Fütterungsbedingte mikrobielle Zusammensetzung von Rinderkot ...

4. Determination of microbial biomass and fungal and bacterial distribution in cattle faeces 25
overestimation of fungal tissue. The negative relationship between galactosamine and
ergosterol suggests that galactosamine was mainly of bacterial origin, in accordance
with the general view in soil science (Amelung et al., 2008), although fungi also
produce galactosamine (Engelking et al., 2007).
The ergosterol to microbial biomass C ratio has been repeatedly used as an index
for the contribution of fungi to the total microbial biomass (Bååth and Anderson, 2003).
Of the anaerobic fungal populations, yeasts such as Candida sp. (Ahmad et al., 2010) or
Saccharomyces cerevisia (Aguilera et al., 2006) contain high concentrations of
ergosterol, also food spoiling Mucor plumbeus (Taniwaki et al., 2009). In contrast, no
ergosterol but high concentrations of cholesterol were measured in chytridiomycetes
(Weete et al., 1989; Kagami et al., 2007). Until now, no information is available on the
ergosterol concentration of anaerobic fungal species found in cattle such Anaeromyces,
Orpinomyces, Caecomyces, or Piromyces (Griffith et al., 2009). The mean ratio of
ergosterol to microbial biomass C of 1.1‰ found in cattle faeces is markedly below that
of soils (Joergensen and Wichern, 2008). Klamer and Bååth (2004) obtained a factor of
190 for converting ergosterol to fungal biomass C in 24 compost fungi, which is within
the range presented by Joergensen and Wichern (2008) and considerably above the
factor of 90 reported by Djajakirana et al. (1996). Using the factor reported by Klamer
and Bååth (2004) would result in a mean fungal biomass C content of 1.8 mg C g -1 DW
in the faeces samples in this study. However, not all faecal fungi may contain ergosterol
as stated above, but all contain glucosamine. The mean ratio of fungal glucosamine to
ergosterol was 190 in cattle faeces and thus somewhat above the mean ratio observed by
Appuhn and Joergensen (2006) in plant roots. During the 4-week incubation of cattle
faeces performed in this study, a decrease in the ergosterol to microbial biomass ratio
was followed by an increase, which may indicate a shift in the microbial community,
especially fungal communities to increasing aerobiosis and decreasing C availability.
This estimation is supported by the inverse changes in the microbial biomass C/N ratio
over the incubation period, i.e. an increase was followed by a decrease. However, in
dynamic systems, ergosterol tends to accumulate for certain periods after fungal death
(Zhao et al., 2005), which should also be considered in the present case.
The majority of microbial data in faeces samples is based on colony forming units
(CFU) or thallus forming units (TFU), counted on plates or as the most probable
number (Griffith et al., 2009). Although the unknown representation of cultivable
microorganisms has raised doubt about converting these counts into microbial biomass