Vania Maria Maciel Melo

Sulfated chitosan as tear substitute with no antimicrobial activity.

Chitosan of high molar mass and with 82% deacetylation was sulfated using two procedures and characterized. In the first method sample chitosan-S1 was produced using chlorosulfonic acid as the sulfating agent and N,N-dimethylformamide as the medium, and in the second method (chitosan-S2) formic acid was also used. The degrees of sulfation were 0.87 (chitosan-S1) and 0.67 (chitosan-S2). FTIR spectra showed bands at 1230, 800 and 580 cm(-1), attributed to sulfation. Moisture content followed the order: chitosan-S-0.87>chitosan-S-0.67>chitosan. Chain depolymerization was verified by GPC. Aqueous solutions showed pseudoplastic behavior and the viscosity at a concentration of 0.3% (w/v) was higher than that of healthy human tears (close to 3 mPas at shear rate 130 s(-1)). Substitutions in the C2NH and in C6OH groups were verified by NMR. Antimicrobial activity against Staphylococcus aureus and Pseudomonas aeruginosa was not observed. Considering that chitosan-S-0.67 had a higher solubility, less chain depolymerization, higher yield and better thermal stability in comparison with chitosan-S-0.87, the derivative with DS 0.67 offered the greatest potential for use in formulations of tear substitutes.

Aquatic toxicity and biodegradability of a surfactant produced by Bacillus subtilis ICA56

ABSTRACT In this work, the environmental compatibility of a biosurfactant produced by a Bacillus subtilis strain isolated from the soil of a Brazilian mangrove was investigated. The biosurfactant, identified as surfactin, is able to reduce surface tension (ST) to 31.5 ± 0.1 mN m−1 and exhibits a lowcritical micelle concentration (CMC) value (0.015 ± 0.003 g L−1). The highest crude biosurfactant concentration (224.3 ± 1.9 mg L−1) was reached at 72 h of fermentation. Acute toxicity tests, carried out with Daphnia magna, Vibrio fischeri and Selenastrum capricornutum indicated that the toxicity of the biosurfactant is lower than that of its chemically derived counterparts. The results of the biodegradability tests demonstrated that the crude surfactin extract was degraded by both Pseudomonas putida and a mixed population from a sewage-treatment plant, in both cases the biodegradation efficiency being dependent on the initial concentration of the biosurfactant. Finally, as the biodegradation percentages obtained fall within the acceptance limits established by the Organization for Economic Co-operation and Development (Guidelines for Testing of Chemicals, OECD 301E), crude surfactin can be classified as a “readily” biodegradable compound.

Distinct bacterial communities across a gradient of vegetation from a preserved Brazilian Cerrado

The Cerrado biome in the Sete Cidades National Park, an Ecological Reserve in Northeastern Brazil, has conserved its native biodiversity and presents a variety of plants found in other savannas in Brazil. Despite this finding the soil microbial diversity and community structure are poorly understood. Therefore, we described soil bacterial diversity and distribution along a savanna vegetation gradient taking into account the prevailing environmental factors. The bacterial composition was retrieved by sequencing a fragment of the 16S ribosomal RNA gene. The bacterial operational taxonomic units (OTUs) were assigned to 37 different phyla, 96 classes, and 83 genera. At the phylum level, a core comprised by Proteobacteria, Acidobacteria, Actinobacteria, Firmicutes, Verrucomicrobia and Planctomycetes, was detected in all areas of Cerrado. ‘Cerrado stricto sensu’ and ‘Cerradao’ share more similarities between edaphic properties and vegetation and also present more similar bacterial communities, while ‘Floresta decidual’ and ‘Campo graminoide’ show the largest environmental differences and also more distinct bacterial communities. Proteobacteria (26%), Acidobacteria (21%) and Actinobacteria (21%) were the most abundant phyla within the four areas. All the samples present similar bacteria richness (alpha diversity) and the observed differences among them (beta diversity) were more related to the abundance of specific taxon OTUs compared to their presence or absence. Total organic C, N and P are the main abiotic factors structuring the bacterial communities. In summary, our findings show the bacterial community structure was clearly different across the Cerrado gradient, but that these environments share a bacterial phylum-core comprising Proteobacteria, Acidobacteria, Actinobacteria, Verrucomicrobia and Planctomycetes with other Brazilian savannas.

Fungal diversity in soils across a gradient of preserved Brazilian Cerrado

The preserved Cerrado from Northeastern Brazil presents different physicochemical properties and plant diversity, which can influence the fungal communities. Therefore, we evaluated the fungal diversity in preserved sites, at Sete Cidades National Park, across a gradient of vegetation that included Campo graminoide, Cerrado stricto sensu, Cerradao, and Floresta decidual. Of all of the operational taxonomic units (OTUs) obtained, the Floresta decidual presented the highest richness. Ascomycota were the most abundant phylum (45%), followed by Basidiomycota (32%). Basal fungi and other phyla accounted for 23% of the total dataset. Agaricomycetes, Eurotiomycetes, Lecanoromycetes, Basidiobolus, Dothideomycetes, and Taphrinomycetes were the most abundant classes of fungi found across the gradient of Cerrado vegetation. In conclusion, our study suggests that the Brazilian Cerrado from Sete Cidades National Park presents a high fungal diversity and includes sources of new fungal species for biotechnological purposes.

Archaea diversity in vegetation gradients from the Brazilian Cerrado

We used 16S rRNA sequencing to assess the archaeal communities across a gradient of Cerrado. The archaeal communities differed across the gradient. Crenarcheota was the most abundant phyla, with Nitrosphaerales and NRPJ as the predominant classes. Euryachaeota was also found across the Cerrado gradient, including the classes Metanocellales and Methanomassiliicoccaceae.

Less abundant bacterial groups are more affected than the most abundant groups in composted tannery sludge-treated soil

The application of composted tannery sludge (CTS) has promoted shifts in soil chemical properties and, therefore, can affect the soil bacterial community. This study assessed the effect of the CTS on the soil bacterial community over time. The CTS was applied at five rates (0, 2.5, 5, 10 and 20 t/ha), and the bacterial community was evaluated for 180 days. The principal curve response (PRC) analysis showed that the most abundant phyla were not influenced by the CTS rates over time, while the analysis of the bacterial community showed that some of the less abundant phyla were influenced by the CTS rates. Similarly, the PRC analysis for the bacterial classes showed the significant effect of the CTS rates. The redundancy analyses for the bacterial phyla and classes showed the relationship between the significant chemical properties and the bacterial community of the soil after the CTS amendment over time. Therefore, there was a shift in the bacterial community over time with the application of the composted tannery sludge. Our study has shown that the less abundant bacterial groups were more influenced by the CTS than the most abundant bacterial groups and that these bacterial groups were driven by soil chemical properties, primarily chromium (Cr) and the soil pH.

The Brazilian Soil Microbiome

Brazil, where several biomes occur with an extraordinary exuberance of flora and fauna, is recognized worldwide as an important hotspot for biodiversity. However, a key but yet unexplored component of this biodiversity is represented by the microbial life that permeates Brazilian soils. This chapter aims to summarize the characteristics and knowledge of microbial life in Brazilian soils—the soil microbiome. Our summary will encompass soils occurring in pristine conditions, such as those from the Amazonia, Caatinga, Atlantic rainforest, Pantanal, and Pampa biomes, in combination with commentaries about soils used for agriculture in Brazilian territory. The chapter provides information about the occurrence and functionality of microbes in soils. Here, we aim to link the occurrence of microbial groups with soil characteristics. A great part of the information on this issue is recent, as promoted by the adoption of culture-independent analyses. We hope to provide here information compiled for people interested in soil microbiology. Possibly, this compilation will constitute the first step toward the inclusion of microbial life in the Brazilian inventory of biodiversity.