Increase In Bacterial Biomass Research Articles

Study on the regulatory mechanism of vinegar grains metabolism via different vinegar starters

The application of biofortification technology in regulating the microbial community of Sichuan bran vinegar (SBV) to enhance its quality has garnered significant attention recently. Here, we utilized Cuqu fortified (JQ) by synthetic microbiota composed of two different strains to enhance SBV fermentation, while simultaneously revealing community succession and metabolic regulatory mechanisms. Compared to control samples, the fortified vinegar grains (ZJV) community exhibited a 1.60-fold increase in bacterial biomass during major stages. Dominant fungi dynamics in ZJV significantly shifted, with a notable increase in Monascus and Rasamsonia. Upregulation of enzymes involved in starch and cellulose degradation led to increased contents of volatiles, 4-ethylguaiacol (4-EG), and raw starch conversion rate in the fermented ZJV by 1.75 times, 40 times, and 21.92%, respectively. Biofortification boosted interspecies interactions, clustering functional microbes into a module. Functional bacteria served as connectors, enhancing fungal-bacterial communication, optimizing information and energy exchange, reducing primary metabolite accumulation like ethanol, and improving nutrient utilization and metabolic conversion for secondary metabolite synthesis. These findings establish crucial groundwork for the practical application of synthetic microbiota in various engineering applications.

Variability of biochemical compounds in surface sediments along the eastern margin of the Arabian Sea

Different fractions of organic matter in surface sediments from three transects along the eastern margin of the Arabian Sea (AS) were quantified to determine the sources of organic matter, and also to study its impact on microbial community structure. From the extensive analyses of different biochemical parameters, it was evident that the distribution of total carbohydrate (TCHO), total neutral carbohydrate (TNCHO), proteins, lipids, and uronic acids (URA) concentrations and yield (% TCHO-C/TOC) are affected by organic matter (OM) sources and microbial degradation of sedimentary OM. Monosaccharide compositions from surface sediment was quantified to assess the sources and diagenetic fate of carbohydrates, suggesting that the deoxysugars (rhamnose plus fucose) had significant inverse relationship (r = 0.928, n = 13, p < 0.001) with hexoses (mannose plus galactose plus glucose) and positive relationship (r = 0.828, n = 13, p < 0.001) with pentoses (ribose plus arabinose plus xylose). This shows that marine microorganisms are the source of carbohydrates and there is no influence of terrestrial OM along the eastern margin of AS. During the degradation of algal material, the hexoses seem to be preferentially used by heterotrophic organisms in this region. Arabinose plus galactose (glucose free wt %) values between 28 and 64wt% indicate that OM was derived from phytoplankton, zooplankton, and non-woody tissues. In the principal component analysis, rhamnose, fucose, and ribose form one cluster of positive loadings while glucose, galactose, and mannose form another cluster of negative loadings which suggest that during OM sinking process, hexoses were removed resulting in increase in bacterial biomass and microbial sugars. Results indicate sediment OM to be derived from marine microbial source along the eastern margin of AS.

The pulmonary microbiome: recent advances in understanding its role in chronic lung allograft dysfunction.

Lung transplantation presents a rescue therapy for those with end-stage lung disease. Survival in lung transplant patients remains limited due to chronic lung allograft dysfunction (CLAD), a range of pathologic manifestations leading to graft loss. The mechanisms underlying CLAD remain poorly understood, and the lung microbiome has been suggested as a potential contributor to this condition. This review aims to explore how the pulmonary microbiome is impacted by lung transplantation, and how alterations in this microbiome may contribute to the pathogenesis of CLAD. The pulmonary microbiome is made up of a range of microorganisms, and it varies considerably in lung transplant patients when compared with healthy controls. The lung microbiome changes over the early transplant period, and the composition of species appears to have an impact on inflammatory responses within the lungs. A number of studies have shown that an increase in bacterial biomass in the allograft, and enrichment with the genera Proteobacteria, or more specifically, Pseudomonas species, is associated with CLAD. This area of research is still in its infancy; however, the suggestion that changes in the composition of the microbiome and enrichment with certain species may predispose to the pathologic changes that underlie CLAD indicate that modulation of the microbiome may be of use in potential future therapeutics.

Jellyfish swarm impair the pretreatment efficiency and membrane performance of seawater reverse osmosis desalination

Circumstantial evidence has suggested that jellyfish swarms impair the operation of seawater reverse osmosis desalination facilities. However, only limited information is currently available on the pretreatment efficiency of jellyfish and their effects on reverse osmosis (RO) membrane performance. Here, we have comprehensively tested the pretreatment efficiency of a dual-media gravity filter and cartridge micro-filtration following the addition of jellyfish into the feedwater. Concurrently, the fouling propensity and performance of the RO membranes were examined. We show that jellyfish demise resulted in seawater eutrophication that triggered a significant increase in bacterial biomass (∼50-fold), activity (∼7-fold), and release of transparent exopolymer particles (∼5-fold), peaking three days after the addition of jellyfish into the feedwater. In parallel, a significant reduction in permeate water flux was recorded (∼10%) while trans-membrane pressure sharply increased (15%), reaching the operation pressure limit of our system (75 bar) after five days. At the conclusion of the experiments, the membrane surface was heavily covered by large chunks of organic-rich material and multilayered biofilms. Our results provide a holistic view on the operational challenges of seawater reverse osmosis (SWRO) desalination triggered by jellyfish swarms in coastal areas. Following the above, it can be inferred that freshwater production will likely be halted three days after drawing the jellyfish into the pretreatment system. Outcomes from these results may lead to the development of science-based operational protocols to cope with growing occurrence of jellyfish swarms around the intake of SWRO desalination facilities worldwide.

Faeces of marine birds and mammals as substrates for microbial plankton communities

The chemical composition of the seawater soluble fraction (WSF) of yellow-legged gulls and harbour seal faeces and their impact on microbial plankton communities from an eutrophic coastal area have been tested. After characterisation of the C:N:P stoichiometry, trace metals content and organic molecular composition of the faeces, significant differences between species have been observed in all parameters. Seagull faeces present about three times larger N content than seal faeces and are also richer in trace elements except for Cu and Zn. Organic nitrogen in seagull faeces is dominated by uric acid, while the proteins are the main N source in seal faeces. It is remarkable that seagull faeces are five times more soluble in seawater than seal faeces and present a much higher N content (48.0 versus 3.5 mg N in the WSF per gram of dry faeces), >85% of which as dissolved organic nitrogen, with C:N molar ratios of 2.4 and 13 for seagull and seal faeces, respectively. Based on this contrasting N content, large differences were expected in their impact on microbial populations. To test this hypothesis, a 3-day microcosm incubation experiment was performed, in which coastal seawater was amended with realistic concentrations of the WSF of seagull or seal faeces. A significant and similar increase in bacterial biomass occurred in response to both treatments. In the case of phytoplankton, the impact of the treatment with seagull faeces was significantly larger that the effect of the treatment with seal faeces. Our data suggest that the distinct competitive abilities of phytoplankton and bacteria largely influence the potential impact of distinct animal faeces on primary productivity in coastal ecosystems. Impacts on the microbial plankton communities do not affect only this trophic level, but the whole trophic chain, contributing to nutrient recycling in coastal areas where large populations of these species are settled.

Discovering the potential of an nZVI-biochar composite as a material for the nanobioremediation of chlorinated solvents in groundwater: Degradation efficiency and effect on resident microorganisms

Abiotic and biotic remediation of chlorinated ethenes (CEs) in groundwater from a real contaminated site was studied using biochar-based composites containing nanoscale zero-valent iron (nZVI/BC) and natural resident microbes/specific CE degraders supported by a whey addition. The material represented by the biochar matrix decorated by isolated iron nanoparticles or their aggregates, along with the added whey, was capable of a stepwise dechlorination of CEs. The tested materials (nZVI/BC and BC) were able to decrease the original TCE concentration by 99% in 30 days. Nevertheless, regarding the transformation products, it was clear that biotic as well as abiotic transformation mechanisms were involved in the transformation process when nonchlorinated volatiles (i.e., methane, ethane, ethene, and acetylene) were detected after the application of nZVI/BC and nZVI/BC with whey. The whey addition caused a massive increase in bacterial biomass in the groundwater samples (monitored by 16S rRNA sequencing and qPCR) that corresponded with the transformation of trichloro- and dichloro-CEs, and this process was accompanied by the formation of less chlorinated products. Moreover, the biostimulation step also eliminated the adverse effect caused by nZVI/BC (decrease in microbial biomass after nZVI/BC addition). The nZVI/BC material or its aging products, and probably together with vinyl chloride-respiring bacteria, were able to continue the further reductive dechlorination of dichlorinated CEs into nonhalogenated volatiles. Overall, the results of the present study demonstrate the potential, feasibility, and environmental safety of this nanobioremediation approach.

Organic amendments exacerbate the effects of silver nanoparticles on microbial biomass and community composition of a semiarid soil

Increased utilization of silver nanoparticles (AgNPs) can result in an accumulation of these particles in the environment. The potential detrimental effects of AgNPs in soil may be associated with the low fertility of soils in semiarid regions that are usually subjected to restoration through the application of organic amendments. Microbial communities are responsible for fundamental processes related to soil fertility, yet the potential impacts of low and realistic AgNPs concentrations on soil microorganisms are still unknown. We studied the effects of realistic citrate-stabilized AgNPs concentrations (0.015 and 1.5 μg kg−1) at two exposure times (7 and 30 days) on a sandy clay loam Mediterranean soil unamended (SU) and amended with compost (SA). We assessed soil microbial biomass (microbial fatty acids), soil enzyme activities (urease, β-glucosidase, and alkaline phosphatase), and composition of the microbial community (bacterial 16S rRNA gene and fungal ITS2 sequencing) in a microcosm experiment. In the SA, the two concentrations of AgNPs significantly decreased the bacterial biomass after 7 days of incubation. At 30 days of incubation, only a significant decrease in the Gram+ was observed at the highest AgNPs concentration. In contrast, in the SU, there was a significant increase in bacterial biomass after 30 days of incubation at the lowest AgNPs concentration. Overall, we found that fungal biomass was more resistant to AgNPs than bacterial biomass, in both SA and SU. Further, the AgNPs changed the composition of the soil bacterial community in SA, the relative abundance of some bacterial taxa in SA and SU, and fungal richness in SU at 30 days of incubation. However, AgNPs did not affect the activity of extracellular enzymes. This study demonstrates that the exposure time and organic amendments modulate the effects of realistic concentrations of AgNPs in the biomass and composition of the microbial community of a Mediterranean soil.

Warming enhances the stimulatory effect of algal exudates on dissolved organic carbon decomposition

Abstract The current paradigm in peatland ecology is that the organic matter inputs from plant photosynthesis (e.g. moss litter) exceed that of decomposition, tipping the metabolic balance in favour of carbon (C) storage. Here, we investigated an alternative hypothesis, whereby exudates released by microalgae can actually accelerate C losses from the surface waters of northern peatlands by stimulating dissolved organic C (DOC) decomposition in a warmer environment expected with climate change. To test this hypothesis, we evaluated the biodegradability of fen DOC in a factorial design with and without algal DOC in both ambient (15°C) and elevated (20°C) water temperatures during a laboratory bioassay. When DOC sources were evaluated separately, decomposition rates were higher in treatments with algal DOC only than with fen DOC only, indicating that the quality of the organic matter influenced degradability. A mixture of substrates (½ algal DOC + ½ fen DOC) exceeded the expected level of biodegradation (i.e. the average of the individual substrate responses) by as much as 10%, and the magnitude of this effect increased to more than 15% with warming. Specific ultraviolet absorbance at 254 nm (SUVA254), a proxy for aromatic content, was also significantly higher (i.e. more humic) in the mixture treatment than expected from SUVA254 values in single substrate treatments. Accelerated decomposition in the presence of algal DOC was coupled with an increase in bacterial biomass, demonstrating that enhanced metabolism was associated with a more abundant microbial community. These results present an alternative energy pathway for heterotrophic consumers to breakdown organic matter in northern peatlands. Since decomposition in northern peatlands is often limited by the availability of labile organic matter, this mechanism could become increasingly important as a pathway for decomposition in the surface waters of northern peatlands where algae are expected to be more abundant in conditions associated with ongoing climate change.

The biostimulating effects of viable microalgal cells applied to a calcareous soil: Increases in bacterial biomass, phosphorus scavenging, and precipitation of carbonates.

Microalgae used in wastewater treatment may be applied to soil as a biofertilizer - this is a novel strategy for recycling of nutrients in the circular economy. There is little information about how the application of large concentrations of unicellular algae to soil will affect soil biochemistry, particularly when they are living algal cells with the potential to form a soil biofilm, whereas soil biofilms are expected to influence plant-microbe interactions. Chlorophyte unicellular algae of the Chlorella genera are widely employed in algae-based water treatment systems, and Chlorella sorokiniana has proven to be highly adaptable for this purpose. We applied three filtrates of a Chlorella sorokiniana culture to soil microcosms, separating the microalgae from other microorganisms, as well as a sterile control filtrate without biological activity. Bacterial biomass in soils receiving the non-filtered (NF) slurry with viable algal cells was increased by 25% in the soil surface (0-8mm), and heterotrophic activity in those treatments increased as measured by CO2-C evolution. Total soil carbon concentrations were increased in the treatment with living algal cells (NF) by 0.4%, but no differences in organic carbon were measured; instead, it was found that inorganic carbon (CaCO3) concentrations increased by 0.6% in the NF treatment only. Soil phosphorus availability was also reduced in the surface of the NF treatment, indicating an increased biological demand. The results show that, when applied to soil, microalgae and associated biofilms will have relevant direct and indirect effects on soil quality and nutrients of agricultural importance.

Optimization of culture medium and growth conditions of the plant growth-promoting bacterium Herbaspirillum seropedicae BR11417 for its use as an agricultural inoculant using response surface methodology (RSM)

Culture media compositions and bioprocess conditions were studied to improve the production of cell biomass and indolic phytohormones by Herbaspirillum seropedicae BR11471, a plant growth promoting bacterium, and different inoculant formulations were also produced and tested for their stability and shelf life. Response surface methodology (RSM) based on central composite rotation designs (CCRD) was used to find bioprocess variables that lead to an increase in bacterial biomass and yield of indolic compounds. The major components of DYGS medium were optimized in small-scale shaken cultivations, in two sets of CCRD. High performance liquid chromatography was used to determine nutrient consumption and to correlate it with cell biomass production, and the Salkowski method was used to quantify indoles. Hydrolytic activity in the formulations was quantified with the fluorescein diacetate assay. Glycerol (5.5 g L−1) and yeast extract (2.8 g L−1), as the main carbon and nitrogen sources, respectively, increased biomass production by 87.5% when compared to original DYGS medium, reaching 3.0 g L−1 of dry cell weight (DCW). In a 2.0 L bioreactor, the optimized medium was used to enhance process conditions for DCW and indole-3-acetic acid (IAA). Biomass production reached 3.4 g L−1 and was restrained at highest air flow levels. The conditions of 34-36 °C, 150 rpm and 4.0 L min−1 of air flow rate resulted in 11.97 mg L−1 of IAA, an increase of 370% over original DYGS at 30 °C. Peat can still be regarded as a good cell carrier for solid state inoculants, whilst the additives tested for liquid formulations are individually more efficient than the mixture. The production of inoculants containing H. seropedicae strain BR11471 can be efficiently improved with the use of the RSM approach i.e. it maximizes the production of biomass and indolic compounds, and reduces culture media components, both key factors for large-scale industrial production.

Exotic earthworms maintain soil biodiversity by altering bottom-up effects of plants on the composition of soil microbial groups and nematode communities.

Bottom-up effects of plants on soil communities can be modified by the activity of exotic earthworms, by altering resource availability for soil food webs through feeding, burrowing, and casting activities. The present study explored effects of plants (planting of shrubs) on soil micro-food webs (composition of soil microbial and nematode communities), and whether these effects were altered by the activity of exotic earthworms (exotic earthworms addition). Planted shrubs resulted in a non-significant increase of bacterial biomass and significantly increased the abundance of different nematode trophic groups and total nematode biomass, indicating that planted shrubs had significant bottom-up effects on soil bacteria and nematodes. Planted shrubs decreased nematode diversity, evenness, and richness, but increased nematode dominance in the plots where the abundance of exotic earthworms was not amended. By contrast, these effects of shrub presence on soil biodiversity were not found in the plots that received exotic earthworms. In addition, planted shrubs increased the total energy flux to the nematode community. By contrast, the elevated activity of exotic earthworms mitigated the increase in total energy flux to nematodes in the presence of shrubs, and increased the ratio of fungal to bacterial PLFAs. Both of these changes indicate reduced energy flux in the plots with added exotic earthworms. Nematode diversity decreased, while nematode dominance increased with increasing total energy flux to nematodes, probably because few species benefited from high energy flux. Our study indicates that exotic earthworms can maintain soil biodiversity by reducing the energy flux through soil food webs.

Biodegradation of biodiesel-oil by Cellulosimicrobium sp. Isolated from Colombian Caribbean soils

ABSTRACT Biodiesel is considered to be a natural substitute for fossil fuel. The comparatively low toxicity of biodiesel and its susceptibility to microbial biodegradation could reduce its environmental impact. Currently, biodiesel is sold previously mixed with petroleum-based hydrocarbons. The aim of this work was to measure the biodegradation potential of commercially available biodiesel, using bacterial strains (BBCOL-001, BBCOL-002, and BBCOL-003) isolated from a tropical forest soils in the Colombian Caribbean. According to nucleotide sequencing of the gene encoding for 16S rRNA, the strains belong to members of the genus Cellulosimicrobium. GC–MS analysis showed that biodiesel-oil alkanes were degraded by an average of 81.5% with optical density reaching 0.2–0.3 in minimal salt media at 37°C for 5 days. Individual diesel-oil alkanes were degraded by the strains at rates between 64.9% to 100%. The increase in bacterial biomass confirmed the use of the substrates by the microorganisms, suggesting these hydrocarbons are a carbon source. Changes in the biochemical behaviour of the strains suggested their capacity to adapt to environmental conditions might be an important resource for bioremediation.

Increased chemical stability but decreased physical protection of soil organic carbon in response to nutrient amendment in a Tibetan alpine meadow

Nutrient amendment increases plant productivity but the effects and mechanisms on soil organic carbon (SOC) accumulation and stability remain unclear, especially in nutrient deficient alpine ecosystem. Here, based on an experiment combining nitrogen (N) and phosphorus (P) input continuously for 15 years, we found that nutrient amendment did not affect total SOC content, but increased mineral-associated C with decreasing soil aggregate stability. Despite increased total phospholipid fatty acid (PLFA) and bacteria PLFA, nutrient amendment decreased soil enzyme activities involved in C cycling. The 13C NMR analyses showed that nutrient amendment decreased the aliphaticity but enhanced aromaticity of SOC. Structural equation models indicated that P availability (Olsen-P content) was most related to shifts in microbial community composition and decreased enzyme activities. Moreover, the concomitantly reduced aggregation and increased mineral-associated C were mainly attributable to the decrease of fungal biomass and increase of bacterial biomass. Together, interconnected factors such as increased acidity, aggregate destabilization, microbial community shift towards bacteria, and loss of oxidative enzyme activities could contribute to the overall response of SOC under intensive N and P input. In particular, available P rather than N may re-shape the pattern of physical and chemical stabilization of SOC, shifting from moderately physical protection to highly chemical stability, implicating the pivotal roles of P management in C cycling of alpine ecosystem.

Biodegradation of malathion, α- and β-endosulfan by bacterial strains isolated from agricultural soil in Veracruz, Mexico

ABSTRACTThe objective of this study was to evaluate the capacity of two bacterial strains isolated, cultivated, and purified from agricultural soils of Veracruz, Mexico, for biodegradation and mineralisation of malathion (diethyl 2-(dimethoxyphosphorothioyl) succinate) and α- and β-endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6-9-methano-2,4,3-benzodioxathiepine-3-oxide). The isolated bacterial strains were identified using biochemical and morphological characterization and the analysis of their 16S rDNA gene, as Enterobacter cloacae strain PMM16 (E1) and E. amnigenus strain XGL214 (M1). The E1 strain was able to degrade endosulfan, whereas the M1 strain was capable of degrading both pesticides. The E1 strain degraded 71.32% of α-endosulfan and 100% of β-endosulfan within 24 days. The absence of metabolites, such as endosulfan sulfate, endosulfan lactone, or endosulfan diol, would suggest degradation of endosulfan isomers through non-oxidative pathways. Malathion was completely eliminated by the M1 strain. The major metabolite was butanedioic acid. There was a time-dependent increase in bacterial biomass, typical of bacterial growth, correlated with the decrease in pesticide concentration. The CO2 production also increased significantly with the addition of pesticides to the bacterial growth media, demonstrating that, under aerobic conditions, the bacteria utilized endosulfan and malathion as a carbon source. Here, two bacterial strains are shown to metabolize two toxic pesticides into non-toxic intermediates.

Applying Central Composite Design and Response Surface Methodology to Optimize Growth and Biomass Production of Haemophilus influenzae Type b.

BackgroundHaemophilus influenzae type b (Hib) is the leading cause of bacterial meningitis, otitis media, pneumonia, cellulitis, bacteremia, and septic arthritis in infants and young children. The Hib capsule contains the major virulence factor, and is composed of polyribosyl ribitol phosphate (PRP) that can induce immune system response. Vaccines consisting of Hib capsular polysaccharide (PRP) conjugated to a carrier protein are effective in the prevention of the infections. However, due to costly processes in PRP production, these vaccines are too expensive.ObjectivesTo enhance biomass, in this research we focused on optimizing Hib growth with respect to physical factors such as pH, temperature, and agitation by using a response surface methodology (RSM).Materials and MethodsWe employed a central composite design (CCD) and a response surface methodology to determine the optimum cultivation conditions for growth and biomass production of H. influenzae type b. The treatment factors investigated were initial pH, agitation, and temperature, using shaking flasks. After Hib cultivation and determination of dry biomass, analysis of experimental data was performed by the RSM-CCD.ResultsThe model showed that temperature and pH had an interactive effect on Hib biomass production. The dry biomass produced in shaking flasks was about 5470 mg/L, which was under an initial pH of 8.5, at 250 rpm and 35° C.ConclusionsWe found CCD and RSM very effective in optimizing Hib culture conditions, and Hib biomass production was greatly influenced by pH and incubation temperature. Therefore, optimization of the growth factors to maximize Hib production can lead to 1) an increase in bacterial biomass and PRP productions, 2) lower vaccine prices, 3) vaccination of more susceptible populations, and 4) lower risk of Hib infections.

Comparative responses of river biofilms at the community level to common organic solvent and herbicide exposure.

Residual pesticides applied to crops migrate from agricultural lands to surface and ground waters. River biofilms are the first aquatic non-target organisms which interact with pesticides. Therefore, ecotoxicological experiments were performed at laboratory scale under controlled conditions to investigate the community-level responses of river biofilms to a chloroacetanilide herbicide (alachlor) and organic solvent (methanol) exposure through the development referenced to control. Triplicate rotating annular bioreactors, inoculated with river water, were used to cultivate river biofilms under the influence of 1 and 10 μg L(-1) of alachlor and 25 mg L(-1) of methanol. For this purpose, functional (thymidine incorporation and carbon utilization spectra) and structural responses of microbial communities were assessed after 5 weeks of development. Structural aspects included biomass (chlorophyll a, confocal laser scanning microscopy) and composition (fluor-conjugated lectin binding, molecular fingerprinting, and diatom species composition). The addition of alachlor resulted in a significant reduction of bacterial biomass at 1 μg L(-1), whereas at 10 μg L(-1), it induced a significant reduction of exopolymer lectin binding, algal, bacterial, and cyanobacterial biomass. However, there were no changes in biofilm thickness or thymidine incorporation. No significant difference between the bacterial community structures of control and alachlor-treated biofilms was revealed by terminal restriction fragment length polymorphism (T-RFLP) analyses. However, the methanol-treated bacterial communities appeared different from control and alachlor-treated communities. Moreover, methanol treatment resulted in an increase of bacterial biomass and thymidine incorporation as well. Changes in dominant lectin binding suggested changes in the exopolymeric substances and community composition. Chlorophyll a and cyanobacterial biomass were also altered by methanol. This study suggested that the concentration-dependent effect of alachlor mainly remains limited to biomass and growth inhibition without apparent changes of structural and functional characteristics measured. Our work also establishes the potential toxic effects of organic solvents on river biofilm in ecotoxicological experiments. For the ecotoxicological experiments, the alternative of dissolution in organic solvent followed by its evaporation, depositing the chemical on a glass surface prior to dissolution in river water used here, appears to allow exposure while minimizing the effect of organic solvent.

Effects of 100 years wastewater irrigation on resistance genes, class 1 integrons and IncP-1 plasmids in Mexican soil.

Long-term irrigation with untreated wastewater can lead to an accumulation of antibiotic substances and antibiotic resistance genes in soil. However, little is known so far about effects of wastewater, applied for decades, on the abundance of IncP-1 plasmids and class 1 integrons which may contribute to the accumulation and spread of resistance genes in the environment, and their correlation with heavy metal concentrations. Therefore, a chronosequence of soils that were irrigated with wastewater from 0 to 100 years was sampled in the Mezquital Valley in Mexico in the dry season. The total community DNA was extracted and the absolute and relative abundance (relative to 16S rRNA genes) of antibiotic resistance genes (tet(W), tet(Q), aadA), class 1 integrons (intI1), quaternary ammonium compound resistance genes (qacE+qacEΔ1) and IncP-1 plasmids (korB) were quantified by real-time PCR. Except for intI1 and qacE+qacEΔ1 the abundances of selected genes were below the detection limit in non-irrigated soil. Confirming the results of a previous study, the absolute abundance of 16S rRNA genes in the samples increased significantly over time (linear regression model, p < 0.05) suggesting an increase in bacterial biomass due to repeated irrigation with wastewater. Correspondingly, all tested antibiotic resistance genes as well as intI1 and korB significantly increased in abundance over the period of 100 years of irrigation. In parallel, concentrations of the heavy metals Zn, Cu, Pb, Ni, and Cr significantly increased. However, no significant positive correlations were observed between the relative abundance of selected genes and years of irrigation, indicating no enrichment in the soil bacterial community due to repeated wastewater irrigation or due to a potential co-selection by increasing concentrations of heavy metals.

Contrasting pelagic plankton in temperate Irish lakes: the relative contribution of heterotrophic, mixotrophic, and autotrophic components, and the effects of extreme rainfall events

The mobilisation of energy from allocthonous carbon by heterotrophic bacterioplankton can be proportionally more important than autotrophic production in humic lakes. Moreover, increasing levels of dissolved organic carbon (DOC) in many aquatic systems linked to increases in precipitation, which in turn may be related to changing climate, mean that this heterotrophic component of the food web may play an increasing role in the overall transfer and production of energy, particularly within peatland catchments. While such catchments are common in the temperate northwest Atlantic regions of Europe, studies describing the seasonal dynamics of the heterotrophic, mixotrophic, and autotrophic components of their aquatic food webs are rare. In this study, the biomass of these pelagic components was enumerated over 1 year in 2 oligotrophic lakes, both situated in peatland catchments in the west of Ireland but with contrasting DOC concentrations. Bacterial biomass dominated the pelagic food web of the more humic lake, Lough Feeagh, while autotrophic phytoplankton biomass was greatest in the clearwater lake, Lough Guitane. The biomass of potentially mixotrophic flagellates was also slightly larger in the Lough Guitane, while phagotrophic ciliate biomass was comparable between the 2 lakes. An extreme precipitation event led to a significant increase in bacterial biomass while simultaneously depressing autotrophic production for several months in the humic lake. Extreme precipitation in the clearwater lake also depressed autotrophic production but did not give rise to significant increases in bacterial biomass. This quantification of autotrophic, mixotrophic, and heterotrophic components provides a vital first step in understanding how pelagic communities contribute to net ecosystem productivity, and thus how Irish peatland lakes may be affected by projected climate changes.

The assessment of the impact of oil palm and rubber plantations on the biotic and abiotic properties of tropical peat swamp soil in Indonesia

Current intensification of agricultural activities in Indonesia has led to increased use of tropical peat swamp forests for agriculture. Ideally, peat swamp ecosystems should not be disturbed as they provide essential services such as soil erosion control, ecosystem stabilization and moderation of climate and energy fluxes as well as reducing carbon emission and conserving biodiversity. In this study, agricultural land from Giam Siak Kecil–Bukit Batu Biosphere Reserve in Indonesia was evaluated to assess the impact of oil palm (burning and without burning) and rubber (5–10 and >40 years old) plantations on soil properties through comparisons with soils from a natural forest (NF). Substantial changes in the physico-chemical properties of soils from both plantations were observed including significant reductions in soil organic matter (4–18%) and water holding capacity (22–53%), but an increase in bulk density (ρb) (0.08–0.17 g cm−3). A significant increase in bacterial biomass was also observed following conversion of the NF to plantation (p<0.05). However, the oil palm plantation (OPP) (without burning) showed reduced microbial activities and the lowest Shannon diversity values (2.90) compared to other samples. Community-level physiological profiling showed impaired community function only in soils from the OPP but higher CO2 exchange rates in most plantation soils. Soils from the rubber plantation (RP) were less impaired in terms of their natural function and therefore RPs appeared to be more suitable for sustainable agricultural use than OPP.

Short-term changes in zooplankton density and community structure in response to different sources of dissolved organic carbon in an unconstrained lowland river: evidence for food web support

The zooplankton community changes that may occur with increases in concentration of allochthonous dissolved organic carbon (DOC) are not well understood in unconstrained lowland rivers. We examined in mesocoms over 8 days the short-term responses of river zooplankton to amendments of DOC from two different sources, glucose and leachates of a common riparian tree (Eucalyptus camaldulensis; river red gum) both alone and with inorganic nutrients added. DOC additions with and without nutrients increased heterotrophic respiration and led to significant increases in bacterial biomass. These responses varied between glucose and leachate addition. In treatments with added DOC, zooplankton density significantly increased relative to controls. Some zooplankton genera only responded to the leachate as a DOC source, and community structures significantly varied between the control and the glucose and leachate amendments. Zooplankton are particularly important in lowland river systems as they are key organisms for the transfer of carbon to higher trophic levels and this study indicates that allochthonous DOC has the potential to be an important basal resource to lowland river food webs. This may be particularly important in lowland sections of unconstrained flood plain rivers during and immediately following floods when allochthonous DOC is more available.