Mutation of serine residue 318 in the class C β-lactamase of Enterobacter cloacae 908R

The involvement of the serine residue 318 in the specificity of a class C beta-lactamase was investigated. Multiple site-directed mutants at this position were generated using a polymerase chain reaction technique. These mutants were then probed for their activity towards various beta-lactam compounds. One mutant, S318G was further purified and its physico-chemical and catalytic properties determined. It was shown that the observed minimal inhibitory concentration values of this mutant could be correlated to its kinetic properties using a 'diffusion-hydrolysis' model. However, the data showed that residue 318 has little influence on the specificity of class C beta-lactamases.     

The Effect of Hydraulic Loading Rate and Influent Source on the Binding Capacity of Phosphorus Filters

Sorption by active filter media can be a convenient option for phosphorus (P) removal and recovery from wastewater for on-site treatment systems. There is a need for a robust laboratory method for the investigation of filter materials to enable a reliable estimation of their longevity. The objectives of this study were to (1) investigate and (2) quantify the effect of hydraulic loading rate and influent source (secondary wastewater and synthetic phosphate solution) on P binding capacity determined in laboratory column tests and (3) to study how much time is needed for the P to react with the filter material (reaction time). To study the effects of these factors, a 2² factorial experiment with 11 filter columns was performed. The reaction time was studied in a batch experiment. Both factors significantly (α = 0.05) affected the P binding capacity negatively, but the interaction of the two factors was not significant. Increasing the loading rate from 100 to 1200 L m⁻² d⁻¹ decreased P binding capacity from 1.152 to 0.070 g kg⁻¹ for wastewater filters and from 1.382 to 0.300 g kg⁻¹ for phosphate solution filters. At a loading rate of 100 L m⁻² d⁻¹, the average P binding capacity of wastewater filters was 1.152 g kg⁻¹ as opposed to 1.382 g kg⁻¹ for phosphate solution filters. Therefore, influent source or hydraulic loading rate should be carefully controlled in the laboratory. When phosphate solution and wastewater were used, the reaction times for the filters to remove P were determined to be 5 and 15 minutes, respectively, suggesting that a short residence time is required. However, breakthrough in this study occurred unexpectedly quickly, implying that more time is needed for the P that has reacted to be physically retained in the filter.     

Environmental footprints of British Columbia wood pellets from a simplified life cycle analysis

Purpose  

Environmental footprints of wood pellets produced in British Columbia (BC) of Canada are to be estimated based on industry surveys and published emission factor data.     

Fibronectin Assembly in the Crypts of?Cytokinesis-Blocked?Multilobular Cells Promotes Anchorage-Independent Growth

Anchorage-independent growth is a characteristic feature of cancer cells. However, it is unclear whether it represents a cause or a consequence of tumorigenesis. For normal cells, integrin-mediated adhesion is required for completion of the G1 and cytokinesis stages of the cell cycle. This study identified a mechanism that can drive anchorage-independent growth if the G1 checkpoint is suppressed. Cells with defective G1 checkpoint progressed through several rounds of the cell cycle in suspension in spite of uncompleted cytokinesis, thereby forming bi- and multilobular cells. Aurora B and CEP55 were localized to midbodies between the lobes, suggesting that the cytokinesis process reached close to abscission. Integrin-mediated re-attachment of such cells induced cytokinesis completion uncoupled from karyokinesis in most cells. However, a portion of the cells instead lost the constriction and became binucleated. Also, long-term suspension culture in soft agar produced colonies where the cytokinesis block was overcome. This process was fibronectin-dependent since fibronectin-deficient cells did not form colonies unless fibronectin was expressed or exogenously added. While fibronectin normally is not deposited on non-adherent single cells, bi/multilobular cells accumulated fibronectin in the intussusceptions. Based on our data we conclude: 1) Suppression of the G1 checkpoint allows multiple rounds of the cell cycle in detached cells and thereby enables matrix formation on their surface. 2) Uncompleted cytokinesis due to cell detachment resumes if integrin interactions are re-formed, allowing colony formation in soft agar 3) Such delayed cell division can generate binucleated cells, a feature known to cause chromosomal instability.     

Migration distance does not predict blood parasitism in a migratory songbird

Migration can influence host–parasite dynamics in animals by increasing exposure to parasites, by reducing the energy available for immune defense, or by culling of infected individuals. These mechanisms have been demonstrated in several comparative analyses; however, few studies have investigated whether conspecific variation in migration distance may also be related to infection risk. Here, we ask whether autumn migration distance, inferred from stable hydrogen isotope analysis of summer‐grown feathers (δ²H_f) in Europe, correlates with blood parasite prevalence and intensity of infection for willow warblers (Phylloscopus trochilus) wintering in Zambia. We also investigated whether infection was correlated with individual condition (assessed via corticosterone, scaled mass index, and feather quality). We found that 43% of birds were infected with Haemoproteus palloris (lineage WW1). Using generalized linear models, we found no relationship between migration distance and either Haemoproteus infection prevalence or intensity. There was spatial variation in breeding ground origins of infected versus noninfected birds, with infected birds originating from more northern sites than noninfected birds, but this difference translated into only slightly longer estimated migration distances (~214 km) for infected birds. We found no relationship between body condition indices and Haemoproteus infection prevalence or intensity. Our results do not support any of the proposed mechanisms for migration effects on host–parasite dynamics and cautiously suggest that other factors may be more important for determining individual susceptibility to disease in migratory bird species.     

Serotonin Depletion-Induced Maladaptive Aggression Requires the Presence of Androgens

The sex hormone testosterone and the neurotransmitter serotonin exert opposite effects on several aspects of behavior including territorial aggression. It is however not settled if testosterone exerts its pro-aggressive effects by reducing serotonin transmission and/or if the anti-aggressive effect of serotonin requires the presence of the androgen. Using the resident intruder test, we now show that administration of the serotonin synthesis inhibitor para-chlorophenylalanine (300 mg/kg x 3 days) increases the total time of attack as well as the percentage amount of social behavior spent on attack but not that spent on threat – i.e. that it induces a pattern of unrestricted, maladaptive aggression – in gonadectomized C57Bl/6 male mice receiving testosterone replacement; in contrast, it failed to reinstate aggression in those not given testosterone. Whereas these results suggest the pro-aggressive effect of testosterone to be independent of serotonin, and not caused by an inhibition of serotonergic activity, the pCPA-induced induction of maladaptive aggression appears to require the presence of the hormone. In line with these findings, pCPA enhanced the total time of attack as well the relative time spent on attacks but not threats also in wild-type gonadally intact male C57Bl/6 mice, but failed to reinstate aggression in mice rendered hypo-aggressive by early knock-out of androgen receptors in the brain (AR^NesDel mice). We conclude that androgenic deficiency does not dampen aggression by unleashing an anti-aggressive serotonergic influence; instead serotonin seems to modulate aggressive behavior by exerting a parallel-coupled inhibitory role on androgen-driven aggression, which is irrelevant in the absence of the hormone, and the arresting of which leads to enhanced maladaptive aggression.     

Disentangling the complex evolutionary history of the Western Palearctic blue tits (Cyanistes spp.) – phylogenomic analyses suggest radiation by multiple colonization events and subsequent isolation

Isolated islands and their often unique biota continue to play key roles for understanding the importance of drift, genetic variation and adaptation in the process of population differentiation and speciation. One island system that has inspired and intrigued evolutionary biologists is the blue tit complex (Cyanistes spp.) in Europe and Africa, in particular the complex evolutionary history of the multiple genetically distinct taxa of the Canary Islands. Understanding Afrocanarian colonization events is of particular importance because of recent unconventional suggestions that these island populations acted as source of the widespread population in mainland Africa. We investigated the relationship between mainland and island blue tits using a combination of Sanger sequencing at a population level (20 loci; 12 500 nucleotides) and next‐generation sequencing of single population representatives (>3 200 000 nucleotides), analysed in coalescence and phylogenetic frameworks. We found (i) that Afrocanarian blue tits are monophyletic and represent four major clades, (ii) that the blue tit complex has a continental origin and that the Canary Islands were colonized three times, (iii) that all island populations have low genetic variation, indicating low long‐term effective population sizes and (iv) that populations on La Palma and in Libya represent relicts of an ancestral North African population. Further, demographic reconstructions revealed (v) that the Canary Islands, conforming to traditional views, hold sink populations, which have not served as source for back colonization of the African mainland. Our study demonstrates the importance of complete taxon sampling and an extensive multimarker study design to obtain robust phylogeographical inferences.     

Uptake of extracellular DNA: Competence induced pili in natural transformation of Streptococcus pneumoniae

Transport of DNA across bacterial membranes involves complex DNA uptake systems. In Gram‐positive bacteria, the DNA uptake machinery shares fundamental similarities with type IV pili and type II secretion systems. Although dedicated pilus structures, such as type IV pili in Gram‐negative bacteria, are necessary for efficient DNA uptake, the role of similar structures in Gram‐positive bacteria is just beginning to emerge. Recently two essentially very different pilus structures composed of the same major pilin protein ComGC were proposed to be involved in transformation of the Gram‐positive bacterium Streptococcus pneumoniae – one is a long, thin, type IV pilus‐like fiber with DNA binding capacity and the other one is a pilus structure that was thicker, much shorter and not able to bind DNA. Here we discuss how competence induced pili, either by pilus retraction or by a transient pilus‐related opening in the cell wall, may mediate DNA uptake in S. pneumoniae.