Galdino Andrade

Soil aggregation status and rhizobacteria in the mycorrhizosphere

Soil aggregation is a dynamic process in which plants and the soil microbiota play a major role. This experiment was conducted to determine whether the effects of mycorrhizae on the stability of water-stable soil aggregates (WSA) and on selected groups of soil microorganisms are interrelated. Soil containers consisting of four compartments were utilized. Two compartments on each side of a solid barrier were separated by a 43 μm screen that permitted the passage of hyphae, but not of roots. The roots of Sorghum bicolor plants were split over the center barrier, and the roots on one side were inoculated with an arbuscular-mycorrhizal (AM) fungus. This design produced mycorrhizosphere soils (M) by AM roots or hyphosphere (H) soils by AM hyphae in the two compartments on the one side of the barrier, and rhizosphere soils (R) by nonAM roots or root- and hypha-free bulk soil (S) in the two compartments on the other side. At harvest (10 wk), there were significant differences in WSA between soils in the order: M>R>H>S, and WSA stability was significantly correlated with root or hyphal length. Numbers of colony-forming units of the microflora (total bacteria, actinomycetes, anaerobes, P solubilizers, and nonAM fungi) were in general not correlated with root or hyphal length, but in some cases were significantly correlated with WSA. Bacteria isolated from the water-stable soil-aggregate fraction tended to be more numerous than from the unstable fraction. The difference was significant in the M soil for total bacteria and P solubilizing bacteria. NonAM fungi were more numerous in the unstable fraction of the M soil. The data show that the root and fungal components of mycorrhizae enhance WSA stability individually and additively in concert, and suggest that they affect microorganism numbers indirectly by providing a favorable and protective habitat through the creation of habitable pore space in the WSA.

Bacterial associations with the mycorrhizosphere and hyphosphere of the arbuscular mycorrhizal fungus Glomus mosseae

Roots and mycorrhizal fungi may not associate with soil bacteria randomly, but rather in a hierarchical structure of mutual preferences. Elucidation of such structures would facilitate the management of the soil biota to enhance the stability of the plant-soil system. We conducted an experiment utilizing two isolates of soil bacteria to determine their persistence in distinct mycorrhizal regions of the root zone, and their effects on general rhizosphere populations of fluorescent pseudomonads (FP). Split-root sorghum (Sorghum bicolor L.) plants were grown in four-compartment containers, constructed so that the soils in individual compartments held either (1) roots colonized by the arbuscular-mycorrhizal (AM) fungus Glomus mosseae (M), (2) nonAM roots only (R), (3) hyphae of G. mosseae (H), or (4) no mycorrhizal structures (S). The soils were inoculated (107 cells g-1 dry soil) with antibiotic-resistant (rifampicin, rif; streptomycin, sm) strains of the soil bacteria, Alcaligenes eutrophus (rifr50) or Arthrobacter globiformis (smr250), or were left uninoculated as control. A. eutrophus had been isolated from a specific source (hyphosphere soil of G. mosseae), and A. globiformis from mycorrhizosphere soils of two AM fungi. After 10 wk of growth, the presence of A. eutrophus was barely detectable (<10 cfu g-1 dry soil) in nonAM (R and S) soils, but persisted well (104 cfu g-1 dry soil) in AM (H and M) soils. Numbers of A. globiformis were more evenly distributed between all soils, but were highest in the presence of AM roots (M soil). There were varied bacterial effects on root and AM-hyphal development: A. eutrophus decreased hyphal length in H soil, while A. globiformis stimulated root length in M soil. The two bacterial inoculants did not affect numbers of FP in H, R, and M soils, but the AM status of the soils did: the numbers of FP increased in the order M>R>H>S. There was a positive correlation of FP numbers with both bacterial inoculants in M and H soils. Numbers of FP changed with root or hyphal lengths, an effect that was related to changes in the numbers of the inoculated bacteria. The results indicate that the hyphosphere-specific A. eutrophus depended on the presence of G. mosseae, but that the nonspecific A. globiformis did not. The mycorrhizal status of soils may selectively influence persistence of bacterial inoculants as well as affecting the numbers of other native bacteria.

Root mycorrhizal colonization and plant responsiveness are related to root plasticity, soil fertility and successional status of native woody species in southern Brazil

Twelve native woody species were studied to investigate the influences of soil fertility and root morphology on colonization by arbuscular mycorrhizal (AM) fungi during seedling establishment and growth. Seedlings were grown in soils of low and high natural fertility, uninoculated or inoculated with AM fungi, under greenhouse conditions. The mycorrhizal root colonization and plant responsiveness were higher among early successional species than late successional ones. Among early successional species, in both soils, mycorrhizal colonization provided significant increase in total dry mass, growth rates of shoot and root, root length, density of root tissues, root surface area and P concentration and content in the shoot. Early successional species grown with AM fungi displayed significant decreases in carbon allocation to roots, specific root length and the length and incidence of root hairs. Mycorrhizal colonization did not affect the root morphology of the late successional species in either soil. The growth of these woody species was influenced by differences in soil fertility. There was positive correlation between the degree of plant responses to AM inoculation with the percentage of root colonized by AM fungi. In both soils, plant responsiveness and mycorrhizal root colonization correlated positively to root-hair incidence and root-hair length and correlated negatively to fine-root diameter. The results suggest that during the establishment of seedlings, the large responses to the inoculation and colonization of roots by AM fungi are related to both the successional status and root morphological plasticity of the host plant, regardless of soil fertility.

Antibacterial activity of extracellular compounds produced by a Pseudomonas strain against methicillin-resistant Staphylococcus aureus (MRSA) strains.

BackgroundThe emergence of multidrug-resistant bacteria is a world health problem. Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA) strains, is one of the most important human pathogens associated with hospital and community-acquired infections. The aim of this work was to evaluate the antibacterial activity of a Pseudomonas aeruginosa-derived compound against MRSA strains.MethodsThirty clinical MRSA strains were isolated, and three standard MRSA strains were evaluated. The extracellular compounds were purified by vacuum liquid chromatography. Evaluation of antibacterial activity was performed by agar diffusion technique, determination of the minimal inhibitory concentration, curve of growth and viability and scanning electron microscopy. Interaction of an extracellular compound with silver nanoparticle was studied to evaluate antibacterial effect.ResultsThe F3 (ethyl acetate) and F3d (dichloromethane- ethyl acetate) fractions demonstrated antibacterial activity against the MRSA strains. Phenazine-1-carboxamide was identified and purified from the F3d fraction and demonstrated slight antibacterial activity against MRSA, and synergic effect when combined with silver nanoparticles produced by Fusarium oxysporum. Organohalogen compound was purified from this fraction showing high antibacterial effect. Using scanning electron microscopy, we show that the F3d fraction caused morphological changes to the cell wall of the MRSA strains.ConclusionsThese results suggest that P. aeruginosa-produced compounds such as phenazines have inhibitory effects against MRSA and may be a good alternative treatment to control infections caused by MRSA.

Interactions between diazotrophic bacteria and mycorrhizal fungus in maize genotypes

Some diazotrophic bacteria can fix nitrogen biologically in gramineous host plants. Generally, gramineous plants are also associated with mycorrhizal fungi, that can improve mainly plant P uptake. Among the factors affecting plant-microbe interactions, the plant genotype plays an important role. This study evaluates the effect of diazotrophic bacteria and an arbuscular mycorrhizal fungus (AMF), on five genotypes of maize (Zea mays L.), in relation to plant biomass, shoot N and P concentrations, and fine root morphological traits. The experimental design was entirely randomized in a factorial 5 × 4 × 2 arrangement, i.e., five maize genotypes (hybrids C333B, AS3466, and PREMIUM, and the inbreed lines lg40897-1 and lg40505-1), three diazotrophic bacteria (Azospirillum lipoferum, A. amazonense, and Burkholderia sp.) in addition to a control without bacterial inoculation, co-inoculated or not with the AMF Glomus clarum. The non-mycorrhizal plants inoculated with Azospirillum exhibited the highest N concentrations. The lines lg40897-1 and lg40505-1 showed higher P concentrations as compared to the hybrids, mainly when colonized by AMF. The higher levels of mycorrhizal colonization (90%) occurred in the C333B and lg40897-1 genotypes, which also exhibited a greater root diameter. Mycorrhiza increased shoot and root biomass, besides root traits as total length, specific length, total surface, and incidence of root hairs in all genotypes. In addition, mycorrhiza also stimulated the root colonization by diazotrophic bacteria. The bacteria did not affect root morphological traits and mycorrhizal colonization.

Evaluation of Bacillus thuringiensis bioinsecticidal protein effects on soil microorganisms

The effect of B. thuringiensis and its crystal protein on plant growth and on functional groups of microorganisms is not well understood. Soybean (Glycine max) var. Br 322 was grown in non-sterile soil infested with three B. thuringiensis (Bt) inocula: insecticidal crystal protein producer (Cry+), a mutant non-producer (Cry−), or insecticidal crystal protein (ICP), at a rate of 107 cells g−1 dry soil or 1.25 mg of protein g−1 dry soil. Non-inoculated plants were maintained as control. Measurements were carried out on soil samples before sowing (time zero) and after sowing and inoculation (5, 15, 25, 35 and 45 d) on samples of rhizosphere soil. The effect of spore and crystal protein produced by B. thuringiensis on the populations of functional groups of microorganisms (bacteria including actinomycetes and fungi) involved in the biogeochemical cycling of carbon (cellulolytic, amylolytic and proteolytic), phosphorus (arbuscular mycorrhizal fungi), and nitrogen (number of nodules and proteolytic) were evaluated. Population sizes of culturable heterotrophic bacteria and saprophytic fungi were also evaluated. No difference was found in heterotrophic bacterial populations inoculated with B. thuringiensis. Difference was observed in functional groups of C-cycling microorganisms. Nodule formation and plant growth were increased by Cry+ strain and ICP when compared with uninoculated plants. Crystal protein did not show any effect on arbuscular mycorrhiza (AM) colonization. However, a deleterious effect was observed with Cry+ and Cry− strains that inhibited colonization of AM fungi when compared with uninoculated plants.

Studies on fungal and bacterial population of air-conditioned environments

In tropical countries such as Brazil, there is not enough information about microbial contaminants in indoor environments with air conditioning systems. Microbial monitoring of such environments is important for the quality of human life. The aim of this work was to assess the fungal genera and bacterial morphotypes occurring in such environments. Air samples were taken indoors and outdoors from a public auditorium, a hospital, a company and a shopping center during the 2001 winter by using a six-stage impactor Millipore M air T® . Twenty-one fungal genera were identified. Bacterial morphological groups found were Gram positive and negative rods and Gram positive coccus.

Inoculant of Arbuscular Mycorrhizal Fungi (Rhizophagus clarus) Increase Yield of Soybean and Cotton under Field Conditions.

Nutrient availability is an important factor in crop production, and regular addition of chemical fertilizers is the most common practice to improve yield in agrosystems for intensive crop production. The use of some groups of microorganisms that have specific activity providing nutrients to plants is a good alternative, and arbuscular mycorrhizal fungi (AMF) enhance plant nutrition by providing especially phosphorus, improving plant growth and increasing crop production. Unfortunately, the use of AMF as an inoculant on a large scale is not yet widely used, because of several limitations in obtaining a large amount of inoculum due to several factors, such as low growth, the few species of AMF domesticated under in vitro conditions, and high competition with native AMF. The objective of this work was to test the infectivity of a Rhizophagus clarus inoculum and its effectiveness as an alternative for nutrient supply in soybean (Glycine max L.) and cotton (Gossypium hirsutum L.) when compared with conventional chemical fertilization under field conditions. The experiments were carried out in a completely randomized block design with five treatments: Fertilizer, AMF, AMF with Fertilizer, AMF with 1/2 Fertilizer, and the Control with non-inoculated and non-fertilized plants. The parameters evaluated were AMF root colonization and effect of inoculation on plant growth, nutrient absorption and yield. The results showed that AMF inoculation increased around 20 % of root colonization in both soybean and cotton; nutrients analyses in vegetal tissues showed increase of P and nitrogen content in inoculated plants, these results reflect in a higher yield. Our results showed that, AMF inoculation increase the effectiveness of fertilizer application in soybean and reduce the fertilizer dosage in cotton.

Guaraná (Paullinia cupana) seeds: Selective supercritical extraction of phenolic compounds.

Approximately 70% of the Brazilian production of guaraná (Paullinia cupana) seeds is absorbed by the beverage industries. Guaraná has several pharmacological properties: energy stimulant, antimicrobial, chemoprophylactic, antigenotoxic, antidepressive, anxiolytic, and anti-amnesic effects. Supercritical carbon dioxide extraction of bioactive compounds from guaraná seeds was carried out and optimized by an orthogonal array design (OA9(3(4))). The factors/levels studied were: modifier(s) (ethanol and/or methanol), extraction time (20, 40, and 60min), temperature (40, 50, and 60°C), and pressure (100, 200, and 300bar). The statistical design was repeated with increasing proportions of modifiers. The percentage of modifier used was proportional to the amount of polar compounds extracted. The best conditions for the supercritical extraction, based on the content of polyphenols, epicatechin/catechin quantification, yield and operating cost, proved to be: 40% ethanol:methanol during 40min, under 40°C, and 100bar. The temperature had a significant effect on the total phenolic content.

Mortality and risks related to healthcare-associated infection

Healthcare-associated infections are a major cause of morbidity-mortality among hospitalized patients. The aim of this epidemiological study was to determine mortality and risks related to death in adult patients with healthcare-associated infections admitted to a teaching hospital in one year. Patient data were collected from infection medical reports. The mortality rate associated with infections was 38.4%, and it was classified as a contributing factor to deaths in 87.1% of death cases. The correlation between healthcare-associated infection and death was statistically significant among clinical patients (41.3%) presenting comorbidities related to the diagnosis (55.8%), cardiovascular infection (62.2%), pneumonia (48.9%), developing sepsis (69.0%), as well as patients who had been colonized (45.2%) and infected (44.7%) by multidrug resistance microorganisms.