Previous Article | Next Article ![]()
Journal of Bacteriology, March 2001, p. 1819-1823, Vol. 183, No. 5
Division of Applied Life Sciences, Graduate
School of Agriculture, Kyoto University, Kitashirakawa-Oiwake,
Sakyo-ku, Kyoto 606-8502, Japan
Received 2 October 2000/Accepted 4 December 2000
In the long-chain n-alkane degrader
Acinetobacter sp. strain M-1, two alkane hydroxylase
complexes are switched by controlling the expression of two
n-alkane hydroxylase-encoding genes in response to the
chain length of n-alkanes, while rubredoxin and rubredoxin ruductase are encoded by a single gene and expressed constitutively.
Several strains in the genus
Acinetobacter are known as n-alkane utilizers
(4, 10). Among them, our isolate, Acinetobacter sp. strain M-1, is characterized by its ability to degrade a
variety of n-alkanes, including very long chain
n-alkanes (or paraffin wax) with carbon chain lengths of
C20 to C44 that are in a solid state at ambient
temperature (18).
Several pathways have been proposed for the initial reaction of
n-alkane degradation by Acinetobacter strains
(1, 2, 4, 5). Previously, we demonstrated three
n-alkane dioxygenase activities in Acinetobacter
sp. strain M-1, which had been postulated by Finnerty (5).
We assume that these enzymes are involved in the oxidation of
n-alkanes that are slightly dissolved in the cytosol or oil
inclusion of the cell, because the enzymes were found in the soluble
fraction of the cell extract of strain M-1. Recently, the genes
encoding alkane hydroxylase (alkM) (15), rubredoxin (rubA), and rubredoxin reductase
(rubB) (8) in Acinetobacter calcoaceticus strain ADP1 were found, and each of the genes was shown to be indispensable for n-alkane degradation. These
results suggest that a three-component alkane hydroxylase complex
participates in n-alkane degradation in strain ADP1, which
is similar to that in a medium-chain (C6 to
C12) n-alkane degrader, Pseudomonas
oleovorans (24). The difference in the organization
of the genes involved in n-alkane degradation between
P. oleovorans and A. calcoaceticus strain ADP1 is
that these genes are dispersed over the chromosomal DNA in strain ADP1,
while they form an operon on a large OCT plasmid in P. oleovorans.
We describe here the isolation and characterization of genes in strain
M-1 that are homologous to alkM, rubA, and rubB
of strain ADP1. The most characteristic feature of strain M-1 was that
two genes encoded alkane hydroxylases and they were differentially induced in response to the chain length of n-alkanes.
Cloning of two alkane hydroxylase genes, alkMa and
alkMb, from Acinetobacter sp. strain M-1.
We intended to clone the alkane hydroxylase-encoding gene from
Acinetobacter sp. strain M-1 to study the molecular
basis of the alkane hydroxylase complex in this organism. We
designed the PCR primers mono-N and mono-C (Table
1) based on the highly conserved regions
between alkM of A. calcoaceticus strain ADP1
(15) and alkB of P. oleovorans
(11) and used the chromosomal DNA of strain M-1 as a
template. This PCR yielded a 790-bp DNA fragment, and the sequence of
the fragment was identical to a part of the alkMa gene (see
below). Southern blot analysis using the fragment as the probe revealed
that the probe hybridized to at least two bands in the genomic DNA of
strain M-1 that had been digested with various restriction enzymes
(data not shown). The hybridization was performed under low-stringency
conditions at 37°C in the buffer from AlkPhosDirect (Amersham
Pharmacia Biotech UK Ltd., Buckinghamshire, England). From
these results, we cloned two alkane hydroxylase genes, alkMa and alkMb, into pBluescript II SK+ (Stratagene, La Jolla,
Calif.) through colony hybridization as described previously
(17). The four fragments in pMX4.2, pMC2.2, pMH2.5,
and pME3.4 (Table 2) overlapped each
other, and the span contained four complete open reading frames (ORFs)
and a partial ORF, covering a total of 6,089 bp. The 2.7-kb
XbaI fragment in pMX2.7 (Table 2) contained two ORFs and a
partial ORF over a span of 2,868 bp (Fig.
1). Inverse PCR (13)
was performed to amplify the downstream region of
alkMb. The BclI-digested chromosomal DNA of
strain M-1 was self-ligated and used as a template. The primers used
were IPA2up and IPA2dn (Table 1). The resulting PCR-amplified 4-kb
fragment was cloned and sequenced. Since the two cloned fragments
harboring alkMa and alkMb could explain all of
the hybridizing bands that appeared in the Southern blot analysis,
we concluded that strain M-1 has two alkane hydroxylase
genes.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.5.1819-1823.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Gene Structures and Regulation of the Alkane
Hydroxylase Complex in Acinetobacter sp. Strain
M-1
![]()
ABSTRACT
Top
Abstract
Text
References
![]()
TEXT
Top
Abstract
Text
References
TABLE 1.
Plasmids used in this study
TABLE 2.
Sequences of primers used in this study

View larger version (27K):
[in a new window]
FIG. 1.
Gene organization and restriction maps of the cloned
regions, including alkMa, alkMb, and
rubAB operon, and a proposed model for regulation of the
n-alkane hydroxylase complex by n-alkanes in
Acinetobacter sp. strain M-1. Thick arrows indicate the
orientation of each gene. The downstream region of alkMb was
sequenced by inverse PCR (see text). The putative products of the genes
are indicated below the thick arrows. Very long chain
n-alkanes and long-chain n-alkanes induce
alkMa and alkMb, respectively, and each of the
alkane hydroxylase components forms a complex with the constitutively
expressed rubredoxin and rubredoxin reductase.
|
Both alkMa and alkMb function in A. calcoaceticus strain ADP1. We attempted to show that alkMa and alkMb indeed encode functional n-alkane hydroxylases. Since several biochemical experiments were not successful, we took advantage of the genetics in A. calcoaceticus strain ADP1 (ATCC 33305; synonymous with strain BD413) (9, 21), which has both high transformation frequency and site-specific recombination efficiency.
We constructed the alkM disruptant (alkM
) of
A. calcoaceticus ADP1 by inserting the kanamycin-resistance
(Kmr) cassette. The ca. 3.0-kb DNA fragment containing the
alkane hydroxylase gene alkM (15) was PCR
amplified and cloned from the chromosomal DNA of strain ADP1. The
primers used were alkMUp and alkMDn (Table 1). In the BclI
site of alkM, the Kmr cassette, which was PCR
amplified using pKT231 (3) as a template (Table 2), was
inserted, and the resulting plasmid was used to transform strain ADP1.
The primers used for amplification were KmNBam and KmCBam (Table
1). Transformation was performed as described by Palmen et al.
(14). That the proper gene disruption had occurred
was confirmed by Southern blot analysis (data not shown). The
alkM
strain could grow on Luria-Bertani (LB) broth (19) medium containing kanamycin (50 µg/ml), but could
not grow on hexadecane.
On the other hand, pMX4.2 and pMX2.7 (Table 2 and Fig. 1) were each
digested by PstI (which has a unique site in the
multicloning site of the plasmids) and ligated with
PstI-digested pMFY31 (6), and the resulting
plasmids were pMFYalkMa and pMFYalkMb, respectively. These plasmids had
the alkane hydroxylase gene and the corresponding regulator gene from
strain M-1, respectively, and each of them was introduced into the
alkM
strain. Transformants were selected in the presence
of both ampicillin (50 µg/ml) and kanamycin (50 µg/ml).
When the alkM
strain was transformed by pMFYalkMa or
pMFYalkMb, the ability to grow on solidified M9 medium supplemented with hexadecane vapor in the presence of ampicillin and kanamycin was restored. This was not achieved with the control plasmid
pMFY31. All of the transformed plasmids could be recovered from the
transformants (data not shown), suggesting that these plasmids were
maintained but not incorporated into the chromosomal DNA of strain
ADP1. These results show that alkMa and alkMb
could each complement the inability of the alkM
strain to
grow on hexadecane. Therefore, alkMa and alkMb
both encode a functional alkane hydroxylase. However, growth on
n-alkanes of various lengths did not show a detectable difference between the alkM
strain carrying pMFYalkMa and
pMFYalkMb. Therefore, these in vivo assays using strain ADP1 gave no
information on the difference in substrate specificity between the
products of the two alkane hydroxylase genes.
Regulation of alkMa and alkMb expression by
n-alkanes.
The amino acid sequence identity between
AlkRa and AlkRb was only 5.0%, while that between AlkRa and AlkR of
the heterologous strain ADP1 is 53%. These results raised the
possibility that alkMa and alkMb are regulated in
a different manner in strain M-1. Strain M-1 cells were grown on
n-alkanes of various lengths as a carbon source, and
Northern blot analysis was performed using total RNA extracted from
these cells and alkMa- and alkMb-specific probes.
Figure 3 clearly demonstrates that (i)
neither alkMa nor alkMb expression was induced
when strain M-1 was grown on sodium acetate or on hexadecanol, which
induces the alk operon in P. oleovorans
(13) and (ii) alkMa and alkMb were
induced by n-alkanes, although in a different manner.
alkMa expression was induced by solid, very long chain
alkanes (>C22), and alkMb expression was preferentially induced by liquid long-chain alkanes (C16 to
C22).
|
Structure of the rubredoxin and rubredoxin reductase genes
(rubA and rubB) in Acinetobacter
sp. strain M-1.
To gain further insight into the molecular
structure of the n-alkane hydroxylase complex and its
regulation in strain M-1, we cloned the genes rubA and
rubB, encoding rubredoxin and rubredoxin reductase,
respectively, using PCR and inverse PCR techniques and
chromosomal DNA from strain M-1 as a template. The primers used were
RBDXN and RBDXC (Table 1), which had identical sequences to the 5' and
complementary 3' termini, respectively, of the rubA gene of
strain ADP1 (8). Inverse PCR was performed to amplify the
region surrounding rubA using the sequence
information. The primers used were IRBDXN and
IRBDXC (Table 1). EcoRI-digested and self-ligated
chromosomal DNA of strain M-1 was used as the template. The cloning
experiment yielded one 3.0-kb EcoRI fragment harboring two
ORFs for rubA and rubB and one incomplete ORF
(Fig. 1). The rubAB operon was overexpressed under the
tac promoter in Escherichia coli, and the
recombinant rubredoxin and rubredoxin reductase were purified to
apparent homogeneity by sodium dodecyl sulfate-polyacrylamide gel
electrophoresis (data not shown). The specific activity of the purified
recombinant rubredoxin reductase was 1,200 and 1,750 U
mg
1 toward potassium ferricyanide and rubredoxin,
respectively. One unit of activity was defined as the amount of the
enzyme that catalyzes the NADH-dependent reduction of 1 µmol of
ferricyanide or cytochrome c (in the presence of purified
rubredoxin) per min.
Regulation of the rubAB operon. The rubAB operon is constitutively expressed in strain ADP1 (12). We performed Northern blot analysis with total RNA extracted from strain M-1 using rubA and rubB as probes. A hybridizing band was not detectable in strain M-1 that had been grown on any carbon source, including the n-alkanes tested, showing that the rubAB operon was expressed at a very low level. On the other hand, when the cells were grown on glycerol, hexadecane, or triacontane, the specific activity (toward ferricyanide) of the rubredoxin reductase in the cell extract of parent strain M-1 was 0.43, 0.60, and 0.51 U/mg of protein, respectively. In addition, in the intergenic region of rubAB, no transcriptional terminator-like sequence such as an inverted repeat was found. These results suggest that the rubAB operon is constitutively expressed in strain M-1.
Two alkane hydroxylase complexes in response to chain length of n-alkanes in Acinetobacter sp. strain M-1. From these results, we propose a mechanism for the regulation of the n-alkane hydroxylase complex by n-alkanes in Acinetobacter sp. strain M-1 (Fig. 1). According to this model, the organism controls alkane hydroxylase activity in response to the chain length of the substrate by switching the alkane hydroxylase component, AlkMa or AlkMb, without changing other components of the complex, rubredoxin and rubredoxin reductase, which are constitutively expressed. The low sequence similarity between alkRa and alkRb, which are the putative transcriptional regulators of alkMa and alkMb, respectively, may also suggest distinct regulatory mechanisms for alkMa and alkMb expression by n-alkanes.
Unfortunately, we have not been able to detect the enzyme activity of the alkane hydroxylase complex in cell extracts of Acinetobacter spp. or in the in vitro reconstitution experiment using the recombinant proteins from E. coli (data not shown), while the enzyme activity was reported to be detectable in P. oleovorans (22). Possible reasons for the failure to detect the activity are (i) poor solubility of the substrate (such as tridecane or longer-chain alkanes) in the reaction mixture in comparison with that used in the assay of P. oleovorans alkane hydroxylase (22); (ii) unstable nature of the hydroxylase component (12, 16); and (iii) an unknown factor(s) in the alkane hydroxylase complex of Acinetobacter species. An alternative approach to examining the physiological role and substrate specificity of AlkMa and AlkMb may be the use of genetic analyses, such as gene disruption in Acinetobacter sp. strain M-1. However, we have not succeeded in deriving disruptants of alkMa and alkMb due to the very low efficiency of site-specific recombination in this organism. n-Alkane metabolism in Acinetobacter sp. strain M-1 is very complicated due to the diversity and overlapping functions of the enzymes. Genetic and biochemical characterization of n-alkane-metabolizing enzymes in Acinetobacter spp. will shed light on the poorly understood mechanism of the metabolism of very long chain n-alkanes in microorganisms and its regulation.Nucleotide sequence accession numbers. The nucleotide sequence data reported in this paper will appear in the DDBJ/EMBL/GenBank nucleotide sequence databases under accession numbers AB049411(alkMa), AB049412(alkMb), and AB049413(rubAB).
| |
FOOTNOTES |
|---|
* Corresponding author. Mailing address: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa-Oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
| |
REFERENCES |
|---|
|
|
|---|
| 1. | Asperger, O., and H.-P. Kleber. 1991. Metabolism of alkanes by Acinetobacter, p. 323-350. In K. J. Towner, E. Bergogne-Berezin, and C. A. Fewson (ed.), The biology of Acinetobacter. Plenum Press, New York, N.Y. |
| 2. | Asperger, O., A. Naumann, and H.-P. Kleber. 1981. Occurrence of cytochrome P-450 in Acinetobacter strains after growth on n-hexadecane. FEMS Microbiol. Lett. 11:309-312[CrossRef]. |
| 3. | Bagdasarian, M., R. Lurz, B. Rücket, F. C. H. Franklin, M. M. Bagdasarian, J. Frey, and K. N. Timmis. 1981. Specific-purpose plasmid cloning vectors. II. Broad host range, high copy number, RSF1010-derived vectors, and a host-vector system for gene cloning in Pseudomonas. Gene 16:237-247[CrossRef][Medline]. |
| 4. | Bajapai, U., R. C. Kuhad, and S. Khanna. 1998. Mineralization of [14C]octadecane by Acinetobacter calcoaceticus S19. Can. J. Microbiol. 44:681-686[CrossRef]. |
| 5. | Finnerty, W. R. 1988. Lipids of Acinetobacter, p. 184-188. In A. H. Applewhite (ed.), Proceedings of the World Conference on Biotechnology for the Fats and Oils Industry III. American Oil Chemical Society, Champaign, Ill. |
| 6. | Fukuda, M., and K. Yano. 1985. Construction of broad host range cloning vectors for Gram-negative bacteria. Agric. Biol. Chem. 49:2719-2724. |
| 7. | Gallegos, M.-T., R. Schleif, A. Bairoch, K. Hofmann, and J. L. Ramos. 1997. AraC/XylS family of transcriptional regulators. Microbiol. Mol. Biol. Rev. 61:393-410[Abstract]. |
| 8. |
Geissdörfer, W.,
S. C. Frosch,
G. Haspel,
S. Ehrt, and W. Hillen.
1995.
Two genes encoding proteins with similarities to rubredoxin and rubredoxin reductase are required for conversion of dodecane to lauric acid in Acinetobacter calcoaceticus ADP1.
Microbiology
141:1425-1432 |
| 9. |
Juni, E., and A. Janik.
1969.
Transformation of Acinetobacter calcoaceticus (Bacterium anitratum).
J. Bacteriol.
98:281-288 |
| 10. | Kennedy, R. S., and W. R. Finnerty. 1975. Microbial assimilation of hydrocarbons. I. The fine structure of a hydrocarbon oxidizing Acinetobacter sp. Arch. Microbiol. 102:75-83[CrossRef][Medline]. |
| 11. |
Kok, M.,
R. Oldenhuis,
M. P. G. van der Linden,
P. Raatjes,
J. Kingma,
P. H. van Lelyveld, and B. Witholt.
1989.
The Pseudomonas oleovorans alkane hydroxylase gene.
J. Biol. Chem.
264:5435-5441 |
| 12. |
McKenna, E. J., and M. J. Coon.
1970.
Enzymatic -oxidation. IV. Purification and properties of the -hydroxylase of Pseudomonas oleovorans.
J. Biol. Chem.
245:3882-3889 |
| 13. |
Ochman, H.,
A. S. Gerber, and D. L. Hartl.
1988.
Genetic applications of an inverse polymerase chain reaction.
Genetics
120:621-623 |
| 14. |
Palmen, R.,
B. Vosman,
P. Buijsman,
C. K. D. Breek, and K. J. Hellingwerf.
1993.
Physiological characterization of natural transformation in Acinetobacter calcoaceticus.
J. Gen. Microbiol.
139:295-305 |
| 15. |
Ratajczak, A.,
W. Geisdörfer, and W. Hillen.
1998.
Alkane hydroxylase from Acinetobacter sp. strain ADP1 is encoded by alkM and belongs to a new family of bacterial integral-membrane hydrocarbon hydroxylases.
Appl. Environ. Microbiol.
64:1175-1179 |
| 16. |
Ruettinger, R. T.,
S. T. Olson,
R. F. Boyer, and M. J. Coon.
1974.
Identification of the -hydroxylase of Pseudomonas oleovorans as a nonheme iron protein requiring phospholipid for catalytic activity.
Biochem. Biophys. Res. Commun.
57:1011-1017[CrossRef][Medline].
|
| 17. | Sakai, Y., J. Ishikawa, S. Fukasaka, H. Yurimoto, R. Mitsui, H. Yanase, and N. Kato. 1999. A new carboxylesterase from Brevibacterium linens IFO12171 responsible for the conversion of 1,4-butanediol diacrylate to 4-hydroxybutyl acrylate: purification, characterization, gene cloning, and gene expression in Escherichia coli. Biosci. Biotechnol. Biochem. 63:688-697[CrossRef][Medline]. |
| 18. | Sakai, Y., J. H. Maeng, Y. Tani, and N. Kato. 1994. Use of long-chain n-alkanes (C13-C44) by an isolate, Acinetobacter sp. M-1. Biosci. Biotechnol. Biochem. 58:2128-2130. |
| 19. | Sambrook, J., E. F. Fritsch, and T. Maniatis. 1989. Molecular cloning: a laboratory manual, 2nd ed. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. |
| 20. | Shanklin, J., E. Whittle, and B. G. Fox. 1994. Eight histidine residues are catalytically essential in a membrane-associated iron enzyme, stearoyl-CoA desaturase, and are conserved in alkane hydroxylase and xylene monooxygenase. Biochemistry 33:12787-12794[CrossRef][Medline]. |
| 21. | Strätz, M., M. Mau, and K. N. Timmis. 1996. System to study horizontal gene exchange among microorganisms without cultivation of recipients. Mol. Microbiol. 22:207-215[CrossRef][Medline]. |
| 22. | van Beilen, J. B., J. Kingma, and B. Witholt. 1994. Substrate specificity of the alkane hydroxylase system of Pseudomonas oleovorans GPol. Enzyme Microb. Technol. 16:904-911[CrossRef]. |
| 23. |
van Beilen, J. B.,
D. Penninga, and B. Witholt.
1992.
Topology of the membrane-bound alkane hydroxylase of Pseudomonas oleovorans.
J. Biol. Chem.
267:9194-9201 |
| 24. | van Beilen, J. B., M. G. Wubbolts, and B. Witholt. 1994. Genetics of alkane oxidation by Pseudomonas oleovorans. Biodegradation 5:161-174[CrossRef][Medline]. |
This article has been cited by other articles:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»