Bacteria use type IV pili to walk upright and detach from surfaces

Bacterial biofilms are structured multicellular communities involved in a broad range of infections. Knowing how free-swimming bacteria adapt their motility mechanisms near surfaces is crucial for understanding the transition between planktonic and biofilm phenotypes. By translating microscopy movies into searchable databases of bacterial behavior, we identified fundamental type IV pili-driven mechanisms for Pseudomonas aeruginosa surface motility involved in distinct foraging strategies. Bacteria stood upright and "walked" with trajectories optimized for two-dimensional surface exploration. Vertical orientation facilitated surface detachment and could influence biofilm morphology.     

Small-scale natural landscape features and seabird nesting sites: the importance of geodiversity for conservation

Context

Landscape geodiversity, and in particular small natural features (SNF), are crucial components of habitat suitability for many threatened species. Rocky cliffs at the sea-continent interface present complex small-scale geomorphologies which are exploited by nesting seabirds.

Objectives

Elucidation of the relation between nest-site geomorphology and species preference in cliff-nesting seabirds. Evaluation of the potential of cliff-face SNF as seabird conservation tools.

Methods

Nest site geomorphological characteristics of four Atlantic (Brittany, France) cliff-dwelling seabirds (Razorbill, Guillemot, Fulmar, and Kittiwake) were categorized, and scored for degree of enclosure.

Results

Of the 1048 nest sites examined, the greatest species overlap in location was the mid-region of the cliff face: Fulmar was concentrated in the upper half of the cliff, while Kittiwake showed the most extended vertical distribution. A distinct trend was evident with respect to ceiling presence and size: Razorbill?+?Kittiwake?>?Guillemot?>?Fulmar. Clear trends were also evident in ceiling inclination, ledge size, and side wall presence and inclination. A distinct ‘degree of enclosure’ hierarchy was documented, consolidated with the addition of sympatric species known for their extreme preferences: Atlantic Gannets and Guillemots at the extreme ‘open’ end, and Puffins and Storm Petrels at the extreme ‘closed’ end. Some plasticity in site choice was observed, probably corresponding to sub-optimal default choices.

Conclusions

Despite some plasticity, both vertical level and enclosure characteristics are associated with particular seabird species. Given the importance of nesting sites to seabird reproduction, the identification and conservation of these SNF constitute crucial conservation objectives.

     

Growth and luminescence of the symbolic bacteria associated with the terrestrial nematode, Heterorphabditis bacteriophora

The terrestrial nematode, Heterorhabitis bacteriophora contains symbiotic terrestrial bacteria which emit low but detectable luminescence in the symbiotic state. When the nematode is ingested by caterpillar larvae (or other insects), the bacteria are released into t he hemocoel, where they grow rapidly (doubling time of 3 h or less), reach high cell numbers (10⁹ ml^?1 greater), and are brightly luminous. The enzyme that catalyzes light emission is a typical bacterial luciferase as judged by its substrate requirements and the kinetics in vitro. Bacteria grown in synthetic media emit luminescence that is nearly identical in color with that of other luminescent bacteria, while the color of light from infected caterpillar is substantially red-shifted.     

Nitrous oxide emission from animal manures applied to soil under controlled conditions

Animal manures may differ strongly in composition and as a result may differ in the emission of N₂O following application to soil. An incubation study was carried out to assess the effects of type of mineral N fertilizer and manure, application technique and application rate on N₂O emission from a sandy soil with low organic matter content. Fluxes of N₂O were measured 30 times over a 98-day period. The total N₂O emission from mineral N fertilizer ranged from 2.1 to 4.0% of the N applied. High emissions were associated with manures with high contents of inorganic N, easily mineralizable N and easily mineralizable C, such as liquid pig manure (7.3-13.9% of the N applied). The emission from cattle slurries ranged from 1.8 to 3.0% and that of poultry manures from 0.5 to 1.9%. The total N₂O emission during the experimental period tended to increase linearly with increasing N application rate of NH₄NO₃ and liquid pig manure. The N₂O emission from surface-applied NH₄NO₃ was significantly smaller than that following the incorporation of NH₄NO₃ in the soil. The N₂O emission from pig manure placed in a row at 5 cm depth was significantly higher than from surface-application and other techniques in which manure was incorporated in the soil. The results show that modification of the composition and application technique may be tools to mitigate emission of N₂O.     

Reintroduction of a native galaxiid (Galaxias fasciatus) following piscicide treatment in two streams: response and recovery of the fish population

The rehabilitation of native communities by means of eradicating unwanted fish species using piscicides is an example of employing disturbance to achieve conservation successes. Such projects provide a valuable opportunity to test the efficiency of the tool and the impacts on the receiving aquatic communities, as disturbance occurs at a known time. The piscicide ‘rotenone’ has been widely used to eradicate invasive or unwanted fish species worldwide. However, there is little information regarding the impact on native fish being reintroduced to a stream after rotenone treatment. The mass depletion of aquatic invertebrates due to rotenone dosing is of particular concern, as food‐limitation could negatively impact on fish growth, condition and recruitment, compromising the aims of rehabilitation. For the first time in New Zealand, rotenone was employed to eradicate brown trout (Salmo trutta) from two streams that also supported populations of banded kokopu (Galaxias fasciatus). Impacts on fish and aquatic invertebrates were studied in two treatment and two reference streams in Karori, Wellington. Analysis showed that invertebrate densities declined significantly in the treatment streams in the 2‐week to 2‐month period after dosing. Following reintroduction after rotenone treatment, banded kokopu condition declined significantly and levels of fish mobility were variable. One year after rotenone dosing, there was recruitment of banded kokopu juveniles in the treatment streams indicating successful reproduction, with no equivalent increase in the reference streams. Results are a positive indication for the use of rotenone as an effective conservation tool to remove unwanted fish species where they threaten native populations.     

Does Biofloc Improve the Energy Distribution and Final Muscle Quality of Shrimp,Litopenaeus vannamei (Boone, 1883)?

In a 45‐d experiment, Litopenaeus vannamei was cultured in two treatments, biofloc technology or clear water recirculating aquaculture system, to evaluate the effect on growth and survival, energy balance, and texture of the marketable product. The experimental design consisted of 40 plastic tanks of 54 L (20 tanks per treatment), with a density of 140 organisms/m³ in each culture system. The final body weight, daily growth coefficient, and survival were significantly higher (P < 0.05) in biofloc technology (12.40 g, 5.0%g/d, and 87.1%, respectively) than in the clear water system (7.0 g, 1.4%g/d, and 74.2%). The retained energy and energy content of exuviae were significantly higher for shrimp in the biofloc technology (448.5 ± 36.4 and 22.4 ± 1.8 J/shrimp/d, respectively) than in clear water (246.3 ± 40.9 and 12.3 ± 2.0 J/shrimp/d, respectively). Routine metabolism was significantly higher for the clear water treatment (411.4 ± 123.8 J/shrimp/d). Shear force was higher in the biofloc technology, indicating greater muscle firmness; this matched the gel electrophoresis patterns of the proteins extracted from the muscle tissues. This suggests that biofloc technology could be used not only to improve growth and survival in L. vannamei but also to enhance the final product quality and acceptability in the market.     

碳同位素分辨率与小麦光合生理指标的关系

为了解碳同位素分辨率(Δ)与小麦光合生理指标的关系,以洛旱6号和西农389的154个F4代株系中的24个高Δ株系和24个低Δ株系及亲本为供试材料,分析了陕西杨凌和永寿两种不同雨养环境条件下小麦籽粒Δ与灌浆期叶片光合生理指标的相关性,并对高、低Δ材料间光合生理指标和产量进行了比较分析。结果表明,在降雨较多的杨凌地区,高Δ株系表现出高的籽粒产量;在降雨较少、相对干旱的永寿地区,高、低Δ株系间籽粒产量差异不显著,但低Δ株系表现出低的气孔导度。在杨凌生态条件下,灌浆中期籽粒Δ与叶片蒸腾速率、光合速率、气孔导度和Ci/Ca生理指标的相关性在小麦整个灌浆期最为显著;在永寿生态条件下,灌浆中期籽粒Δ与蒸腾速率和Ci/Ca均相关显著。说环境条件影响小麦籽粒Δ与光合生理指标的关系。     

Food and habitat preferences of the earthworm Lumbricus terrestris L. for cover crops

Some of the widely used cover crops in temperate agroecosystems (including species of the Brassicaceae and Poaceae) have been shown to exhibit allelopathic effects. In particular, various Brassicaceae have been reported to act as biofumigants against a variety of soil-borne pests through the release of i.a. isothiocyanates (ITC) from glucosinolate precursors. Although these allelochemicals may potentially reduce the need for application of synthetic pesticides, their effects on beneficial soil ecosystem engineers such as earthworms (Lumbricidae) have not been assessed yet.Food choice chambers were used to assess short-term food preferences of Lumbricus terrestris L. for lacy phacelia (Phacelia tanacetifolia BENTH.), the Poaceae Italian ryegrass (Lolium multiflorum LAM.) and oats (Avena sativa L.), and the Brassicaceae yellow mustard (Sinapis alba L.) and rapeseed (Brassica napus L.) while litter bags were used to study long-term litter preference under field conditions. Habitat preference of L. terrestris was determined through simple habitat preference units.Ryegrass residues were a preferred food resource, both in fresh and partly decomposed state, over mustard, phacelia or rapeseed residues, and these were in turn more fed on than oats. Litter disappeared at a fast and variable rate from litter bags under field conditions. No clear relationships with residue C:N ratio were observed. Habitats in which living oat plants were present were avoided in comparison to habitats with bare soil or yellow mustard plants.In conclusion, brassicaceous cover crops are not preferred nor avoided by L. terrestris compared to the other cover crops in this study. Decreased ITC release and earthworm exposure under field conditions may further lower the risk of harmful effects, but further research on the long-term impact is needed.     

Small scale digital soil mapping in Southeastern Kenya

Digital soil mapping techniques appear to be an interesting alternative for traditional soil survey techniques. However, most applications deal with (semi-)detailed soil surveys where soil variability is determined by a limited number of soil forming factors. The question that remains is whether digital soil mapping techniques are equally suitable for exploratory or reconnaissance soil surveys in more extensive areas with limited data availability. We applied digital soil mapping in a 13,500 km² study area in Kenya with the main aim to create a reconnaissance soil map to assess clay and soil organic carbon contents in terraced maize fields. Soil spatial variability prediction was based on environmental correlation using the concepts of the soil forming factors equation. During field work, 95 composite soil samples were collected. Auxiliary spatially exhaustive data provided insight on the spatial variation of climate, land cover, topography and parent material. The final digital soil maps were elaborated using regression kriging. The variance explained by the regression kriging models was estimated as 13% and 37% for soil organic carbon and clay respectively. These results were confirmed by cross-validation and provide a significant improvement compared to the existing soil survey.     

日光温室热环境模拟模型的构建

该文建立了日光温室热环境模拟模型,定量描述了日光温室内的太阳辐射、对流换热、辐射换热、热传导、自然通风和水分相变带来的潜热对日光温室热环境的影响,根据质能平衡和传热学理论,得到一组关于覆盖物、室内空气、温室分层后墙、分层地面土壤、分层后坡和作物热平衡的微分方程组。利用MATLAB的强大计算能力与VB的良好用户界面建立模拟计算软件,可求得温室各组成部分的温度。通过试验验证,该模型能够比较准确预测日光温室环境温度。