Elcia Margareth Souza Brito

In search of a Cr(VI) removal bioprocess, within a circular economy perspective, we combined two autochthonous bacterial consortia obtained from industrial residues and an agricultural waste (rice husk of Oryza sativa). After characterizing the rice husk (rh) properties, the bacterial growth and biofilm formation, we studied the taxonomical profile of the bacterial consortia (C55, C33, and C21, the last is a combination 2:1 of the previous ones). By using SEM analysis, we confirmed the presence of a smooth layer of exopolysaccharides (EPS) over the rice husk surface. Total bacterial biodiversity, assessed through MiSeq analysis, showed that the addition of Cr(VI) stimulated the growth of two main populations ( Cellulosimicrobium and Siminovitchia ) while inhibiting Peptoniphilus , Cutibacterium and Rhodococcus . We also evaluated chromium depletion, in batch experiments, with particular emphasis on its sorption to the agroresidue and its biotransformation by the biomass. When exposed to 200 mg.L ^-1 Cr(VI), the system containing both rh and the bacterial consortium completely removed Cr(VI) from the effluent with half-times between 53 and 67 h. The combination of Cr(VI) biosorption by rh and its biotransformation to Cr(III) by bacterial consortia confirmed an effective synergy capable of removing 92% of Cr(VI). This work supports the potential of an innovative bioprocess based on bacterial biofilms grown on rh for the mitigation of Cr(VI) contamination.

Two bacterial consortia (C55 and C33), obtained from an industrial residue contaminated with hexavalent chromium (Cr(VI)), were used to study the behavior of their mixture for depleting this ion in liquid media. In the absence of Cr(VI), C55 showed a greater growth rate than C33, while the latter exhibited biofilm formation. In the presence of this ion, C55 showed resistance up to 800 mg·L ⁻¹ and an ability to diminish up to 400 mg·L ⁻¹ of the Cr(VI) from the medium, while for C33, these concentrations were 400 and 200 mg·L ⁻¹ , respectively. Bacterial synergism between these consortia was evaluated using different compound ratios (C55:C33 ratios of 1:1, 1:2, and 2:1), growing at 50, 100, and 200 mg·L ⁻¹ Cr(VI). The best half‐lives of Cr(VI) decrease were 16, 31, and 98 h, respectively, for the 1:1 mixture. The ability of C33 and the mixed consortia to form biofilms was verified. MiSeq sequencing revealed 4 major populations for C55 (in a total of 14) and 3 for C33 (8), most of which were common. After an isolation process, 2 bacterial strains were obtained from C55 and 4 from C33. Three of these strains (QRePLB33E, similar to Oceanobacillus profundus ; QRePLB33G, to Shouchella clausii ; and QRePLB55C, to Cellulosimicrobium funkei ) showed resistance to Cr(VI) and the ability to remove 100% of it at least up to 300 mg·L ⁻¹ . Thus, synergism between different bacterial consortia obtained from the same site is possible and can improve, by complementing their capacities, both the growth rate and the ability to diminish the xenobiotic from the medium.

Guanajuato town is an important touristic center of Mexico, and one of its main attractions is its tunnel network (subterranean streets). In this work the air quality inside this tunnel network was evaluated using samples of Tillandsia usneoides as a biomonitor. Twenty-one plastic passive samplers, containing 50 g of plants each, were installed at different points of this tunnel network. In addition, surface layer of the tunnel walls, close to the plant sampling sites, were collected. Estimates for the enrichment factor, using Fe as reference and standard metal crustal data, suggest that the origin of the suspended metals is probably geogenic for Cr, a mix for Cu, and anthropogenic for Zn and Hg. It is important to emphasize that the Guanajuato’s tunnel network is used both by pedestrians and vehicular traffic and, probably, the last one is acting as the main source for toxic elements for the tunnel’s air.

Xichú River is a Mexican river located in an environmental preservation area called Sierra Gorda Biosphere Reserve. Around it, there are tons of abandoned mine residues that represent a serious environmental issue. Sediment samples of Xichú River, visibly contaminated by flows of an acid mine drainage, were collected to study their prokaryotic diversity. The study was based on both cultural and non-cultural approaches. The analysis of total 16S rRNA gene by MiSEQ sequencing allowed to identify 182 Operational Taxonomic Units. The community was dominated by Pseudomonadota, Bacteroidota, “Desulfobacterota” and Acidobacteriota (27, 21, 19 and 16%, respectively). Different culture conditions were used focusing on the isolation of anaerobic bacteria, including sulfate-reducing bacteria (SRB) and arsenate-reducing bacteria (ARB). Finally, 16 strains were isolated. Among them, 12 were phylogenetically identified, with two strains being SRB, belonging to the genus Solidesulfovibrio (“Desulfobacterota”), while ten are ARB belonging to the genera Azospira (Pseudomonadota), Peribacillus (Bacillota), Raineyella and Propionicimonas (Actinomycetota). The isolate representative of Raineyella genus probably corresponds to a new species, which, besides arsenate, also reduces nitrate, nitrite, and fumarate.

The rapid growth of the use of nanomaterials in different modern industrial branches makes the study of the impact of nanoparticles on the human health and environment an urgent matter. For instance, it has been reported that titanium dioxide nanoparticles (TiO₂ NPs) can be found in wastewater treatment plants. Previous studies have found contrasting effects of these nanoparticles over the activated sludge process, including negative effects on the oxygen uptake. The non-utilization of oxygen reflects that aerobic bacteria were inhibited or decayed. The aim of this work was to study how TiO₂ NPs affect the bacterial diversity and metabolic processes on an activated sludge. First, respirometry assays of 8 h were carried out at different concentrations of TiO₂ NPs (0.5–2.0 mg/mL) to measure the oxygen uptake by the activated sludge. The bacterial diversity of these assays was determined by sequencing the amplified V3–V4 region of the 16S rRNA gene using Illumina MiSeq. According to the respirometry assays, the aerobic processes were inhibited in a range from 18.5 ± 4.8% to 37.5 ± 2.0% for concentrations of 0.5–2.0 mg/mL TiO₂ NPs. The oxygen uptake rate was affected mainly after 4.5 h for concentrations higher than 1.0 mg/mL of these nanoparticles. Results indicated that, in the presence of TiO₂ NPs, the bacterial community of activated sludge was altered mainly in the genera related to nitrogen removal (nitrogen assimilation, nitrification and denitrification). The metabolic pathways prediction suggested that genes related to biofilm formation were more sensitive than genes directly related to nitrification–denitrification and N-assimilation processes. These results indicated that TiO₂ NPs might modify the bacteria diversity in the activated sludge according to their concentration and time of exposition, which in turn impact in the performance of the wastewater treatment processes.

Poultry litter is widely applied as agricultural fertilizer and can affect the soil microbiome through nutrient overload and antibiotic contamination. In this study, we assessed changes in soil bacterial diversity using high-throughput sequencing approaches. Four samples in triplicate were studied: soils with short- and long-term fertilization by poultry litter (S1 = 10 months and S2 = 30 years, respectively), a soil inside a poultry shed (S3), and a forest soil used as control (S0). Samples S0, S1, and S2 revealed a relatively high richness, with confirmed operational taxonomic units (OTUs) in the three replicates of each sample ranging from 1243 to 1279, while richness in S3 was about three times lower (466). The most abundant phyla were Proteobacteria, Bacteroidetes, and Actinobacteria. Acidobacteria, Planctomycetes, and Verrucomicrobia were also abundant but highly diminished in S3, while Firmicutes was less abundant in S0. Changes in bacterial communities were very evident at the genera level. The genera Gaiella, Rhodoplanes, Solirubacter, and Sphingomonas were predominant in S0 but strongly decreased in the other soils. Pedobacter and Devosia were the most abundant in S1 and were diminished in S2, while Herbiconiux, Brevundimonas, Proteiniphilum, and Petrimonas were abundant in S2. The most abundant genera in S3 were Deinococcus, Truepera, Rhodanobacter, and Castellaniella. A predictive analysis of the metabolic functions with Tax4Fun2 software suggested the potential presence of enzymes associated with antibiotic resistance as well as with denitrification pathways, indicating that the S3 soil is a potential source of nitrous oxide, a powerful greenhouse gas.

A novel Gram-negative, non-spore-forming, vibrio-shaped, anaerobic, alkaliphilic, sulfate-reducing bacterium, designated strain PAR22N^T, was isolated from sediment samples collected at an alkaline crater lake in Guanajuato (Mexico). Strain PAR22N^T grew at temperatures between 15 and 37 °C (optimum, 32 °C), at pH between pH 8.3 and 10.1 (optimum, pH 9.0–9.6), and in the presence of NaCl up to 10 %. Pyruvate, 2-methylbutyrate and fatty acids (4–18 carbon atoms) were used as electron donors in the presence of sulfate as a terminal electron acceptor and were incompletely oxidized to acetate and CO₂. Besides sulfate, both sulfite and elemental sulfur were also used as terminal electron acceptors and were reduced to sulfide. The predominant fatty acids were summed feature 10 (C_18 : 1  ω7c and/or C_18 : 1 ω9t and/or C_18 : 1 ω12t), C_18 : 1  ω9c and C_16 : 0. The genome size of strain PAR22N^T was 3.8 Mb including 3391 predicted genes. The genomic DNA G+C content was 49.0 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that it belongs to the genus Desulfobotulus within the class Deltaproteobacteria . Its closest phylogenetic relatives are Desulfobotulus alkaliphilus (98.4 % similarity) and Desulfobotulus sapovorans (97.9 % similarity). Based on phylogenetic, phenotypic and chemotaxonomic characteristics, we propose that the isolate represents a novel species of the genus Desulfobotulus with the name Desulfobotulus mexicanus sp. nov. The type strain is PAR22N^T (=DSM 105758^T=JCM 32146^T).