Screening of plant growth promotion ability among bacteria isolated from field-grown sorghum under different managements in Brazilian drylands

Sorghum [Sorghum bicolor (L.) Moench] is a multipurpose grass cultivated in drylands due to its adaptation to drought. However the characteristics of sorghum-associated bacteria are not known in the Brazilian drylands. The aim of this study was to isolate and evaluate the plant growth promotion potential bacteria from field-grown sorghum under two irrigation and manure application levels in a Brazilian semi-arid reagion. Sorghum was irrigated with 3 or 1 mm day^?1 and fertilized or not with liquid goat manure. Bacteria were obtained from surface-disinfected roots applying two nitrogen-free semi-solid media. The bacteria were evaluated for the presence of nifH gene, 16S rRNA sequences, calcium-phosphate solubilization, production of auxins and siderophores and for sorghum growth promotion. We obtained 20 out of 24 positive bacteria for nifH. The isolates were classified as in six different genera. All isolates produced auxins “in vitro”, six bacteria produced siderophores and three Enterobacteriaceae solubilized calcium-phosphate. At least ten bacteria resulted in the increased total N content in the sorghum shoots, comparable to fertilization with 50 mg N plant^?1 week^?1 and to inoculation with Azospirillum brasilense Ab-V5. Enterobacter sp. ESA 57 was the best sorghum plant-growth promoting bacteria isolated in this study.     

Wildfires in the Eastern Arc Mountains of Tanzania: Burned areas,underlying causes and management challenges

The Eastern Arc Mountains are one of the most important ecosystems that conserve biodiversity in the world. These ecosystems are threatened by the increasing occurrence of wildfires. Nevertheless, there is inadequate information useful for the development of effective strategies to prevent or respond to future fires. This paper analyses the current extent of dry season fires, underlying causes and the effectiveness of the fire management strategy being implemented in and around the Uluguru Nature Forest Reserve (UNFR) between 2016 and 2021. Differenced Normalised Burn Ratio derived from Landsat satellite images was applied to determine the extent of burned areas, and focus group discussions were held to determine the underlying causes of fires and the extent of implementation of fire management strategies. About 2% (472 ha) of reserved UNFR and 5% (2,854 ha) of unreserved forests were burned in 2017. Some of the fires impacted on 60% (370 ha) of the grassy Lukwangule plateau, which is home to a fire‐sensitive endemic species. The underlying causes of fires varied spatially across the mountains but generally, fire escaping from farm preparation and hunting activities were found to be the most prevalent. On average, survey participants perceived that fire management strategy objectives were achieved by only 29% mainly constrained by a shortage of financial and human resources. Our findings suggest that ignitions and fire spread in UNFR could be prevented or controlled through sustainable funding of fire management activities and the effective engagement of local communities in the management of the reserve.     

Recovery of the pubic symphysis on primiparous young and multiparous senescent mice at postpartum

It has been observed that parturition has a significant effect on female skeletal architecture and that age alters musculoskeletal tissues and their functions. We therefore hypothesized that multiparity affects the recovery of the pubic symphysis in senescent mice at postpartum and the morphology of the interpubic tissues. The pubic symphysis of primiparous young, virgin senescent (VS) and multiparous senescent (MS) Swiss mice was examined by light microscopy, transmission electron microscopy, morphometric analysis and immunohistochemistry. The mouse pubic symphysis was remodeled during the first pregnancy: the cellular phenotype and morphology changed to ensure a structurally safe birth canal, followed by recovery of the interpubic articulation after birth. The morphology of the pubic symphysis in the VS group was maintained in a state similar to that observed in virgin young mice. In contrast, MS mice exhibited an interpubic ligament characterized by extended fibrocyte-like cells, an opened interpubic articulation gap, compacted and thin collagen fibrils and scarce galectin-3-positive cells. Thus, we found that the cellular and extracellular characteristics of the pubic symphysis were altered by multiparity in senescent mice. These particular tissue characteristics of the MS group might be associated with an impaired recovery process at postpartum. Thus, a better understanding of the alterations that occur in the birth canal, including the pubic symphysis, due to multiparity in reproductively aged mice may contribute to our comprehension of the biological mechanisms that modify the skeleton and pelvic ligaments and even play a role in the murine model of pelvic organ prolapse.     

The effects of the C-terminal amidation of mastoparans on their biological actions and interactions with membrane-mimetic systems

Polycationic peptides may present their C-termini in either amidated or acidic form; however, the effects of these conformations on the mechanisms of interaction with the membranes in general were not properly investigated up to now. Protonectarina-MP mastoparan with an either amidated or acidic C-terminus was utilized to study their interactions with anionic and zwitterionic vesicles, using measurements of dye leakage and a combination of H/D exchange and mass spectrometry to monitor peptide–membrane interactions. Mast cell degranulation, hemolysis and antibiosis assays were also performed using these peptides, and the results were correlated with the structural properties of the peptides. The C-terminal amidation promotes the stabilization of the secondary structure of the peptide, with a relatively high content of helical conformations, permitting a deeper interaction with the phospholipid constituents of animal and bacterial cell membranes. The results suggested that at low concentrations Protonectarina-MP interacts with the membranes in a way that both terminal regions remain positioned outside the external surface of the membrane, while the α-carbon backbone becomes partially embedded in the membrane core and changing constantly the conformation, and causing membrane destabilization. The amidation of the C-terminal residue appears to be responsible for the stabilization of the peptide conformation in a secondary structure that is richer in α-helix content than its acidic congener. The helical, amphipathic conformation, in turn, allows a deeper peptide–membrane interaction, favoring both biological activities that depend on peptide structure recognition by the GPCRs (such as exocytosis) and those activities dependent on membrane perturbation (such as hemolysis and antibiosis).     

Cytogenetic divergence in two sympatric fish species of the genus Astyanax Baird and Girard, 1854 (Characiformes,Characidae) from northeastern Brazil

The fish genus Astyanax is widespread throughout the Neotropical region and is one of the most species-rich genera of the Characiformes. Cytogenetic studies of Astyanax have revealed marked intra- and interspecific diversity, with the identification of various species complexes. In this report, we describe the karyotypic structure of two sympatric species of Astyanax (Astyanax sp. and Astyanax aff. fasciatus) from the Middle Contas River basin in the northeastern Brazilian state of Bahia. Both species had 2n = 48 but differed in their karyotypic formulae. Small heterochromatic blocks and multiple nucleolar organizer regions (NORs) were identified in both species. Terminal CMA₃⁺/DAPI⁻ signals were observed in Astyanax sp. and A. aff. fasciatus, mostly coincident with NORs. These results show that chromosomal markers can be used to identify species in this fish complex. These markers can provide useful information for evolutionary studies and investigations on the mechanisms of chromosomal diversity in Astyanax.     

Effects of increased temperature and aquatic fungal diversity on litter decomposition

Climate warming and biodiversity loss are two major factors threatening freshwaters. Aquatic hyphomycetes are fungi that play a key role in organic matter turnover in streams. To assess the impacts of temperature increase and aquatic hyphomycete diversity on plant-litter decomposition, we manipulated fungal assemblage composition at two levels of diversity (four and eight species) under ambient temperature of 16 °C and two regimes of temperature increase differing in 8 °C: abrupt versus gradual increase from 16 to 24 °C. The effects were evaluated on leaf-litter decomposition, fungal biomass and reproduction. Results showed faster leaf decomposition under increased temperature, but no differences were found between an abrupt and a gradual increase in temperature. Assemblage composition was the major factor controlling fungal biomass and reproduction, while fungal diversity was only critical to maintain reproduction.     

Can we use plant traits and soil characteristics to predict leaf damage in savanna woody species?

Although several hypotheses aim to explain insect herbivory on plants, the relative importance of plant traits, environment, and organizational scale (i.e., individual or community) to herbivory damage level is not well understood. We used an approach based on a local scale, divided into individual and community levels, to test if plant traits, soil characteristics, and plant density explain leaf damage. We sampled 983 individuals in 49 plots distributed over dense and open savanna formations in Emas National Park. In order to explain plant damage, we performed a multi-model inference analysis of four plant traits associated with plant damage, five soil characteristics, and plant density. We did not find any support to plant vigor or plant stress hypotheses at individual plant level. However, the resource concentration hypothesis and plant stress hypothesis explained leaf damage at the community level. We found that increased availability of calcium (Ca) in soils reduced plant damage at the community level. Because soil Ca concentration is a major constraint to plant development in the Brazilian savanna, we postulated that its increasing availability permits plants to invest more in defense strategies. We demonstrate that plant density, Ca soil concentration, and leaf size can be used to predict the plant damage suffered by woody species in savannas at community level.     

Genetic diversity and structure of natural populations of Gossypium mustelinum,a wild relative of cotton,in the basin of the De Contas River in Bahia,Brazil

Gossypium mustelinum is a wild cotton relative found only in the semiarid region of Bahia state in Brazil, and changes caused by humans in the natural habitat of this species have endangered the existence of several natural populations. Information about the occurrence and genetic composition of these populations is necessary to design effective conservation measures. The aim of this study was to characterize the in situ maintenance mode and assess the genetic diversity of G. mustelinum populations in the basin of the De Contas River. A sample of 205 G. mustelinum specimens was collected from the margins of the Jacaré, Riacho Quixaba, Riacho Serra Azul, and Riacho Riachão rivers and genotyped using 13 SSR primer pairs. In general, all G. mustelinum populations exhibit inadequate in situ maintenance, predominantly due to the deforestation of riparian vegetation and herbivory. The observed total genetic diversity of G. mustelinum was significant (H _E = 0.489), highly structured (F _ST = 0.534), and organized in homozygous genotypes (F _IS = 0.873). The high observed inbreeding level is consistent with the predominance of self-fertilization and geitonogamy (t _m = 0.234). In addition, the pattern of genetic structure tended to form groups that coincided with the collection sites, i.e., first clustering within subpopulations, then within populations, and finally within the closest populations. Thus, the observed genetic diversity is likely to be rapidly lost, and conservation measures should therefore be undertaken.     

Finding Near-Optimal Groups of Epidemic Spreaders in a Complex Network

In this paper, we present algorithms to find near-optimal sets of epidemic spreaders in complex networks. We extend the notion of local-centrality, a centrality measure previously shown to correspond with a node''s ability to spread an epidemic, to sets of nodes by introducing combinatorial local centrality. Though we prove that finding a set of nodes that maximizes this new measure is NP-hard, good approximations are available. We show that a strictly greedy approach obtains the best approximation ratio unless P = NP and then formulate a modified version of this approach that leverages qualities of the network to achieve a faster runtime while maintaining this theoretical guarantee. We perform an experimental evaluation on samples from several different network structures which demonstrate that our algorithm maximizes combinatorial local centrality and consistently chooses the most effective set of nodes to spread infection under the SIR model, relative to selecting the top nodes using many common centrality measures. We also demonstrate that the optimized algorithm we develop scales effectively.     

Non-native prey species supporting fish assemblage biomass in a Neotropical reservoir

The present study aimed to investigate the role of four non-native invertebrates in supporting fish biomass as well as their influence on the carbon flow into the Volta Grande reservoir food web. The fish samples were carried out quarterly between October 2015 and July 2016 using gillnets. At the sampled sites, four non-native invertebrates (golden mussel, Asian clam, trumpet snail and Amazonian prawn), which are potential prey for fish in the Volta Grande reservoir, were collected by targeted sampling using a Petersen-type bottom dredger and semi-circular sieves. The gut contents of the fish were collected and analyzed under stereoscope, and samples of muscle tissue of these fish, as well as the four non-native invertebrate species sampled, were submitted for isotopic analysis. Results obtained by the present study, by both gut content and stable isotopic analyses, pointed to a trophic structure where non-native species represent not only a strong component of the fish community, but also their main carbon source. Based on gut contents and isotopic mixing models, we found that together, non-native prey are essential carbon sources for the fish fauna, fuelling more than 40.0% of the biomass in four dominant fish species. The consumption rate of non-native bivalves by the native omnivorous fish Leporinus friderici suggested these filter-feeding organisms potentially constitute an important trophic connection between littoral consumers and pelagic energy sources. In addition, non-native prey were also prominent carbon sources for non-native fish, fuelling more than half of the biomass in peacock bass and silver croaker, suggesting these prey have a fundamental role in maintaining non-native fish populations in this system. Our results may help to understand fundamental ecological issues bringing to light the extent to which these new combinations of species influence the energy flow and ecosystem properties of the Volta Grande reservoir.