No abstract

Pseudomonas aeruginosa (PA) forms biofilms in lungs of cystic fibrosis CF) patients, a process regulated by quorum sensing molecules including N-(3-oxododecanoyl)-L-homoserine lactone, C12. C12 (10–100 μM) rapidly triggered events commonly associated with the intrinsic apoptotic pathway in JME (CFΔF508CFTR, nasal surface) epithelial cells: depolarization of mitochondrial (mito) membrane potential (Δψmito) and release of cytochrome C (cytoC) from mitos into cytosol and activation of caspases 3/7, 8 and 9. C12 also had novel effects on the endoplasmic reticulum (release of both Ca2+ and ER-targeted GFP and oxidized contents into the cytosol). Effects began within 5 minutes and were complete in 1–2 hrs. C12 caused similar activation of caspases and release of cytoC from mitos in Calu-3 (wtCFTR, bronchial gland) cells, showing that C12-triggered responses occurred similarly in different airway epithelial types. C12 had nearly identical effects on three key aspects of the apoptosis response (caspase 3/7, depolarization of Δψmito and reduction of redox potential in the ER) in JME and CFTR-corrected JME cells (adenoviral expression), showing that CFTR was likely not an important regulator of C12-triggered apoptosis in airway epithelia. Exposure of airway cultures to biofilms from PAO1wt caused depolarization of Δψmito and increases in Cacyto like 10–50 μM C12. In contrast, biofilms from PAO1ΔlasI (C12 deficient) had no effect, suggesting that C12 from P. aeruginosa biofilms may contribute to accumulation of apoptotic cells that cannot be cleared from CF lungs. A model to explain the effects of C12 is proposed.

ABSTRACTThe autotrophic communities in the lakes of the McMurdo Dry Valleys, Antarctica, have generated interest since the early 1960s owing to low light transmission through the permanent ice covers, a strongly bimodal seasonal light cycle, constant cold water temperatures, and geographical isolation. Previous work has shown that autotrophic carbon fixation in these lakes provides an important source of organic matter to this polar desert. Lake Bonney has two lobes separated by a shallow sill and is one of several chemically stratified lakes in the dry valleys that support year-round biological activity. As part of an International Polar Year initiative, we monitored the diversity and abundance of major isoforms of RubisCO in Lake Bonney by using a combined sequencing and quantitative PCR approach during the transition from summer to polar winter. Form ID RubisCO genes related to a stramenopile, a haptophyte, and a cryptophyte were identified, while primers specific for form IA/B RubisCO detected a diverse autotrophic community of chlorophytes, cyanobacteria, and chemoautotrophic proteobacteria. Form ID RubisCO dominated phytoplankton communities in both lobes of the lake and closely matched depth profiles for photosynthesis and chlorophyll. Our results indicate a coupling between light availability, photosynthesis, andrbcLmRNA levels in deep phytoplankton populations. Regulatory control ofrbcLin phytoplankton living in nutrient-deprived shallow depths does not appear to be solely light dependent. The distinct water chemistries of the east and west lobes have resulted in depth- and lobe-dependent variability in RubisCO diversity, which plays a role in transcriptional activity of the key gene responsible for carbon fixation.

The McMurdo Dry Valleys of Antarctica harbor numerous permanently ice-covered lakes, which provide a year-round oasis for microbial life. Microbial eukaryotes in these lakes occupy a variety of trophic levels within the simple aquatic food web ranging from primary producers to tertiary predators. Here, we report the first molecular study to describe the vertical distribution of the eukaryotic community residing in the photic zone of the east lobe (ELB) and west lobe (WLB) of the chemically stratified Lake Bonney. The 18S ribosomal RNA (rRNA) libraries revealed vertically stratified populations dominated by photosynthetic protists, with a cryptophyte dominating shallow populations (ELB-6 m; WLB-10 m), a haptophyte occupying mid-depths (both lobes 13 m) and chlorophytes residing in the deepest layers (ELB-18 and 20 m; WLB-15 and 20 m) of the photic zone. A previously undetected stramenopile occurred throughout the water column of both lobes. Temporal variation in the eukaryotic populations was examined during the transition from Antarctic summer (24-h sunlight) to polar night (complete dark). Protist diversity was similar between the two lobes of Lake Bonney due to exchange between the photic zones of the two basins via a narrow bedrock sill. However, vertical and temporal variation in protist distribution occurred, indicating the influence of the unique water chemistry on the biology of the two dry valley watersheds.

Monoculture (MC) soybean, a common practice in the Northeast China, causes significant declines in soybean yield and quality. The objective of this study was to evaluate the responses of the soil microbial community and soybean yield to different soybean cropping systems. Three cropping systems were compared, (1) corn-soybean rotation (corn-cornsoybean, CS), (2) MC soybean for 3 years (S3), (3) MC soybean for 9 years (S9). Both bulk and rhizosphere soil samples were collected at three growth stages: two trifoliate (V2), full bloom (R2), and full seed (R6), respectively. Soil microbial DNA was analyzed using polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) to assess changes in composition of bacterial and fungal communities. Prominent DGGE bands were excised and sequenced to gain insight into the identities of the predominant microbial populations. Some prominent differences were observed in bacterial DGGE patterns of amplified 16S rDNA (V3 region) among rhizosphere soils. These major differences included one DGGE band (showing 100% similarity to Arthrobacter sp.) that was enriched at R2 stages in CS and S9, and another band with 97% sequence similarity to an uncultured actinobacterium was detected at R6 stage in CS, and at R2 and R6 stages in S9. The bacterial community from bulk soil showed no significant band change in DGGE patterns among different cropping systems. In fungal DGGE patterns of the amplified 18S rDNA partial fragment, one specific band (showing 98% similarity to Trichoderma viride) occurred in rhizosphere soil of treatment CS at V2 and R6 stages and treatment S9 at R6 stage. None of the above bands were detected in treatment S3. The soybean yields and plant heights from CS and S9 were greater than those from S3. Moreover, catalase activities from CS and S9 at V2 and R2 stages were higher than those tested from S3 at the corresponding times in rhizosphere soil. The present results showed that DGGE patterns were not able to detect significant differences in diversity or evenness among microbial communities, but significant differences were found in the composition of bacterial and fungal community structures. Some distinguished bands from bacterial and fungal DGGE patterns were only enriched in CS and S9 soil, which could potentially play an important role in soybean growth development.

Oxytetracycline reduces the functional diversity of soil microbial community, and the combination of Cu and oxytetracycline leads to a further reduction. AbstractThere are increasing concerns over the effects of veterinary antibiotics and heavy metals in agricultural soils. The widely used veterinary antibiotic oxytetracycline (OTC), Cu and their combination on soil microbial community function were assessed with the Biolog method. The microbial community was extracted from the soil and exposed to a 0.85% sodium chloride solution containing OTC (0, 1, 5, 11, 43, 109 and 217 mM), or Cu (0, 10, 20, 100 and 300 mM), or combination of the two pollutants (OTC 0, 5, 11 mM and Cu 0, 20 mM). Functional diversity, evenness, average well color development (AWCD) and substrate utilization decreased significantly with increasing concentrations of OTC or Cu ( p < 0.005). The critical concentrations were 11 mM for OTC and 20 mM for Cu. The combination of OTC and Cu significantly decreased Shannon's diversity, evenness and utilization of carbohydrates and carboxylic acids compared to individual one of the contaminants. The antibiotic OTC and Cu had significant negative effects on soil microbial community function, particularly when both pollutants were present.

Plant uptake of antibiotic oxytetracycline is energy-dependent. AbstractA series of experiments were conducted in a hydroponic system to investigate the uptake of oxytetracycline (OTC) and its toxicity to alfalfa (Medicago sativa L.). OTC inhibited alfalfa shoot and root growth by up to 61% and 85%, respectively. The kinetics of OTC uptake could be well described by MichaeliseMenten equation with V max of 2.25 mmol g À1 fresh weight h À1 , and K m of 0.036 mM. The uptake of OTC by alfalfa was strongly inhibited by the metabolic inhibitor, 2,4-DNP (2,4-dinitrophenol), at pH 3.5 and 6.0, but not by the aquaporin competitors, glycerol and Ag þ . OTC uptake, however, was significantly inhibited by Hg 2þ , suggesting that the inhibition of influx was due to general cellular stress rather than the specific action of Hg 2þ on aquaporins. Results from the present study suggested that OTC uptake into alfalfa is an energy-dependent process.

No abstract