Sampling, Biomass Estimation and Counts of Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 93

Eukaryotes

Gram-negative bacteria

Gram-positive bacteria

60

Eukaryotes
increase

40

Gram
negative
decrease

20

5 days 9 days 15 days

Figure 2.26 Mixed experimental
biofilm: Changes in constituent
organisms and total biomass. Top
graph: Proportions of eukaryotic and
prokaryotic organisms after three
periods of biofilm growth (PLFA
analysis). The 15-day biofilm is
dominated by eukaryotes - mainly
fungi and algae. Bottom graph: Typ-
ical biofilm growth curve. Biomass
increase determined from estima-
tion of carbohydrate accumulation.
Adapted and redrawn from Droppo
et al ., 2007.

Duration of biofilm

200

150

100

Lag phase

50

0

0 5 10 15

Days

populations (including a variety of algae) within the
biofilm. This can be assessed in two main ways - by
direct cell counts and by use of molecular techniques.

orviashakingbyhand(largercells-ciliates,diatoms,
other non-filamentous algae and filamentous algae).
Suspensions of the latter were transferred to sedimen-
tation chambers and counted after 24 h based on their
morphological characteristics.

Biofilm cell counts

Molecular techniques

Cell counts can only be made after the biofilm matrix
hasbeenbrokenupandbioilmcellsreleasedintosus-
pension. This approach was used by Augspurger etal .
(2008) for biofilms grown on tiles. These biofilms
were scraped off into filter-sterilised tap water, fixed
in formaldehyde or Bouin's fluid to stabilise the cells
and then biofilm cells released from the matrix either
by sonication (small cells - bacteria and flagellates)

Information on the community composition of
biofilms can be readily obtained using molecular
or biochemical techniques such as phospholipid,
nucleotide and chlorophyll analyses. These provide
information ranging from broad taxonomic cate-
gories down to genus level.