water treatment
per layers consist mainly of cocci, while mainly bacilli
and filamentous microorganisms occur in the middle
and lower layers. Molecular phylogenetic analyses
of the actual population structures established by
this method were undertaken and are to be reported
elsewhere.
This method can be used successfully to investi-
gate many aspects of the complex population struc-
ture of floating sulphur biofilms. However, there are
limitations that need to be taken into account. The
most important relates to a long-standing problem in
microbial ecology studies, highlighted by Amann
et al
(1995) and others, that only those groups present in
the biofilm that are able to grow under the conditions
established in the gradient tube experimental system
will be easily identified and therefore studied. These
are the organisms used to present any descriptive
account of the system. Other organisms present in the
biofilm that are unable to grown in the medium pres-
ent in the gradient tube will go unnoticed and this may
bias any conclusions drawn.
Conclusions
The gradient tube method is a novel application that
enables the study of microbial population structure
and function in thin biofilm layers and does this by
expanding the size of sample over which experimental
investigation is possible.
The results show that gradients are effectively
established in this system with respect to sulphide,
sulphur and TOC and to a lesser extent also sulphate.
Organisms of different morphological types were
observed at different points within the gradients that
were established along the tube length.
Follow-up molecular phylogenetic studies of the
microbial populations in floating sulphur biofilms, and
correlation of these results with biofilm structure, as
determined by microprobe measurements, have been
undertaken and are to be reported elsewhere.
The gradient tube method provides an instrument
that may be used in conjunction with other method-
ological approaches to throw light on the microbial
ecology of floating sulphur biofilm systems. A better
understanding of these structures may facilitate their
development in bioprocess applications including acid
mine drainage wastewater treatment.
References
References for this article are available from the edi-
tor, Glynnis Koch at
25
Chemical Technology • September 2013
