Biofilms: new ideas for an old problem

Microbial cells, under moist conditions, are able to adhere to surfaces and to form structured communities embedded in a matrix of extracellular polymeric substances (EPS). In industrial environments, biofilms can cause heat and mass transfer limitations whilst in medical facilities they can be a source of contamination and proliferation of infections. Biofilm formation is related to the pathogenicity of some bacterial strains and cells in biofilms are usually resistant to antimicrobials agents, which increases the interest in new and sound methods for their prevention and destruction.     

New twists on an old story: hemoglobin

New determinations of oxygen and carbon monoxide binding to human hemoglobin, indicating an extremely small population of triply ligated species, suggest a close relationship with structural features that govern the allosteric mechanism of cooperativity.     

Enlightenment of old ideas from new investigations: more questions regarding the evolution of bacteriogenic light organs in squids

Bioluminescence is widespread among many different types of marine organisms. Metazoans contain two types of luminescence production, bacteriogenic (symbiotic with bacteria) or autogenic, via the production of a luminous secretion or the intrinsic properties of luminous cells. Several species in two families of squids, the Loliginidae and the Sepiolidae (Mollusca: Cephalopoda) harbor bacteriogenic light organs that are found central in the mantle cavity. These light organs are exceptional in function, that is, the morphology and the complexity suggests that the organ has evolved to enhance and direct light emission from bacteria that are harbored inside. Although light organs are widespread among taxa within the Sepiolidae, the origin and development of this important feature is not well studied. We compared light organ morphology from several closely related taxa within the Sepiolidae and combined molecular phylogenetic data using four loci (nuclear ribosomal 28S rRNA and the mitochondrial cytochrome c oxidase subunit I and 12S and 16S rRNA) to determine whether this character was an ancestral trait repeatedly lost among both families or whether it evolved independently as an adaptation to the pelagic and benthic lifestyles. By comparing other closely related extant taxa that do not contain symbiotic light organs, we hypothesized that the ancestral state of sepiolid light organs most likely evolved from part of a separate accessory gland open to the environment that allowed colonization of bacteria to occur and further specialize in the eventual development of the modern light organ.     

Ten years in the library: new data confirm paleontological patterns

A comparison is made between compilations of times of origination and extinction of fossil marine animal families published in 1982 and 1992. As a result of ten years of library research, half of the information in the compendia has changed: families have been added and deleted, low-resolution stratigraphic data been improved, and intervals of origination and extinction have been altered. Despite these changes, apparent macroevolutionary patterns for the entire marine fauna have remained constant. Diversity curves compiled from the two data bases are very similar, with a goodness-of-fit of 99%; the principal difference is that the 1992 curve averages 13% higher than the older curve. Both numbers and percentages of origination and extinction also match well, with fits ranging from 83% to 95%. All major events of radiation and extinction are identical. Therefore, errors in large paleontological data bases and arbitrariness of included taxa are not necessarily impediments to the analysis of pattern in the fossil record, so long as the data are sufficiently numerous.     

Arrhenius and Gleason revisited: new hybrid models resolve an old controversy

Aim Studies have typically employed species–area relationships (SARs) from sample areas to fit either the power relationship or the logarithmic (exponential) relationship. However, the plots from empirical data often fall between these models. This article proposes two complementary and hybrid models as solutions to the controversy regarding which model best fits sample‐area SARs. Methods The two models are and , where S_A is number of species in an area, A, where z, b, c₁ and c₂ are predetermined parameters found by calculation, and where d and n are parameters to be fitted. The number of parameters is reduced from six to two by fixing the model at either end of the scale window of the data set, a step that is justified by the condition that the error or the bias, or both, in the first and the last data points is negligible. The new hybrid models as well as the power model and the logarithmic model are fitted to 10 data sets. Results The two proposed models fit well not only to Arrhenius’ and Gleason’s data sets, but also to the other six data sets. They also provide a good fit to data sets that follow a sigmoid (or triphasic) shape in log–log space and to data sets that do not fall between the power model and the logarithmic model. The log‐transformation of the dependent variable, S, does not affect the curve fit appreciably, although it enhances the performance of the new models somewhat. Main conclusions Sample‐area SARs have previously been shown to be convex upward, convex downward (concave), sigmoid and inverted sigmoid in log–log space. The new hybrid models describe successfully data sets with all these curve shapes, and should therefore produce good fits also to what are termed triphasic SARs.     

Cell locomotion: new research tests old ideas on membrane and cytoskeletal flow

Recent studies on the mobility of membrane markers on crawling cells indicate that there is no long-range centripetal flow of membrane proteins or lipids during cell locomotion. In this article we reflect on the history of ideas about membrane flow in cells, and we discuss how these new findings will shift the focus of research in cell locomotion away from the cell surface to the molecular interactions and dynamics of the actin cytoskeleton.     

Serotonin neurochemistry revisited: A new look at some old axioms

A number of principles have long guided research into serotonin neurochemistry and some of them are presently reconsidered with a slightly different outlook. An increasing amount of experimental data does not always support these older axioms and as more empirical observations are made, some of these may require modification. For example, increases in 5-HT produced by injections of l-tryptophan do not necessarily indicate that tryptophan hydroxylase is less than saturated with its substrate in vivo; injections of l-tryptophan increase 5-HT and its turnover but do not appear to increase its release; 5-HT release can apparently occur from the cytoplasm and need not involve exocytosis; presynaptic autoreceptors do not appear to modulate 5-HT release; and, 5-HIAA most accurately reflects monoamine oxidase activity, not release of 5-HT or activity of 5-HT neurons.     

Recognition of methylated histones: new twists and variations

Histone tails undergo methylation at their lysines and arginines. These chemical marks act as traffic signals that direct activity of chromatin remodeling complexes to appropriate regions of the genome. A surprisingly diverse group of effector protein modules in chromatin remodeling complexes and their associated factors are involved in the recognition of histone methyllysines. Previous studies generally painted a picture of individual lysines recognized by these protein modules in a 1:1 fashion. However, recent structural studies show more complex interactions where the critical lysines are recognized in pairs, or in the context of nucleosomal DNA, or within the central pore of repeat motifs. These interactions extend our understanding of how histone tail recognition can be enhanced through coupled interactions within a single module or through the cooperation of two different molecules.     

GABA signalling during development: new data and old questions

In addition to being the major inhibitory neurotransmitter, gamma-aminobutyric acid (GABA) is thought to play a morphogenetic role in embryonic development. During the last decade, considerable progress has been made in elucidating the molecular mechanisms involved in GABA synthesis and biological action. The present review is an attempt to summarise recent results on the ontogeny of the different components of embryonic GABA signalling with an emphasis on the synthesis of GABA by different molecular forms of glutamic acid decarboxylase (GAD).     

Polyploidy and its effect on evolutionary success: old questions revisited with new tools

Polyploidy, the condition of possessing more than two complete genomes in a cell, has intrigued biologists for almost a century. Polyploidy is found in many plants and some animal species and today we know that polyploidy has had a role in the evolution of all angiosperms. Despite its widespread occurrence, the direct effect of polyploidy on evolutionary success of a species is still largely unknown. Over the years many attractive hypotheses have been proposed in an attempt to assign functionality to the increased content of a duplicated genome. Among these hypotheses are the proposal that genome doubling confers distinct advantages to a polyploid and that these advantages allow polyploids to thrive in environments that pose challenges to the polyploid''s diploid progenitors. This article revisits these long-standing questions and explores how the integration of recent genomic developments with ecological, physiological and evolutionary perspectives has contributed to addressing unresolved problems about the role of polyploidy. Although unsatisfactory, the current conclusion has to be that despite significant progress, there still isn''t enough information to unequivocally answer many unresolved questions about cause and effect of polyploidy on evolutionary success of a species. There is, however, reason to believe that the increasingly integrative approaches discussed here should allow us in the future to make more direct connections between the effects of polyploidy on the genome and the responses this condition elicits from the organism living in its natural environment.