SOURCE:

Faculty: Biosences
Department: Applied Microbiology And Brewing

CONTRIBUTORS:

Uba, B. O.
Chukwura, E. I.

ABSTRACT:

The aquatic ecosystem of the Niger Delta region of Nigeria faces increasing ecological and toxicological problems from the release of environmental pollutants such as aromatic compounds, heavy metals and pesticides. It is important to assess the risks of these persistent pollutants for potential toxic contaminants and explore safe, effective and economic alternative method of environmental clean ups. In this study, the toxicological effects and bioremediatiing potentials of marine bacteria isolated from sediment and water samples of contaminated marine environments of Rivers State were evaluated. The methods employed for toxicological analyses include:physico- chemical analyses, marine microalga toxicity test, phytotoxicity, Artemiatoxicity test,Toxi – chromo test, sub – chronic health effect using mice model while the methods employed for bioremediation studies include: isolation and characterization techniques, screening and selection test, substrate specificity test, biodegradation assay, TLC analysis, GC-MS analysis, PCR analysis and plasmid analysis. The toxicological results revealed that Rivers State marine environments contain higher quantities of aromatic hydrocarbons, heavy metals and other physico-chemical parameters in the sediment samples than water samples. The three aromatic hydrocarbons (xylene, anthracene and pyrene) when mixed with sediment/water samples from the sampling sitesdemonstrated more acute dose dependent ecotoxicity effects(<1 mg/l < LC50/EC50<100 mg/l) on Phaeodactylum tricornutum(microalga), Sinapsis alba(mustard seeds), Artemia franciscana (brine shrimp) and mutant E. coli(bacterium) than the individual test samples with highly strong significant positive correlation at increasing test concentrations (P < 0.05). Higher molecular weight aromatic hydrocarbons demonstrated more significant acute dose dependent sub – chronic healtheffects (P < 0.05) than lower molecular weight in the order of benzo (a) pyrene> pyrene > anthracene > xylene with mild/adaptive pathological changes at the lowest – observable – effect – level (LOEL) of 20 mg/kg to mice after 35 – days’ of exposure. Also, it revealed that the sampling sites harbour a lot of efficient bacterial strains belonging to the genera: Providencia, Alcaligenes, Brevundimonas, Myroides, Serratia, and Bacillus able to significantly (P < 0.05) tolerate, grow and resist aromatic compounds, other petroleum products and heavy metals at various volumes/concentrations and 300 mg/l. The bacterial strains especially Serratia marcescens XYL7 significantly (P < 0.05) removed 99.50 ± 0.05 % and 60.00 ± 0.02 % in weights of xylene and pyrene, respectively while Alcaligenes faecalis PYR5 significantly (P < 0.05) degraded 97.40 ± 0.01 % in weight of anthracene. TLC and GC/MS analyses of metabolites formedrevealed evidences ofsmall low intensity spots visualized under UV illumination at 235 nm compare to control with large high intensity spots; via two main pathways and catechol was the major constant product that appeared in each of the three hydrocarbons after 24 - days’ degradation period.The existence of catabolic and surfactant genes namely catechol dioxygenase (C23O), rhamnolipid enzyme (rhlB)and surfactin/lichenysin enzyme (SrfA3/LicA3) genes were detected in only four (4) out of the nine (9) marine aromatic degrading bacteria and the gene locationswere confirmed to be plasmid - mediated. Hence, the toxicity results (EC50/LC50/LOEL) of this study hope to alert dischargers as well as monitoring agencies the potential public health effects/implications of these pollutants/contaminants in order to get rid of their dangerous outcomes; and the excellent degradative abilities of these bacterial strains especially Serratia marcescens XYL7 could be exploited in bioremediation campaigns for aromatic hydrocarbon - contaminated ecosystems in the Niger Delta.