Tracing carbon monoxide uptake by Clostridium ljungdahlii during ethanol fermentation using 13C-enrichment technique

Conversion of synthesis gas (CO and H₂) to ethanol can be an alternative, promising technology to produce biofuels from renewable biomass. To distinguish microbial utilization of carbon source between fructose and synthesis gas CO and to evaluate biological production of ethanol from CO, we adopted the ¹³C-enrichment of the CO substrate and hypothesized that the residual increase in δ¹³C of the cell biomass would reflect the increased contribution of ¹³C-enriched CO. Addition of synthesis gas to live culture medium for ethanol fermentation by Clostridum ljungdahlii increased the microbial growth and ethanol production. Despite the high ¹³C-enrichment in CO (99 atom % ¹³C), however, microbial δ¹³C increased relatively small compared to the microbial growth. The uptake efficiency of CO estimated using the isotope mass balance equation was also very low: 0.0014 % for the low CO and 0.0016 % for the high CO treatment. Furthermore, the fast production of ethanol in the early stage indicated that the presence of sugar in fermentation medium would limit the utilization of CO as a carbon source by C. ljungdahlii.     

Vertical distribution of bacterial community is associated with the degree of soil organic matter decomposition in the active layer of moist acidic tundra

The increasing temperature in Arctic tundra deepens the active layer, which is the upper layer of permafrost soil that experiences repeated thawing and freezing. The increasing of soil temperature and the deepening of active layer seem to affect soil microbial communities. Therefore, information on soil microbial communities at various soil depths is essential to understand their potential responses to climate change in the active layer soil. We investigated the community structure of soil bacteria in the active layer from moist acidic tundra in Council, Alaska. We also interpreted their relationship with some relevant soil physicochemical characteristics along soil depth with a fine scale (5 cm depth interval). The bacterial community structure was found to change along soil depth. The relative abundances of Acidobacteria, Gammaproteobacteria, Planctomycetes, and candidate phylum WPS-2 rapidly decreased with soil depth, while those of Bacteroidetes, Chloroflexi, Gemmatimonadetes, and candidate AD3 rapidly increased. A structural shift was also found in the soil bacterial communities around 20 cm depth, where two organic (upper Oi and lower Oa) horizons are subdivided. The quality and the decomposition degree of organic matter might have influenced the bacterial community structure. Besides the organic matter quality, the vertical distribution of bacterial communities was also found to be related to soil pH and total phosphorus content. This study showed the vertical change of bacterial community in the active layer with a fine scale resolution and the possible influence of the quality of soil organic matter on shaping bacterial community structure.     

Effects of phosphate addition on biofilm bacterial communities and water quality in annular reactors equipped with stainless steel and ductile cast iron pipes

The impact of orthophosphate addition on biofilm formation and water quality was studied in corrosion-resistant stainless steel (STS) pipe and corrosion-susceptible ductile cast iron (DCI) pipe using cultivation and culture-independent approaches. Sample coupons of DCI pipe and STS pipe were installed in annular reactors, which were operated for 9 months under hydraulic conditions similar to a domestic plumbing system. Addition of 5 mg/L of phosphate to the plumbing systems, under low residual chlorine conditions, promoted a more significant growth of biofilm and led to a greater rate reduction of disinfection by-products in DCI pipe than in STS pipe. While the level of THMs (trihalomethanes) increased under conditions of low biofilm concentration, the levels of HAAs (halo acetic acids) and CH (chloral hydrate) decreased in all cases in proportion to the amount of biofilm. It was also observed that chloroform, the main species of THM, was not readily decomposed biologically and decomposition was not proportional to the biofilm concentration; however, it was easily biodegraded after the addition of phosphate. Analysis of the 16S rDNA sequences of 102 biofilm isolates revealed that Proteobacteria (50%) was the most frequently detected phylum, followed by Firmicutes (10%) and Actinobacteria (2%), with 37% of the bacteria unclassified. Bradyrhizobium was the dominant genus on corroded DCI pipe, while Sphingomonas was predominant on non-corroded STS pipe. Methylobacterium and Afipia were detected only in the reactor without added phosphate. PCR-DGGE analysis showed that the diversity of species in biofilm tended to increase when phosphate was added regardless of the pipe material, indicating that phosphate addition upset the biological stability in the plumbing systems.     

Corn uptake and microbial immobilization of 15N-labeled urea-N in soil as affected by composted pig manure

The tolerance of 24 genotypes of barley was assessed by estimating their survival in saline conditions either in a glasshouse or in a controlled environment cabinet. Two cultivars, sensitive Triumph and resistant Gerbel, were picked for further study, which involved sequential harvesting of plants grown in a range of salinities. After about one month in 200 mol m^–3 sodium chloride, the sodium concentration in the roots and shoots of the sensitive Triumph was about 1.5 times that in the roots of resistant Gerbel. The addition of Na to the root medium reduced the potassium transport to the shoot in Triumph to a much greater extent than in Gerbel, so the K:Na ratio of Gerbel was twice that for Triumph, when averaged over all treatments and harvests. The sodium, potassium and chloride concentrations within the major subcellular compartments of the cortical cells of roots of Triumph and Gerbel were determined by X-ray microanalysis following freeze-substitution and dry-sectioning. The mean cytoplasmic sodium concentration (245 mol m^–3 analysed volume) in Triumph grown in 200 mol m^–3 NaCl for 15 d was almost 1.4 times greater than that in the resistant Gerbel: the potassium concentration in Gerbel showed a lower reduction than did that of Triumph. Another major difference between the two cultivars was the higher concentrations of sodium and chloride in the cell walls of Triumph than Gerbel: the sodium concentration in the cortical cell walls of the salt-sensitive cultivar was about 1.75 times that in the more salt-resistant cultivar. The exchange capacity of the cell walls of Gerbel was greater than that of Triumph. We hypothesise that ion transport to the shoot reflects cytosolic ion concentrations, with a more sensitive cultivar having a higher sodium concentration in its cytoplasm than a more resistant variety. It is noteworthy that the difference in the K:Na ratio between the shoots of Gerbel and Triumph after 15 days of exposure to 200 mol m^–3 NaCl was similar to the difference in their symplastic K:Na ratios.     

Dry matter and nitrogen accumulation and partitioning in rice (Oryza sativa L.) exposed to experimental warming with elevated CO2

Effects of elevated CO₂ concentration ([CO₂]) and air temperature (T_air) on accumulation and intra-plant partitioning of dry matter (DM) and nitrogen in paddy rice were investigated by performing a pot experiment in six natural sunlit temperature gradient chambers (TGCs) with or without CO₂ fumigation. Rice (Oryza sativa L.) plants were grown in TGCs for a whole season under two levels of [CO₂] (ambient, 380 ppm; elevated, 622 ppm) and two daily T_air regimes (ambient, 25.2°C; elevated, 27.3°C) in split-plot design with triplication. The effects of elevated [CO₂] and T_air on DM were most dramatic for grain and shoot with a significant (P?<?0.05) interaction between [CO₂] and T_air. Overall, total grain DM increased with elevated [CO₂] by 69.6% in ambient T_air but decreased with elevated T_air by 33.8% in ambient [CO₂] due to warming-induced floral sterility. Meanwhile, shoot DM significantly increased with elevated T_air by 20.8% in ambient [CO₂] and by 46.6% in elevated [CO₂]. Although no [CO₂]?×?T_air interaction was detected, the greatest total DM was achieved by co-elevation of [CO₂] and T_air (by 42.8% relative to the ambient conditions) via enhanced shoot and root DM accumulation, but not grain. This was attributed largely both to increase in tiller number and to accumulation of photosynthate in the shoot and root due to inhibition of photosynthate allocation to grain caused by warming-induced floral sterility. Distribution of N (both soil N and fertilizer ¹⁵N) among rice parts in responding to climatic variables entirely followed the pattern of DM. Our findings demonstrate that the projected warming is likely to induce a significant reduction in grain yield of rice by inhibiting DM (i.e., photosynthates) allocation to grain, though this may partially be mitigated by elevated [CO₂].     

Photosynthetic characteristics and growth responses of dwarf apple (Malus domestica Borkh. cv. Fuji) saplings after 3 years of exposure to elevated atmospheric carbon dioxide concentration and temperature

Growth and photosynthetic responses of dwarf apple saplings (Malus domestica Borkh. cv. Fuji) acclimated to 3 years of exposure to contrasting atmospheric CO₂ concentrations (360 and 650 µmol mol^-1) in combination with current ambient or elevated (ambient +5°C) temperature patterns were determined. Four 1-year-old apple saplings grafted onto M.9 rootstocks were each enclosed in late fall 1997 in a controlled environment unit in nutrient-optimal soil. Soil moisture regimes were automatically controlled by drip irrigation scheduled at 50 kPa of soil moisture tension. For the elevated CO₂ concentration alone, overall tree growth was suppressed. However, tree growth was slightly enhanced when warmer temperatures were combined with the elevated CO₂ concentration. Neither temperature nor CO₂ concentration affected leaf chlorophyll content and stomatal density. The elevated CO₂ concentration decreased mean leaf area, but increased starch accumulation, thus resulting in a higher specific dry mass of leaves. An elevated temperature reduced starch accumulation. Light-saturated rates of leaf photosynthesis were suppressed due to the elevated CO₂ concentration, but this effect was removed or enhanced with warmer temperatures. The elevated CO₂ concentration increased the optimum temperature for photosynthesis by ca. 4°C, while the warmer temperature did not. The results of this study suggested that the long-term adaptation of apple saplings to growth at an elevated CO₂ concentration may be associated with a potential for increased growth and productivity, if a doubling of the CO₂ concentration also leads to elevated temperatures.     

Recovery of fertilizer-derived inorganic-15N in a vegetable field soil as affected by application of an organic amendment

To examine the effect of organic amendment application on the fate of inorganic-N accumulated in a vegetable field soil during conversion from inorganic to organic input, a pot experiment using ¹⁵N-labeled soil was conducted. The soil was labeled with ¹⁵N through addition of urea-¹⁵N (98 atom % ¹⁵N) and was then incubated for 1 year resulting in inorganic soil-N concentration and ¹⁵N abundance of 211 mg kg^–1 soil and 4.950 atom %, respectively. Chinese cabbage [Brassica campestris (L.) Samjin] plants were grown in the labeled soil for 30 and 60 days after application of organic amendment at the rates of 0 (control), 200, 400, and 600 mg N kg^–1 soil. Although organic amendment application did not show any significant effect on the uptake efficiency of inorganic-N by Chinese cabbage during the first 30 days, it significantly (P<0.05) increased inorganic-N uptake efficiency as well as total-N uptake and dry matter yield at the end of the 60-day growth period. Application of the organic amendment also increased microbial immobilization of inorganic-N in both growth periods. Between 30 and 60 days of growth, however, the amount of immobilized N from the inorganic-¹⁵N pool decreased, indicating re-mineralization of previously immobilized N. Although the amount of inorganic-¹⁵N lost was virtually the same among treatments at day 30, increased immobilization of inorganic-¹⁵N caused by organic amendment application led to the higher retention of inorganic-N in the soil and less loss of N at day 60 as compared to the control. These results indicate that increased immobilization by organic amendment application in the early growth season and the subsequent gradual re-mineralization may play an important role in increasing plant uptake of inorganic-¹⁵N, while minimizing N loss.     

Changes in nitrogen isotopic compositions during composting of cattle feedlot manure: effects of bedding material type

Temporal changes in delta(15)N of cattle feedlot manure during its composting with either rice hull (RHM) or sawdust (SDM) as bedding materials were investigated. Regardless of the bedding material used, the delta(15)N of total N in the manure increased sharply from +7.6 per thousand to +9.9 per thousand and from +11.4 per thousand to +14.3 per thousand, respectively, in RHM or SDM, within 10 days from the commencement of composting. Such increases could be attributed primarily to N loss via NH(3) volatilization and denitrification based on the very high delta(15)N values (greater than +20 per thousand) of NH(4)(+) and NO(3)(-) in the co-composted manure. The delta(15)N of total N in RHM was substantially lower (by more than 3 per thousand) than that in SDM, suggesting that the delta(15)N of the composted manure was affected not only by N loss but also by the type of bedding material used. Specifically, the higher N concentration in the rice hull than in the saw dust could lead to a greater (15)N isotope dilution.     

Natural 15N abundances of maize and soil amended with urea and composted pig manure

To investigate the effect of inorganic fertilizer and composted manure amendments on the N isotope composition (delta ¹⁵N) of crop and soil, maize (Zea mays L.) was cultivated under greenhouse conditions for 30, 40, 50, 60, and 70 days. Composted pig manure (delta ¹⁵N= +13.9) and urea (-2.3) were applied at 0 and 0 kg N ha^–1 (C0U0), 0 and 150 kg N ha^–1 (C0U2), 150 and 0 kg N ha^–1 (C2U0), and 75 and 75 kg N ha^–1 (C1U1), respectively. The delta ¹⁵N of total soil-N was not affected by both amendments, but delta ¹⁵N of NH⁺ ₄ and NO^– ₃ provided some information on the N isotope fractionation in soil. During the early growth stage, significant differences (P < 0.05) in delta ¹⁵N among maize subjected to different treatments were observed. After 30 days of growth, the delta ¹⁵N values of maize were +6.6 for C0U0, +1.1 for C0U2, +7.7 for C2U0, and +4.5 for C1U1. However, effects of urea and composted manure application on maize delta ¹⁵N progressively decreased with increasing growth period, probably due to isotope fractionation accompanying N losses and increased uptake of soil-derived N by maize. After 70 days of growth, delta ¹⁵N of leaves and grains of maize amended with composted pig manure were significantly (P < 0.05) higher than those with urea. The temporal variations in delta ¹⁵N of maize amended with urea and composted manure indicate that plant delta ¹⁵N is generally not a good tracer for N sources applied to field. Our data can be used in validation of delta ¹⁵N fractionation models in relation to N source inputs.