Although the emission of N₂ via anaerobic ammonium oxidation (anammox) is a key process in the elimination of nitrogenous compounds from aquatic environments, little information is available regarding its significance and the relevant microorganisms (anammox bacteria) in eutrophic freshwater lakes. In the present study, the anammox bacteria in the sediment of a eutrophic lake in Japan, Lake Kitaura, were examined using a ¹⁵N-tracer technique to measure their potential anammox activity. Potential anammox activity was localized to the northern region of the lake where a stable supply of both NH₄⁺ and NO₃^- existed in the sediment. These results suggest the contribution of anammox bacteria to the total emission of N₂ from sediment in this eutrophic lake to not be negligible. Moreover, selective PCR successfully amplified anammox bacteria-related (Brocadiales-related) 16S rRNA genes from sediment samples in which potential anammox activity was observed. The clone libraries consisted of diverse phylotypes except the genus “Scalindua”-lineages, and the lineages of genus “Brocadia” were dominantly recovered, followed by the genus “Kuenenia”-lineages. Most of them, however, were novel and phylogenetically distinguishable from known Brocadiales species. A unique population of anammox bacteria inhabits and potentially contributes to the emission of N₂ from Lake Kitaura.

抄録全体を表示

South Korea uses more antibiotics for animal production than any other member of the OECD. The excessive use could potentially lead to a greater incidence of antibiotic resistant microorganisms, some of which may be pathogenic. In this study, we examined potential diarrheagenic and extraintestinal pathogenic E. coli (ExPEC) isolates using virulence gene profiling (eaeA, est, elt, ipaH, stx1 and stx2 as diarrheagenic and afa/dra, iutA, kpsMT II, papA/C, and sfa/foc as extraintestinal pathogenic virulence genes). A cluster analysis of DNA fingerprint data indicated that certain genotypes of chicken E. coli isolates are likely ExPEC. Moreover, our results showed 38 of the 60 potential diarrheagenic and ExPEC isolates obtained from animals and humans were also resistant to antibiotics, mostly to tetracycline groups, penicillin groups, and folate pathway inhibitors. Our results suggest that the use of antibiotics in agriculture should be controlled due to potential impacts on human health.

抄録全体を表示

Microbes in sediments below fish farming cages are exposed to a variety of compounds used in aquaculture, such as antifoulants, antimicrobials and mercury. Here, we assessed the abundance of the mercury resistance gene merA in the sediment of four fish farms and four pristine sites using quantitative PCR, and at three fish farms and two pristine sites by constructing clone libraries and sequencing merA amplicons. The abundance of merA was consistently greater at fish farm sites than at pristine sites, and the merA phylotypes were different between fish farm and pristine sites. Mercury concentrations were too low to cause selection pressure and did not differ significantly among samples. The primers designed specifically for this study were capable of detecting two new potential merA clades.

抄録全体を表示

Laboratory-scale solid-phase denitrification (SPD) reactors for nitrate removal were constructed by acclimating activated sludge with poly (L-lactic acid) (PLLA) having weight-average molecular weights (M_w) of 9,900, 12,000, and 45,100 g mol^-1. A good nitrate removal rate (3.5-5.3 mg NO₃^--N g [dry wt]^-1 h^-1) was found in the reactor containing PLLA of 9,900 g mol^-1, whereas the other two reactors with the higher M_w PLLA showed low nitrate removal efficiency. Microbial community dynamics in the low M_w PLLA-acclimated reactor were studied by 16S rRNA gene-targeted PCR-denaturing gradient gel electrophoresis and quinone profiling. Nonmetric multidimensional scaling analyses of these data sets revealed a marked population shift during acclimation of the SPD reactor with low M_w PLLA. The 16S rRNA gene clone library and culture-dependent analyses showed that bacteria belonging to the family Comamonadaceae predominated and played the primary role in denitrification in the PLLA-using reactor; however, none of the bacterial isolates from the reactor degraded PLLA. These results suggest that the nitrate removal property of the PLLA-using SPD reactor is attained through the bioavailability of hydrolysates released abiotically from the solid substrate.

抄録全体を表示

This study focused on the evaluation of cellulolytic and hemicellulolytic fungi isolated from sawdust compost (SDC) and coffee residue compost (CRC). To identify fungal isolates, the ITS region of fungal rRNA was amplified and sequenced. To evaluate enzyme production, isolates were inoculated onto wheat bran agar plates, and enzymes were extracted and tested for cellulase, xylanase, β-glucanase, mannanase, and protease activities using different azurine cross-linked (AZCL) substrates. In total, 18 isolates from SDC and 29 isolates from CRC were identified and evaluated. Four genera (Aspergillus, Galactomyces, Mucor, and Penicillium) and five genera (Aspergillus, Coniochaeta, Fusarium, Penicillium, and Trichoderma/Hypocrea) were dominant in SDC and CRC, respectively. Penicillium sp., Trichoderma sp., and Aspergillus sp. displayed high cellulolytic and hemicellulolytic activities, while Mucor isolates exhibited the highest β-glucanase and mannanase activities. The enzyme analyses revealed that Penicillium, Aspergillus, and Mucor isolates significantly contributed to the degradation of SDC, whereas Penicillium, Aspergillus, and Trichoderma isolates had a dominant role in the degradation of CRC. Notably, isolates SDCF5 (P. crustosum), CRCF6 (P. verruculosum), and CRCF2 and CRCF16 (T. harzianum/H. lixii) displayed high activity regarding cellulose and hemicellulose degradation, which indicates that these species could be beneficial for the improvement of biodegradation processes involving lignocellulosic materials.

抄録全体を表示

Fungal communities associated with roots play an important role in nutrient cycling, supporting plant growth and the biocontrol of plant diseases. Experiments were conducted in 2004-2006 to isolate and characterize, based on their morphological features, rhizosphere and rhizoplane fungi from perennial grasses of the subfamily Panicoideae growing in forests of the Western Ghats in India. Fungal species were isolated on potato dextrose, czapeck dox and water agar, in different locations and seasons. The results obtained on PDA were used for detailed analysis since most fungi occurred in high percentages. While certain grasses harbored diverse fungal species, others supported only a few species. Most fungi were isolated during winter followed by the rainy and summer seasons. The species richness, diversity and evenness of fungal assemblages in the rhizosphere and rhizoplane depended on the grass species and season. Ascomycetes were isolated in large numbers in most grass species. Species of Aspergillus, Chaetomium, Penicillium and Trichoderma occurred frequently. Certain others and non-sporulating fungi were grass species-specific. Most fungal species colonized the middle of the root more than the root tip or root base. Results suggest that perennial grasses harbor diverse fungal communities whose potential could be tapped for producing secondary metabolites and managing plant diseases.

抄録全体を表示

Microorganisms uplifted during dust storms survive long-range transport in the atmosphere and could colonize high-altitude snow. Bacterial communities in alpine snow on a Mont Blanc glacier, associated with four depositions of Saharan dust during the period 2006-2009, were studied using 16S rRNA gene sequencing and flow cytometry. Also, sand from the Tunisian Sahara, Saharan dust collected in Grenoble and Mont Blanc snow containing no Saharan dust (one sample of each) were analyzed. The bacterial community composition varied significantly in snow containing four dust depositions over a 3-year period. Out of 61 phylotypes recovered from dusty snow, only three phylotypes were detected in more than one sample. Overall, 15 phylotypes were recognized as potential snow colonizers. For snow samples, these phylotypes belonged to Actinobacteria, Proteobacteria and Cyanobacteria, while for Saharan sand/dust samples they belonged to Actinobacteria, Bacteroidetes, Deinococcus-Thermus and Proteobacteria. Thus, regardless of the time-scale, Saharan dust events can bring different microbiota with no common species set to alpine glaciers. This seems to be defined more by event peculiarities and aeolian transport conditions than by the bacterial load from the original dust source.

抄録全体を表示

Soil type is one of the key factors affecting soil microbial communities. With regard to ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), however, it has not been determined how soil type affects their community size and soil nitrification activity. Here we quantitatively analyzed the ammonia monooxygenase genes (amoA) of these ammonia oxidizers in fields with three different soil types (Low-humic Andosol [LHA], Gray Lowland Soil [GLS], and Yellow Soil [YS]) under common cropping conditions, and assessed the relationships between soil nitrification activity and the abundance of each amoA. Nitrification activity of LHA was highest, followed by that of GLS and YS; this order was consistent with that for the abundance of AOB amoA. Abundance of AOB amoA showed temporal variation, which was similar to that observed in nitrification activity, and a strong relationship (adjusted R²=0.742) was observed between the abundance of AOB amoA and nitrification activity. Abundance of AOA amoA also exhibited a significant relationship (adjusted R²=0.228) with nitrification activity, although this relationship was much weaker. Our results indicate that soil type affects the community size of AOA and AOB and the resulting nitrification activity, and that AOB are major contributors to nitrification in soils, while AOA are partially responsible.

抄録全体を表示

Effects of different land uses on densities of Escherichia coli, enterococci, and Clostridium perfringens in the water and soil of a tropical watershed were investigated. Densities of fecal indicator bacteria (FIBs) in the watershed exhibited a clear land-use dependency in the stream water. Significantly higher concentrations were detected in the urban portion of the stream (417, 420, and 44 CFU 100 mL^-1 for E. coli, enterococci, and C. perfringens, respectively) than in the forest portion (54, 32, and 5 CFU 100 mL^-1 for E. coli, enterococci, and C. perfringens, respectively). High concentrations of FIBs were also detected in the soil of the watershed with concentration ranges of 603-1,820,000, 69-17,000, and 0-525 CFU 100 g soil^-1 for E. coli, enterococci, and C. perfringens, respectively, which however were not affected by the different land uses. Prior cumulative rainfall significantly correlated with concentrations of E. coli and enterococci in the urban stream water (r=0.73-0.87, P<0.05), but not with the alternative FIB C. perfringens. Poor correlations were observed in the forest reach of the stream for all FIBs. Furthermore, the concentration of C. perfringens only correlated strongly and significantly with E. coli and enterococci in stream water (r=0.70-0.82, P<0.05), but not in tropical soil, indicating different survival and transport behaviors.

抄録全体を表示

A high-density 16S rRNA gene microarray was used to analyze microbial communities in a slurry of ethanol-amended, uranium-contaminated subsurface sediment. Of specific interest was the extent to which the microarray could detect temporal patterns in the relative abundance of major metabolic groups (nitrate-reducing, metal-reducing, sulfate-reducing, and methanogenic taxa) that were stimulated by ethanol addition. The results show that the microarray, when used in conjunction with geochemical data and knowledge of the physiological properties of relevant taxa, provided accurate assessment of the response of key functional groups to biostimulation.

抄録全体を表示

Twenty-five replicates of growth medium for anaerobic ammonium oxidation (anammox) containing ¹⁵N-labeled ammonium and non-labeled nitrite were inoculated into an anammox enrichment culture at low density, and anaerobically incubated batchwise. In the headspace, ²⁹N₂ partial pressure linearly increased via anammox in 25 vials, confirming that anammox populations were viable in all subcultures. On prolonged incubation, exponential increases in ²⁹N₂ were not observed in all but 13 subcultures, suggesting that the anammox population may not proliferate unless all conditions for growth are satisfied. The estimated first-order rate coefficients in those 13 subcultures varied from 0.0029 to 0.0048 h^-1.

抄録全体を表示