Comparison of microbial communities during the anaerobic digestion of <Emphasis Type="Italic">Gracilaria</Emphasis> under mesophilic and thermophilic conditions

Mesophilic and thermophilic anaerobic digesters (MD and TD, respectively) utilizing Gracilaria and marine sediment as the substrate and inoculum, respectively, were compared by analyzing their performances and microbial community changes. During three successive transfers, the average cumulative methane yields in the MD and TD were 222.6 ± 17.3 mL CH₄/g volatile solids (VS) and 246.1 ± 11 mL CH₄/g VS, respectively. The higher hydrolysis rate and acidogenesis in the TD resulted in a several fold greater accumulation of volatile fatty acids (acetate, propionate, and butyrate) followed by a larger pH drop with a prolonged recovery than in the MD. However, the operational stability between both digesters remained comparable. Pyrosequencing analyses revealed that the MD had more complex microbial diversity indices and microbial community changes than the TD. Interestingly, Methanomassiliicoccales, the seventh methanogen order was the predominant archaeal order in the MD along with bacterial orders of Clostridiales, Bacteriodales, and Synergistales. Meanwhile, Coprothermobacter and Methanobacteriales dominated the bacterial and archaeal community in the TD, respectively. Although the methane yield is comparable, both MD and TD show a different profile of pH, VFA and the microbial communities.     

Ammonium inhibition through the decoupling of acidification process and methanogenesis in anaerobic digester revealed by high throughput sequencing

Objective

To reveal the shifts of microbial communities along ammonium gradients, and the relationship between microbial community composition and the anaerobic digestion performance using a high throughput sequencing technique.

Results

Methane production declined with increasing ammonium concentration, and was inhibited above 4 g l^?1. The volatile fatty acids, especially acetate, accumulated with elevated ammonium. Prokaryotic populations showed different responses to the ammonium concentration: Clostridium, Tepidimicrobium, Sporanaerobacter, Peptostreptococcus, Sarcina and Peptoniphilus showed good tolerance to ammonium ions. However, Syntrophomonas with poor tolerance to ammonium may be inhibited during anaerobic digestion. During methanogenesis, Methanosarcina was the dominant methanogen.

Conclusion

Excessive ammonium inhibited methane production probably by decoupling the linkage between acidification process and methanogenesis, and finally resulted in different performance in anaerobic digestion.

     

Microbial community in a pilot-scale bioreactor promoting anaerobic digestion and sulfur-driven denitrification for domestic sewage treatment

A pilot-scale reactor treating domestic sewage was operated to promote anaerobic digestion and denitrification using endogenous electron donors. While 55 % of organic matter was removed, nitrogen and sulfur showed a different dynamics during the operation. Pyrosequencing analysis clarified this behavior revealing that specific microbial communities inhabited the anaerobic (47.05 % of OTUs) and anoxic (31.39 % of OTUs) chambers. Analysis of 16S rRNA gene partial sequences obtained through pyrosequencing revealed a total of 1727 OTUs clustered at a 3 % distance cutoff. In the anaerobic chamber, microbial community was comprised of fermentative, syntrophic and sulfate-reducing bacteria. The majority of sequences were related to Aminobacterium and Syntrophorhabdus. In the anoxic chamber, the majority of sequences were related to mixotrophic and strictly autotrophic denitrifiers Arcobacter and Sulfuricurvum, respectively, both involved in sulfur-driven denitrification. These results show that pyrosequencing was a powerful tool to investigate the microbial panorama of a complex system, providing new insights to the improvement of the system.     

Taxonomical and functional microbial community dynamics in an Anammox-ASBR system under different Fe (III) supplementation

In the present study, we explored the metabolic versatility of anaerobic ammonium oxidation (anammox) bacteria in a variety of Fe (III) concentrations. Specifically, we investigated the impacts of Fe (III) on anammox growth rates, on nitrogen removal performance, and on microbial community dynamics. The results from our short-term experiments revealed that Fe (III) concentrations (0.04–0.10 mM) significantly promote the specific anammox growth rate from 0.1343 to 0.1709 d^?1. In the long-term experiments, the Anammox-anaerobic sequencing batch reactor (ASBR) was operated over 120 days and achieved maximum NH₄ ⁺-N, NO₂ ^?-N, and TN efficiencies of 90.98 ± 0.35, 93.78 ± 0.29, and 83.66 ± 0.46 %, respectively. Pearson’s correlation coefficients between anammox-(narG + napA), anammox-nrfA, and anammox-FeRB all exceeded r = 0.820 (p < 0.05), confirming an interaction and ecological association among the nitrogen and iron-cycling-related microbial communities. Illumina MiSeq sequencing indicated that Chloroflexi (34.39–39.31 %) was the most abundant phylum in an Anammox-ASBR system, followed by Planctomycetes (30.73–35.31 %), Proteobacteria (15.40–18.61 %), and Chlorobi (4.78–6.58 %). Furthermore, we found that higher Fe (III) supplementation (>0.06 mM) could result in the community succession of anammox species, in which Candidatus Brocadia and Candidatus Kuenenia were the dominant anammox bacteria species. Combined analyses indicated that the coupling of anammox, dissimilatory nitrogen reduction to ammonium, and iron reduction accounted for nitrogen loss in the Anammox-ASBR system. Overall, the knowledge gained in this study provides novel insights into the microbial community dynamics and metabolic potential of anammox bacteria under Fe (III) supplementation.     

The effect of temperature and retention time on methane production and microbial community composition in staged anaerobic digesters fed with food waste

Background

Food waste is a large bio-resource that may be converted to biogas that can be used for heat and power production, or as transport fuel. We studied the anaerobic digestion of food waste in a staged digestion system consisting of separate acidogenic and methanogenic reactor vessels. Two anaerobic digestion parameters were investigated. First, we tested the effect of 55 vs. 65 °C acidogenic reactor temperature, and second, we examined the effect of reducing the hydraulic retention time (HRT) from 17 to 10 days in the methanogenic reactor. Process parameters including biogas production were monitored, and the microbial community composition was characterized by 16S amplicon sequencing.

Results

Neither organic matter removal nor methane production were significantly different for the 55 and 65 °C systems, despite the higher acetate and butyrate concentrations observed in the 65 °C acidogenic reactor. Ammonium levels in the methanogenic reactors were about 950 mg/L NH₄ ⁺ when HRT was 17 days but were reduced to 550 mg/L NH₄ ⁺ at 10 days HRT. Methane production increased from ~ 3600 mL/day to ~ 7800 when the HRT was decreased. Each reactor had unique environmental parameters and a correspondingly unique microbial community. In fact, the distinct values in each reactor for just two parameters, pH and ammonium concentration, recapitulate the separation seen in microbial community composition. The thermophilic and mesophilic digesters were particularly distinct from one another. The 55 °C acidogenic reactor was mainly dominated by Thermoanaerobacterium and Ruminococcus, whereas the 65 °C acidogenic reactor was initially dominated by Thermoanaerobacterium but later was overtaken by Coprothermobacter. The acidogenic reactors were lower in diversity (34–101 observed OTU_0.97, 1.3–2.5 Shannon) compared to the methanogenic reactors (472–513 observed OTU_0.97, 5.1–5.6 Shannon). The microbial communities in the acidogenic reactors were > 90% Firmicutes, and the Euryarchaeota were higher in relative abundance in the methanogenic reactors.

Conclusions

The digestion systems had similar biogas production and COD removal rates, and hence differences in temperature, NH₄ ⁺ concentration, and pH in the reactors resulted in distinct but similarly functioning microbial communities over this range of operating parameters. Consequently, one could reduce operational costs by lowering both the hydrolysis temperature from 65 to 55 °C and the HRT from 17 to 10 days.

     

Predictive functional profiling using marker gene sequences and community diversity analyses of microbes in full-scale anaerobic sludge digesters

Anaerobic digestion (AD) is widely used in treating the sewage sludge, as it can reduce the amount of sludge, eliminate pathogens and produce biofuel. To enhance the operational performance and stability of anaerobic bioreactors, operational and conventional chemical data from full-scale sludge anaerobic digesters were collected over a 2-year period and summarized, and the microbial community diversity of the sludge sample was investigated at various stages of the AD process. For the purpose of distinguishing between the functional and community diversity of the microbes, Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) software was used to impute the prevalence of 16S rDNA marker gene sequences in the difference in various sludge samples. Meanwhile, a taxa analysis was also carried out to investigate the different sludge samples. The microbial community diversity analysis of one AD sludge sample showed that the most dominant bacterial genera were Saccharicrinis, Syntrophus, Anaerotruncus and Thermanaerothrix. Among archaea, acetoclastic Methanosaeta represented 56.0 %, and hydrogenotrophic Methanospirillum, Methanoculleus, Methanothermus and Methanolinea accounted for 41.3 % of all methanogens. The taxa, genetic and functional prediction analyses of the feedstock and AD sludge samples suggested great community diversity differences between them. The taxa of bacteria in two AD sludge samples were considerably different, but the abundances of the functional KEGG pathways took on similar levels. The numbers of identified pathogens were significantly lower in the digested sludge than in the feedstock, but the PICRUSt results showed the difference in “human diseases” abundances in the level-1 pathway between the two sludge samples was small.     

Prokaryotic diversity in a Tunisian hypersaline lake,Chott El Jerid

Prokaryotic diversity was investigated in a Tunisian salt lake, Chott El Jerid, by quantitative real-time PCR, denaturing gradient gel electrophoresis (DGGE) fingerprinting methods targeting the 16S rRNA gene and culture-dependent methods. Two different samples S1-10 and S2-10 were taken from under the salt crust of Chott El Jerid in the dry season. DGGE analysis revealed that bacterial sequences were related to Firmicutes, Proteobacteria, unclassified bacteria, and Deinococcus-Thermus phyla. Anaerobic fermentative and sulfate-reducing bacteria were also detected in this ecosystem. Within the domain archaea, all sequences were affiliated to Euryarchaeota phylum. Quantitative real-time PCR showed that 16S rRNA gene copy numbers of bacteria was 5 × 10⁶ DNA copies g^?1 whereas archaea varied between 5 × 10⁵ and 10⁶ DNA copies g^?1 in these samples. Eight anaerobic halophilic fermentative bacterial strains were isolated and affiliated with the species Halanaerobium alcaliphilum, Halanaerobium saccharolyticum, and Sporohalobacter salinus. These data showed an abundant and diverse microbial community detected in the hypersaline thalassohaline environment of Chott El Jerid.     

Linkages of <Emphasis Type="Italic">Firmicutes</Emphasis> and <Emphasis Type="Italic">Bacteroidetes</Emphasis> populations to methanogenic process performance

To identify potential linkages between specific bacterial populations and process performance in anaerobic digestion, the dynamics of bacterial community structure was monitored with high-throughput sequencing in triplicate anaerobic digesters treating animal waste. Firmicutes and Bacteroidetes were found as the two most abundant populations, however, with contrasting population dynamics in response to organic overloading. Firmicutes dominated the bacterial community during stable process performance at low organic loading rate, representing over 50 % of the bacterial abundance. In contrast, the onset of organic overloading raised the relative abundance of Bacteroidetes from 20 ± 2.6 to 44 ± 3.1 %. In addition to the significant negative correlation between the relative abundance of Firmicutes and Bacteroidetes, populations of Firmicutes and Bacteroidetes were found to be linked to process parameters including organic loading rate, volatile fatty acids concentration, and methane production. Therefore, the population abundance ratio of Firmicutes to Bacteroidetes (F/B ratio) was suggested as a potential indicator for process performance. The interactions between Firmicutes and Bacteroidetes populations could be exploited to develop strategies for the prevention of performance perturbation in anaerobic digestion processes.     

Changes in the microbial community during repeated anaerobic microbial dechlorination of pentachlorophenol

Pentachlorophenol (PCP) has been widely used as a pesticide in paddy fields and has imposed negative ecological effect on agricultural soil systems, which are in typically anaerobic conditions. In this study, we investigated the effect of repeated additions of PCP to paddy soil on the microbial communities under anoxic conditions. Acetate was added as the carbon source to induce and accelerate cycles of the PCP degradation. A maximum degradation rate occurred at the 11th cycle, which completely transformed 32.3 μM (8.6 mg L^?1) PCP in 5 days. Illumina high throughput sequencing of 16S rRNA gene was used to profile the diversity and abundance of microbial communities at each interval and the results showed that the phyla of Bacteroidates, Firmicutes, Proteobacteria, and Euryarchaeota had a dominant presence in the PCP-dechlorinating cultures. Methanosarcina, Syntrophobotulus, Anaeromusa, Zoogloea, Treponema, W22 (family of Cloacamonaceae), and unclassified Cloacamonales were found to be the dominant genera during PCP dechlorination with acetate. The microbial community structure became relatively stable as cycles increased. Treponema, W22, and unclassified Cloacamonales were firstly observed to be associated with PCP dechlorination in the present study. Methanosarcina that have been isolated or identified in PCP dechlorination cultures previously was apparently enriched in the PCP dechlorination cultures. Additionally, the iron-cycling bacteria Syntrophobotulus, Anaeromusa, and Zoogloea were enriched in the PCP dechlorination cultures indicated they were likely to play an important role in PCP dechlorination. These findings increase our understanding for the microbial and geochemical interactions inherent in the transformation of organic contaminants from iron rich soil, and further extend our knowledge of the PCP-transforming microbial communities in anaerobic soil conditions.     

Persistence of <Emphasis Type="Italic">Methanosaeta</Emphasis> populations in anaerobic digestion during process instability

Anaerobic digestion is a sustainable technology for the treatment of organic waste and production of biogas. Acetoclastic methanogenesis accounts for the majority of methane production in anaerobic digestion. Therefore, sustaining robust acetoclastic methanogens is important for stable process performance. Due to faster growth kinetics at high acetate concentrations, it has been considered that Methanosarcina would be more prevalent than Methanosaeta in unstable anaerobic digestion processes which frequently experience high acetate levels. Methanogen population dynamics were monitored in multiple continuous anaerobic digesters for 500 days. Results from quantitative polymerase chain reaction analysis show that Methanosaeta dominated over Methanosarcina in anaerobic digestion at high acetate levels up to 44 mM, suggesting the potential of Methanosaeta as a robust and efficient acetoclastic candidate for resilient anaerobic methane conversion. Further efforts are needed to identify mechanisms contributing to the unexpected competitiveness of these methanogens at high acetate levels observed in this study.     

Surface-attached and suspended bacterial community structure as affected by C/N ratios: relationship between bacteria and fish production

Bacteria play crucial roles in the combined system of substrate addition and C/N control, which has been demonstrated to improve aquaculture production. However, the complexity of surface-attached bacteria on substrates and suspended bacteria in the water column hamper further application of this system. This study firstly applied this combined system into the culture of grass carp, and then explored the relationship between microbial complexes from surface-attached and suspended bacteria in this system and the production of grass carp. In addition, this study investigated bacterial community structures as affected by four C/N ratios using Illumina sequencing technology. The results demonstrated that the weight gain rate and specific growth rate of grass carp in the CN20 group (C/N ratio 20:1) were the highest (P < 0.05), and dietary supplementation of the microbial complex had positive effects on the growth of grass carp (P < 0.05). Sequencing data revealed that, (1) the proportions of Verrucomicrobiae and Rhodobacter (surface-attached), sediminibacterium (suspended), and emticicia (surface-attached and suspended) were much higher in the CN20 group compared with those in the other groups (P < 0.05); (2) Rhodobacter, Flavobacterium, Acinetobacter, Pseudomonas, Planctomyces, and Cloacibacterium might be important for the microbial colonization on substrates; (3) as the C/N ratio increased, proportions of Hydrogenophaga (surface-attached and suspended), Zoogloea, and Flectobacillus (suspended) increased, but proportions of Bacillus, Clavibacter, and Cellvibro (surface-attached and suspended) decreased. In summary, a combined system of substrate addition and C/N control increased the production of grass carp, and Verrucomicrobiae and Rhodobacter in the surface-attached bacterial community were potential probiotic bacteria that contributed to the enhanced growth of grass carp.     

Impact of elevated CO<Subscript>2</Subscript> in <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> rooted stem cuttings inoculated with <Emphasis Type="Italic">Frankia</Emphasis>

Impact of different levels of elevated CO ₂ on the activity of Frankia (Nitrogen-fixing actinomycete) in Casuarina equisetifolia rooted stem cuttings has been studied to understand the relationship between C. equisetifolia, Frankia and CO₂. The stem cuttings of C. equietifolia were collected and treated with 2000 ppm of Indole Butyric Acid (IBA) for rooting. Thus vegetative propagated rooted stem cuttings of C. equisetifolia were inoculated with Frankia and placed in the Open top chambers (OTC) with elevated CO₂ facilities. These planting stocks were maintained in the OTC for 12 months under different levels of elevated CO₂ (ambient control, 600 ppm, 900 ppm). After 12 months, the nodule numbers, bio mass, growth, and photosynthesis of C. equisetifolia rooted stem cuttings inoculated with Frankia were improved under 600 ppm of CO₂. The rooted stem cuttings of C. equisetifolia inoculated with Frankia showed a higher number of nodules under 900 ppm of CO₂ and cuttings without Frankia inoculation exhibited poor growth. Tissue Nitrogen (N) content was also higher under 900 ppm of CO₂ than ambient control and 600 ppm levels. The photosynthetic rate was higher (17.8 μ mol CO₂ m^?2 s^?1) in 900 ppm of CO₂ than in 600 ppm (13.2 μ mol CO₂ m^?2 s^?1) and ambient control (8.3 μ mol CO₂ m^?2 s^?1). This study showed that Frankia can improve growth, N fixation and photosynthesis of C. equietifolia rooted stem cuttings under extreme elevated CO₂ level conditions (900 ppm).     

Nitric oxide: a novel inducer for enhancement of microbial lipase production

The purpose of this study was to elucidate whether exogenous nitric oxide (NO) has a potential beneficial effect on lipase production capacity of some microorganisms. Sodium nitroprusside (SNP) was used as an exogenous NO donor in production medium. In comparison with the control (0 nM SNP), SNP concentrations from 10 to 100 nM induced lipase production in mesophilic bacterium Bacillus subtilis and cold-adapted yeast Yarrowia lipolytica. Especially, the maximum lipase activities for Y. lipolytica (81.2 U/L) and B. subtilis (74.5 U/L) were attained at 30 and 50 nM SNP concentrations, respectively. When compared to the control, the optimal SNP concentrations resulted in about 5.14 and 2.27-fold increases in lipase activities of B. subtilis and Y. lipolytica, respectively. Besides, it was found that the optimal SNP concentrations provided shorter incubation periods for lipase production. Conversely, no significant positive effect of exogenous NO on lipase production was determined for thermophilic bacterium Geobacillus stearothermophilus. This study showed for the first time that exogenous NO could be used as an inducer in the production of microbial lipases.     

Engineered <Emphasis Type="Italic">E. coli</Emphasis> W enables efficient 2,3-butanediol production from glucose and sugar beet molasses using defined minimal medium as economic basis

Background

Efficient microbial production of chemicals is often hindered by the cytotoxicity of the products or by the pathogenicity of the host strains. Hence 2,3-butanediol, an important drop-in chemical, is an interesting alternative target molecule for microbial synthesis since it is non-cytotoxic. Metabolic engineering of non-pathogenic and industrially relevant microorganisms, such as Escherichia coli, have already yielded in promising 2,3-butanediol titers showing the potential of microbial synthesis of 2,3-butanediol. However, current microbial 2,3-butanediol production processes often rely on yeast extract as expensive additive, rendering these processes infeasible for industrial production.

Results

The aim of this study was to develop an efficient 2,3-butanediol production process with E. coli operating on the premise of using cost-effective medium without complex supplements, considering second generation feedstocks. Different gene donors and promoter fine-tuning allowed for construction of a potent E. coli strain for the production of 2,3-butanediol as important drop-in chemical. Pulsed fed-batch cultivations of E. coli W using microaerobic conditions showed high diol productivity of 4.5 g l^?1 h^?1. Optimizing oxygen supply and elimination of acetoin and by-product formation improved the 2,3-butanediol titer to 68 g l^?1, 76% of the theoretical maximum yield, however, at the expense of productivity. Sugar beet molasses was tested as a potential substrate for industrial production of chemicals. Pulsed fed-batch cultivations produced 56 g l^?1 2,3-butanediol, underlining the great potential of E. coli W as production organism for high value-added chemicals.

Conclusion

A potent 2,3-butanediol producing E. coli strain was generated by considering promoter fine-tuning to balance cell fitness and production capacity. For the first time, 2,3-butanediol production was achieved with promising titer, rate and yield and no acetoin formation from glucose in pulsed fed-batch cultivations using chemically defined medium without complex hydrolysates. Furthermore, versatility of E. coli W as production host was demonstrated by efficiently converting sucrose from sugar beet molasses into 2,3-butanediol.

     

Assessment of active methanogenic archaea in a methanol-fed upflow anaerobic sludge blanket reactor

Methanogenic archaea enrichment of a granular sludge was undertaken in an upflow anaerobic sludge blanket (UASB) reactor fed with methanol in order to enrich methylotrophic and hydrogenotrophic methanogenic populations. A microbial community assessment, in terms of microbial composition and activity—throughout the different stages of the feeding process with methanol and acetate—was performed using specific methanogenic activity (SMA) assays, quantitative real-time polymerase chain reaction (qPCR), and high-throughput sequencing of 16S ribosomal RNA (rRNA) genes from DNA and complementary DNA (cDNA). Distinct methanogenic enrichment was revealed by qPCR of mcrA gene in the methanol-fed community, being two orders of magnitude higher with respect to the initial inoculum, achieving a final mcrA/16S rRNA ratio of 0.25. High-throughput sequencing analysis revealed that the resulting methanogenic population was mainly composed by methylotrophic archaea (Methanomethylovorans and Methanolobus genus), being also highly active according to the RNA-based assessment. SMA confirmed that the methylotrophic pathway, with a direct conversion of methanol to CH₄, was the main step of methanol degradation in the UASB. The biomass from the UASB, enriched in methanogenic archaea, may bear great potential as additional inoculum for bioreactors to carry out biogas production and other related processes.     

Medium factors on anaerobic production of rhamnolipids by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> SG and a simplifying medium for in situ microbial enhanced oil recovery applications

Aerobic production of rhamnolipid by Pseudomonas aeruginosa was extensively studied. But effect of medium composition on anaerobic production of rhamnolipid by P. aeruginosa was unknown. A simplifying medium facilitating anaerobic production of rhamnolipid is urgently needed for in situ microbial enhanced oil recovery (MEOR). Medium factors affecting anaerobic production of rhamnolipid were investigated using P. aeruginosa SG (Genbank accession number KJ995745). Medium composition for anaerobic production of rhamnolipid by P. aeruginosa is different from that for aerobic production of rhamnolipid. Both hydrophobic substrate and organic nitrogen inhibited rhamnolipid production under anaerobic conditions. Glycerol and nitrate were the best carbon and nitrogen source. The commonly used N limitation under aerobic conditions was not conducive to rhamnolipid production under anaerobic conditions because the initial cell growth demanded enough nitrate for anaerobic respiration. But rhamnolipid was also fast accumulated under nitrogen starvation conditions. Sufficient phosphate was needed for anaerobic production of rhamnolipid. SO₄ ^2? and Mg²⁺ are required for anaerobic production of rhamnolipid. Results will contribute to isolation bacteria strains which can anaerobically produce rhamnolipid and medium optimization for anaerobic production of rhamnolipid. Based on medium optimization by response surface methodology and ions composition of reservoir formation water, a simplifying medium containing 70.3 g/l glycerol, 5.25 g/l NaNO₃, 5.49 g/l KH₂PO₄, 6.9 g/l K₂HPO₄·3H₂O and 0.40 g/l MgSO₄ was designed. Using the simplifying medium, 630 mg/l of rhamnolipid was produced by SG, and the anaerobic culture emulsified crude oil to EI₂₄ = 82.5 %. The simplifying medium was promising for in situ MEOR applications.     

Digestive enzyme activities and gastrointestinal fermentation in wood-eating catfishes

To determine what capabilities wood-eating and detritivorous catfishes have for the digestion of refractory polysaccharides with the aid of an endosymbiotic microbial community, the pH, redox potentials, concentrations of short-chain fatty acids (SCFAs), and the activity levels of 14 digestive enzymes were measured along the gastrointestinal (GI) tracts of three wood-eating taxa (Panaque cf. nigrolineatus “Marañon”, Panaque nocturnus, and Hypostomus pyrineusi) and one detritivorous species (Pterygoplichthys disjunctivus) from the family Loricariidae. Negative redox potentials (?600 mV) were observed in the intestinal fluids of the fish, suggesting that fermentative digestion was possible. However, SCFA concentrations were low (<3 mM in any intestinal region), indicating that little GI fermentation occurs in the fishes’ GI tracts. Cellulase and xylanase activities were low (<0.03 U g^?1), and generally decreased distally in the intestine, whereas amylolytic and laminarinase activities were five and two orders of magnitude greater, respectively, than cellulase and xylanase activities, suggesting that the fish more readily digest soluble polysaccharides. Furthermore, the Michaelis–Menten constants (K _m) of the fishes’ β-glucosidase and N-acetyl-β-d-glucosaminidase enzymes were significantly lower than the K _m values of microbial enzymes ingested with their food, further suggesting that the fish efficiently digest soluble components of their detrital diet rather than refractory polysaccharides. Coupled with rapid gut transit and poor cellulose digestibility, the wood-eating catfishes appear to be detritivores reliant on endogenous digestive mechanisms, as are other loricariid catfishes. This stands in contrast to truly “xylivorous” taxa (e.g., beavers, termites), which are reliant on an endosymbiotic community of microorganisms to digest refractory polysaccharides.     

Parameterization of surface irradiance and primary production in Århus Bay,SW Kattegat,Baltic Sea

The aims of the present study were to develop a parameterization of a one-year-long observed PAR time-series, apply the PAR parameterization in a primary production relation, and compare calculated and observed time-series of primary production. The PAR parameterization was applied in the generally used relation for the primary production (P _d): P _d = a(BI ₀ Z ₀) + b with observed photic depth (Z ₀) and Chl-a concentrations (B). It was tested whether the PAR parameterization in combination with this simple relation for primary production was able to describe the actual measured primary production. The study is based on a one year long time-series of PAR, CTD-casts (n = 45), and primary production measurements (n = 24) from Århus Bay (56°09′ N; 10°20′ E), south west Kattegat. Results showed a high and positive correlation between observed and calculated primary production in the bay, as based on the present PAR parameterization combined with the simple primary production relation. The developed PAR parameterization, which calculates total daily surface irradiance per day (M photons m^?2 d^?1), can be applied in any ecological application taking into account that it was developed for the latitude of 56° N.     

The rhizosphere microbial community response to a bio-organic fertilizer: finding the mechanisms behind the suppression of watermelon <Emphasis Type="Italic">Fusarium</Emphasis> wilt disease

We aimed to evaluate the capability of bio-organic fertilizer suppressing watermelon Fusarium wilt disease, compare the variations of the rhizosphere bacterial and fungal community compositions after treatment with different fertilizers, and explore mechanisms causing disease suppression in rhizosphere microbial community. A rhizobacterium (Bacillus amyloliquefaciens JDF35) was identified to control watermelon Fusarium wilt disease. Bio-organic fertilizer JDF35 (BOF) was generated by inoculating JDF35 into the organic fertilizer (OF) composed of cow and chicken manure compost (1:50 v/w). A three successive growing season pot experiment was designed to evaluate the effects of BOF compared with OF and chemical fertilizer (CF). Next-generation sequencing using the Illumina MiSeq platform was used to investigate the variations in rhizosphere microbial community composition. The growth of the watermelon plants, soil pH, and available N, P and K concentrations were the highest in the BOF treatment. The Fusarium wilt incidence in the BOF treatment was lower than that in the CF and OF treatment, and the differences for disease incidence were significant (P < 0.001). The diversity of the rhizosphere bacterial community was higher, and that of the fungal was lower in the BOF treatment. Most importantly, the BOF treatment had lowest abundances of Fusarium. The application of the BOF altered the composition of rhizosphere microbial community, suppressing Fusarium wilt disease and promoting plant growth.