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J. Bacteriol. doi:10.1128/JB.00872-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

An extremely oligotrophic bacterium, Rhodococcus erythropolis N9T-4 isolated from crude oil

Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan

^* To whom correspondence should be addressed. Email: yoshidan{at}bs.naist.jp.

	Abstract

Rhodococcus erythropolis N9T-4, which was isolated from crude oil, showed extremely oligotrophic growth and formed its colonies on a minimal salt medium solidified using agar or silica gel without any additional carbon source. N9T-4 did not grow under CO₂-limiting conditions, but could grow on a medium containing NaHCO₃ under the same conditions, suggesting that the oligotrophic growth of N9T-4 depends on CO₂. Proteomic analysis of N9T-4 revealed that two proteins, with molecular masses of 45 and 55 kDa, were highly induced under the oligotrophic conditions. The primary structures of these proteins exhibited striking similarities to those of methanol: N,N'-dimethyl-4-nitrosoaniline oxidoreductase and an aldehyde dehydrogenase from Rhodococcus sp., respectively. These enzyme activities were 3-times higher under the oligotrophic conditions than under n-tetradecane containing, heterotrophic conditions and gene disruption for the aldehyde dehydrogenase caused the lack of growth on the minimal salt medium. Furthermore, 3-hexulose 6-phosphate synthase and phospho-3-hexuloisomerase activities, which are key enzymes in the ribulose monophosphate pathway in methylotrophic bacteria, were detected specifically in the cell-free extract of oligotrophically grown N9T-4. These results suggest that CO₂ fixation is concerned with the methanol (formaldehyde) metabolism in the oligotrophic growth of R. erythropolis N9T-4.