Robert J. Mitchell

Fine root branch orders respond differentially to carbon source-sink manipulations in a longleaf pine forest.

Fine roots are a key component of carbon (C) flow and nitrogen (N) cycling in forest ecosystems. However, the complexity and heterogeneity of the fine root branching system have hampered the assessment and prediction of C and N dynamics at ecosystem scales. We examined how root morphology, biomass, and chemistry differed with root branch orders (1–5 with root tips classified as first order roots) and how different root orders responded to increased C sink strength (via N fertilization) and reduced carbon source strength (via canopy scorching) in a longleaf pine (Pinus palustris L.) ecosystem. With increasing root order, the diameter and length of individual roots increased, whereas the specific root length decreased. Total root biomass on an areal basis was similar among the first four orders but increased for the fifth order roots. Consequently, total root length and total root surface area decreased systematically with increasing root order. Fine root N and lignin concentrations decreased, while total non-structural carbohydrate (TNC) and cellulose concentrations increased with increasing root order. N addition and canopy disturbance did not alter root morphology, but they did influence root chemistry. N fertilization increased fine root N concentration and content per unit area in all five orders, while canopy scorching decreased root N concentration. Moreover, TNC concentration and content in fifth order roots were also reduced by canopy scorching. Our results indicate that the small, fragile, and more easily overlooked first and second order roots may be disproportionately important in ecosystem scale C and N fluxes due to their large proportions of fine root biomass, high N concentrations, relatively short lifespans, and potentially high decomposition rates.

A biosensor for the detection of gas toxicity using a recombinant bioluminescent bacterium

A whole-cell biosensor was developed for the detection of gas toxicity using a recombinant bioluminescent Escherichia coli harboring a lac::luxCDABE fusion. Immobilization of the cells within LB agar has been done to maintain the activity of the microorganisms and to detect the toxicity of chemicals through the direct contact with gas. Benzene, known as a representative volatile organic compound, was chosen as a sample toxic gas to evaluate the performance of this biosensor based on the bioluminescent response. This biosensor showed a dose-dependent response, and was found to be reproducible. The immobilizing matrices of this biosensor were stored at 4 degrees C and were maintained for at least a month without any noticeable change in its activity. The optimal temperature for sensing was 37 degrees C. A small size of this sensor kit has been successfully fabricated, and found to be applicable as a disposable and portable biosensor to monitor the atmospheric environment of a workplace in which high concentrations of toxic gases could be discharged.

The Future of Butyric Acid in Industry

In this paper, the different applications of butyric acid and its current and future production status are highlighted, with a particular emphasis on the biofuels industry. As such, this paper discusses different issues regarding butyric acid fermentations and provides suggestions for future improvements and their approaches.

The dual probiotic and antibiotic nature of Bdellovibrio bacteriovorus.

Bdellovibrio bacteriovorus is a predatory bacterium which attacks and consumes other bacterial strains, including the well known pathogens E. coli O157 : H7, Salmonella typhimurium and Helicobacter pylori. This remarkable activity has been the focus of research for nearly five decades, with exciting practical applications to medical, agriculture and farming practices recently being published. This article reviews many of the exciting steps research into this bacterium, and similar bacteria, has taken, focusing primarily on their use as both an antibiotic to remove harmful and pathogenic bacteria and as a probiotic to help curb and control the bacterial populations within the intestinal tract. Owing to the unique and dual nature of this bacterium, this review proposes the use of amphibiotic to describe these bacteria and their activities.

Competitive responses of seedlings and understory plants in longleaf pine woodlands: separating canopy influences above and below ground

A trenching study was used to investigate above- and below-ground competition in a longleaf pine (Pinus pal- ustris P. Mill.) woodland. Trenched and nontrenched plots were replicated in the woodland matrix, at gap edges, and in gap centers representing a range of overstory stocking. One-half of each plot received a herbicide treatment to remove the understory. We monitored pine survival and growth, understory productivity, light level (gap fraction), and soil resources. The overstory facilitated pine seedling survival. Pine seedling growth was reduced as overstory stocking increased. Re- duced growth of seedlings was also observed in gaps when the understory was left intact. Understory plants competed with seedlings by filling the root gaps that developed as a result of overstory disturbance. Hardwood growth increased in gaps, owing to decreased belowground competition with adult pines, while growth of herbaceous plants and pine seedlings increased with light availability. Large overstory gaps are not required to initiate regeneration in longleaf pine woodlands. Retaining overstory dispersed throughout the stand but variable in density, through single-tree selection approaches, may be an alternative to gap-based approaches. This approach would allow for the fuel continuity needed to sustain the fre- quent fire required to maintain the diversity characteristic of this type of woodland. Resume´ : Un dispositif de tranchees a eteutilisepour etudier la competition aerienne et souterraine dans une station for- estiere dominee par le pin des marais (Pinus palustris P. Mill.). Des placettes avec ou sans tranchees ont eterepetees dans une matrice forestiere, en bordure de trouees et au centre de trouees, ce qui correspondait a un gradient de densiterelative du couvert. La moitiede chaque placette a etetraiteealaide dun herbicide pour eliminer les plantes du sous-etage. Nous avons suivi la survie et la croissance des pins, la productivitedes plantes du sous-etage, la lumiere (ouverture du couvert) et les ressources du sol. Les ouvertures dans le couvert dominant ont augmentele taux de survie des semis de pin. La croissance des semis de pin a etereduite par une augmentation de la densiterelative du couvert dominant. Une diminution

Soil nitrogen dynamics in a fire-maintained forest ecosystem: results over a 3-year burn interval

Abstract Longleaf pine ecosystems throughout the southeastern United States developed under recurring fire disturbance, which often leads to conditions of low fertility, particularly reduced N pools in the soil. While numerous studies have documented short-term effects of prescribed burning on nutrient dynamics, few have evaluated the consequences of repeated fire on N availability and ecosystem productivity over longer time frames, such as a 3-year fire return interval. We assessed the environmental controls on soil inorganic N flux over a typical burn interval (3xa0yr) and related N availability patterns to aboveground net primary productivity (ANPP) and N demand across a hydrologic gradient in a longleaf pine—wiregrass landscape. Net N mineralization was measured within 0–10 and 0–90xa0cm soil depths to determine the influence of belowground litter inputs (via fine root turnover) on N dynamics. After 42xa0mos, annual estimates of N mineralization were 11.8, 6.8 and 3.5xa0kgxa0ha−1xa0yr−1 for the top 10xa0cm of soil and 15.5, 11.4, and 5.3xa0kgxa0ha−1xa0yr−1 for the top 90xa0cm of soil for xeric, mesic and wet-mesic sites, respectively. Overall, N mineralization rates were negatively correlated with both ANPP and bulk soil moisture, and were insufficient to supply estimated ANPP-N demands. These results suggest that belowground litter inputs may indeed influence N cycling patterns in these frequently burned systems but may not entirely account for the discrepancy between N availability and ANPP-N demand.

Continuous hydrogen and butyric acid fermentation by immobilized Clostridium tyrobutyricum ATCC 25755: Effects of the glucose concentration and hydraulic retention time

The effects of the hydraulic retention time (HRT=8, 10, 12 or 16.7 h) and glucose concentration (30, 40 or 50 g/L) on the production of hydrogen and butyrate by an immobilized Clostridium tyrobutyricum culture, grown under continuous culturing conditions, were evaluated. With 30 g/L glucose, the higher HRTs tested led to greater butyrate concentrations in the culture, i.e., 9.3 g/L versus 12.9 g/L with HRTs of 8 h and 16.7 h, respectively. In contrast, higher biogas and hydrogen production rates were generally seen when the HRT was lower. Experiments with different glucose concentrations saw a significant amount of glucose washed out when 50 g/L was used, the highest being 22.7 g/L when the HRT was 16.7 h. This study found the best conditions for the continuous production of hydrogen and butyric acid by C. tyrobutyricum to be with an HRT of 12 h and a glucose concentration of 50 g/L, respectively.

Interactions among overstory structure, seedling life-history traits, and fire in frequently burned neotropical pine forests.

Abstract Fire-dependent pine forests in the Caribbean Basin cover extensive areas in the coastal plain of the Caribbean Sea and Gulf of Mexico and on several islands in the Bahamas Archipelago, Cuba, Hispaniola, and the Honduran Bay islands. These forests are high in conservation value but, unfortunately, remain mostly unprotected. Moreover, even though they are fire dependent, the use of fire for forest management often suffers from poor public perception and is prohibited by law in several countries. In this paper, we describe the fundamental links among fire, forest regeneration, and forest persistence in these ecosystems. We identify two general strategies based on the presence or absence of pine seedling adaptations for fire survival and describe management implications of these two strategies. We also introduce conceptual models describing fire, forest structure, and regeneration strategy linkages.

Bdellovibrio bacteriovorus Inhibits Staphylococcus aureus Biofilm Formation and Invasion into Human Epithelial Cells

Bdellovibrio bacteriovorus HD100 is a predatory bacterium that attacks many Gram-negative human pathogens. A serious drawback of this strain, however, is its ineffectiveness against Gram-positive strains, such as the human pathogen Staphylococcus aureus. Here we demonstrate that the extracellular proteases produced by a host-independent B. bacteriovorus (HIB) effectively degrade/inhibit the formation of S. aureus biofilms and reduce its virulence. A 10% addition of HIB supernatant caused a 75% or greater reduction in S. aureus biofilm formation as well as 75% dispersal of pre-formed biofilms. LC-MS-MS analyses identified various B. bacteriovorus proteases within the supernatant, including the serine proteases Bd2269 and Bd2321. Tests with AEBSF confirmed that serine proteases were active in the supernatant and that they impacted S. aureus biofilm formation. The supernatant also possessed a slight DNAse activity. Furthermore, treatment of planktonic S. aureus with the supernatant diminished its ability to invade MCF-10a epithelial cells by 5-fold but did not affect the MCF-10a viability. In conclusion, this study illustrates the hitherto unknown ability of B. bacteriovorus to disperse Gram-positive pathogenic biofilms and mitigate their virulence.

Nitrogen decreases and precipitation increases ectomycorrhizal extramatrical mycelia production in a longleaf pine forest

The rates and controls of ectomycorrhizal fungal production were assessed in a 22-year-old longleaf pine (Pinus palustris Mill.) plantation using a complete factorial design that included two foliar scorching (control and 95% plus needle scorch) and two nitrogen (N) fertilization (control and 5xa0g N m−2 year−1) treatments during an annual assessment. Ectomycorrhizal fungi production comprised of extramatrical mycelia, Hartig nets and mantles on fine root tips, and sporocarps was estimated to be 49xa0g m−2 year−1 in the control treatment plots. Extramatrical mycelia accounted for approximately 95% of the total mycorrhizal production estimate. Mycorrhizal production rates did not vary significantly among sample periods throughout the annual assessment (pu2009=u20090.1366). In addition, reduction in foliar leaf area via experimental scorching treatments did not influence mycorrhizal production (pu2009=u20090.9374), suggesting that stored carbon (C) may decouple the linkage between current photosynthate production and ectomycorrhizal fungi dynamics in this forest type. Nitrogen fertilization had a negative effect, whereas precipitation had a positive effect on mycorrhizal fungi production (pu2009=u20090.0292; r2u2009=u20090.42). These results support the widely speculated but poorly documented supposition that mycorrhizal fungi are a large and dynamic component of C flow and nutrient cycling dynamics in forest ecosystems.