Occurrence of hydrocarbon-degrading nitrogen-fixing bacteria in the rhizosphere of Paspalum vaginatum Sw.
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Date
2018-04-18
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Publisher
Plovdiv University Press "Paisii Hilendarski"
Abstract
This study investigated the influence of nitrogen-fixing hydrocarbon-degrading bacteria from the rhizosphere of plants in the biodegradation of crude oil in the polluted soil. Several nitrogen-fixing and crude oil utilizing bacteria were isolated from the rhizosphere of the turf grass Paspalum vaginatum Sw. using crude oil as carbon and energy source. The isolates showed between 98%-99% 16S rRNA gene similarity with species of Alcaligenes, Brevundimonasand klebsiella. Three of the isolates, BrevundimonasdiminutaC4B, Alcaligenes faecalis B5 and Alcaligenes faecalis D4A with the ability to grow well in crude oil as carbon and energy source were selected for further studies. Alcaligenes faecalis B5 had the highest growth rate constant of 0.038 μ-1with a mean generation time of 18.46 h. Analysis of culture extracts by gas chromatography with flame ionization detector showed that Alcaligenes faecalisB5 degraded 90.5% of crude oil in 24 days, while Alcaligenes faecalisD4A and Brevundimonas diminutaC4B biodegraded 84.6% and 82.1% of the oil respectively. Only Alcaligenes faecalis C1B, Klebsiella varicola C3B and Klebsiella varicolaC3BB had the nifH gene; and the genes responsible for nitrogen-fixing abilities of all the isolates were not plasmid-borne. Confirmation of nitrogen-fixing ability was determined by the acetylene reduction assay (ARA). Alcaligenes faecalisB5 produced the highest amount of ethylene (15.18 nmol) after 24 h of incubation, while Alcaligenes faecalisD4A and Brevundimonas diminutaC4B produced 12.10 nmol and 9.60 nmol of ethylene respectively. Nitrogen-fixing hydrocarbon utilizers are therefore potential seeds in the bioaugmentation of nitrogen-limited hydrocarbon-polluted environments.
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Keywords
Nitrogen fixers, biodegradation, acetylene reduction, ethylene, rhizodegradation, rhizosphere, crude oil