Feedback control architecture and the bacterial chemotaxis network

Bacteria move towards favourable and away from toxic environments by changing their swimming pattern. This response is regulated by the chemotaxis signalling pathway, which has an important feature: it uses feedback to 'reset' (adapt) the bacterial sensing ability, which allows the bacteria to sense a range of background environmental changes. The role of this feedback has been studied extensively in the simple chemotaxis pathway of Escherichia coli. However it has been recently found that the majority of bacteria have multiple chemotaxis homologues of the E. coli proteins, resulting in more complex pathways. In this paper we investigate the configuration and role of feedback in Rhodobacter sphaeroides, a bacterium containing multiple homologues of the chemotaxis proteins found in E. coli. Multiple proteins could produce different possible feedback configurations, each having different chemotactic performance qualities and levels of robustness to variations and uncertainties in biological parameters and to intracellular noise. We develop four models corresponding to different feedback configurations. Using a series of carefully designed experiments we discriminate between these models and invalidate three of them. When these models are examined in terms of robustness to noise and parametric uncertainties, we find that the non-invalidated model is superior to the others. Moreover, it has a 'cascade control' feedback architecture which is used extensively in engineering to improve system performance, including robustness. Given that the majority of bacteria are known to have multiple chemotaxis pathways, in this paper we show that some feedback architectures allow them to have better performance than others. In particular, cascade control may be an important feature in achieving robust functionality in more complex signalling pathways and in improving their performance.     

Does genotypic variation in nitrogen remobilisation efficiency contribute to nitrogen efficiency of winter oilseed-rape cultivars (Brassica napus L.)?

Aims

Winter oilseed-rape production is characterized by a low N efficiency, due to low N uptake and insufficient N remobilisation to the seeds. In particular, a reduction of leaf N losses might be one way to improve N efficiency of this crop. It was tested if variations in leaf N losses and in stem residual N amounts at maturity exist between cultivars differing in N efficiency.

Methods

In a 3-year field experiment, four oilseed rape cultivars were cultivated at limiting, medium, and high N supply.

Results

N harvest indices in this study were comparatively high (around 0.79) and leaf N losses amounted to at most 13 kg N ha^?1. 86 % of the leaf N present at the beginning of flowering was remobilised, irrespective of N rate or cultivar. Nevertheless, genotypic variation in leaf N loss existed. They were mainly due to differences in leaf N accumulation until flowering. Residual N in stems (up to 33 kg N ha^?1) was higher than leaf N losses and varied more between treatments but was not related to genotypic variation in yield.

Conclusions

N uptake after flowering was more important than N remobilisation from vegetative biomass for genotypic variation in seed yield both at low and high N supply.     

Molecular Identification and Biofilm-Forming Ability of Culturable Aquatic Bacteria In Microbial Biofilms Formed in Drinking Water Distribution Networks

Drinking water distribution networks are known to harbor microbial biofilms. The aim of the present work is to (i) identify the culturable bacteria presented in the drinking-water distribution network, (ii) investigate the ability of isolated bacteria to form biofilm under some environmental stress conditions and some eliminating or removing treatments. To achieve it, 57 strains were isolated from biofilm (43 isolates) and water samples (14 isolates) collected from five stations in drinking-water distribution network in Taif city, Kingdom of Saudi Arabia (KSA). Partial sequences of 16S rRNA gene in the 57 isolates ensured the presence of only 22 different strains in biofilm samples. Among these strains, only 14 strains were also detected in water samples. Gram-negative Aeromonas hydrophila was the most occurred bacterium in the microbial biofilm obtained from the purified-water storage tanks followed by Gram-negative Pseudomonas sp. Gram-positive Bacillus subtilis was the most occurred bacterium in the microbial biofilm collected from the ends of the distribution pipes. Among the 22 isolated strains, 13 strains were strong biofilm producers at 30 and 37°C. The effects of environmental stresses including nutrient starvation (diluted TSB, 20:1), heating (100°C for 10 min), UV-treatment (240 nm for 10 min) and dynamic incubation (150 rpm min^?1) on the formation of biofilm were also investigated. These conditions affected the biofilm formation ability of the isolated strains at different levels. Nutrient starvation enhanced biofilm formation by most of the isolates. Among some biofilm deforming treatments, SDS and trypsin had considerable effects on preventing biofilm formation by most of the isolated strains. In conclusion, the results of the present work indicated that not all biofilm strains released from biofilm to the drinking water. Also, not all biofilm strains were able to form biofilm. Most of isolated bacteria had ability to form biofilm at suboptimum temperature of growth. These results may provide basic information on formation of microbial biofilms and overcome the problem of deteriorating of water quality in the drinking-water distribution networks.     

Disproportionate thermophysiological strain between intensively- and extensively-managed goats during summer

Goat keeping is feasible for smallholder farmers in many world regions especially those best suited for extensive management. However, summertime grazing in arid zones entails major challenges to animal thermoregulation and well-being. An experiment was conducted to evaluate the thermoregulatory performance and selected hemogramic parameters in intensively (INT) or extensively (EXT) managed goat kids (N = 14). We applied a previously established technique to evaluate body thermal state of freely ranging animals, in which contemporaneous temperatures of the core (T_c) and periphery (T_p) are chronically recorded. Animals were initially kept for 12 days under INT management. Subsequently, seven animals were transferred to a grazing pasture and gradually transitioned over a four-day acclimatization period, then kept for the last 22 days under EXT conditions. Water drinking was limited to twice daily in both groups. Excessive solar radiation-induced heat load – with daytime black globe temperatures (T_bg) often exceeding 40 °C – under EXT was primarily responsible (r² = 0.49; P < 0.05) for 0.57 and 1.72 °C rises in T_c and T_p, respectively, over INT kids. Unlike the typically biphasic pattern noticed for daily temperatures of both body sites in INT goats, that of EXT counterparts became rather polyphasic, whereby water drinking had drastic and prolonged thermolytic effect, inducing 0.40–0.41 and 0.79–1.45 °C declines in T_c and T_p, on midday and afternoon watering bouts, respectively. Despite indication for added daytime heat load, EXT goats displayed lower early morning T_c than INT. All animals exhibited hypohydration, as reflected by rises in hematocrit, serum osmolality, albumin, potassium, and sodium, being more pronounced in EXT conditions. Results emphasize the excessive thermophysiological strain facing grazing animals in arid zones during the summer.     

Inhibition of hepatitis B virus replication in cultured cells and in vivo using 2′-O-guanidinopropyl modified siRNAs

Silencing hepatitis B virus (HBV) gene expression with exogenous activators of the RNA interference (RNAi) pathway has shown promise as a new mode of treating infection with the virus. However, optimizing efficacy, specificity, pharmacokinetics and stability of RNAi activators remains a priority before clinical application of this promising therapeutic approach is realised. Chemical modification of synthetic short interfering RNAs (siRNAs) provides the means to address these goals. This study aimed to assess the benefits of incorporating nucleotides with 2′-O-guanidinopropyl (GP) modifications into siRNAs that target HBV. Single GP residues were incorporated at nucleotide positions from 2 to 21 of the antisense strand of a previously characterised effective antiHBV siRNA. When tested in cultured cells, siRNAs with GP moieties at selected positions improved silencing efficacy. Stability of chemically modified siRNAs in 80% serum was moderately improved and better silencing effects were observed without evidence for toxicity or induction of an interferon response. Moreover, partially complementary target sequences were less susceptible to silencing by siRNAs with GP residues located in the seed region. Hydrodynamic co-injection of siRNAs with a replication-competent HBV plasmid resulted in highly effective knock down of markers of viral replication in mice. Evidence for improved efficacy, reduced off target effects and good silencing in vivo indicate that GP-modifications of siRNAs may be used to enhance their therapeutic utility.     

Analysis of hemoglobin electrophoresis results and physicians investigative practices in Saudi Arabia

BACKGROUND AND OBJECTIVES:

Riyadh and central province falls in a moderate prevalent zone of hemoglobinopathies in Saudi Arabia. However, it has been observed that the physicians working in Saudi Arabia invariably advise all cases of anemia for hemoglobin electrophoresis (HE). The present work was carried out to study the yield of the HE in Riyadh and the investigative practices of the physicians advising HE.

SETTINGS AND DESIGN:

The study was carried out in the hospitals of King Saud University from 2009 to 2011 in order to assess the yield of HE in referred cases of clinical anemia.

MATERIALS AND METHODS:

A total of 1073 cases divided in two groups of males and females had undergone complete blood count and red blood cell morphology. Cellulose acetate HE was performed and all the positive results were reconfirmed on the high performance liquid chromatography (HPLC). The results were analyzed for the type of hemoglobinopathies. For statistical analysis Statistical Package for Social Sciences 15 version (SPSS Inc., Chicago, IL, USA) was used.

RESULTS:

A total of 405 males and 668 females blood samples were included in the present study. 116 (28.5%) males and 167 (25%) females showed an abnormal pattern on HE. The incidence of beta thalassemia trait was higher in females while sickle cell trait was predominantly seen in males. Red cell indices were reduced considerably in thalassemias, but were unaffected in sickle cell disorders, except those which had concurrent alpha trait. The total yield of HE was 26.6% which was much less than expected.

CONCLUSION:

The physicians are advised to rule out iron deficiency and other common causes of anemia before investigating the cases for hemoglobinopathies, which employs time consuming and expensive tests of HE and HPLC.     

Seasonal pattern of zooplankton communities and their environmental response in subtropical maritime channels systems in the Bay of Bengal,Bangladesh

Zooplankton are a primary component of aquatic food chain and play an important role in the functioning of aquatic food webs. Seasonal variation in community structures of zooplankton and potential environmental drivers were studied, during a 1-year cycle (summer 2015 – spring 2016) in subtropical maritime channels systems in the Bay of Bengal, coastal waters in Bangladesh. A total of 32 species representing 25 families, 13 orders and 15 taxonomic groups were identified. Of these species, 23 distributed in all four season of which 8 were dominant species with high contributions of the total communities. Species number was peaked in autumn and fell in summer while maximum abundance was in the winter and minimum in summer. Multivariate analyses showed that there was a clear seasonal shift in zooplankton community structures in relation with environmental conditions. Species diversity and evenness peaked in summer while the high value of species richness was found in autumn. Multivariate correlation (RELATE) and BIO-ENV analysis demonstrated that seasonal variation in community patterns was significantly correlated with temporal shift of environmental conditions and that variation mainly driven by water transparency, salinity, DO, TSS and nutrients. Thus, this finding implies that the zooplankton community represented a clear seasonal shift shaped by environmental drivers in subtropical channels systems.     

Overexpression of <Emphasis Type="Italic">AlTMP2</Emphasis> gene from the halophyte grass <Emphasis Type="Italic">Aeluropus littoralis</Emphasis> in transgenic tobacco enhances tolerance to different abiotic stresses by improving membrane stability and deregulating some stress-related genes

Herein, we report isolation of the AlTMP2 gene from the halophytic C4 grass Aeluropus littoralis. The subcellular localization suggested that AlTMP2 is a plasma membrane protein. In A. littoralis exposed to salt and osmotic stresses, the AlTMP2 gene was induced early and at a high rate, but was upregulated relatively later in response to abscisic acid and cold treatments. Expression of AlTMP2 in tobacco conferred improved tolerance against salinity, osmotic, H₂O₂, heat, and freezing stresses at the germination and seedling stages. Under control conditions, no growth or yield penalty were mentioned in transgenic plants due to the constitutive expression of AlTMP2. Interestingly, under greenhouse conditions, the seed yield of transgenic plants was significantly higher than that of non-transgenic (NT) plants grown under salt or drought stress. Furthermore, AlTMP2 plants had less electrolyte leakage, higher membrane stability, and lower Na⁺ and higher K⁺ accumulation than NT plants. Finally, six stress-related genes were shown to be deregulated in AlTMP2 plants relative to NT plants under both control and stress conditions. Collectively, these results indicate that AlTMP2 confers abiotic stress tolerance by improving ion homeostasis and membrane integrity, and by deregulating certain stress-related genes.