Comparative studies of the biological activities of lysosomotropic aminoesters and quaternary ammonium salts on the yeast Saccharomyces cerevisiae.

The biological activity of lysosomotropic n-alkyl N,N-dimethylglycinates (DMG-n) was compared with that of a quaternary ammonium salt IM (methochloride of DMG-12). The activity of the glycinates appeared to be carbon chain length dependent and was similar at pH 6 and pH 8. Nutritional auxotrophy and respiratory deficiencies have no influence on DMG-n sensitivity. Both IM and DMG-n inhibit plasma membrane H+-ATPase activity while mitochondrial ATPase is relatively non-sensitive to glycinates. No cross-resistance to IM and DMG-n was observed.     

Effect of variable surrounding on species creation

We constructed a model of speciation from evolution in an ecosystem consisting of a limited amount of energy recources. The species possesses genetic information, which is inherited according to the rules of the Penna model of genetic evolution. The increase in the number of the individuals of each species depends on the quality of their genotypes and the available energy resources. The decrease in number of the individuals results from genetic death or maximum-age reaching by the individual. The amount of energy resources is represented by a solution of the differential logistic equation, where the growth rate of the amount of the energy resources has been modified to include the number of individuals from all species in the ecosystem under consideration. The fluctuating surrounding is modelled with the help of the function V(x, t) = 1/4 x4 + 1/2 b(t)x2, where x represents phenotype and the coefficient b(t) shows the cos(omega t) time dependence. The closer the value x of an individual to the minimum of V(x, t), the better adapted its genotype to the surrounding. We observed that the life span of the organisms strongly depends on the value of the frequency omega. It becomes shorter the more frequent the changes of the surrounding. However, there is a tendency for the species that have a higher value of the reproduction age aR to win the competition with the other species. Another observation is that small evolutionary changes of the inherited genetic information lead to spontaneous bursts of the evolutionary activity when many new species may appear in a short period.     

Effect of simulated fall heat waves on cold hardiness and winter survival of hemlock looper,Lambdina fiscellaria (Lepidoptera: Geometridae)

The hemlock looper (Lambdina fiscellaria) is an important pest of eastern Canadian forests. The ongoing climate warming could modify the seasonal ecology of this univoltine species that lays eggs at the end of summer and overwinters at this stage. Indeed, the increase in frequency and intensity of extreme climatic events such as fall heat waves could interfere with the winter metabolism of the hemlock looper. Moreover, the host plant quality, which influences the quantity of insect energetic reserves, the geographic origin of populations and the conditions prevailing during the cold acclimation period, could cause various responses of this pest to climate warming. The main objective of this study is to determine the impact of these factors on hemlock looper winter biology. In October 2010, hemlock looper eggs initially collected from two geographic areas in the province of Québec, and from parents reared on two host plants, were exposed to fall heat waves of different intensities during 5 consecutive days. Supercooling points and cryoprotectant levels were measured on eggs on four different dates in 2010–2011 and survival rate was measured in April 2011. Our results show that hemlock looper eggs have a very low supercooling point and high levels of trehalose, glucose and mannitol in September and November. However, there is no clear relationship between the concentration of these compounds and the decrease in supercooling points. Contents in trehalose, glucose and mannitol were significantly influenced by fall heat waves and by the origin of the population. Winter survival of eggs from the temperate population was negatively affected by strong heat waves while the boreal population was not affected. This study suggests that the metabolism and winter survival of temperate hemlock looper populations in Québec will be more affected by fall heat waves that will increase in frequency due to climate change, than boreal populations.     

Tyrophagus putrescentiae (Sarcoptiformes: Acaridae) in the in vitro cultures of slime molds (Mycetozoa): accident,contamination, or interaction?

Experimental and Applied Acarology - Tyrophagus putrescentiae (Schrank), commonly known as the cereal mite, cheese mite, or ham mite, is a cosmopolitan species reported from various environments in...     

Where does bacterial replication start? Rules for predicting the oriC region

Three methods, based on DNA asymmetry, the distribution of DnaA boxes and dnaA gene location, were applied to identify the putative replication origins in 120 chromosomes. The chromosomes were classified according to the agreement of these methods and the applicability of these methods was evaluated. DNA asymmetry is the most universal method of putative oriC identification in bacterial chromosomes, but it should be applied together with other methods to achieve better prediction. The three methods identify the same region as a putative origin in all Bacilli and Clostridia, many Actinobacteria and gamma Proteobacteria. The organization of clusters of DnaA boxes was analysed in detail. For 76 chromosomes, a DNA fragment containing multiple DnaA boxes was identified as a putative origin region. Most bacterial chromosomes exhibit an overrepresentation of DnaA boxes; many of them contain at least two clusters of DnaA boxes in the vicinity of the oriC region. The additional clusters of DnaA boxes are probably involved in controlling replication initiation. Surprisingly, the characteristic features of the initiation of replication, i.e. a cluster of DnaA boxes, a dnaA gene and a switch in asymmetry, were not found in some of the analysed chromosomes, particularly those of obligatory intracellular parasites or endosymbionts. This is presumably connected with many mechanisms disturbing DNA asymmetry, translocation or disappearance of the dnaA gene and decay of the Escherichia coli perfect DnaA box pattern.     

Lysosomotropic N,N- dimethyl alpha-aminoacid N-alkyl esters and their quaternary ammonium salts as plasma membrane and mitochondrial ATPases inhibitors

A set of n-alkyl esters of N,N-dimethylglycine (DMG-n) and their methobromides (DMGM-n) was synthesized, and their activities on yeast Saccharomyces cerevisiae were compared. The compounds differ in the number of carbon atoms in the aliphatic chain. Aminoesters with 12 carbon atoms appeared to be most active. Unlike quaternary ammonium salts previously tested, the activities of the compounds were not pH-dependent; the minimal inhibitory concentrations (MIC) were identical at pH 8 and at pH 6. In contrast to quaternary ammonium salts, aminoesters showed similar effects on respiratory sufficient (rho+) and respiratory deficient (rho0) mutants. When tested on glucose stimulated proton extrusion, aminoesters applied at MIC increased external pH. Aminoesters inhibited the plasma membrane H+-ATPase, whereas they were less inhibitory on the mitochondrial ATPase. In order to further compare the aminoesters and their corresponding quaternary ammonium salts, derivatives of N,N-dimethylalanine (DMAL-n and DMALM-n, respectively) were synthesized. The quaternary ammonium salts appeared to have a higher inhibitory potency than aminoesters, especially at pH 8, and alanine derivatives inhibited growth at a lower concentration than glycine derivatives. Both alanine derivatives of the aminoester and the quaternary ammonium salt inhibited the plasma membrane H+- ATPase at lower concentrations than glycine derivatives, but the alanine aminoester was without a detectable effect on the mitochondrial ATPase.     

Extremely miniaturised and highly complex: The thoracic morphology of the first instar larva of Mengenilla chobauti (Insecta,Strepsiptera)

Thoracic structures of the extremely small first instar larva of the strepsipteran species Mengenilla chobauti (ca. 200 μm) were examined, described and reconstructed 3-dimensionally. The focus is on the skeletomuscular system. The characters were compared to conditions found in other insect larvae of very small (Ptiliidae) or large (Dytiscus) size (both Coleoptera) and features of “triungulin” larvae, first instar larvae of Rhipiphoridae, Meloidae (both Coleoptera), and Mantispidae (Neuroptera).The specific lifestyle and the extreme degree of miniaturisation result in numerous thoracic modifications. Many sclerites of the exo- and endoskeleton are reduced. Cervical sclerites, pleural ridges, furcae and spinae are absent. Most of the longitudinal muscles are connected within the thorax, and a pair of ventral longitudinal muscles is present in the pleural region of the meso- and metathorax. This results in a high intersegmental flexibility. Due to the size reduction and the correlated shift of the brain to the thorax, with 94 identified muscles the thoracic musculature appears highly compact. Compared to larger larvae the number of both the individual muscles and the muscle bundles are distinctly reduced. The thorax of the first instar larvae displays many additional strepsipteran autapomorphies. At least partly due to the highly specialised condition, potential synapomorphies with other groups were not found.