Abstract
Rhizophora racemosa (red mangrove tree) belongs to the family Rhizophoraceae; it is an important constituent of the mangrove swamp in Niger Delta, an oil producing region in Nigeria. The remediation of soils containing organic pollutants is possible with the use of microbial communities when the ecology is understood for potentials maximization. This study investigated the biodegradation potential of rhizospheric microorganisms of Rhizophora racemosa in crude oil- contaminated mangrove swamp in the Niger Delta.The total microbial count was determined by the serial dilution method. The hydrocarbon-utilizing bacteria and fungi were enumerated using Mineral Salts Agar containing crude oil as the sole carbon source. The biodegradation potential of these rhizomicrobes was determined using screen test, shake flask degradation tests, Total Organic Gas (TOG) and Total Petroleum Hydrocarbon (TPH) InfraCal Analyzer (HATR-T2 and CH). The turbidity, total organic gas (TOG-N) and total petroleum hydrocarbon were measured weekly for twenty-eight days. Hydrocarbon-degrading microbes isolated from the rhizosphere were identified as Marinococcus sp., Azotobacter sp., Acinetobacter sp. Aspergillus niger, Aspergillus flavus and Candida albicans. The highest rate of TPH reduction was recorded in Acinetobacter sp. (from 150 mg/L on day 1 to ˂0.0031 mg/L on day 14). This was followed by Candida albicans (148mg/L on day 1 to 2.68mg/L on day 28) and Aspergillus flavus (150mg/L on day 1 to 4.21mg/L on day 28) In conclusion, it can be inferred that the some rhizospheric microbes of Rhizophora racemosa can efficienctly degrade hydrocarbon up to 100% rate over a period of 28 days.
Highlights
Rhizophora racemosa is a special plant which can survive in marine environment
TOTAL HYDROCARBON UTILIZING MICROBIAL COUNT Table 1 shows the total count for the hydrocarbon utilizing bacterial and fungal isolates; ISO B2 had the highest count among the bacterial isolates, followed by ISO B1 and ISO B3 had the least count
Findings from this work on the biodegradation potential of the rhizospheric microorganisms of R. racemosa in crude oil contaminated mangrove swamp in the Niger Delta demonstrated that there were presence of fungi and bacteria in the rhizosphere of R. racemosa. This result supports a previous report that diverse groups of bacteria and fungi occur in the rhizosphere of plants (Compant et al, 2010; Kumar et al.,2012).The microorganisms found in the rhizosphere of Rhizophora racemosa have the capacity to degrade hydrocarbon in polluted soil
Summary
Rhizophora racemosa is a special plant which can survive in marine environment It is common along the coastal regions where there is constant flooding. The ecosystem is made up of some plants that have the ability to survive and live conveniently in water; some of these plants are ferns, palms, trees, shrubs and vines (Adegbehin, 1993; Flowers and Colmer, 2015). This ecosystem is a major source of food and materials for people in the coastal region to which the Niger Delta belongs. Mangrove forests provide fruits, firewood, timber, charcoal, fish etc. for people living in the region. (Adegbehin, 1993; Eleanya et al, 2015)
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