Reduction In Microbial Activity Research Articles

Effects of biodegradation of starch-nanocellulose films incorporated with black tea extract on soil quality

This study aimed to investigate the biodegradation behaviour of starch/nanocellulose/black tea extract (SNBTE) films in a 30-day soil burial test. The SNBTE films were prepared by mixing commercial starch, nanocellulose (2, 4, and 6%), and an aqueous solution of black tea extract by a simple mixing and casting process. The chemical and morphological properties of the SNBTE films before and after biodegradation were characterized using the following analytical techniques such as field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and fourier transform infrared (FTIR). The changes in soil composition, namely pH, electrical conductivity (EC), moisture content, water holding capacity (WHC), soil respiration, total nitrogen, weight mean diameter (MDW), and geometric mean diameter (GMD), as a result of the biodegradation process, were also estimated. The results showed that the films exhibited considerable biodegradability (35–67%) within 30 days while increasing soil nutrients. The addition of black tea extract reduced the biodegradation rate due to its polyphenol content, which likely resulted in a reduction in microbial activity. The addition of nanocellulose (2–6% weight of starch) increased the tensile strength, but decreased the elongation at break of the films. These results suggest that starch nanocellulose and SNBTE films are not only biodegradable under soil conditions but also positively contribute to soil health, highlighting their potential as an environmentally friendly alternative to traditional plastic films in the packaging industry.

Quality changes in high hydrostatic pressure treated enriched tomato sauce.

Use of high hydrostatic pressure (HHP) with reduced processing times is gaining traction in the food industry as an alternative to conventional thermal treatment. In order to enhance functional benefits while minimizing processing losses, functionalized products are being developed with such novel techniques. In this study, changes in quality parameters for HHP treated enriched tomato sauce were evaluated, with the aim to assess its viability as an alternative to conventional thermal treatment methods. HHP treatments at 500 MPa, 30 °C/50 °C significantly increased the total phenolic and lycopene content of the sauce samples, achieving 6.7% and 7.5% improvements over conventionally treated samples. The antioxidant capacity of the HHP-treated samples was also found to match or be better than conventionally treated samples. Furthermore, a T2 relaxation time study revealed that pressure-temperature processing treatments were effective in maintaining the structural integrity of water molecules. Microbiological analyses revealed that 500 MPa/50 °C 5 min treatment can offer 8 logs reduction colony formation, matching the results of conventional thermal treatment. Combined pressure-temperature treatments improve results, reduce time consumption. 500 MPa/50 °C treatments provided retention of quality parameters and significant reduction in microbial activity. © 2024 The Author(s). Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Analysis of Degradability of Blackberry (Rubus glaucus) Subjected to Different Storage Conditions

The purpose of this study was to assess how different storage conditions and types of containers affect blackberries (Rubus Glaucus), fruits that are particularly susceptible to post-harvest deterioration. Comparisons were made between two temperature conditions: room temperature (19 °C) and refrigeration (4 °C), and three types of container materials: low-density polyethylene (LDPE), polypropylene (PP), and polylactic acid (PLA). The findings indicated that refrigeration is the most effective strategy for maintaining the quality of blackberries during storage. This method significantly preserved the weight and stability of the fruit, with PLA standing out in this respect. Additionally, a considerable reduction in microbial activity was observed under refrigeration, with LDPE proving to be the most effective at inhibiting mold growth. These results underscore the importance of properly controlling both temperature and container materials type to extend shelf life and preserve the quality of blackberries, which is crucial not only for the food industry, where maintaining freshness and flavor is imperative, but also for consumers who seek high-quality fruit products.

Enhancing Escherichia coli Inactivation: Synergistic Mechanism of Ultraviolet Light and High-Voltage Electric Field.

This study investigated the bactericidal effects of ultraviolet (UV) radiation, a high-voltage electric field (HVEF), and their combination on Escherichia coli. The results indicated that UV and combined disinfection were more effective with longer exposure, leading to significant reductions in microbial activity. Specifically, the single UV disinfection alone reduced activity by 3.3 log after 5 min, while combined disinfection achieved a 4.2 log reduction. In contrast, short-term HVEF treatment did not exhibit significant bactericidal effects, only achieving a reduction of 0.17 log in 5 min. Furthermore, prolonged exposure to both UV disinfection and an HVEF was found to damage cell membranes, ultimately causing cell death, while shorter durations did not. Despite rapid cell count decreases, flow cytometry did not detect apoptotic or necrotic cells, likely due to rapid cell rupture. This study suggests that combining UV radiation and an HVEF could be a promising approach for inhibiting bacterial reproduction, with HVEF enhancing UV effects. These findings provide insights for using combined HVEF and UV disinfection in food safety and preservation.

Comprehensive experimental study of microbial respiration during self-heating in biomass storage piles

As a critical renewable energy source, biomass has substantial potential for reducing carbon emissions and promoting sustainable development. However, its long-term storage in large volumes for modern bioenergy poses challenges due to inherent self-heating driven by exothermic microbial, physical and chemical processes, which can lead to spontaneous ignition and severe fire incidents. While physical and chemical aspects of self-heating in biomass piles greatly benefit from extensive research and experience borrowed from coal pile self-heating, microbial activities in biomass self-heating have received less attention. To address this knowledge gap, we conduct a series of comprehensive studies to gain a deeper understanding of microbial activities in biomass self-heating, aiming to develop a numerical model for reliably predicting biomass self-heating and minimizing fire risks in stored biomass. This paper presents the results of our experimental investigation into microbial respiration during biomass storage. Six commonly used biomass feedstocks with varying initial moisture content are subjected to different storage conditions over a seven-day testing period, during which the main metabolic byproduct (CO2) released from microbial degradation of the biomass is continuously measured. Our findings reveal that an increase in feedstock moisture content significantly enhances microbial activity when the initial moisture content is below 136 %. However, further increases in initial moisture content do not notably enhance, and in some cases, may even weaken microbial activity. Additionally, a temperature range of 25 °C to 45 °C is identified as conducive to rapid microbial decomposition for different biomass materials, and deviation from this range results in a significant reduction in microbial activity. Furthermore, under identical temperature and initial moisture content conditions, the order of carbon dioxide evolution rate is as follows: corn stalk > soybean hull > rice straw > wheat straw > cotton stalk > pepper stalk. Our respiration intensity test results also create a fundamental experimental database for model development and validation, and contribute to the broader understanding of biomass storage and its associated challenges.

Seasonal soil moisture thresholds inhibit bacterial activity and decomposition during drought in a tallgrass prairie

Soil moisture reductions during drought often inhibit soil microbial activity and inhibit decomposition rates by reducing microbial biomass or by altering microbial communities. Evidence suggests that soil water must drop below a critical threshold to inhibit microbial activity. Thus, it is likely that the seasonal timing of drought will determine the extent to which belowground processes are adversely impacted by drought. Specifically, the effects of drought might be minimal during cool, wet periods typical of late spring but dramatic during hot summer months with high evapotranspiration rates that lower soil moisture levels below the critical threshold. Here, we present results from a study designed to quantify the effect of drought on soil microbial abundance, community composition, and soil water diffusion across four months, and to then assess how drought impacts the microbial decomposition of leaf matter. We imposed a season‐long drought in a Wisconsin tallgrass prairie and measured soil moisture, bacterial composition and abundance, microbial respiration, and decomposition rates throughout the growing season. Bacterial communities varied considerably among dates, but drought did not affect either bacterial abundance or community composition. Microbial respiration declined significantly during periods of drought when soil pores likely became hydrologically isolated, ultimately reducing cumulative microbial respiration by 10%. The reduction in microbial activity in drought treatments caused a 50% decline in the decomposition of refractory material. Our study highlights that sublethal effects of drought on microbial communities, occurring only when soil moisture declined below a tolerance threshold, can have large impacts on microbial carbon release or decomposition, highlighting the need to incorporate such measures into future studies.

Shifts in bacterial traits under chronic nitrogen deposition align with soil processes in arbuscular, but not ectomycorrhizal-associated trees.

Nitrogen (N) deposition increases soil carbon (C) storage by reducing microbial activity. These effects vary in soil beneath trees that associate with arbuscular (AM) and ectomycorrhizal (ECM) fungi. Variation in carbon C and N uptake traits among microbes may explain differences in soil nutrient cycling between mycorrhizal associations in response to high N loads, a mechanism not previously examined due to methodological limitations. Here, we used quantitative Stable Isotope Probing (qSIP) to measure bacterial C and N assimilation rates from an added organic compound, which we conceptualize as functional traits. As such, we applied a trait-based approach to explore whether variation in assimilation rates of bacterial taxa can inform shifts in soil function under chronic N deposition. We show taxon-specific and community-wide declines of bacterial C and N uptake under chronic N deposition in both AM and ECM soils. N deposition-induced reductions in microbial activity were mirrored by declines in soil organic matter mineralization rates in AM but not ECM soils. Our findings suggest C and N uptake traits of bacterial communities can predict C cycling feedbacks to N deposition in AM soils, but additional data, for instance on the traits of fungi, may be needed to connect microbial traits with soil C and N cycling in ECM systems. Our study also highlights the potential of employing qSIP in conjunction with trait-based analytical approaches to inform how ecological processes of microbial communities influence soil functioning.

PMo12 as a redox mediator for bio-reduction of Cr(VI): Promotor or inhibitor?

Slow reduction rate and low reduction ability were the main limitations of bio-reduction of Cr(VI). As an efficient redox mediator, how phosphomolybdic acid (PMo12) affected bio-reduction of Cr(VI) was worthy of exploration. In this study, short-term and long-term effects of PMo12 on Cr(VI) reduction were investigated to reveal the relevant mechanism. After evaluating the short-term effect of PMo12 concentration from 0.05 to 1.00 mM on Cr(VI) bio-reduction, 0.50 mM was found to be optimum by improving Cr(VI) reduction rate by 16.3 % and microbial electron transport system activity (ETSA) by 43.0 % with Cr(VI) reduction efficiency of 100 % in short-term (22 h) batch experiments. By contrast, in long-term (28 days) continuous flow experiments, 0.50 mM PMo12 exhibited serious inhibition on Cr(VI) bio-reduction. The cumulative toxicity of Mo, strong oxidative stress (reactive oxygen species increased by 16.5 %), the inhibition of extracellular polymeric substances production and the reduction of microbial activity were proved to be the main inhibition mechanism. In terms of microbial electron transport system, the main electron carriers including flavin mononucleotide (FMN), nitrate reductase (NAR), nitrite reductase (NIR) were seriously inhibited. BugBase analysis confirmed that the relative abundance of biofilm forming bacteria decreased after PMo12 addition, and the relative abundance of oxidative stress tolerance bacteria continued to increase.

Cooperation of heterotrophic bacteria enables stronger resilience of halophilic assimilation biosystem than nitrification system under long-term stagnation

Long-term stagnation of biosystems (with no or very little wastewater) owing to seasonal downtime or failure maintenance brings great challenges to the performance recovery after system restart. In particular, the reduction of microbial activity and change of dissolved organic matter (DOM) affect the effluent quality and subsequent treatment procedures. Monitoring the dynamics and resilience of biosystems after long-term stagnation is important to formulate targeted countermeasures for system stability. However, the influence of long-term stagnation on autotrophic nitrification (AN) and heterotrophic assimilation (HA) biosystems has not been systematically explored. Here, we used halophilic AN and HA systems to study the stability and resilience of two nitrogen removal consortia after long-term stagnation. The results showed that 97.5 % and 93 % of ammonium and 47.0 % and 90.1 % of total nitrogen were removed using the halophilic AN and HA systems, respectively, in the stable period. After four weeks of stagnation, the HA system showed stronger resilience than AN system, in terms of faster recovery of treatment performance, and less fluctuations in sludge settleability and extracellular polymeric substances. In addition, after the stagnation period, the DOM of AN system was rich in low-molecular refractory humic acid, whereas that of HA system was rich in high-molecular proteins. The stagnation period led to the replacement of the dominant heterotrophic functional microorganisms, Paracoccus and Halomonas, with Muricauda and Marinobacterium in the HA system. The microbial network results revealed that the cooperation of heterotrophic bacteria enables stronger resilience of the HA system from prolonged stagnation than the AN system. In addition, the nitrogen removal efficiency, protein to polysaccharide ratio of EPS and fluorescence intensity of DOM were significantly correlated with the microbial community composition. These results suggest that AN system has greater risks in terms of treatment performance and sludge stability than the system after long-term stagnation.

The gut microbiome may influence post-prandial nitrogen handling in an elasmobranch, the Pacific spiny dogfish (Squalus suckleyi)

Nitrogen recycling through the gut microbiome is an important mechanism used throughout vertebrates to reclaim valuable nitrogen trapped in urea. Evidence suggests it may be especially important in nitrogen limited animals, yet little is known about its role in marine elasmobranchs, which are said to be severely nitrogen limited. In the present study we used antibiotics to deplete the gut microbiome of Pacific spiny dogfish and assessed the role of the microbiome in nitrogen handling in both fed and fasted states. In fed animals, antibiotic treatment eliminated the activity of the microbial enzyme urease and reduced cellulase activity by 78%. This reduction in microbial enzyme activity resulted in significantly lower plasma urea levels which then trended upward as urea excretion rates decreased. Ammonia excretion rates were also significantly lower in antibiotic treated fish compared to the control fed. Finally, antibiotic treated fed individuals lost an average of 7.4% of their body mass while the fed controls lost only 1.8% of their body mass. Nitrogen handling in fasted animals was not significantly impacted by a reduction in microbial activity. These results suggest that compromising the gut microbiome significantly influences post-prandial nitrogen handling in spiny dogfish, and that the recycling of urea‑nitrogen may be vital to maintaining nitrogen balance in these fish.

Transformation of inherent microorganisms in Wyoming-type bentonite and their effects on structural iron

Bentonite is one of the materials used to construct engineered barriers in high-level radioactive nuclear waste geological disposal with its many advantageous features such as low hydraulic conductivity, self-sealing ability, durability, adsorption and immobilization of metals and radionuclides and reduction of microbial activity. Many of these properties are linked with the bentonite swelling capability. Transformations of indigenous microorganism communities from Wyoming-type bentonite and the Finnish repository site groundwater and their effects on the bentonite structural iron over five years were studied in repository relevant anoxic and oxic slurry conditions. Active sulfate reduction (0.06 nmol mL−1 day−1) was detected in the anoxic microcosm waters after a year, however after two years sulfate reduction was not active anymore. Microbial numbers determined by quantitative PCR in the bentonite slurry of both experiment types supported the finding of decrease of overall microbial activity after a year of incubation that was not maintained anymore by the dissolving organic carbon from the bentonite. Regular electron donor additions (final concentration of 2 mM for formate and acetate each, three times per year) activated the microbiome resulting in increasing numbers of bacterial 16S rRNA gene copies and sulfate reducers (dsrB gene copies) as well as detection of sulfide in the water phase of both experiment types. After 4.9 years the structural iron in the fine portion of the montmorillonite had become completely reduced in all microbial microcosms and minor smectite illitization was detected especially in anoxic microcosms. Dominating bacterial groups at the end of the experiment were mainly known sulfur/sulfate and iron reducers. Archaea and fungi constituted a minor part of the microbiomes. In originally oxic microcosms, the bacterial 16S RNA and dsrB gene copy numbers were lower than in the anoxic experiment but started to significantly increase after the electron donor additions. Microorganisms originating from the repository environment could reduce the bentonite structural iron in a few years to an extent likely to affect the bentonite swelling ability if sufficient amounts of suitable electron donors are available in localized areas where bentonite is not at high density and pressure in the geological disposal.

Urban soil microbial community and microbial-related carbon storage are severely limited by sealing

PurposeUrbanisation causes changes in land use, from natural or rural to urban, leading to the sealing of soil and the replacement of vegetation by buildings, roads and pavements. The sealing process impacts soil properties and services and can lead to negative consequences for microbial attributes and processes in soil. At present, information about the microbial community following soil sealing is limited. As such, we investigated how changes in soil physical and chemical properties caused by sealing affect the soil microbial community and soil ecosystem services.Material and methodsSoils were sampled beneath impervious pavements (sealed) and from adjacent pervious greenspace areas (unsealed). Soil properties (total C, total N, C:N ratio and water content) and microbial attributes (microbial biomass C, N-mineralisation and phospholipid fatty acids—PLFA) were measured and correlated.Results and discussionA reduction of total C, total N, and water content were observed in sealed soil, whilst the C:N ratio increased. Sealed soil also presented a reduction in microbial attributes, with low N-mineralisation revealing suppressed microbial activity. PLFA data presented positive correlations with total C, total N and water content, suggesting that the microbial community may be reduced in sealed soil as a response to soil properties. Furthermore, fungal:bacterial and gram-positive:gram-negative bacterial ratios were lower in sealed soil indicating degradation in C sequestration and a consequential effect on C storage.ConclusionsSealing causes notable changes in soil properties leading to subsequent impacts upon the microbial community and the reduction of microbial activity and soil C storage potential.

Developing a method for measurement of dehydrogenase activity in biological wastewater treatment processes applied for toxic compounds degradation

Biological wastewater treatment processes are among the environmentally friendly techniques for degradation of organic compounds. They are also preferred to the physical and chemical processes which are due to the ability of biological processes to treat wide range of organic compounds with lower operational costs. However, biological processes are usually affected by variation in the inlet wastewater quality and quantity. In order to investigate the performance of the wastewater treatment plant, various parameters in case of effluent quality such as COD, BOD, TSS, TDS etc. are required to be measured. Microorganisms in bioreactors use various enzymes to degrade the organic contaminants. Higher toxic organic load on the biological process may lead to the deterioration of the process performance which is due to the reduction in microbial activity of the biomass. Dehydrogenase enzyme produced in biological processes could be used as an indicator for the biological wastewater treatment. Present study introduces a simple and modified method for evaluation of biological wastewater treatment process measuring dehydrogenase activity. In the present study, the effective parameters such as incubation time and types of solvent were investigated and the best procedure is developed for measuring the dehydrogenase activity in biological wastewater treatment process.

Inhibitory action of thymol on fecal microbial activity in Tamandua tetradactyla and its effect on glucocorticoid metabolite measurement

Faecal glucocorticoid measurement is a potentially important tool for improving wildlife conservation, but its use is still limited by methodological issues including the need to avoid modifications of steroids by faecal microorganisms during storage. The freezing of faeces is recommended as a means of avoiding such alterations, but this is costly under non-controlled environmental conditions. The present study was designed to determine whether the application of thymol reduced the proliferation of microorganisms in the faeces of Tamandua tetradactyla and whether it influenced faecal glucocorticoid metabolite (FGM) measurements. Tamandua tetradactyla faeces were individually collected after defaecation, divided into fractions (5.5 g each) and kept in sealed glass Petri dishes at 22 ± 2 °C. A thymol solution (550 µL; 5 mg g−1 feces; 80% ethanol) or an 80% ethanol solution (550 µL, control) was added before storage of faeces. Negative controls for FGM consisted of samples without thymol or ethanol solutions. All samples were evaluated at 0, 24, 48 and 72 h post-defaecation. Thymol was first incubated with a glucocorticoid standard in a faeces-free tube or in a faecal sample in order to determine whether it interfered with FGM measurements. Data showed that thymol did not affect FGM measurements. Post-defaecation time caused a significant reduction in FGM measurements in the negative control, an increment at 48 h in the control, and no change in FGM measurements in thymol treatment. FGM measurements were significantly different between groups (negative control > control – treatment). Thymol caused a significant reduction of up to three orders of magnitude in total coliforms, total aerobic and anaerobic heterotrophic mesophilic bacteria, mold and yeast per gram of faeces at 24, 48 and 72 h. The reduction in microbial activity presumably contributed to the stability of FGM over time. Spore-forming bacteria (SFB) in faeces were not reduced by thymol. We propose thymol as an alternative to freezing since it stabilizes FGMs for at least 3 days after collection in the faeces of Tamandua tetradactyla.

Impact of carbonatation lime addition on composting of vegetable oil refining sludge

The aim of the present work is to evaluate how the vegetable oil refining sludge produced by the agro-food industry could be composted using carbonatation lime and green waste as bulking agents. To achieve this goal, three windrows were prepared with different mixtures: windrow 1 contained oil sludge and green waste (20:10 on a wet mass basis) while windrow 2 contained oil sludge, green waste and carbonatation lime (20:10:10, on a wet mass basis). The composition of windrow 3 was: oil sludge, green waste and carbonatation lime (20:10:20, on a wet mass basis). The results showed that the use of carbonatation lime for composting vegetable oil refining sludge was able to regulate the high acidity of the sludge and thus to obtain an optimal pH value for the launching and maintenance of the composting process. The addition of carbonatation lime also gave better reduction of microbial activity without any negative effect on composting. The compost prepared with oil refining sludge (49% fresh mass), carbonatation lime (27%) and green waste (24%) exhibited the best quality with C/N ratio and pH values within the norm NFU44-051. These promising results could be a sustainable solution for the valorization of both oil refining sludge and sugar carbonatation lime.

Nitrogen additions reduce rhizospheric and heterotrophic respiration in a subtropical evergreen broad-leaved forest

Increasing global atmospheric nitrogen (N) deposition has a considerable impact on soil respiration. Due to different carbon dioxide (CO2) resources of different components of soil respiration, there may be different mechanisms by which soils respond to N additions. The aims of this study are to investigate the effects of N additions on total soil respiration (RST), rhizospheric respiration (RSR) and heterotrophic respiration (RSH), and to elucidate the potential causal mechanisms. An artificial N addition experiment was conducted in an evergreen broad-leaved forest at the western edge of the Sichuan Basin in China. The effects of three N treatment levels (+0, +50, +150 kg N ha−1 yr.−1) were measured, with the N application initiated in April 2013. Trenching method was used for partitioning RST into RST and RSR. The values of RST and its components were measured monthly from May 2015 to April 2016. The mean annual RST was 1.92 ± 0.18 μmol CO2 m−2 s−1, with RSH and RSR contributing 75 ± 1% and 25 ± 1% to RST, respectively. Nitrogen addition significantly reduced RST and its two components, as well as the contribution of RSR to RST. Microbial biomass carbon (C) and pH in bulk soil decreased significantly after N application. Nitrogen addition had no effect on rhizospheric soil biochemical properties. RSR was significantly positively correlated with root biomass of Castanopsis platyacantha, while RSH was significantly positively correlated with the concentrations of microbial biomass C (MBC) and microbial biomass N (MBN) for bulk soil. The positive correlation between RSR and root biomass indicates that N application reduced RSR by reducing belowground C allocation and thus C inputs to the rhizosphere. The value of RSH decreased primarily due to a reduction in microbial activity and soil organic matter decomposition in root-free soil after N was added. The presence of plant roots may mitigate the effect of N inputs to the rhizosphere via alteration of root morphology and exudates.

Effect of Soil Amendments on Microbial Resilience Capacity of Acid Soil Under Copper Stress.

An incubation study was undertaken to study microbial resilience capacity of acid soil amended with farmyard manure (FYM), charcoal and lime under copper (Cu) perturbation. Copper stress significantly reduced enzymatic activities and microbial biomass carbon (MBC) in soil. Percent reduction in microbial activity of soil due to Cu stress was 74.7% in dehydrogenase activity, 59.9% in MBC, 48.2% in alkaline phosphatase activity and 15.1% in acid phosphatase activity. Soil treated with FYM + charcoal showed highest resistance index for enzymatic activities and MBC. Similarly, the highest resilience index for acid phosphatase activity was observed in soil amended with FYM (0.40), whereas FYM + charcoal-treated soil showed the highest resilience indices for alkaline, dehydrogenase activity and MBC: 0.50, 0.22 and 0.25, respectively. This investigation showed that FYM and charcoal application, either alone or in combination, proved to be better than lime with respect to microbial functional resistance and resilience of acid soil under Cu perturbation.

Digestate and Fugate - Fertilizers with Ecotoxicological Risks

Increasing number of decentralised biogas plants increases not only the amount of biogas produced, but also the production of digestate. Digestate and fugate are believed to be good fertilizers. However, there is often a tradeoff between other environmental impacts linked to agricultural production like eutrophication or ecotoxicity. Only limited ecotoxicological information is known about the effects of digestate or fugate on terrestrial fauna and flora. This is the first study comparing the survival and reproduction of collembolans as the representative soil fauna and the root growth and photosynthetic activity of Sinapis alba and Panicum miliaceum plants when exposed to digestate and fugate. Comparison of ecotoxicological results with chemical analysis of both digestate and fugate has led to the conclusions that application of digestate and fugate was beneficial neither for tested plants, nor for zooedaphon. Under practically used dosing both digestate and fugate can represent potential ecotoxicological problems, which can affect zooedaphon diversity and reproduction resulting in degradation of soil structure, reduction of microbial activity or water retention capacity of treated soils. That is why we do recommend at least simplified ecotoxicological testing of digestate as presented in this study. Ecotoxicity testing can support decision of direct application on soil, or mixing the digestate with other materials (like compost, manure, pond sediments, or biochar), what will help to utilize nutrients and consequently can prevent degradation of soil fertility.

Differences in the nutrient concentrations, in vitro methanogenic potential and other fermentative traits of tropical grasses and legumes for beef production systems in northern Australia.

In northern Australia, beef cattle grazed extensively on tropical rangelands are responsible for 5% of the nation's total greenhouse gas emissions. Methane (CH4 ) is a potent greenhouse gas and in grazing ruminants might be mitigated by selecting forages that, when consumed, produce less CH4 when fermented by rumen microbes. This study examined variability in the in vitro fermentation patterns, including CH4 production of selected tropical grasses and legumes, to identify candidates for CH4 mitigation in grazing livestock in northern Australia. Nutritive values and fermentation parameters varied between plant species and across seasons. Grasses with a relatively low methanogenic potential were Urochloa mosambicensis (wet summer), Bothriochloa decipiens (autumn), Sorghum plumosum (winter) and Andropogon gayanus (spring), while the legumes were Calliandra calothyrsus (wet summer and autumn), Stylosanthes scabra (winter) and Desmanthus leptophyllus (spring). There was some correlation between CH4 production and overall fermentation (volatile fatty acid concentrations) in grasses (R2 = 0.67), but not in legumes (R2 = 0.01) and there were multiple plants that had lower CH4 not associated with reduction in microbial activity. Differences in nutrient concentrations of tropical grasses and legumes may provide opportunities for productive grazing on these pastures, while offering some CH4 mitigation options in the context of northern Australian extensive beef farming systems. © 2017 Society of Chemical Industry.

Predation by Bdellovibrio bacteriovorus significantly reduces viability and alters the microbial community composition of activated sludge flocs and granules.

We recently isolated and characterised a predatory Bdellovibrio bacteriovorus strain from activated sludge (Ulu Pandan Water Reclamation Plant, Singapore), and this strain, B. bacteriovorus UP, was able to prey upon a broad spectrum of bacterial isolates from the activated sludge when grown as planktonic cells or as biofilms. Here, we have tested the effect of Bdellovibrio predation on floccular and granular sludge to determine if the spatial organisation, loosely or tightly aggregated communities, was protective from predation. The effect of predation was assessed using a combination of biomass quantification, cellular activity measurement and microscopic image analysis to determine community viability. Additionally, changes in the microbial communities due to predation by B. bacteriovorus UP were analysed through total RNA sequencing. Predation led to a significant reduction in microbial activity and total biomass for both floccular and granular sludge communities. Predation was also associated with significant changes in the microbial community composition in both communities, with >90% of the community members reduced in relative abundance after 24 h. Of those community members, the dominant organisms, such as Proteobacteria and Bacteroidetes, were the most affected phylotypes. This suggests that predatory bacteria, which display indiscriminant feeding, could significantly shift the species composition and thus, may disturb the operational performance of wastewater treatment systems.