhaeribacter. The native bacterial community from hydrocarbon contaminated soil was capable of polyethylene degradation.The bacterial community in the hydrocarbon contaminated soil metabolized 12.85± 0.16 percent of polyethylene (10 g/L) as sole carbon source in mineral salt media within 30 days.The UV irradiation of polyethylene enhanced weight loss of 22.80 percent higher than untreated polyethylene. The improvement in bacterial degradation by UV exposure of waste polyethylene in-vitro for 144 hresulted 15.78± 0.32 percent weight loss in 30 days. The photo-oxidation by UV irradiation of polyethylene had surface disruption and was confirmed by Field Emission Scanning Electron Microscopy (FE-SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The photochemical reaction induced by UV irradiation of polyethylene resulted in formation of carbonyl peaks on polymer surface and addition as well as shifting of peaks. The morphological changes of polyethylene by UV exposure enhanced colonization, metabolism by and synergistic effect on polyethylene biodegradation by bacterial community from hydrocarbon contaminated soil.

Bacterial Community Patterns in the Agaricus bisporus Cultivation System, from Compost Raw Materials to Mushroom Caps.

Different from other fungal species that can be largely cultivated in 'axenic conditions' using plant material (e.g., species of Lentinula and Pleurotus in 'sterile' straw-based substrate), the commercial Agaricus bisporus cultivation system relies heavily on ecological relationships with a broad range of microorganisms present in the system (compost and casing). Since the A. bisporus cultivation system consists of a microbial manipulation process, it is important to know the microbial community dynamics during the entire cultivation cycle to design further studies and/or crop management strategies to optimize this system. To capture the bacterial community 'flow' from compost raw materials to the casing to the formation and maturation of mushroom caps, community snapshots were generated by direct DNA recovery (amplicon sequencing). The 'bacterial community flow' revealed that compost, casing and mushrooms represent different niches for bacteria present in the cultivation system, but at the same time, a bacterial exchange between microenvironments can occur for a portion of the community. Within each microenvironment, compost showed intense bacterial populational dynamics, probably due to the environmental changes imposed by composting conditions. In casing, the colonization of A. bisporus appeared, to reshape the native bacterial community which later, with some other members present in compost, becomes the core community in mushroom caps. The current bacterial survey along with previous results provides more cues of specific bacteria groups that can be in association with A. bisporus development and health.

A novel, scalable, and modular bioreactor design for dynamic simulation of the digestive tract.

In vitro gut model systems permit the growth of gut microbes outside their natural habitat and are essential to the study of gut microbiota. Systems available today are limited by a lack of scalability and flexibility in the mode of operation. Here, we describe the development of a versatile bioreactor module that can be easily adjusted for culture size and capable of sensing and controlling of environmental parameters such as pH control of culture medium, rate of influx and efflux of the culture medium, and aerobic/anaerobic atmosphere. Bioreactor modules can be operated as single units or linked in series to construct a model of a digestive tract with multiple compartments to allow the growth of microbiota in vitro. We tested the growth of synthetic and natural bacterial communities in a multicompartment continuous dynamic culture model simulation of the mammalian gut. The distal compartments of a sterile system inoculated with the synthetic bacterial community at the proximal module attained a stable bacterial density by 24 h, and all the genera present in the inoculum were firmly established in the distal modules simulating the large intestine at 5 days of continuous culture. A natural bacterial community simultaneously inoculated into the distal modules attained a stable bacterial composition at the phylum level by Day 7 of continuous culture. The findings illustrate the utility of the system to culture mixed bacterial communities which can be used to study the collective biological activities of the cultured microbiota in the absence of host influence.

Native Bacterial Community Convergence in Augmented and Stimulated Ureolytic MICP Biocementation.

Microbially induced calcite precipitation is a biomineralization process with numerous civil engineering and ground improvement applications. In replicate soil columns, the efficacy and microbial composition of soil bioaugmented with the ureolytic bacterium Sporosarcina pasteurii were compared to a biostimulation method that enriches native ureolytic soil bacteria in situ under conditions analogous to field implementation. The selective enrichment resulting from sequential stimulation treatments strongly selected for Firmicutes (>97%), with Sporosarcina and Lysinibacillus comprising 60 to 94% of high-throughput 16S rDNA sequences in each suspended community sample. Seven species of the former and two of the latter were present in greater than 10% abundance at different times, demonstrating unexpected within-genus diversity and robustness in the suspended phase of this highly selective environment. Based on longer 16S sequences, it was inferred that augmented S. pasteurii competed poorly with natural bacteria, decreasing to below detection after nine treatments, while the native microbial community was enriched to approximately that present in the stimulated columns. These analyses were corroborated by the observed convergence in bulk ureolytic rates and calcite contents between techniques. However, a 10-fold discrepancy between the observed cell density and an activity-based estimate indicates the attached community, uncharacterized despite efforts, substantially contributes to bulk behavior.

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.