Metal removal and morphological changes of B. megaterium in the presence of a spent catalyst

PHB production by Bacillus megaterium strain MNSH1-9K-1 using low-cost media

Plastics are widely used for diverse applications due to their versatility. However, their negative impact on ecosystems is undeniable due to their long-term degradation. Thus, there is a rising need for developing eco-friendlier alternatives to substitute fossil-based plastics, like biopolymers. PHA are synthesized intracellularly by microorganisms under stressful conditions of growth and have similar characteristics to conventional polymers, like their melting point, transition temperatures, crystallinity, and flexibility. Although it is feasible to use biopolymers for diverse industrial applications, their elevated production cost due to the supplies needed for microbiological procedures and the low productivity yields obtained have been the main limiting factors for their commercial success. The present study assessed the ability of Bacillus megaterium strain MNSH1-9K-1 to produce biopolymers using low-cost media from different kinds of fruit-peel residues. The results show that MNSH1-9K-1 can produce up to 58 g/L of PHB when grown in a medium prepared from orange-peel residues. The data obtained provide information to enhance the scalability of these kinds of biotechnological processes.

Enfoques microbiológicos para el tratamiento de catalizadores agotados

Los catalizadores, homogéneos o heterogéneos, son ampliamente utilizados para una gran variedad de procesos industriales, con el fin de producir combustibles limpios y muchos otros productos valiosos, siendo los catalizadores agotados provenientes del hidroprocesamiento los mayores residuos sólidos de la industria de la refinería y la contribución principal a la generación de catalizadores agotados. Debido a su naturaleza peligrosa, el tratamiento y la recuperación de metales de este tipo de residuos han ganado cada vez más importancia, debido al agotamiento de los recursos naturales y a la contaminación ambiental. Aunque ya existen técnicas disponibles para estos fines, éstas generan grandes volúmenes de desechos potencialmente peligrosos y producen emisiones de gases nocivos. Por lo tanto, las técnicas biotecnológicas pueden representar una alternativa promisoria para el biotratamiento y la recuperación de metales contenidos en los catalizadores agotados. Con este fin, se han analizado diversos microorganismos, que comprenden bacterias, arqueobacterias y hongos, capacitados para facilitar la eliminación de losmetales contenidos en estoscatalizadores. En estarevisión se presenta un amplio escenario sobre los avances con respecto al manejo de los catalizadores agotados y su tratamiento tradicional, seguido de una descripción detallada sobre los enfoques microbiológicos reportados hasta la actualidad.

Potential use of Bacillus genera for metals removal from spent catalysts

The aim of the present study was to isolate microorganisms able to tolerate Ni²⁺ and V⁵⁺ from different sites located close to a mineral mine in Guanajuato, Mexico, and then to evaluate their ability to remove metals contained in a spent catalyst. Seventeen isolates were obtained; among them seven presented a minimum inhibitory concentration (MIC) higher than 200 mg/L of Ni²⁺ and V⁵⁺ each. Nickel and Vanadium removal was evaluated in 9 K liquid medium added with spent catalyst at 16% (s/v) pulp density and incubated at 30 °C, 150 rpm for 7 days. Only three isolates which were coded as PRGSd-MS-2, MNSH2-AH-3, and MNSS-AH-4 showed a significant removal at the end of treatment corresponding in mg kg^-1 (or percentage metal removal) of 138 (32%), 123 (29%), and 101 (24%) for Ni, respectively; and 557 (26%), 737 (34%), and 456 (21%) mg kg^-1 for V, respectively. The same isolates were capable to remove also Al, Fe, As, and Mg at different extent. Cell morphology changes were observed, in comparison to the control system at the end of biological treatment as a higher quantity of spores for MNSH2-AH-3, 2 μm cells in pairs for MNSS-AH-4, also long chain-vegetative cells having inclusions into the cell surface were observed for PRGSd-MS-2. The three isolated microorganisms were identified by sequencing of the 16S gene as Bacillus thuringiensis, Bacillus megaterium, and Bacillus sp, respectively, suggesting its potential use in the treatment of this solid industrial waste.