Bioremediation of hydrocarbon pollutants is advantageous owing to the cost-effectiveness of the technology and the ubiquity of hydrocarbon-degrading microorganisms in the soil. Soil microbial diversity is affected by hydrocarbon perturbation, thus selective enrichment of hydrocarbon utilizers occurs. Hydrocarbons interact with the soil matrix and soil microorganisms determining the fate of the contaminants relative to their chemical nature and microbial degradative capabilities, respectively. Provided the polluted soil has requisite values for environmental factors that influence microbial activities and there are no inhibitors of microbial metabolism, there is a good chance that there will be a viable and active population of hydrocarbon-utilizing microorganisms in the soil. Microbial methods for monitoring bioremediation of hydrocarbons include chemical, biochemical and microbiological molecular indices that measure rates of microbial activities to show that in the end the target goal of pollutant reduction to a safe and permissible level has been achieved. Enumeration and characterization of hydrocarbon degraders, use of micro titer plate-based most probable number technique, community level physiological profiling, phospholipid fatty acid analysis, 16S rRNA- and other nucleic acid-based molecular fingerprinting techniques, metagenomics, microarray analysis, respirometry and gas chromatography are some of the methods employed in bio-monitoring of hydrocarbon remediation as presented in this review.

Crude oil-polluted marine sediment from Bonny River loading jetty Port Harcourt, Nigeria was treated in seven 2.5 l stirred-tank bioreactors designated BNPK, BNK5, BPD, BNO3, BUNa, BAUT, and BUK over a 56-day period. Five bioreactors were biostimulated with either K2HPO4, NH4NO3, (NH4)2SO4, NPK, urea or poultry droppings while unamended (BUNa) and heat-killed (BAUT) treatments were controls. For each bioreactor, 1 kg (wet weight) sediment amended with 1 l seawater were spiked with 20 ml and 20 mg of crude oil and anthracene which gave a total petroleum hydrocarbons (TPH) range of 106.4–116 ppm on day 0. Polycyclic aromatic hydrocarbons (PAH) in all spiked sediment slurry ranged from 96.6 to 104.4 ppm. TPH in each treatment was ≤14.9 ppm while PAH was ≤6.8 ppm by day 56. Treatment BNO3 recorded highest heterotrophic bacterial count (9.8 × 108 cfu/g) and hydrocarbon utilizers (1.15 × 108 cfu/g). By day 56, the percentages of biodegradation of PAHs, as measured with GC–FID were BNK5 (97.93%), BNPK (98.38%), BUK (98.82%), BUNa (98.13%), BAUT (93.08%), BPD (98.92%), and BNO3 (98.02%). BPD gave the highest degradation rate for PAH. TPH degradation rates were as follows: BNK5 (94.50%), BNPK (94.77%), BUK (94.10%), BUNa (94.77%), BAUT (75.04%), BPD (95.35%), BNO3 (95.54%). Fifty-six hydrocarbon utilizing bacterial isolates obtained were Micrococcus spp. 5 (9.62%), Staphylococcus spp. 3 (5.78%), Pseudomonas spp. 7 (13.46%), Citrobacter sp. 1 (1.92%), Klebsiella sp. 1 (1.92%), Corynebacterium spp. 5 (9.62%), Bacillus spp. 5 (9.62%), Rhodococcus spp. 7 (13.46%), Alcanivorax spp. 7 (13.46%), Alcaligenes sp. 1 (1.92%), Serratia spp. 2 (3.85%), Arthrobacter spp. 7 (13.46%), Nocardia spp. 2 (3.85%), Flavobacterium sp. 1 (1.92%), Escherichia sp. 1 (1.92%), Acinetobacter sp. 1 (1.92%), Proteus sp. 1 (1.92%) and unidentified bacteria 10 (17%). These results indicate that the marine sediment investigated is amenable to bioreactor-based bioremediation and that abiotic factors also could contribute to hydrocarbon attenuation as recorded in the heat-killed (BAUT) control.

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