The genus Pseudo-nitzschia (Bacillariophyceae) in continental shelf waters of Argentina (Southwestern Atlantic Ocean, 38–55°S)

The distribution pattern of Pseudo-nitzschia species, associated phytoplankton flora and its relationships with main environmental factors were studied for the first time in continental shelf surface waters of the Argentine Sea (Southwestern Atlantic Ocean, 38–55°S). Both qualitative and quantitative samples, collected during summer and fall 2003, were examined using light and scanning electron microscopy. Results indicated that the genus Pseudo-nitzschia has a wide distribution along the studied area. It was present at low densities, with infrequent peak abundances and appeared most frequently as a minor component of the diatom populations that typically develop on the continental shelf of the Argentine Sea. Moreover, phytoplankton communities were numerically dominated by unidentified phytoflagellates (≤5 μm) throughout almost all samples analyzed. Eight Pseudo-nitzschia species were identified in our study: P. australis, P. fraudulenta, P. heimii, P. lineola, P. pungens, P. cf. subcurvata, P. turgidula and P. turgiduloides. Of these, P. heimii, P. lineola and P. turgiduloides are new records for the Argentine Sea. Their presence in the area is attributable to the influence of southerly cold water masses. Spatial and temporal variations of the environmental parameters recorded in the study area generally determined the distribution of Pseudo-nitzschia species. P. pungens and P. australis were widely distributed and reached high densities, especially in waters with elevated temperatures and salinities (around 15 °C, 33.8 psu) and low nutrients concentrations. On the other hand, P. heimii, P. lineola, P. turgidula and P. turgiduloides showed a more restricted distribution, with lower densities in relatively cold, less saline (8 °C, 32.45 psu) and nutrient-rich waters. From the Pseudo-nitzschia species found throughout this survey, P. australis, P. fraudulenta, P. pungens and P. turgidula are known as domoic acid (DA) producers around the world, but there is little information on the potential toxicity of these species in Argentina.     

Cross‐species comparison of mammalian saliva using an LC–MALDI based proteomic approach

Despite the importance of saliva in the regulation of oral cavity homeostasis, few studies have been conducted to quantitatively compare the saliva of different mammal species. Aiming to define a proteome signature of mammals’ saliva, an in‐depth SDS‐PAGE–LC coupled to MS/MS (GeLC–MS/MS) approach was used to characterize the saliva from primates (human), carnivores (dog), glires (rat and rabbit), and ungulates (sheep, cattle, horse). Despite the high variability in the number of distinct proteins identified per species, most protein families were shared by the mammals studied with the exception of cattle and horse. Alpha‐amylase is an example that seems to reflect the natural selection related to digestion efficacy and food recognition. Casein protein family was identified in all species but human, suggesting an alternative to statherin in the protection of hard tissues. Overall, data suggest that different proteins might assure a similar role in the regulation of oral cavity homeostasis, potentially explaining the specific mammals’ salivary proteome signature. Moreover, some protein families were identified for the first time in the saliva of some species, the presence of proline‐rich proteins in rabbit's saliva being a good example.     

Conditional QTL mapping of protein content in wheat with respect to grain yield and its components

Grain protein content in wheat (Triticum aestivum L.) is generally considered a highly heritable character that is negatively correlated with grain yield and yield-related traits. Quantitative trait loci (QTL) for protein content was mapped using data on protein content and protein content conditioned on the putatively interrelated traits to evaluate possible genetic interrelationships between protein content and yield, as well as yield-related traits. Phenotypic data were evaluated in a recombinant inbred line population with 302 lines derived from a cross between the Chinese cultivar Weimai 8 and Luohan 2. Inclusive composite interval mapping using IciMapping 3.0 was employed for mapping unconditional and conditional QTL with additives. A strong genetic relationship was found between protein content and grain yield, and yield-related traits. Unconditional QTL mapping analysis detected seven additive QTL for protein content, with additive effects ranging in absolute size from 0.1898% to 0.3407% protein content, jointly accounting for 43.45% of the trait variance. Conditional QTL mapping analysis indicated two QTL independent from yield, which can be used in marker-assisted selection for increasing yield without affecting grain protein content. Three additional QTL with minor effects were identified in the conditional mapping. Of the three QTLs, two were identified when protein content was conditioned on yield, which had pleiotropic effects on those two traits. Conditional QTL mapping can be used to dissect the genetic interrelationship between two traits at the individual QTL level for closely correlated traits. Further, conditional QTL mapping can reveal additional QTL with minor effects that are undetectable in unconditional mapping.     

The C-Terminal Domain of the Virulence Factor MgtC Is a Divergent ACT Domain

MgtC is a virulence factor of unknown function important for survival inside macrophages in several intracellular bacterial pathogens, including Mycobacterium tuberculosis. It is also involved in adaptation to Mg²⁺ deprivation, but previous work suggested that MgtC is not a Mg²⁺ transporter. In this study, we demonstrated that the amount of the M. tuberculosis MgtC protein is not significantly increased by Mg²⁺ deprivation. Members of the MgtC protein family share a conserved membrane N-terminal domain and a more divergent cytoplasmic C-terminal domain. To get insights into MgtC functional and structural organization, we have determined the nuclear magnetic resonance (NMR) structure of the C-terminal domain of M. tuberculosis MgtC. This structure is not affected by the Mg²⁺ concentration, indicating that it does not bind Mg²⁺. The structure of the C-terminal domain forms a βαββαβ fold found in small molecule binding domains called ACT domains. However, the M. tuberculosis MgtC ACT domain differs from canonical ACT domains because it appears to lack the ability to dimerize and to bind small molecules. We have shown, using a bacterial two-hybrid system, that the M. tuberculosis MgtC protein can dimerize and that the C-terminal domain somehow facilitates this dimerization. Taken together, these results indicate that M. tuberculosis MgtC does not have an intrinsic function related to Mg²⁺ uptake or binding but could act as a regulatory factor based on protein-protein interaction that could be facilitated by its ACT domain.     

Biodegradation of bilge waste from Patagonia with an indigenous microbial community

Oily residues that are generated in normal ship operation are considered hazardous wastes. A biodegradation assay with autochthonous microbiota of Bilge Waste Oily Phase (BWOP) was performed in a bioreactor under controlled conditions. Petroleum, diesel oil, and PAH degraders were isolated from bilge wastes. These bacteria belong to the genus Pseudomonas and are closely related to Pseudomonas stutzeri as shown by 16S rDNA phylogenetic analysis. The indigenous microbial community of the bilge waste was capable of biodegrading the BWOP (1% v/v) with biodegradation efficiencies of 70% for hexane extractable material (HEM), 68% for total hydrocarbons (TH) and 90% for total aromatics hydrocarbons (TA) in 14 days. Solid phase microextraction (SPME) was successfully applied to evaluate hydrocarbon evaporation in a control experiment and demonstrated a mass balance closure of 88%. The SPME and biodegradation results give useful information to improve and scale up the process for BWOP treatment.     

Impacts of hunting on mammals in African tropical moist forests: a review and synthesis

• 1 Available information on the consumption of wild meat in West and Central Africa is reviewed. We show that mammals are the prime source of bushmeat, and that ungulates and rodents make up the highest proportion of biomass extracted.
• 2 We present data on current knowledge of extraction patterns of wild mammals in West and Central Africa, and evidence that at current off‐take levels, within the range states, mammals as bushmeat are being depleted on an unprecedented scale. Extraction rates are orders of magnitude higher there than in comparable ecosystems like the Amazon, and much less likely to be sustainable.
• 3 However, basic knowledge of the biology of harvestable tropical moist forest mammals, and the consequences of hunting on mammalian communities, which permits accurate estimation of maximal production rate (the excess of growth over replacement rate), is largely unavailable, and this hinders estimation of hunting quotas and sustainability. Comparisons are made with the existing information available on Amazon basin mammals and hunting patterns reported there.

     

Bottom-up regulation of bacterial growth in tropical phytotelm bromeliads

Evaluating the factors that regulate bacterial growth in natural ecosystems is a major goal of modern microbial ecology. Phytotelm bromeliads have been used as model ecosystems in aquatic ecology as they provide many independent replicates in a small area and often encompass a wide range of limnological conditions. However, as far as we know, there has been no attempt to evaluate the main regulatory factors of bacterial growth in these aquatic ecosystems. Here, we used field surveys to evaluate the main bottom-up factors that regulate bacterial growth in the accumulated water of tank bromeliads. Bacterial production, water temperature, water color, chlorophyll-a, and nutrient concentrations were determined for 147 different tank bromeliads in two different samplings. Bromeliad position and the season of sampling were also noted. Bacterial production was explained by ion ammonium concentration and water temperature, but the total variance explained was low (r ² = 0.104). Sampling period and bromeliad position were included in additional models that gave empirical support for predicting bacterial production. Bromeliad water tanks are extremely variable aquatic ecosystems in space (among bromeliads) and time (environmental conditions can change within hours), and it is well known that bacterial production responds rapidly to environmental change. Therefore, we concluded that several factors could independently regulate bacterial growth in phytotelm bromeliads depending on the characteristics of each bromeliad, such as location, amount of detritus, and ambient nutrient concentrations. A clear bottom-up limitation pattern of bacterial production in tropical phytotelm bromeliads was not found. Handling editor: Luigi Naselli-Flores     

Effects of osmotic and matric potential on radial growth and accumulation of endogenous reserves in three isolates of Pochonia chlamydosporia

For the first time, the effects of varying osmotic and matric potential on fungal radial growth and accumulation of polyols were studied in three isolates of Pochonia chlamydosporia. Fungal radial growth was measured on potato dextrose agar modified osmotically using potassium chloride or glycerol. PEG 8000 was used to modify matric potential. When plotted, the radii of the colonies were found to grow linearly with time, and regression was applied to estimate the radial growth rate (mm day^?1). Samples of fresh mycelia from 25-day-old cultures were collected and the quantity (mg g^?1 fresh biomass) of four polyols (glycerol, erythritol, arabitol and mannitol) and one sugar (glucose) was determined using HPLC. Results revealed that fungal radial growth rates decreased with increased osmotic or matric stress. Statistically significant differences in radial growth were found between isolates in response to matric stress (P<0.006) but not in response to osmotic stress (P=0.759). Similarly, differences in the total amounts of polyols accumulated by the fungus were found between isolates in response to matric stress (P<0.001), but not in response to osmotic stress (P=0.952). Under water stress, the fungus accumulated a combination of different polyols important in osmoregulation, which depended on the solute used to generate the stress. Arabitol and glycerol were the main polyols accumulated in osmotically modified media, whereas erythritol was the main polyol that was accumulated in media amended with PEG. The results found that Pochonia chlamydosporia may use different osmoregulation mechanisms to overcome osmotic and matric stresses.