Inoculum Composition Research Articles

Ecological drift during colonization drives within-host and between-host heterogeneity in an animal-associated symbiont.

Specialized host-microbe symbioses canonically show greater diversity than expected from simple models, both at the population level and within individual hosts. To understand how this heterogeneity arises, we utilize the squash bug, Anasa tristis, and its bacterial symbionts in the genus Caballeronia. We modulate symbiont bottleneck size and inoculum composition during colonization to demonstrate the significance of ecological drift, the noisy fluctuations in community composition due to demographic stochasticity. Consistent with predictions from the neutral theory of biodiversity, we found that ecological drift alone can account for heterogeneity in symbiont community composition between hosts, even when 2 strains are nearly genetically identical. When acting on competing strains, ecological drift can maintain symbiont genetic diversity among different hosts by stochastically determining the dominant strain within each host. Finally, ecological drift mediates heterogeneity in isogenic symbiont populations even within a single host, along a consistent gradient running the anterior-posterior axis of the symbiotic organ. Our results demonstrate that symbiont population structure across scales does not necessarily require host-mediated selection, as it can emerge as a result of ecological drift acting on both isogenic and unrelated competitors. Our findings illuminate the processes that might affect symbiont transmission, coinfection, and population structure in nature, which can drive the evolution of host-microbe symbioses and microbe-microbe interactions within host-associated microbiomes.

A landscape-scale field survey demonstrates the role of wheat volunteers as a local and diversified source of leaf rust inoculum

Deploying disease-resistant cultivars is one of the most effective control strategies to manage crop diseases such as wheat leaf rust, caused by Puccinia triticina. After harvest, this biotrophic fungal pathogen can survive on wheat volunteers present at landscape scale and constitute a local source of primary inoculum for the next cropping season. In this study, we characterised the diversity of P. triticina populations surveyed on wheat volunteer seedlings for six consecutive years (2007–2012) at the landscape scale. A total of 642 leaf rust samples classified in 52 virulence profiles (pathotypes) were collected within a fixed 5-km radius. The pathotype composition (identity and abundance) of field-collected populations was analyzed according to the distance between the surveyed wheat plots and to the cultivars of origin of isolates. Our study emphasised the high diversity of P. triticina populations on wheat volunteers at the landscape scale. We observed an impact of cultivar of origin on pathogen population composition. Levels of population diversity differed between cultivars and their deployment in the study area. Our results suggest that wheat volunteers could provide a significant though highly variable contribution to the composition of primary inoculum and subsequent initiation of leaf rust epidemics.

Quantitative differences in synthetic gut microbial inoculums do not affect the final stabilized in vitro community compositions.

In vitro studies of synthetic gut microbial communities (SGMCs) can provide valuable insights into the ecological structure and function of gut microbiota. However, the importance of the quantitative composition of an SGMC inoculum and its effect on the eventual stable in vitro microbial community has not been studied. To address this, we constructed two 114-member SGMCs differing only in their quantitative composition-one reflecting the average human fecal microbiome and another mixed in equal proportions based on cell counts. We inoculated each in an automated anaerobic multi-stage in vitro gut fermentor simulating two different colonic conditions, mimicking proximal and distal colons. We replicated this setup with two different nutrient media, periodically sampled the cultures for 27 days, and profiled their microbiome compositions using 16S rRNA gene amplicon sequencing. While nutrient medium explained 36% of the variance in microbiome composition, initial inoculum composition failed to show a statistically significant effect. Under all four conditions, paired fecal and equal SGMC inoculums converged to reach stable community compositions resembling each other. Our results have broad implications for simplifying in vitro SGMC investigations. IMPORTANCE In vitro cultivation of synthetic gut microbial communities (SGMCs) can provide valuable insights into the ecological structure and function of gut microbiota. However, it is currently not known whether the quantitative composition of the initial inoculum can influence the eventual stable in vitro community structure. Hence, using two SGMC inoculums consisting of 114 unique species mixed in either equal proportions (Eq inoculum) or resembling proportions in an average human fecal microbiome (Fec inoculum), we show that initial inoculum compositions did not influence the final stable community structure in a multi-stage in vitro gut fermentor. Under two different nutrient media and two different colon conditions (proximal and distal), both Fec and Eq communities converged to resemble each other's community structure. Our results suggest that the time-consuming preparation of SGMC inoculums may not be needed and has broad implications for in vitro SGMC studies.

Hydrodynamic disintegration of thickened excess sludge and maize silage to intensify methane production: Energy effect and impact on microbial communities

The aim of this project was to study the combination of two methods to increase methane production: feedstock pretreatment by hydrodynamic disintegration and co-digestion of maize silage (MS) with thickened excess sludge (TES). Disintegration of TES alone resulted in a 15% increase in specific methane production from 0.192 Nml/gVS (TES + MS) to 0.220 Nml/gVS (pretreated TES + MS). The energy balance revealed additional energy (0.14 Wh) would cover only the energy expenditure for the mechanical pretreatment and would not allow for net energy profit. Identification of the methanogenic consortia by 16S rRNA gene amplicon sequencing revealed that Chloroflexi, Bacteroidota, Firmicutes, Proteobacteria and Actinobacteriota were five most abundant bacteria phyla, with Methanothrix and Methanolinea as the dominant methanogens. Principal component analysis did not show any effect of feedstock pretreatment on methanogenic consortia. Instead, the composition of inoculum was the decisive factor in shaping the microbial community structure.

Effect of inoculum composition on the microbial community involved in the anaerobic digestion of sugarcane bagasse

ABSTRACT In anaerobic digestion (AD), the choice of inoculum type seems to be relevant for methane production for complex substrates, such as lignocellulosic material. Previous work demonstrated that the addition of fresh manure and ruminal fluid to anaerobic sludge improved methane productivity and kinetics of AD of crude sugarcane bagasse (CSB). Considering that the improvement of methane production could be a result of a more adapted microbial community, the present study performed the Next Generation Sequencing analysis to identify changes in the microbiome of anaerobic sludge inoculum, resulting from fresh manure and ruminal fluid addition. In comparison with AD performed only with anaerobic sludge inoculum (50:50, U), accumulated methane production was 15% higher with anaerobic sludge plus ruminal fluid inoculum (50:50, UR) and even higher (68%) with anaerobic sludge with fresh bovine manure inoculum (50:50, UFM), reaching the value of 143 NmLCH4.gVS −1. Clostridium species were highly abundant in all inocula, playing an important role during the hydrolysis and fermentation of CSB, and detoxifying potential inhibitors. Microbial composition also revealed the occurrence of Pseudomonas and Anaerobaculum at UFM inoculum that seem to have contributed to the higher methane production rate, mainly due to their hydrolytic and fermentative ability on lignocellulosic substrates. On the other hand, the presence of Alcaligenes might have had a negative effect on methane production due to their ability to perform methane oxidation.

Exploring the phycosphere of Emiliania huxleyi: From bloom dynamics to microbiome assembly experiments.

Coccolithophores have global ecological and biogeochemical significance as the most important calcifying marine phytoplankton group. The structure and selection of prokaryotic communities associated with the most abundant coccolithophore and bloom-forming species, Emiliania huxleyi, are still poorly known. In this study, we assessed the diversity of bacterial communities associated with an E. huxleyi bloom in the Celtic Sea (Eastern North Atlantic), exposed axenic E. huxleyi cultures to prokaryotic communities derived from bloom and non-bloom conditions, and followed the dynamics of their microbiome composition over one year. Bloom-associated prokaryotic communities were dominated by SAR11, Marine group II Euryarchaeota and Rhodobacterales and contained substantial proportions of known indicators of phytoplankton bloom demises such as Flavobacteriaceae and Pseudoalteromonadaceae. The taxonomic richness of bacteria derived from natural communities associated with axenic E. huxleyi rapidly shifted and then stabilized over time. The succession of microorganisms recruited from the environment was consistently dependent on the composition of the initial bacterioplankton community. Phycosphere-associated communities derived from the E. huxleyi bloom were highly similar to one another, suggesting deterministic processes, whereas cultures from non-bloom conditions show an effect of stochasticity. Overall, this work sheds new light on the importance of the initial inoculum composition in microbiome recruitment and elucidates the temporal dynamics of its composition and long-term stability.

Antioxidant properties of water-soluble polysaccharides prepared by co-culture fermentation of straw and shrimp shell.

Herein, we present a method for producing water-soluble polysaccharides (WSPs) by co-culture fermentation of straw and shrimp shells. The chitin-degrading strain was isolated and genotypically identified as the non-pathogen Photobacterium sp. LYM-1 in this study. Photobacterium sp. LYM-1 and Aureobasidium pullulans 2012 could coexist without antagonism. WSPs concentrations were higher in co-culture fermentations of Photobacterium sp. LYM-1 and A. pullulans 2012 (PsL/AP-WSPs) compared to monocultures (PsL-WSPs and AP-WSPs). FTIR was used to examine the polysaccharide properties of three WSP fractions. The monosaccharide compositions of three WSPs fractions were primarily composed of mannose, ribose, glucosamine, glucose, galactose, and arabinose with varying molecular weights and molar ratios according to HPLC analysis. PsL/AP-WSPs showed better scavenging effects on DPPH, ABTS, and OH free radicals, demonstrating the application potential of PsL/AP-WSPs from straw and shrimp shells. The maximum yield obtained under optimum conditions (fermentation time of 6 days, temperature of 31°C, inoculum concentration of 10% (w/v), and inoculum composition of 2:1) was 5.88 ± 0.40 mg/mL, based on the PsL/AP-WSPs production optimization by orthogonal design. The results suggest that an environmentally friendly approach for WSPs production from agro-food wastes straw and shrimp shells was developed.

Intensification of Hydrogen Production by a Co-culture ofSyntrophomonas wolfei and Rhodopseudomonas palustrisEmploying High Concentrations of Butyrate as a Substrate.

The purpose of this study is to present an effective form of developing a sequential dark (DF) and photo (PF) fermentation using volatile fatty acids (VFAs) and nitrogen compounds as bonding components between both metabolic networks of microbial growing in each fermentation. A simultaneous (co-)culture of Syntrophomonas wolfei (with its ability to consume butyrate and produce acetate) and Rhodopseudomonas palustris (that can use the produced acetate as a carbon source) performed a syntrophic metabolism. The former bacteria consumed the acetate/butyrate mixture reducing the butyrate concentration below 2.0g/L, permitting Rhodopseudomonas palustris to produce hydrogen. Considering that the inoculum composition (Syntrophomonas wolfei/Rhodopseudomonas palustris) and the nitrogen source (yeast extract) define the microbial biomass specific productivity and the butyrate consumption, a response surface methodology defined the best inoculum design and yeast extract (YE) yielding to the highest biomass concentration of 1.1g/L after 380.00h. A second culture process (without a nitrogen source) showed the biomass produced in the previous culture process yields to produce a total cumulated hydrogen concentration of 3.4 mmol. This value was not obtained previously with the pure strain Rhodopseudomonas palustris if the culture medium contained butyrate concentration above 2.0g/L, representing a contribution to the sequential fermentation scheme based on DF and PF.

Selection, composition, and validation of standard inoculum for anaerobic digestion assays

The inoculum is the initial source of microorganisms for the anaerobic digestion (AD). An active inoculum aids the success of organic matter degradation experiments. Enrichment and acclimation strategies have been studied in search of more efficient tests. The present study aimed to compose an active anaerobic mesophilic inoculum in the laboratory for test standardization. For this purpose, inoculums from different sources available in the study region, such as digested cattle manure (DCM), digested sewage sludge (DSS), digested food waste (DFW), digested swine manure (DSM), fresh cattle manure (FCM), cattle rumen (CR) and some compositions between them were tested in Biochemical methane potential (BMP) assays with microcrystalline cellulose as reference substrate, in addition to fruit and vegetable waste (FVW). The inoculums originated from anaerobic processes showed a greater aptitude for the AD process, being the mixture of DFW, DSM and DCM (Mix 4) presented an abundance of the genus of bacteria DMER64 and Archaeas Methanosaeta, greater production of biogas for the reference substrate, and greater production of biogas and methane for FVW. The aptitude control tests demonstrated that the maintenance of the laboratory reactor with Mix 4 inoculum was efficient. It was evident that the characteristics of inoculum can vary from one collection to another, which validates the fact that the maintenance of an active anaerobic mesophilic inoculum in the laboratory is essential for carrying out AD experiments with standardized and reliable results.

Improving the efficacy of potato clonal micropropagation by inoculation with the rhizosphere bacteria Azospirillum baldaniorum Sp245 and Ochrobactrum cytisi IPA7.2.

Sustainable development of agriculture depends on the provision of quality seeds to the market. Inoculation with plant-growth-promoting rhizobacteria in in vitro culture can be used to improve the growth eff icacy and performance of microplants. We examined the effect of in vitro inoculation of microplants of the cultivars Nevsky and Kondor with the strains Azospirillum baldaniorum Sp245 and Ochrobactrum cytisi IPA7.2 separately and in combination. We examined the morphological variables of plant growth in in vitro culture and under ex vitro adaptation conditions; we also investigated the growth and performance of the plants in the greenhouse. The dependence of the inoculation eff icacy on potato genotype, growth stage, and inoculum composition was ascertained throughout the experiment. In vitro, A. baldaniorum Sp245 alone and in combination with O. cytisi IPA7.2 promoted the formation of roots on the microplants of both cultivars and the growth of Nevsky shoots. During plant growth ex vitro, all growth variables of the Nevsky microplants were promoted by O. cytisi IPA7.2 alone and in combination with A. baldaniorum Sp245. In both cultivars grown in the greenhouse, shoot growth was promoted in most inoculation treatments. The survival ability of the Nevsky microplants in the greenhouse increased 1.7-fold under the effect of simultaneous inoculation. Inoculation of microplants with a combination of A. baldaniorum Sp245 and O. cytisi IPA7.2 increased the number of Nevsky minitubers 1.5-fold and the number of Kondor minitubers 3.5-fold. Inoculation with the tested strains can be used to promote the growth of microplants and increase the yield of minitubers in potato seed breeding for the production of healthy planting material.

Coculturing of Mucor plumbeus and Bacillus subtilis bacterium as an efficient fermentation strategy to enhance fungal lipid and gamma-linolenic acid (GLA) production

This study aimed to improve lipid and gamma-linolenic acid (GLA) production of an oleaginous fungus, Mucor plumbeus, through coculturing with Bacillus subtilis bacteria, optimising the environmental and nutritional culture conditions, and scaling them for batch fermentation. The maximum levels of biomass, lipid, fatty acid, and GLA in a 5 L bioreactor containing cellobiose and ammonium sulfate as the optimal carbon and nitrogen sources, respectively, achieved during the coculturing processes were 14.5 ± 0.4 g/L, 41.5 ± 1.3, 24 ± 0.8, and 20 ± 0.5%, respectively. This strategy uses cellobiose in place of glucose, decreasing production costs. The nutritional and abiotic factor results suggest that the highest production efficiency is achieved at 6.5 pH, 30 °C temperature, 10% (v/v) inoculum composition, 200 rpm agitation speed, and a 5-day incubation period. Interestingly, the GLA concentration of cocultures (20.0 ± 0.5%) was twofold higher than that of monocultures (8.27 ± 0.11%). More importantly, the GC chromatograms of cocultures indicated the presence of one additional peak corresponding to decanoic acid (5.32 ± 0.20%) that is absent in monocultures, indicating activation of silent gene clusters via cocultivation with bacteria. This study is the first to show that coculturing of Mucor plumbeus with Bacillus subtilis is a promising strategy with industrialisation potential for the production of GLA-rich microbial lipids and prospective biosynthesis of new products.

Establishment and characterization of stable, diverse, fecal-derived in vitro microbial communities that model the intestinal microbiota

Efforts to probe the role of the gut microbiota in disease would benefit from a system in which patient-derived bacterial communities can be studied at scale. We addressed this by validating a strategy to propagate phylogenetically complex, diverse, stable, and highly reproducible stool-derived communities invitro. We generated hundreds of invitro communities cultured from diverse stool samples in various media; certain media generally preserved inoculum composition, and inocula from different subjects yielded source-specific community compositions. Upon colonization of germ-free mice, community composition was maintained, and the host proteome resembled the host from which the community was derived. Treatment with ciprofloxacin invivo increased susceptibility to Salmonella invasion invitro, and the invitro response to ciprofloxacin was predictive of compositional changes observed invivo, including the resilience and sensitivity of each Bacteroides species. These findings demonstrate that stool-derived invitro communities can serve as a powerful system for microbiota research.

Towards a Standardized Procedure for the Production of Infective Spores to Study the Pathogenesis of Dermatophytosis.

Dermatophytoses are superficial infections of human and animal keratinized tissues caused by filamentous fungi named dermatophytes. Because of a high and increasing incidence, as well as the emergence of antifungal resistance, a better understanding of mechanisms involved in adhesion and invasion by dermatophytes is required for the further development of new therapeutic strategies. In the last years, several in vitro and in vivo models have emerged to study dermatophytosis pathogenesis. However, the procedures used for the growth of fungi are quite different, leading to a highly variable composition of inoculum for these models (microconidia, arthroconidia, hyphae), thus rendering difficult the global interpretation of observations. We hereby optimized growth conditions, including medium, temperature, atmosphere, and duration of culture, to improve the sporulation and viability and to favour the production of arthroconidia of several dermatophyte species, including Trichophyton rubrum and Trichophyton benhamiae. The resulting suspensions were then used as inoculum to infect reconstructed human epidermis in order to validate their ability to adhere to and to invade host tissues. By this way, this paper provides recommendations for dermatophytes culture and paves the way towards a standardized procedure for the production of infective spores usable in in vitro and in vivo experimental models.

The microbial composition of the initial insult can predict the prognosis of experimental sepsis

We hypothesized that the composition of sepsis-inducing bacterial flora influences the course of fecal peritonitis in rodents. Saline or fecal suspensions with a standardized dose range of bacterial colony-forming units (CFUs) were injected intraperitoneally into Sprague–Dawley rats. The qualitative composition of the initial inoculum and the ascites was analyzed separately by MALDI-TOF mass spectrometry. Invasive monitoring was conducted in separate anesthetized groups (n = 12–13/group) after 12, 24, 48 and 72 h to determine rat-specific organ failure assessment (ROFA) scores. Death and ROFA scores peaked at 24 h. At this time, 20% mortality occurred in animals receiving a monomicrobial E. coli suspension, and ROFA scores were significantly higher in the monomicrobial subgroup than in the polymicrobial one (median 6.5; 5.0–7.0 and 5.0; 4.75–5.0, respectively). ROFA scores dropped after 48 h, accompanied by a steady decrease in ascites CFUs and a shift towards intra-abdominal monomicrobial E. coli cultures. Furthermore, we found a relationship between ascites CFUs and the evolving change in ROFA scores throughout the study. Hence, quantitatively identical bacterial loads with mono- or polymicrobial dominance lead to a different degree of sepsis severity and divergent outcomes. Initial and intraperitoneal microbiological testing should be used to improve translational research success.

Comprehensive evaluation of starter culture impact on the bioreactor performance and microbial kinetics

The present study investigated the disregarded impact of microbial community composition, diversity and abundance of the starter biomass on lab-scale bioreactor performance, steady-state long time operation, biodegradation outcome and microbial kinetics. Standard lab-scale experiments are usually initiated with inoculum taken from wastewater treatment plants (WWTPs) without considering microbial community composition. Two identical sequencing batch bioreactors (SBR-1, SBR-2) were operated with inocula obtained from two domestic WWTPs to assess the role of inoculum composition on reactor performance and treatment efficacy. Filamentous microorganisms were dominated in SBR-1 (SVI: 265 mL/g), whereas their supremacy was diminished in SBR-2 (SVI: 160 mL/g). Next generation sequencing analyses verified high abundance of Candidatus Microthrix (14%) and Kouleothrix spp. (3%) in SBR-1. Although Chloroflexi C10-SB1A metagenome accounted for 16% of WWTP-2 community, SBR-2 was operated at steady-state for longer period without deterioration. Statistical indicators based on molecular studies showed that WWTP-2 has higher diversity than WWTP-1. Higher biodiversity in WWTP-2 community supported the stable process performance. Modelling studies denoted an increase in half saturation coefficients (Ks) in filamentous microorganisms dominated reactor. The results of this study provide insight on how the filamentous organisms typically found in WWTPs become a fundamental constituent during the bioreactor operation.

Proteomic analysis reveals how pairing of a Mycorrhizal fungus with plant growth-promoting bacteria modulates growth and defense in wheat.

Plants rely on their microbiota for improving the nutritional status and environmental stress tolerance. Previous studies mainly focused on bipartite interactions (a plant challenged by a single microbe), while plant responses to multiple microbes have received limited attention. Here, we investigated local and systemic changes induced in wheat by two plant growth-promoting bacteria (PGPB), Azospirillum brasilense and Paraburkholderia graminis, either alone or together with an arbuscular mycorrhizal fungus (AMF). We conducted phenotypic, proteomic, and biochemical analyses to investigate bipartite (wheat-PGPB) and tripartite (wheat-PGPB-AMF) interactions, also upon a leaf pathogen infection. Results revealed that only AMF and A. brasilense promoted plant growth by activating photosynthesis and N assimilation which led to increased glucose and amino acid content. The bioprotective effect of the PGPB-AMF interactions on infected wheat plants depended on the PGPB-AMF combinations, which caused specific phenotypic and proteomic responses (elicitation of defense related proteins, immune response and jasmonic acid biosynthesis). In the whole, wheat responses strongly depended on the inoculum composition (single vs. multiple microbes) and the investigated organs (roots vs. leaf). Our findings showed that AMF is the best-performing microbe, suggesting its presence as the crucial one for synthetic microbial community development.

Effect of polymer type on the colonization of plastic pellets by marine bacteria

Plastic is omnipresent in the oceans and serves as surface for biofilm-forming microorganisms. Plastic debris comprises different polymers, which may influence microbial colonization and here, we evaluated if polymer type affects bacterial biofilm formation. Quantifying the biofilm on polyethylene (PE), polypropylene (PP) or polystyrene (PS) pellets by six marine bacterial strains (Vibrio, Pseudoalteromonas, Phaeobacter) demonstrated that each strain had a unique colonization behavior with either a preference for PS or PP over the other polymer types or no preference for a specific plastic type. PE, PP, and PS pellets were exposed to natural seawater microbiota using free-living or total communities as inoculum. Microbial assembly as determined by 16S rRNA (V4) amplicon sequencing was affected by the composition of the initial inoculum and also by the plastic type. Known polymer and hydrocarbon degraders such as Paraglaciecola, Oleibacter, and Hydrogenophaga were found in the plastic biofilms. Thus, on a community level, bacterial colonization on plastic is influenced by the microorganisms as well as the polymer type, and also individual strains can demonstrate polymer-specific colonization.

Yeast and bacteria co-culture-based lipid production through bioremediation of palm oil mill effluent: a statistical optimization

In the present study, a co-culture of yeast (Lipomyces starkeyi) and bacterium (Bacillus cereus) was used to optimize lipid accumulation capability and simultaneous treatment of wastewater using palm oil mill effluent (POME) as a carbon source. The influence of process parameters (i.e., inoculum composition, pH, temperature, and time) on the lipid accumulation and the chemical oxygen demand (COD) removal were optimized using design of experiments (DoE) as a statistical tool. The DoE results suggested that the maximum lipid accumulation of 2.95 g/L and COD removal efficiency of 86.54% could be obtained while the inoculum composition, pH, temperature, and incubation time were 50:50, 6.50, 32.5 ??C, and 90 h, respectively. The predicted results were very close to the experimental results (<???5% deviation); hence, the proposed model could be useful to predict the lipid accumulation and COD removal performance of a yeast and bacteria co-culture.

54 Substrate and inoculum composition affect in vitro model of ruminal acidosis

Abstract The objective was to create an in vitro model of ruminal acidosis. Ruminal acidosis is a prevalent metabolic disorder in beef feedlot cattle characterized by low rumen pH. Experiment 1 was a 3×3 factorial design testing the interaction between inoculum composition and quantity of substrate. Eighteen flasks containing 150 mL of inoculum were used to evaluate treatments in duplicate. Treatments evaluated inoculum ratios (buffer: rumen fluid) 2:1, 4:1, and 6:1 in combination with substrate levels 5 g, 7.5 g, and 10 g. Manual pH was collected every 4 h for 36 h. Experiment 2 was a completely randomized design with 5 treatments evaluated in triplicate. Treatments consisted of a 4:1 inoculum ratio (150 mL) with the substrate (7.5 g) consisting of 70% corn (PCON), 40% corn (NCON), or increasing inclusions (10, 20, and 30%) of wheat in place of corn (W10, W20, and W30). Flasks were incubated at 39°C for 36 h with continual pH measurement. In exp. 1, 7.5 g of substrate remained between a pH of 5.6 and 5.0 (P ≤ 0.01) for a longer period (880 min) than 10 g of substrate (520 min). In experiment 2, a treatment by time interaction (P ≤ 0.05) was observed for pH with NCON having the greatest pH over 8-36 h and PCON having the lowest pH over 4-8 h. A treatment by time interaction (P = 0.02) was observed for lactate at 20 h with PCON having the greatest and W30 having the lowest concentration. Treatment PCON had the greatest (P &amp;lt; 0.01) acetate and propionate concentration. The W20 treatment remained between a pH of 5.6 and 5.0 (P &amp;lt; 0.01) for a longer period than PCON. Results suggest W20 and PCON may be the most useful in vitro models of ruminal acidosis.

Variability of arbuscular mycorrhizal fungal communities within the root systems of individual plants is high and influenced by host species and root phosphorus

The spatial distribution of arbuscular mycorrhizal (AM) fungal communities has been studied at many scales, from global to local, but few studies have explored variation within the root system of individual plants. Spatial variation within root systems might be expected partly due to differences in the physiology, morphology and anatomy of different roots, as well as due to spatial variation in the composition of inoculum in soil. Here, we assessed AM fungal community variability at various local scales: within individual plant root systems and among plants separated by distances of a few centimetres to up to several metres. To do so, we sampled roots from four plant species (two grasses and two forbs) growing in a grassland experiencing experimentally altered rainfall patterns in replicated field plots. We found that AM fungal communities were highly dissimilar both within the same individual and among different plants. Communities sampled within the same root system were as dissimilar as those sampled from adjacent neighbours, but less dissimilar from those sampled at larger distances. The degree of within root system variability was as high for each watering treatment but varied among plant species in a way that was dependent on root phosphorus content. Overall, our results show that community dissimilarity levels are high even within the root systems of individual plants, possibly due to localised community assembly processes (e.g., priority effects and interactions among AM fungal species), but that the degree of homogenisation within a root system is partly dependent on host plant attributes.