Critical Review: Microbiome of highly polluted coal mine drainage from Onyeama, Nigeria, and its potential for sequestrating toxic heavy metals

 Alonzo Bell

Critical Review Report

Article : Microbiome of highly polluted coal mine drainage from Onyeama, Nigeria, and its potential for sequestrating toxic heavy metals

Authors : Ganiyu Oladunjoye Oyetibo, JoyAimiede Enahoro, Chimuanya Amarachi Ikwubuzo, Chiamaka Shileakanwa Ukwuoma

Journal : Scientific Reports

1. Comments to Authors

The authors do a thorough job of examining metal pollutants in Onyeama, Nigeria. They did a good job of using reference sites with similar environments such as coal mines in Russia and the US. The major contribution of the paper is that it describes many different aspects and parameters of the acid mining drainage occuring in Onyeama, Nigeria and they describe accumulated metal pollutants. The major strength is that it details the presence of abundant microbes respiring in these coal mine drainage areas. Another strength is that the authors do a thorough job of detailing heavy metals and correlating their presence to data and figures which is consistent with the argument. In the study the authors use many different factors to determine the heavy metal concentration from the Onyeama coal mine in Nigeria. The study sets out to observe the occurrence of heavy metals which are leaching from the coal mine. Metals such as Cd, Pb, Co, Ni, Fe, Cr, As and many more could possibly contaminate nearby surface water and environments. There is plenty of data, figures, graphs and illustrations describing which microorganisms were found, which heavy metals were most abundant and also how using bacteria consortium can be a remediating solution in these coal mine environments. The complex assessment of these bacterial communities has allowed the authors to isolate bacteria which can help reduce these excessive permissible limits of pollutants. 

2. General

This article is interesting for people wanting to learn more about bioremediation of harmful pollutants into the environment. The study gives some background on the environmental condition of coal mines in Onyeama, Nigeria; and the authors provide research that can help reduce some of the contaminants in extreme environments. The writing is concise and easy to follow. The scientific soundness of the article was good because it made compelling arguments while supporting those with correlating data and information. The authors displayed originality in being unique and studying the different chemical, environmental, and biological dynamics of Onyeama coal mines of Nigeria. The paper was organized and does a good job of advocating for a solution regarding the environmental hazard which they are facing in Nigeria. The authors assessed the microbial activity of the coal mine and have incorporated that information into graphs and cladograms. This allows readers to see the types of microorganisms that might be able to degrade some of these leaching metals and sulfides. The cohesiveness of the argument is consistent throughout the article, and they continually iterate that a bacterial consortium strain may be tolerant to metal pollutants thus allowing it to degrade these pollutants. Cadmium and Lead are most occurring toxic chemicals released into the acid mine drainage and by observing the most abundant species, authors were able to isolate a bacterial strain which can effectively degrade these toxins because of their increased biological  activity, in these metal polluted drains. Conclusions are supported by data and throughout the article and conveys the main points of the study. Quality parameters are compared to the World Health Organization, in which pollutants were excessively higher than that of the WHO’s permissible limits.

3. Specific

1. Presentation

The paper tells a cohesive story about the heavy metal pollutants in the Onyeama coal mine in Nigeria. They give background information on the environmental conditions in these acid mine drains such as ; pH, temperature, dissolved oxygen, EC, heavy metal concentrations and many other parameters . They discuss the many abiotic and biotic factors which ultimately influence the different microbial activities of prokaryotes and eukaryotes. The argument stays consistent in arguing that Pb and Cd are the most abundant metal pollutants, and the study isolates a bacterial consortium which is capable of respiring in these metal and sulfur enriched environments. Since these chemicals have no biological significance to most microorganisms, the authors used abundant populations to help remediate these toxic compounds.

2. Length 

The length is appropriate for the amount of research being discussed. Although, at times the article tends to wander to different subjects. This is a complex study which requires an extensive assessment of the coal mine in Onyeama, Nigeria. I do feel as if the results could have been condensed and simplified, to reiterate the main arguments of the study. Other than that, I feel as if the data in combination with the methods and results, made the reading easy to follow and understand. By comparing their findings to data with the World Health Organization, they were able to express the need for a beneficial solution to this environmental predicament. 

3.  Methods 

The methods contained three replicates of soil sampling from the coal mine in Nigeria. Methods are complete and described in a way which a competent science person can repeat. The study collects random samples of biofilm from coal drains in Onyeama, Nigeria which were cooled at 4 degrees Celsius for microbial culturing and cooled at -40 degrees Celsius for geochemical analysis. The authors also used 16S rRNA for sequencing and amplification of abundant microbes in these environments. 

4. Data Representation 

Data can be verified through experimentation and data which is illustrated on the graphs, figures and illustrations. The consortium of bacteria which was most susceptible to these metal pollutant enriched environments were able to degrade under 70% of heavy metal pollutants in the acid mine drain. The authors explain that Cd and Pb concentrations were the highest and their content values were Cadmium :  (3.87±3.87 mg l −1) and Lead : ( (326.0±26.8 mg l −1) which is illustrated in Table A.1. The analysis of the most abundant microorganisms of animalia, plantae and fungi kingdoms in Oneya, Nigeria, were reported : Proteobacteria (50.8%), Bacteroidetes (18.9%), Acidobacteria (7.5%), Ascomycota (60.8%), Ciliphora (12.6%) and Arthoproda (8.5%). These results are shown on Figure 1, and helps to provide readers a resource to see which microorganisms are thriving most in these extremely acidic environments. Through urease activity these persistent bacteria and eukarya are able to degrade toxic pollutants in coal mine environments. All of the tables and figures are labeled correctly and necessary; to explain the environmental parameters of the Onyeama coal mine and the potential of degrading pollutants with the isolated bacteria consortium. 

5. Statistical Design and Analysis 

The statistical design and analysis was thoroughly planned and consistently relevant to the main arguments. The way the authors compiled the data, methods, tables and figures the reader can easily discern measurements significant to acid mine drainage in Onyeama, Nigeria in contrast to similar environments. The authors thoroughly assessed many parameters of this drainage environment such as ; total dissolved solids, pH, electric conductivity, temperature, total organic carbon, dissolved sulfur and heavy metal concentrations and provided specific values of each measurement. These are important parameters which strengthen the scientific soundness and statistical design of the article and its findings. 

6. Errors 

I didn’t notice many if any errors throughout the paper. I would just suggest using more capitalization in headings and subheadings. Capitalizing every word of subtitles catches the reader's attention and creates consistency throughout articles.

7. Citations

All citations are cited appropriately and correctly labeled. 

8. Overlap

Similar types of studies have been done in coal mines in the US, Russia, China, Spain and other countries. This article may have used similar methods to other studies but is unique because it assesses the acid main drainage in Nigeria and uses the native bacteria as a resolution of these heavily contaminated mines. This study is unique because it isolated specific microorganisms in Onyeama, Nigeria which have been susceptible to high levels of metal pollutants and toxicity. With the help of 16S rRNA sequencing, authors were able to use a bacterial consortium which isolated a strain capable of degrading heavy metal pollutants; which has never been done in the coal mines of Onyeama, Nigeria. The data reported in this study is original and has not been published.