Production of humic substances through coal-solubilizing bacteria

Abstract

In this paper, the production of humic substances (HS) through the bacterial solubilization of low rank coal (LRC) was evaluated. The evaluation was carried out by 19 bacterial strains isolated in microenvironments with high contents of coal wastes. The biotransformed LRC and the HS produced were quantified in vitro in a liquid growth medium. The humic acids (HA) obtained from the most active bacterial strain were characterized via elemental composition (C, H, N, O), IR analyses, and the E4/E6 ratio; they were then compared with the HA extracted chemically using NaOH. There was LRC biotransformation ranged from 25 to 37%, and HS production ranged from 127 to 3100 mg.L−1. More activity was detected in the isolated strains of Bacillus mycoides, Microbacterium sp, Acinetobacter sp, and Enterobacter aerogenes. The HA produced by B. mycoides had an IR spectrum and an E4/E6 ratio similar to those of the HA extracted with NAOH, but their elemental composition and their degree of aromatic condensation was different. Results suggest that these bacteria can be used to exploit the LRC resulting from coal mining activities and thus produce HS in order to improve the content of humified organic matter in soils.

Assessment of a low rank coal inoculated with coal solubilizing bacteria as an organic amendment for a saline-sodic soil

“…The results presented in Table 4 show that, throughout the experiment, treatments C-AB and C-P had the highest microbiological activity with significant differences (P < 0.05) as compared to the other treatments. Treatments C-BM and C-M showed significant differences (P < 0.05), as compared to the control during the first 2 months, evidence that the CSB stimulated the microbial activity; this may explain the reason why the biotransformation of LRC by these bacteria leads to the release of HOM [21], which contribute to the formation of aggregates in the soil [44], growth and microbial activity, soil aeration and moisture retention. Therefore, the results show that there was a greater effect of microbial activity when the LRC was applied to saline-sodic soils in conjunction with the bacterial inoculum CSB13 and Pool.…”

“…Clearly, it presents a greater effect when the LRC is applied with each CSB or pooled, probably indicating a releasable HS contained in LRC through biosolubilization of the LRC [21]; it has been reported that HOM releases polyelectrolytes and increases the CEC. Also, LRC itself is a material with a high CEC due to the presence of phenolic and carboxylic groups, among other exchange sites [49].…”

“…(4) The results of the soil treatments C, C-M and C-BM suggest that the effect of LRC was similar when applied alone or with the CSB. It is probable that, by releasing the HS from the LRC [21], either the CSB activity or the native inoculated soil microbiota, in response Also, it can be seen that these variables were inversely related to the effect of soil treatment with the pool of three CSB, microbiological activity, activity of the laccase and LiP enzymes, respiration and CEC. This indicates that the pooled soil treatment had the best effect, exerted by causing attenuation in the variables related to salinity, and also reflected an increased microbial activity, proven by the result of hydrolysis of the FDA and soil respiration, which also suggests that ligninolytic enzymes are possibly generated by native soil microorganisms or accompanying LRC flora.…”

“…In a previous study in Colombia, three bacteria (Bacillus mycoides, Acinetobacter baumannii and Microbacterium sp.) that exhibit an LRC solubilizing capacity and that release HOM [21] were isolated and selected from environmental samples with coal residues in the open coal mine pit "El Cerrejón, " located in La Guajira (Colombia).…”

Effect of low-rank coal inoculated with coal solubilizing bacteria on edaphic materials used in post-coal-mining land reclamation: a greenhouse trial

“…In a previous study, it was found that, in environments exposed to carbonaceous wastes that come from the extraction, transport, storage, and washing of coal in the El Cerrejón mine, there are bacterial populations that are able to biotransform the LRC and to release humic substances (HS) by solubilizing these materials [8]. Also, native strains of coal solubilizing bacteria (CSB) were selected and identified, which are able to grow in culture media with LRC as the sole carbon source and solubilize this material, generating HS [9].…”