any ‘mouldy location’ and may already be sensitive to P.
chrysogenum (Denning et al. 2006). Similarly, particulate matter
present in the air of the Underground was clearly visible on
our sample plates (Fig 1), however, these Underground particulates,
mainly consisting of iron oxide, are thought to be
relatively safe for people at low respiratory risk (Colvile 2005;
Seaton et al. 2005). Additionally, the recent diversity found
within the Chrysogenum complex may have implications
regarding known fungal allergens produced by P. chrysogenum
(Denning et al. 2006).
The differences in fungal populations observed between
locations, such as Underground lines, could be the result of
local-scale environmental variation. A diagrammatic map by
Transport for London (2010) highlights variability of air temperature
between Underground lines; particularly in the
coolness of the Jubilee Line. The lower temperatures, around
24 C, recorded here could partly explain why lower proportions
of Penicillium were seen on the Jubilee Line, England
to the Bakerloo and Central. Fitting with this hypothesis, the
temperatures on the Bakerloo and Central range from around
31e35 C and genera counts revealed increased Penicillium
proportions. However, the data displayed on the diagrammatic
map were collected during a short 4 d window in
Jul. 2010 between the hr of 1600 and 1800. Although this
temperature survey is very limited, similar patterns in temperatures
are likely to be observed outside these time periods
and remain relative between different lines. The Milan
underground study specifically provides data showing Penicillium
colonies directly correlating with rise in temperature
(Picco & Rodolfi 2000). The Cairo metro study reports slightly
higher proportions of Penicillium at an underground station
than that of an overground station (Awad 2002). Penicillium
populations in the Underground are known to vary between
stations (Gilleberg et al. 1998) and our data support this. It has
been suggest that the fungi present are more likely to be
“indicative of local moulding” rather than transportation of
conidia from outdoor air (Gilleberg et al. 1998).
Our results and previous research demonstrate evidence
that the distributions and populations of fungi are different
on the Underground to that above ground. The diagnostic
tool we developed and applied has provided some interesting
preliminary data and will inform future investigations into
the ecology of fungal communities in Underground rail networks.
As the primary aim of this research was to prove the
efficacy and application of our diagnostic tools, the statistical
analysis of sample environments in this study has some
limitations. First, the concentration of airborne fungi can
vary throughout the day along with change of weather.
Second, due to the nature of air sampling, more than one
spore can be impinged at a single point onto the culture
media leading to a false reflection of the true number of
fungal colonies. Additionally, we used two different culture
media and three air sample volumes; however, we found no
statistical difference between these variables. Taking these
limitations into account, we have nonetheless demonstrated
significant differences between sample environments which
need further investigation. Research primarily designed to
explore the poorly understood ecology of Chrysogenum
complex could utilise our species-specific PCR diagnostic for
location comparison.
Mating types in a near 1:1 ratio present in both P. chrysogenum
and P. rubens provide further evidence to support
sexual reproduction. The sample sizes (24 and 22 respectively)
used for the mating-type distribution analyses are relatively
small compared to the larger analyses within this paper,
therefore, firm conclusions cannot be drawn. However, the
sexual reproduction of Penicillium has recently received
increasing interest due to the scope of having the ability to
artificially mate strains in the laboratory (Hoff et al. 2008; Dyer
& O’Gorman 2011). Although this has been similarly achieved
in Aspergillus (O’Gorman et al. 2009), it has not yet been
observed in Penicillium which, if achieved, may have implications
for production of penicillin or other metabolites by
means of sexually improving strains (Hoff et al. 2008; Dyer &
O’Gorman 2011).
Finally, it seems suitable to conclude by mentioning that
air samples from Fleming’s Laboratory contained more P.
rubens than any other location sampled in St Mary’s Hospital.
Although our findings may show Alexander Fleming to not
have been particularly lucky in observing P. rubens, further
exploration of the natural ecology of P. rubens and its closest
relatives may yet reveal underlying causes of Fleming’s
observation. The ancillary roles of the scientists Chain and
Florey, who translated Fleming’s observations and research
into medical practice, are recognised in the names of our new
species.