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In an effort to develop alternate techniques to recover metals from waste electrical and electronic equipment (WEEE), this research evaluated the bioleaching efficiency of gold (Au), copper (Cu) and nickel (Ni) by two strains of Aspergillus niger in the presence of gold-plated finger integrated circuits found in computer motherboards (GFICMs) and cellular phone printed circuit boards (PCBs). These three metals were analyzed for their commercial value and their diverse applications in the industry. Au-bioleaching ranged from 42 to 1% for Aspergillus niger strain MXPE6; with the combination of Aspergillus niger MXPE6 + Aspergillus niger MX7, the Au-bioleaching was 87 and 28% for PCBs and GFICMs, respectively. In contrast, the bioleaching of Cu by Aspergillus niger MXPE6 was 24 and 5%; using the combination of both strains, the values were 0.2 and 29% for PCBs and GFICMs, respectively. Fungal Ni-leaching was only found for PCBs, but with no significant differences among treatments. Improvement of the metal recovery efficiency by means of fungal metabolism is also discussed.

Several nitrogen fixing consortia (NFC) were isolated from kerosene contaminated soil, where Phaseolus vulgaris plants were being cultivated. The capability of these consortia for kerosene hydrocarbons removal was investigated and demonstrated. The NFC cultivated under aerobic conditions, and kerosene as sole carbon source, effected a maximum of 75% of reduction of the total kerosene hydrocarbons. Also, from experiments conducted to evaluate their atmospheric nitrogen fixing capability, all consortia showed nitrogenase activity: from 4 to 183 nmol N2/3E09 bacteria.day. To our knowledge, this is the first report that shows a group of bacteria with the dual characteristic of fixing atmospheric nitrogen and capability to use kerosene hydrocarbons as a sole carbon source. Application of these microorganisms to soil bioremediation processes is discussed.

This work investigated biosurfactant production by Pseudomonas putida in combined C/P, C/Ninorganic, C/Fe, C/Mg nutrient ratios and peptone concentration. Analysis of the 2(5-1) fractional factorial experimental design showed that only the C/Fe ratio had a significant (p<0.02) effect on biosurfactant production. The highest amount of biosurfactant was obtained at low C/Fe ratios, but net surface tension did not show significant differences. In addition, low amounts of peptone and the C/P-C/Mg nutrient ratios interaction significantly (p < 0.05) enhanced the biomass produced by P. putida. Analysis of biosurfactant by gas chromatography (GC) showed that the hydrophilic fraction was composed by rhamnose and the hydrophobic fraction, mainly by palmitic (C16), stearic (C18:0), oleic (C18:1) and linoleic (C18:2) fatty acids.

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An alternative for sustainable management in the cultivation of Capsicum annuum L. has focused on the use of plant growth promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF). This research selected PGPRPGPR and AMF based on their effect on Bell Pepper and Jalapeño bell pepper plants. Five bacterial strains isolated from different localities in the state of Mexico (P61 [Pseudomonas tolaasii], A46 [P. tolaasii], R44 [Bacillus pumilus], BSP1.1 [Paenibacillus sp.] and OLs-Sf5 [Pseudomonas sp.]) and 3 AMF treatments (H1 [consortium isolated from Chile rhizosphere in the state of Puebla], H2 [Rhizophagus intraradices] and H3 [consortium isolated from lemon rhizosphere from the state of Tabasco]). In addition, a fertilized treatment (Steiner solution 25%) and an absolute control were included. Jalapeño bell pepper “Caloro” and Bell Pepper “California Wonder” seedlings were inoculated with AMF at sowing and with CPB 15 days after emergence, and grown under controlled environment chamber conditions. In Jalapeño bell pepper, the best bacterial strain was P61 and the best AMF treatment was H1; in Bell Pepper the best strain was R44 and the best AMF were H3 and H1. These microorganisms increased the growth of jalapeño bell pepper and Bell Pepper seedlings compared to the unfertilized control. Likewise, P61 and R44 positively benefited the photosynthetic capacity of PSII.

Los hongos micorrízicos arbusculares (HMA) y las bacterias promotoras del crecimiento vegetal (BPCV) se asocian simbióticamente y de forma natural con las plantasde chile poblano. El objetivo fue evaluar el efecto de la inoculación de HMA y BPCV,en la eficiencia fotoquímica del fotosistema II y el crecimiento de plántulas de chile poblano. El experimento se realizó en invernadero,bajo un diseño completamente al azar, combinando tres grupos de HMA [Funneliformis geosporum + Claroideoglomus spp. (FGC), Claroideoglomus etunicatum (CE) y sin micorriza (SM)] y dos niveles de rizobacteria [Arthrobacter spp.(AB) y sin rizobacteria (SB)], generando seis tratamientos: [T1) FGC + AB, T2) FGC + SB, T3) CE + AB, T4) CE + SB, T5) SM + AB y T6) SM + SB (Testigo)],con 15 repeticiones cada uno, para un total de 90 unidades experimentales. Se utilizaron 7 g de sustrato como inóculos de HMA,propagados en cultivo trampa durante seis meses con pasto Ray-grass (140 y 128 esporas); la bacteria utilizada fue Arthrobacter spp.,preparada en medio liquido con caldo nutritivo, agregando 1 mL de inoculo por cavidad con 166 x 108 UFC mL−1. Las variables evaluadas fueron altura de plántula, número de hojas, área foliar, biomasa seca,colonización micorrízica y la eficiencia fotoquímica del fotosistemaII. El T1 generó mayor altura, número de hojas, área foliar, biomasa seca y colonización micorrízica, mientras que la eficiencia fotoquímica del fotosistemaII, expresada en Fv/Fm y Fv/Fo, fue superior en el T2. La inoculación de HMA y BPCV son alternativas para mejorar el crecimiento de plántulas en chile poblano.

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