The challenge of estimating kelp production in a turbid marine environment

Coastal kelp forests produce substantial marine carbon due to high annual net primary production (NPP) rates, but upscaling of NPP estimates over time and space remains difficult. We investigated the impact of variable underwater photosynthetically active radiation (PAR) and photosynthetic parameters on photosynthetic oxygen production of Laminaria hyperborea, the dominant NE-Atlantic kelp species, throughout summer 2014. Collection depth of kelp had no effect on chlorophyll a content, pointing to a high photoacclimation potential of L. hyperborea towards incident light. However, chlorophyll a and photosynthesis versus irradiance parameters differed significantly along the blade gradient when normalized to fresh mass, potentially introducing large uncertainties in NPP upscaling to whole thalli. Therefore, we recommend a normalization to kelp tissue area, which is stable over the blade gradient. Continuous PAR measurements revealed a highly variable underwater light climate at our study site (Helgoland, North Sea) in summer 2014, reflected by PAR attenuation coefficients (K_d) between 0.28 and 0.87 m⁻¹. Our data highlight the importance of continuous underwater light measurements or representative average values using a weighted K_d to account for large PAR variability in NPP calculations. Strong winds in August increased turbidity, resulting in a negative carbon balance at depths >3–4 m over several weeks, considerably impacting kelp productivity. Estimated daily summer NPP over all four depths was 1.48 ± 0.97 g C · m⁻² seafloor · d⁻¹ for the Helgolandic kelp forest, which is in the range of other kelp forests along European coastlines.     

A life cycle assessment of Agaricus bisporus mushroom production in the USA

The International Journal of Life Cycle Assessment - Stakeholders across the food product supply chain are increasingly interested in understanding the environmental effects of food production....     

Comparative studies on the infectivity of Theileria parva in ticks fed in vitro and those fed on cattle

Nymphs of the brown ear tick, Rhipicephalus appendiculatus, were fed on heparinised bovine blood infected with Theileria parva parasites in an in vitro feeding system consisting of rabbit skin membranes. The main feeding and development parameters such as the mean attachment rate, feeding duration and engorgement weights of membrane-fed ticks were not significantly different from nymphs fed on cattle. The moulting rate was also comparable although a slight significant difference was observed. Assessment of infection prevalence and abundance with T. parva in adults indicated that the membrane-fed ticks acquired infection to the same level as those fed on cattle. Stabilates prepared from both the membrane- and cattle-fed adult ticks were found to be infective and caused severe reactions in susceptible cattle. When the immunised cattle were challenged with a lethal homologous dose of T. parva (Marikebuni), they were found to be immune.     

ExbB and ExbD do not function independently in TonB-dependent energy transduction

ExbB and ExbD proteins are part of the TonB-dependent energy transduction system and are encoded by the exb operon in Escherichia coli. TonB, the energy transducer, appears to go through a cycle during energy transduction, with the absence of both ExbB and ExbD creating blocks at two points: (i) in the inability of TonB to respond to the cytoplasmic membrane proton motive force and (ii) in the conversion of TonB from a high-affinity outer membrane association to a high-affinity cytoplasmic membrane association. The recent observation that ExbB exists in 3.5-fold molar excess relative to the molarity of ExbD in E. coli suggests the possibility of two types of complexes, those containing both ExbB and ExbD and those containing only ExbB. Such distinct complexes might individually manifest one of the two activities described above. In the present study this hypothesis was tested and rejected. Specifically, both ExbB and ExbD were found to be required for TonB to conformationally respond to proton motive force. Both ExbB and ExbD were also required for association of TonB with the cytoplasmic membrane. Together, these results support an alternative model where all of the ExbB in the cell occurs in complex with all of the ExbD in the cell. Based on recently determined cellular ratios of TonB system proteins, these results suggest the existence of a cytoplasmic membrane complex that may be as large as 520 kDa.     

Dynamic Proteome Response of Pseudomonas aeruginosa to Tobramycin Antibiotic Treatment

Genetically susceptible bacteria become antibiotic tolerant during chronic infections, and the mechanisms responsible are poorly understood. One factor that may contribute to differential sensitivity in vitro and in vivo is differences in the time-dependent tobramycin concentration profile experienced by the bacteria. Here, we examine the proteome response induced by subinhibitory concentrations of tobramycin in Pseudomonas aeruginosa cells grown under planktonic conditions. These efforts revealed increased levels of heat shock proteins and proteases were present at higher dosage treatments (0.5 and 1 μg/ml), while less dramatic at 0.1 μg/ml dosage. In contrast, many metabolic enzymes were significantly induced by lower dosages (0.1 and 0.5 μg/ml) but not at 1 μg/ml dosage. Time course proteome analysis further revealed that the increase of heat shock proteins and proteases was most rapid from 15 min to 60 min, and the increased levels sustained till 6 h (last time point tested). Heat shock protein IbpA exhibited the greatest induction by tobramycin, up to 90-fold. Nevertheless, deletion of ibpA did not enhance sensitivity to tobramycin. It seemed possible that the absence of sensitization could be due to redundant functioning of IbpA with other proteins that protect cells from tobramycin. Indeed, inactivation of two heat shock chaperones/proteases in addition to ibpA in double mutants (ibpA/clpB, ibpA/PA0779 and ibpA/hslV) did increase tobramycin sensitivity. Collectively, these results demonstrate the time- and concentration-dependent nature of the P. aeruginosa proteome response to tobramycin and that proteome modulation and protein redundancy are protective mechanisms to help bacteria resist antibiotic treatments.The opportunistic pathogen Pseudomonas aeruginosa is ubiquitous in the natural environment and causes human infections (1). P. aeruginosa can metabolize various carbon and nitrogen compounds and persists under nutrient-poor and hostile growth environments (2, 3). One example is P. aeruginosa pulmonary infection of cystic fibrosis (CF) patients. Despite stress induced by host defenses and high concentrations of antibiotics, P. aeruginosa cells are able to persistently colonize CF airways (4).The aminoglycoside tobramycin is a front-line drug currently used in the treatment of P. aeruginosa in CF and other diseases. It is supplied in the forms of inhaled solution (TOBI) and intravenous injection. The tobramycin concentrations in airways after 300-mg dosage TOBI inhalation can reach 1,000 μg per g of sputum (5, 6). This concentration is in the range of 10 to 1,000 times of the minimal inhibitory concentration (MIC) for P. aeruginosa clinical isolates tested ex vivo (6). However, even with such high tobramycin concentrations, chronic P. aeruginosa infections are rarely eradicated (6). This is true even when the infecting bacteria are antibiotic sensitive, as is the case early in disease (7).One possible reason for P. aeruginosa persistence in vivo could relate to the time dependence of local concentrations of tobramycin experienced by P. aeruginosa in CF patient airways. Many factors, including inflammatory responses, blood and lymphatic circulations, and air flow distribution (for inhaled antibiotics), can alter the local antibiotic concentrations. In addition, P. aeruginosa cells can form biofilms in CF lungs and other infection sites (8), and biofilm exopolysaccharide layers may slow the diffusion of tobramycin (9, 10). P. aeruginosa cells in the inner layers of biofilms may experience lower concentrations and more gradual increase of tobramycin levels than those in outer layers (10, 11). Furthermore, even if final tobramycin concentration levels inside the biofilm eventually grow to match the highest levels experienced elsewhere, bacteria in these inner regions have experienced a slower increase, during which time proteome levels could be altered to promote the “adapted resistant state” (12). Adaptive resistance can also be induced in planktonic (free-living) P. aeruginosa (13, 14), and conventional MIC assays are not designed to measure this.Once induced, the adaptive resistance confers bacteria higher resistance to antibiotic treatments (13, 14) and is associated with decreased clinical antibiotic treatment efficacy (15). Interestingly, the adaptive resistance is time dependent and reversible. Typical adaptive resistance was observed starting 1 h after antibiotic exposure, and the drug susceptibility was regained after 36 h intervals (14, 15). Thus, adaptive resistance mechanisms may contribute in part to the disparity of in vivo persistence and ex vivo susceptibility to antibiotics in MIC tests.As an initial step toward defining adaptive resistance mechanisms, we investigated the time- and concentration-dependence of P. aeruginosa proteome response to tobramycin in planktonic conditions. Since the most effective protective responses may operate before killing begins and the rate of change of drug levels is likely to depend on ambient conditions, we studied bacteria exposed to low, subinhibitory levels of tobramycin (0.1, 0.5, and 1.0 μg/ml) at a range of time points (15, 60, 120, and 360 min) after exposure. The candidate proteome marker of P. aeruginosa for tobramycin response, heat shock protein IbpA, was further investigated with genetic mutagenesis and MIC assays.     

Linkage disequilibrium between alleles at highly polymorphic mini- and micro-satellite loci of Theileria parva isolated from cattle in three regions of Kenya

Theileria parva schizont-infected lymphocyte culture isolates from western, central and coastal Kenya were analysed for size polymorphism at 30 T. parva-specific variable number tandem repeat (VNTR) loci using a panel of mini- and micro-satellite markers. The mean number of alleles ranged from 3 to 11 at individual loci and 183 distinct alleles were observed in total, indicating high genetic diversity within the T. parva gene pool in Kenyan cattle. The frequency distribution of the length variation of specific alleles among isolates ranged from normal to markedly discontinuous. Genetic relationships between isolates were analysed using standard indices of genetic distance. Genetic distances and dendrograms derived from these using neighbour-joining algorithms did not indicate significant clustering on a geographical basis. Analysis of molecular variance demonstrated that the genetic variation between individual isolates was 72%, but only 2.3% when isolates from different regions were pooled. Both these observations suggest minimal genetic sub-structuring relative to geographical origin. Linkage disequilibrium was observed between pairs of loci within populations, as in certain Ugandan T. parva populations. A novel observation was that disequilibrium was also detected between alleles at three individual pairs of VNTR loci when isolates from the three regional meta-populations were pooled for analysis.     

Timing and technique impact the effectiveness of road‐based,mobile acoustic surveys of bats

Mobile acoustic surveys are a common method of surveying bat communities. However, there is a paucity of empirical studies exploring different methods for conducting mobile road surveys of bats. During 2013, we conducted acoustic mobile surveys on three routes in north‐central Indiana, U.S.A., using (1) a standard road survey, (2) a road survey where the vehicle stopped for 1 min at every half mile of the survey route (called a “start‐stop method”), and (3) a road survey with an individual using a bicycle. Linear mixed models with multiple comparison procedures revealed that when all bat passes were analyzed, using a bike to conduct mobile surveys detected significantly more bat passes per unit time compared to other methods. However, incorporating genus‐level comparisons revealed no advantage to using a bike over vehicle‐based methods. We also found that survey method had a significant effect when analyses were limited to those bat passes that could be identified to genus, with the start–stop method generally detecting more identifiable passes than the standard protocol or bike survey. Additionally, we found that significantly more identifiable bat passes (particularly those of the Eptesicus and Lasiurus genera) were detected in surveys conducted immediately following sunset. As governing agencies, particularly in North America, implement vehicle‐based bat monitoring programs, it is important for researchers to understand how variations on protocols influence the inference that can be gained from different monitoring schemes.     

Silencing of EEF2K (eukaryotic elongation factor-2 kinase) reveals AMPK-ULK1-dependent autophagy in colon cancer cells

EEF2K (eukaryotic elongation factor-2 kinase), also known as Ca²⁺/calmodulin-dependent protein kinase III, functions in downregulating peptide chain elongation through inactivation of EEF2 (eukaryotic translation elongation factor 2). Currently, there is a limited amount of information on the promotion of autophagic survival by EEF2K in breast and glioblastoma cell lines. However, the precise role of EEF2K in carcinogenesis as well as the underlying mechanism involved is still poorly understood. In this study, contrary to the reported autophagy-promoting activity of EEF2K in certain cancer cells, EEF2K is shown to negatively regulate autophagy in human colon cancer cells as indicated by the increase of LC3-II levels, the accumulation of LC3 dots per cell, and the promotion of autophagic flux in EEF2K knockdown cells. EEF2K negatively regulates cell viability, clonogenicity, cell proliferation, and cell size in colon cancer cells. Autophagy induced by EEF2K silencing promotes cell survival and does not potentiate the anticancer efficacy of the AKT inhibitor MK-2206. In addition, autophagy induced by silencing of EEF2K is attributed to induction of protein synthesis and activation of the AMPK-ULK1 pathway, independent of the suppression of MTOR activity and ROS generation. Knockdown of AMPK or ULK1 significantly abrogates EEF2K silencing-induced increase of LC3-II levels, accumulation of LC3 dots per cell as well as cell proliferation in colon cancer cells. In conclusion, silencing of EEF2K promotes autophagic survival via activation of the AMPK-ULK1 pathway in colon cancer cells. This finding suggests that upregulation of EEF2K activity may constitute a novel approach for the treatment of human colon cancer.