Content uploaded by David F Ackerley
Author content
All content in this area was uploaded by David F Ackerley on Feb 02, 2015
Content may be subject to copyright.
New Zealand Science Review Vol 66 (2) 2009
70
In 2001, after responding to an advertisement in Nature, I was
offered a postdoctoral position in the laboratory of Professor
A.C. Matin in the Microbiology and Immunology Department
of Stanford University, with the following proviso. ‘I will em-
ploy you for a year. If you can obtain a fellowship within that
time you can stay; if not – well, you’d better be damn good.’
Fortunately the FRST Science and Technology Postdoctoral
Fellowship saved me from being put to the test! Otherwise this
article might have been much shorter.
And so I found myself in the dry heat of Northern California
– conditions that after ten or so happy but slightly soggy years
at Otago University I was willing to acclimatise to. Stanford is
located in the heart of Silicon Valley in the San Francisco Bay
Area, and has been a key player in the high-tech industry that
the region is most famous for. For example, SUN Microsystems
started life as a Stanford University Network communications
project; and Hewlett-Packard and Google (back when it was a
noun rather than a verb) were also Stanford-derived. The Bay
Area has also developed into one of the world’s leading biotech-
nology hubs, with Stanford again playing an integral role. Stan
Cohen of Cohen-Boyer fame (i.e. the rst recombinant DNA
experiment, which in very short order enabled cloning of the
human insulin gene and the concomitant launch of the leading
biotechnology company Genentech) is still in the Department
of Genetics there; and indeed, the Life Sciences academic staff
member who is not on the board of, or consulting for, one or
more biotech companies in the area is probably the exception
rather than the rule. The desire of these companies to be af-
liated with Stanford really reects the top-notch work that
so many of these scientists are doing. In my building alone
were father and son Arthur and Roger Kornberg, Nobel prize
winners in Medicine and Chemistry, respectively (it turns out
that the research Roger was doing when he used to yell down
the atrium at us to ‘…for God’s sake SHUT UP’ during Friday
happy hours actually was quite important); Lubert Stryer, whom
I met at one such happy hour and who was quite bewildered
to hear that one of my fellow PhD students back at Otago had
taken his biochemistry text-book on a world tour complete with
photographs at the Eiffel Tower, the Colosseum, etc; and Stan
Falkow, often referred to as the father of molecular microbial
pathogenesis, who recently won the 2008 Lasker-Koshland
Award for Special Achievement in Medical Science (perhaps
the top Biology award outside of the Nobels) and who used to
love talking about his annual holidays y shing in Nelson. All
in all, it was a very vibrant and exciting scientic environment
to suddenly be immersed in.
My postdoctoral research aimed to study and enhance the
ability of environmental bacteria to ‘bioremediate’ hexavalent
chromium (Cr (VI)), the toxic pollutant featured in the movie
Erin Brockovich. For those unfamiliar with it, the movie is
based on a civil class action lawsuit brought against the energy
company Pacic Gas and Electric, who were sued for dumping
Cr (VI) (which they used as a rust inhibitor in gas compressor
cooling towers) into unlined ponds in the Mojave Desert, near
the small township of Hinkley. Because Cr (VI) is extremely
water-soluble it was able to migrate into the aquifer compris-
ing the community’s major water supply and consequently the
residents suffered ‘many physical ailments, including bloody
noses, various intestinal ailments, bad backs, rotten teeth and
tumors’ (Sharp 2000). However, the effects of oral exposure to
hexavalent chromium are poorly established and the underlying
science, which was already a matter of some debate, was – inevi-
tably – further muddied during the trial. In an extreme example,
one paper (Zhang & Li 1997) that was a key piece of evidence
for Pacic Gas and Electric was recently retracted by the journal
on the basis of undisclosed ‘nancial and intellectual input to
the paper by outside parties’ (Brandt-Rauf 2006). Adding to the
intrigue, the same researchers had previously interpreted the
same data quite differently, suggesting that there was in fact
a positive correlation between Cr (VI) ingestion and stomach
cancer (Zhang & Li 1987). Nonetheless, because stomach acid
is able to instantly reduce Cr (VI) to the non-bioavailable form
Cr (III), it is not immediately clear how the polluted water might
have caused the various disorders (although one expert witness,
whom I spoke to informally at a conference, has suggested
that inhalation of contaminated steam in the shower may have
constituted an important route of exposure).
Although the movie did not really feature any science at all,
that did not stop me littering my research posters and seminars
2001 New Zealand Science and Technology Postdoctoral Fellowship
Molecular approaches for hexavalent chromium
bioremediation: Stanford Medical Center
David F. Ackerley
School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington
David Ackerley is a Senior Lecturer in the School of Biological Sciences at Victoria University of
Wellington.
David’s current research interests are: applications of bacterial oxidoreductase enzymes, in par-
ticular in anti-cancer gene therapy; and secondary metabolite synthesis by non-ribosomal peptide
synthetase enzymes. He may be contacted at david.ackerley@vuw.ac.nz
New Zealand Science Review Vol 66 (2) 2009 71
with gratuitous shots of Julia Roberts and the original Erin
(herself a former beauty queen), and the publicity also did
not seem to hurt our various grant applications. Apart from
FRST, our work was funded primarily by the US Department
of Energy, who generated – and are now trying to address
– a number of heavily Cr (VI)-contaminated sites, primarily
as a by-product of nuclear weapons manufacture during the
arms-race era. Without human intervention, Cr (VI) has been
projected to persist at dangerous levels at such waste sites for
well over 1000 years (Okrent & Xing 1993). Similar to the
stomach acid example above, strategies for decontamination of
environmental chromate focus on reducing it to non-bioavailable
Cr (III). Chemical methods for this are prohibitively expensive
for large-scale environmental application and frequently have
damaging consequences of their own (Cervantes et al. 2001),
and so bacterial bioremediation is of considerable interest as an
environmentally friendly and affordable solution to chromate
pollution. The main problem here is that, although many types
of bacteria have the ability to reduce Cr (VI) to Cr (III), none of
them seem to do it particularly well. This may be partly because
Cr (VI) is a fairly recent anthropogenic pollutant, and bacteria
simply have not yet evolved efcient systems for converting it.
However, much of our research (as well as that of other groups)
has also indicated that Cr (VI) reduction unavoidably entails
the generation of toxic intermediates that are deleterious to
the remediating organism (Keyhan et al. 2003; Ackerley et al.
2004a, b; Ackerley et al. 2006). The effects of this were particu-
larly evident in some chromate-challenged Escherichia coli cell
preparations that I once sent to a friend for electron micrograph;
he quickly called me back to tell me that my samples must have
become contaminated, as the Cr (VI)-treated one had been taken
over by some kind of crazy lamentous microbe – or possibly
by silly putty – but in fact these were the same E. coli cells three
hours post-challenge, which had continued to elongate but had
shut down cell division as a stress response (Figure 1).
We hoped to use genetic and protein-engineering strategies
to maximise chromate reduction while minimising toxicity to
remediating cells. Professor Matin had previously conducted
some ground-breaking research into trichloroethylene (TCE)
bioremediation, in which he had shown that placing a TCE-con-
verting gene under control of a ‘starvation promoter’ was an ef-
fective way of maximising remediation under low-nutrient eld
conditions (Matin et al. 1995), and he felt that a similar strategy
might work well with Cr (VI). Meanwhile, I was dead keen to
try my hand at directed evolution, an exciting series of random
mutagenesis techniques recently developed in California for
improving enzyme activity with particular substrates of interest
(Chen & Arnold 1993; Stemmer 1994). These ideas were quite
complementary, both requiring identication and isolation of a
gene encoding an enzyme with at least some Cr (VI)-reducing
ability. To cut a long and fairly technical story short, we ended
up identifying two different families of Cr (VI)-reducing enzyme
and showed that they both contributed to Cr (VI) reduction by
the host cell. Both types of enzyme were able to carry out a full
conversion through to Cr (III), generating different levels of
toxic intermediates and reactive oxygen species in the process
(Gonzalez et al. 2003; Ackerley et al. 2004a, b). Consistent with
the idea that Cr (VI) reduction is likely a ‘promiscuous’ property,
we demonstrated that the primary biological role of at least one
of these enzymes is probably defence against oxidative stress
(Gonzalez et al. 2005) – and this was highly encouraging, as it
suggested that this same enzyme might be able to mop up some
of its own mess during Cr (VI) reduction. As it was also the
enzyme that appeared to generate the fewest toxic chromium
intermediates in the process, it was the logical candidate for
our directed evolution schemes, aiming to generate a pimped
up Cr (VI)-reducing super-enzyme. From one perspective,
these efforts were actually quite successful – we ultimately
managed to evolve an enzyme with 300-fold improvement in
kcat/Km (a measure of its Cr (VI)-reducing efciency) (Barak et
al. 2006a). Unfortunately, however, when we actually popped
this souped-up enzyme back into bacterial cells it transpired that
we had now outstripped the ability of these cells to internalise
Cr (VI); and consequently we only saw a modest 2- to 3-fold
increase in the total rate of Cr (VI) reduction. Ongoing efforts in
the Matin laboratory are now aimed at addressing the bacterial
Cr (VI) uptake issue prior to any starvation promoter work and
assessment of potential bioremediation utility.
Being the man I am, I was happy to leave this as ‘Someone
Else’s Problem’. At the end of 2004 I was offered a position at
Victoria University of Wellington (VUW), which, after some
negotiation of the formal start date, I was pleased to accept. For
reasons both scientic and personal (Figure 2), I was keen to
stay on at Stanford for another year; and as long as I came back
to New Zealand to help establish their new teaching programme
in biotechnology and give a whirlwind urry of lectures, VUW
seemed happy to accommodate me. FRST were also enormously
supportive during this process, allowing me to apply for (and
Figure 1: Representative scanning electron micrographs of Escherichia coli W3110 cells grown for 3 hours in (left) Luria
Broth; or (right) Luria Broth amended with 250 µM K2CrO4.
New Zealand Science Review Vol 66 (2) 2009
72
ultimately granting) Bridge to Employment funding slightly
outside of the usual dates. Not only did this award doubtless
make my candidacy more attractive to VUW, it also provided
them with some exible funds to assist with my laboratory
start-up package; and I am grateful to both FRST and VUW
for their generosity in this regard.
At VUW I am continuing to work on the characterisation, en-
gineering, and evolution of potentially useful bacterial enzymes,
in particular following an interesting offshoot from the chromate
project, where we showed that the same (wildly promiscuous!)
enzymes are able to activate a variety of anti-cancer prodrugs
(Barak et al. 2006b). This anti-cancer gene therapy potential has
led to a very exciting multi-disciplinary collaboration with an
amazingly talented group of molecular biologists and medicinal
chemists at the Auckland Cancer Society Research Centre, in
particular Drs Adam Patterson, Jeff Smaill, and Mike Hay, and
Professors Bill Wilson and Bill Denny. This collaboration and
an association with the Maurice Wilkins Centre for Molecular
Biodiscovery have helped me obtain funding for the seven
postgraduate students who are presently working in my labora-
tory; and I have even been lucky enough to get two postdoctoral
research fellows of my very own.
Overall, I simply cannot emphasise enough how valuable the
Science and Technology Postdoctoral Fellowships Scheme has
been to my career. Without it, there may or may not have been
funding for me to stay on at Stanford after my rst (relatively
unsuccessful) year was up; and while there were no hard-and-
fast demands for me to come back to New Zealand at the end,
the Scheme and the associated Bridge to Employment funding
do certainly provide incentives to return. I found FRST to be
very supportive and easy to work with, and, as a direct contact,
Christine Romanes in particular was extremely helpful. To para-
phrase Stuart McCutcheon’s comment in the previous issue of
this publication, the only reasonable criticism of the Fellowships
is also a measure of their outstanding success – that it would
be nice to have more of them. The Foundation does provide
the only major source of postdoctoral research funding in New
Zealand outside of individual grants; and now that I am on the
other side of the academic fence I am better able to appreciate
the enormous value and benet that a talented postdoctoral
research fellow can bring to a research laboratory. Not only do
‘postdocs’ have better training and higher skill levels than gradu-
ate students, they have the exibility to work on and contribute
to multiple projects without being bound by thesis constraints
– and this type of coordination and independence can really help
a laboratory transition from a collection of individuals into a
unied research group. But they are awfully expensive… and
therein lies the problem. I appreciate that funding is always
limited, and lines must be drawn. It does, however, seem that
the Fellowships are getting ever harder to obtain, and that people
who are a lot more qualied than I was back in 2001 are miss-
ing out. I guess my point, ultimately, is that my Science and
Technology Postdoctoral Fellowship provided one of the most
valuable and formative experiences of my life, and it would be
great to see more people having those opportunities.
In conclusion, I would like to thank FRST one more time for
giving me that opportunity. Also Professor A.C. Matin and my
co-workers in his laboratory, in particular Claudio Gonzalez,
Yoram Barak, and Sue Lynch – thanks guys, I had a blast.
References
Ackerley, D.F.; Barak, Y.; Lynch, S.V.; Curtin, J.; Matin, A. 2006.
Effect of chromate stress on Escherichia coli K-12. Journal of
Bacteriology 188: 3371–3381.
Ackerley, D.F.; Gonzalez, C.F.; Park, C.H.; Blake, R.; Keyhan,
M.; Matin, A. 2004a. Chromate-reducing properties of soluble
avoproteins from Pseudomonas putida and Escherichia coli.
Applied and Environmental Microbiology 70: 873–882.
Ackerley, D.F.; Gonzalez, C.F.; Keyhan, M.; Blake, R.; Matin, A.
2004b. Mechanism of chromate reduction by the Escherichia
coli protein, NfsA, and the role of different chromate reductases
in minimizing oxidative str ess during chro mate reduction.
Environmental Microbiology 6: 851–860.
Barak, Y.; Thorne, S.H.; Ackerley, D.F.; Lynch, S.V.; Contag, C.H.;
Matin, A. 2006a. New enzyme for reductive cancer chemotherapy
(YieF) and its improvement by directed evolution. Molecular
Cancer Therapeutics 5: 97–103.
Barak, Y.; Ackerley, D.F.; Dodge, C.J.; Lal, B.; Alex, C.; Francis,
A.J.; Matin, A. 2006b. Analysis of novel soluble chromate and
uranyl reductases and generation of an improved enzyme using
directed evolution. Applied and Environmental Microbiology 72:
7074–7082.
Brandt-Rauf, P. 2006. Editorial retraction. Cancer mortality in a Chinese
population exposed to hexavalent chromium in water. Journal of
Occupational and Environmental Medicine 48: 749.
Cervantes, C.; Campos-Garcia, J.; Devars, S.; Gutierrez-Corona, F.;
Loza-Tavera, H.; Torres-Guzman, J.C.; Moreno-Sanchez, R. 2001.
Interactions of chromium with microorganisms and plants. FEMS
Microbiology Reviews 25: 335–347.
Chen, K,; Arnold, F.H. 1993. Tuning the activity of an enzyme for
unusual environments: sequential random mutagenesis of subtilisin
E for catalysis in dimethylformamide. Proceedings of the National
Academy of Sciences USA 90: 5618–5622.
Gonzalez, C.F.; Ackerley, D.F.; Lynch, S.V.; Matin, A. 2005. ChrR,
a soluble quinone reductase of Pseudomonas putida that defends
against H2O2. Journal of Biological Chemistry 280: 22590–
22595.
Gonzalez, C.F.; Ackerley, D.F.; Park, C.H.; Keyhan, M.; Matin, A.
2003. A soluble avoprotein contributes to chromate reduction
Figure 2: Dave and his major scientic discovery at Stanford – wife
Joanna MacKichan, who completed her PhD in 2004 in Stan Falkow’s
laboratory (it wasn’t really the shing stories that Dave was after) and
is now investigating the molecular mechanisms of pathogenesis of
Neisseria meningitidis at ESR (Institute of Environmental Science and
Research Ltd).
New Zealand Science Review Vol 66 (2) 2009 73
and tolerance by Pseudomonas putida. Acta Biotechnologica 23:
233–239.
Keyhan, M.; Ackerley, D.F.; Matin, A. 2003. Targets of improvement
in bacterial chromate bioremediation. Pp. 143–151 in: Pellei, M;
Porta, A (Eds) Remediation of contaminated sediments. Batelle
Press, Columbus, Ohio.
Matin, A.; Little, C.D.; Fraley, C.D.; Keyhan, M. 1995. Use of
starvation promoters to limit growth and selectively enrich
expression of trichloroethylene- and phenol-transforming activity
in recombinant Escherichia coli. Applied and Environmental
Microbiology 61: 3323–3328.
Okrent, D.; Xing, L. 1993. Future risk from a hypothesized RCRA site
disposing of carcinogenic metals should a loss of societal memory
occur. Journal of Hazardous Materials 34: 363–384.
Sharp, K. 2000. “Erin Brockovich”: The real story. Arts and
Entertainment Section, www.salon.com, April 14.
Stemmer, W.P. 1994. Rapid evolution of a protein in vitro by DNA
shufing. Nature 370: 389–391.
Zhang, J.D.; Li, S. 1997. Cancer mortality in a Chinese population
exposed to hexavalent chromium in water. Journal of Occupational
and Environmental Medicine 39: 315–319.
Zhang, J.D.; Li, X.L. 1987. Chromium pollution of soil and water in
Jinzhou. Zhonghua Yu Fang Yi Xue Za Zhi (Chinese Journal of
Preventive Medicine) 21: 262–264.
News
New Dean of Science for the University of Auckland
Professor Grant Guilford will be the new Dean of Science at the University of Auckland,
succeeding Professor Dick Bellamy who retired at the end of 2008.
Professor Guilford has held senior roles at Massey University, and is currently Head
of its Institute of Natural Sciences. Prior to that, he spent ten years as Head of the
Institute of Veterinary, Animal and Biomedical Sciences. During his tenure the institute
became the rst veterinary school in the southern hemisphere to win accreditation by
the American Veterinary Medical Association. He also led the creation of the Hopkirk
Research Institute, a multi-million dollar joint venture between Massey University and
AgResearch.
‘Professor Guilford brings to the University of Auckland his considerable experience in university education,
research management and the commercialization of intellectual property,’ says Auckland Vice-Chancellor,
Professor Stuart McCutcheon.
‘This is a very important appointment given that the Faculty of Science is our largest Faculty and one that is
critical to our objectives for the enhancement of quality teaching, the postgraduate programme and research
impact.’
Professor Guilford holds Bachelor of Philosophy and Bachelor of Veterinary Science degrees from Massey
University and a PhD in Nutrition from the University of California, Davis. He is an accomplished researcher
who has published widely and is experienced in establishing research consortia and partnerships for research
excellence. Several successful commercial products have been developed from Professor Guilford’s research,
and he has led or participated in the commercialisation of nine start-up companies.
‘It will be a privilege to lead the Faculty of Science, which plays a pivotal role in science in New Zealand and an
increasingly signicant role internationally,’ says Professor Guilford. ‘I look forward to continuing to foster the
intellectual freedom and highly creative environment in which research and learning can ourish.’
Professor McCutcheon paid tribute to Professor Dick Bellamy, who stepped down after 50 years’ association
with the University. He also acknowledged the contribution of Professor Alan Lee as Acting Dean since Profes-
sor Bellamy’s retirement.
Professor Guilford will take up the position of Dean of Science in August 2009.
