Abstract The aim of this work was to identify biotechnological alternatives for transforming the coal into simpler compounds in liquid state. An updated bibliographic review related to the use of humified organic matter was done. The documentary analysis showed that humified organic matter in the soil improves its physical and chemical properties, stimulates microbial populations and promotes plant growth and development. Low-evolved coals or low rank coals have been considered a good source of humic substances. Extraction of these substances can be performed by chemical methods or through solubilization of low rank coals using microorganisms. However, the development of an efficient and low-cost technology has not been possible. A natural control of coal transformation may take place in the soil in the same way as the decomposition of lignin.

Resumen El objetivo de este trabajo fue identificar alternativas biotecnológicas para transformar el carbón en compuestos más simples en estado líquido. Se realizó una revisión bibliográfica actualizada relacionada con el uso de la materia orgánica humificada. El análisis documental mostró que la materia orgánica humificada en el suelo mejora las características físicas y químicas del mismo, estimula las poblaciones microbianas y promueve el crecimiento y desarrollo de las plantas. Los carbones de bajo rango se han considerado una buena fuente de sustancias húmicas. La extracción de estas sustancias se puede realizar mediante métodos químicos o a través de la solubilización de carbones de bajo rango utilizando microorganismos. Sin embargo, no ha sido posible el desarrollo de una tecnología eficiente y de bajo costo. En el suelo podría tener lugar un control natural de la transformación del carbón por microorganismos, similar a lo que ocurre con la descomposición de la lignina.

The humic acid (HA) obtained with the activity of three bacterial strains that transformed a lignite-type low rank coal (LRC) and released humified organic matter (HOM) was characterized. The HA obtained with the activity of Bacillus mycoides, Microbacterium sp. and Acinetobacter baumannii were compared with HA obtained with the traditional alkaline extraction method using NaOH 0.5 M (HA-NaOH). These characterizations included the elemental composition (C, H, N, O), Fourier transform infrared (FTIR) analysis, cross polarization-magic angle spinning-nuclear magnetic resonance (13C-CPMAS-NMR), tetramethylammonium hydroxide (TMAH)-thermochemolysis followed by gas chromatography-mass spectrometry (GC-MS) and size exclusion chromatography. The two evaluated HA types showed differences in the elemental composition, aromaticity degree, content of aliphatic groups, molecular weight, polydispersity, profile of the spectra 13C-CPMAS-NMR and products of TMAH-thermochemolysis. The results indicate that the process of biotransformation of LRC with bacterial activity results in the structural transformations of HA, which leads to the formation of HA with a lower degree of aromaticity, more of a hydrophilic tendency, lower oxygen content, enriched with nitrogenated functional groups and polar aliphatic chains, as compared with HA-NaOH. The HA generated with the three bacterial strains exhibited a high structural similarity to each other; however, some differences were evident in the type of metabolites generated by the TMAH-thermochemolysis of the HA obtained with B. mycoides, as well as a higher polydispersity for the HA generated with A. baumannii.

Abstract In this work a rapid test to evaluate the bioactivity of humic acids (HA) obtained from a lignite coal through two methods was tested: 1) through chemical extraction with NaOH (HA-Q), and 2) by activity of a bacterial strain (Enterobacter aerogenes). For this, the capacity of the HAs to enhance cellular elongation in coleoptiles of wheat was determined, as well as the ability to induce root proliferation and elongation on pregerminated seeds; AH concentrations between 2,0 and 120 mg C. L-1 were tested with reference to the effect enhanced by an AIA 2,0 mgL-1 solution. It was found that treatment with AH-Q at 40 mg C.L-1 enhance a greater elongation of coleoptiles and roots, whereas a concentration of 20 mg C.L-1 of AH-B enhanced highest bioactivity in all growth parameters evaluated. The results indicate that the evaluated HAs exhibit bioactivity that depends on the type of extraction and on the concentration applied.

Resumen En este trabajo se probó un test rápido para evaluar la bioactiviad de ácidos húmicos (AH) obtenidos a partir de un carbón lignito a través de dos métodos: 1) mediante extracción química con NaOH (AH-Q) y 2) mediante actividad de una cepa bacteriana (Enterobacter aerogenes). Para ello se determinó la capacidad de los AH para ocasionar la elongación celular en coleóptilos de trigo, así como la capacidad para inducir la proliferación y alargamiento de raíces a partir de semillas pregerminadas. Se probaron concentraciones de AH entre 2,0 y 120 mg C. L-1 tomando como referencia el efecto ocasionado por una solución de AIA 2,0 mgL-1. Se encontró que el tratamiento con AH-Q a 40 mg C.L-1 ocasionó un mayor alargamiento de coleóptilos y raíces, mientras que una concentración de 20 mg C.L-1 de AH-B presentó bioactividad superior en todos los parámetros evaluados. Los resultados indican que los AH evaluados presentan bioactividad que depende del tipo de extracción y de la concentración aplicada.