Verbal Fluency Development Across Childhood: Normative Data from Brazilian-Portuguese Speakers and Underlying Cognitive Processes.

OBJECTIVE: Verbal fluency (VF) tasks are widely used to investigate children's lexical knowledge and executive functions skills. Consistency of measurement of the strategic retrieval components is still an issue and performance of Brazilian-Portuguese speaking children are currently not available. A cross-sectional study investigated the effects of age, school type (public × private) and the influence of language, memory and inhibitory control on VF. METHOD: We assessed 414 Brazilian children, aged 6-12, in the number of words produced and both clustering and switching components, with two measures of VF: letter (LVF) and semantic (SVF). RESULTS: Analysis of the number of words produced showed a significant increase between 6-8-year-olds, 9-10-year-olds and 11-12-year-olds in SVF, while in LVF, the differences were significant only in the later age group. In SVF, the numbers of clusters and switches increased with age, whereas in LVF, the number of switches increased in all age groups, but clusters increased only in the older group. Structural equation model analyses showed that oral and written language, verbal memory and inhibitory control are associated with VF performance and IQ, while age mediated VF performance. CONCLUSIONS: The results indicate a different development pattern between LVF and SVF in the number of words produced and in clustering and switching, with the latter predicting VF performance in words produced. VF development is shown to depend on language, memory and inhibitory control. Our results have important implications to clinical neuropsychology.

The impact of failure: unsuccessful bacterial invasions steer the soil microbial community away from the invader's niche.

Although many environments like soils are constantly subjected to invasion by alien microbes, invaders usually fail to succeed, succumbing to the robust diversity often found in nature. So far, only successful invasions have been explored, and it remains unknown to what extent an unsuccessful invasion can impact resident communities. Here we hypothesized that unsuccessful invasions can cause impacts to soil functioning by decreasing the diversity and niche breadth of resident bacterial communities, which could cause shifts to community composition and niche structure-an effect that is likely exacerbated when diversity is compromised. To examine this question, diversity gradients of soil microbial communities were subjected to invasion by the frequent, yet oft-unsuccessful soil invader, Escherichia coli, and evaluated for changes to diversity, bacterial community composition, niche breadth, and niche structure. Contrary to expectations, diversity and niche breadth increased across treatments upon invasion. Community composition and niche structure were also altered, with shifts of niche structure revealing an escape by the resident community away from the invader's resources. Importantly, the extent of the escape varied in response to the community's diversity, where less diverse communities experienced larger shifts. Thus, although transient and unsuccessful, the invader competed for resources with resident species and caused tangible impacts that modified both the diversity and functioning of resident communities, which can likely generate a legacy effect that influences future invasion attempts.

Effect of agricultural management regime on Burkholderia community structure in soil.

The main objective of this study was to determine the Burkholderia community structure associated with areas under different agricultural management and to evaluate to which extent this community structure is affected by changes in agricultural management. Two fields with distinct soil history (arable land and permanent grassland) were exposed to three agricultural management regimes (crop rotation, maize monoculture, and grassland). By using a culture-independent approach, based on a Burkholderia-specific polymerase chain reaction-denaturing gradient gel electrophoresis system, it was possible to observe the conversion of Burkholderia communities typical for permanent grassland to those of arable land after four consecutive years. However, the time needed to achieve the reverse transition, i.e., converting the Burkholderia community associated with arable land to that of grassland, was beyond the duration of the field experiment. In addition, by applying principal response curves, the direction and extent of the conversion from grassland to arable land (maize monoculture and to crop rotation) were determined. Hence, the results suggested that agricultural practices, such as fertilization and tillage, were more effective in changing the Burkholderia community structure than agricultural management regime. To determine the effect of agricultural management on the Burkholderia population with biocontrol abilities, the culturable fraction of the Burkholderia community was assessed. The areas under permanent grassland and grassland converted to maize monoculture had the highest percentages of Burkholderia strains with antagonistic activity against Rhizoctonia solani AG-3, mainly Burkholderia pyrrocinia and Burkholderia sp. LMG 22929. The isolation frequency of antagonistic isolates from arable land was extremely low. Our results indicate that (changes in) agricultural management, mainly crop rotation, affect the frequency of isolation of antagonistic Burkholderia strains and that grassland represents a reservoir of Burkholderia species with great potential for agricultural applications.

Burkholderia phytofirmans sp. nov., a novel plant-associated bacterium with plant-beneficial properties.

A Gram-negative, non-sporulating, rod-shaped, motile bacterium, with a single polar flagellum, designated strain PsJN(T), was isolated from surface-sterilized onion roots. This isolate proved to be a highly effective plant-beneficial bacterium, and was able to establish rhizosphere and endophytic populations associated with various plants. Seven related strains were recovered from Dutch soils. Based on 16S rRNA gene sequence data, strain PsJN(T) and the Dutch strains were identified as representing a member of the genus Burkholderia, as they were closely related to Burkholderia fungorum (98.7 %) and Burkholderia phenazinium (98.5 %). Analysis of whole-cell protein profiles and DNA-DNA hybridization experiments confirmed that all eight strains belonged to a single species. Strain PsJN(T) had a DNA G+C content of 61.0 mol%. Only low levels of DNA-DNA hybridization to closely related species were found. Qualitative and quantitative differences in fatty acid composition between strain PsJN(T) and closely related species were identified. The predominant fatty acids in strain PsJN(T) were 16 : 0, 18 : 1omega7c and summed feature 3 (comprising 16 : 1omega7c and/or iso-15 : 0 2-OH). Isolate PsJN(T) showed high 1-aminocyclopropane-1-carboxylate deaminase activity and is therefore able to lower the ethylene level in a developing or stressed plant. Production of the quorum-sensing signal compound 3-hydroxy-C8-homoserine lactone was detected. Based on the results of this polyphasic taxonomic study, strain PsJN(T) and the seven Dutch isolates are considered to represent a single, novel species, for which the name Burkholderia phytofirmans sp. nov. is proposed. The type strain is strain PsJN(T) (=LMG 22146(T) = CCUG 49060(T)).