[Isolation and characterization of a facultative anaerobe Pantoea agglomerans MFC-3 and its humic substance-and Fe(III) - respiring activity].

A strain of humic substance- and Fe(III)- reducing bacterium was isolated from the subterranean forest sediment and designated as MFC-3. The strain is facultative anaerobic, Gram-negative, motile and rod (1.0-3.0 microm long, 0.5-1.0 microm wide) and identified as Pantoea agglomerans with the 16S rDNA sequence analyses. Batch experiments were conducted to investigate its humic substance-and Fe(III)-respiring activity. The results showed that MFC-3 was capable of anaerobic respiration on anthraquinone-2,6-disulphonate (AQDS) as the sole terminal electron acceptor with glucose as the electron donor. Within 48 h, MFC-3 could reduce 0.3 mmol x L(-1) AQDS at the expense of 4.5 mmol x L(-1) glucose, and the population of bacteria was increased by 7 times. The strain could use sucrose, glucose, citrate, lactate and formate as electron donors for anaerobic respiration, and the reduction rates of AQDS ranked as sucrose (77%) > glucose (66%) > citrate (50%) > lactate (33%) > glycerol (25%) > formate (17%). MFC-3 can also effectively reduce four types of Fe(III) oxides. After 25 d, the total Fe(II) concentration in the tests of using ferrihydrite, alpha-FeOOH, gamma-FeOOH or alpha-Fe2 O3 as electron acceptor reached 2.5, 2.1, 2.3 and 0.8 mmol x L(-1), respectively. As a strain of environmental origin, MFC-3 is quite useful for the study of extracellular respiration and bioremediation of chlorinated organic pollutants in Fe(III)/humic substance-rich environments.