Environmental pollution has been on the rise in the past few decades owing to increased human activities on energy reservoirs, unsafe agricultural practices and rapid industrialization. Amongst the pollutants that are of environmental and public health concerns due to their toxicities are: heavy metals, nuclear wastes, pesticides, green house gases, and hydrocarbons. Remediation of polluted sites using microbial process (bioremediation) has proven effective and reliable due to its eco-friendly features. Bioremediation can either be carried out ex situ or in situ, depending on several factors, which include but not limited to cost, site characteristics, type and concentration of pollutants. Generally, ex situ techniques apparently are more expensive compared to in situ techniques as a result of additional cost attributable to excavation. However, cost of on-site installation of equipment, and inability to effectively visualize and control the subsurface of polluted sites are of major concerns when carrying out in situ bioremediation. Therefore, choosing appropriate bioremediation technique, which will effectively reduce pollutant concentrations to an innocuous state, is crucial for a successful bioremediation project. Furthermore, the two major approaches to enhance bioremediation are biostimulation and bioaugmentation provided that environmental factors, which determine the success of bioremediation, are maintained at optimal range. This review provides more insight into the two major bioremediation techniques, their principles, advantages, limitations and prospects.

This study was carried out to evaluate the biostimulant potentials of Capra aegagrus hircus manure for bioremediation of crude oil contaminated soil (COCS) under tropical conditions. 1 kg of COCS sample was amended with 0.02 kg of C. a. hircus manure and monitored at 14-day intervals for total petroleum hydrocarbon (TPH), nutrient content, and changes in microbial counts. At the end of the study period, there was 62.08% decrease in the concentration of TPH in the amended sample compared to 8.15% decrease in the unamended sample, with significant differences (P < 0.05) in TPH concentrations for both samples at different time intervals. Similarly, there was a gradual decrease in the concentrations of total organic carbon, nitrogen, phosphorus, and potassium in both samples. The culturable hydrocarbon-utilizing bacteria (CHUB) increased steadily from 8.5 × 105 cfu/g to 2.70 × 106 cfu/g and from 8.0 × 105 cfu/g to 1.78 × 106 cfu/g for both samples. Acinetobacter, Achromobacter, Bacillus, Flavobacterium, Klebsiella, Micrococcus, Pseudomonas, and Staphylococcus were isolated from amended sample with Pseudomonas being the predominant isolated bacterial genus. This study demonstrated that C. a. hircus manure is a good biostimulant, which enhanced the activities of indigenous hydrocarbonoclastic bacteria resulting in significant decrease in TPH concentration of COCS.

Cupriavidus necator H16 is gaining significant attention as a microbial chassis for range of biotechnological applications. Whilst the bacterium is a major producer of bioplastics, its lithoautotrophic and versatile metabolic capabilities make the bacterium a promising microbial chassis for biofuels and chemicals using renewable resources. It remains necessary to develop appropriate experimental resources to permit controlled bioengineering and system optimization of this microbe. Here we employed statistical design of experiments to gain understanding of the impact of components of defined media on C. necator growth and built a model that can predict the bacterium's cell density based on media components. This highlighted media components, and interaction between components, having the most effect on growth: fructose, amino acids, trace elements, CaCl2 and Na2HPO4 contributed significantly to growth (t < -1.65 or > 1.65); copper and histidine were found to interact and must be balanced for robust growth. Our model was experimentally validated and found to correlate well, r2 = 0.85. Model validation at large culture scales showed correlations between our model predicted growth ranks and experimentally determined ranks at 100 mL in shake flasks (ρ = 0.87) and 1 L in bioreactor (ρ = 0.90). Our approach provides valuable and quantifiable insights on the impact of media components on cell growth and can be applied to model other C. necator responses that are crucial for its deployment as a microbial chassis. This approach can be extended to other non-model microbes of medical and industrial biotechnological importance. Importance Chemically defined media (CDM) for cultivation of C. necator vary in components and compositions. This lack of consensus makes it difficult optimizing new processes for the bacterium. This study employed statistical design of experiments (DOE) to understand how basic components of defined media affect C. necator growth. Our growth model predicts that C. necator can be cultivated to high-cell-density with components held at low concentrations, arguing that CDM for large scale cultivation of the bacterium for industrial purposes will be economically competitive. Although existing CDM for the bacterium are without amino acids, addition of few amino acids to growth medium shortened lag phase of growth. The interactions highlighted by our growth model shows how factors can interact with each other during a process to positively or negatively affect process output. This approach is efficient, relying on few well-structured experimental runs to gain maximum information on a biological process, growth.

Acute and chronic pollution of environments with crude oil does not bode well for biota living within the vicinity of polluted environments. This is due to environmental and public health concerns on the negative impact of crude oil pollution on living organisms. Enhancing microbial activities by adding nutrients and other amendments had proved effective in pollutant removal during bioremediation. This study was carried out to determine how microbial group respond during remediation by enhanced natural attenuation (RENA) during a field-scale bioremediation. Crude oil-polluted soil samples were collected (before, during, and after remediation) from a site undergoing remediation by enhanced natural attenuation (RENA) at Ikarama Community, Bayelsa State, Nigeria, and were analyzed for total petroleum hydrocarbon (TPH), polyaromatic hydrocarbon (PAH), and a shift in microbial community. The gas chromatography-flame ionization detector (GC-FID) results showed that the pollutant concentrations (TPH and PAH) reduced by 98 and 85%, respectively, after the remediation. Culturable hydrocarbon utilizing bacteria (CHUB) was highest (8.3 9 10 4 cfu/g) for sample collected during the remediation studies, whilst sample collected after remediation had low CHUB (6