3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
The material hydrophobicity was determined by contact
angle measurement. The results are summarised in the
Table I. If value of contact angle is less than 90 ° the material
is considered to be hydrophilic, if contact angle is greater
than 90 ° the material is hydrophobic.
The cell hydrophobicity was determined by the BATH
test. It was found that Rhodococcus erythropolis belongs to
microorganisms with hydrophobic cell envelope character;
the determined hydrophobicity is 89.0 ± 6.3 %.
The quantity of proteins and saccharides in EPS is
shown in the Table II. Both proteins and saccharides amount
is approximately two times higher in biofilm EPS from silicon
carriers.
Table II
The concentration of saccharides and proteins in EPS
EPS composition
silicon glass
Saccharides 4.9 2.7
Proteins 4.8 2.5
Rate of adhesion during initial period of cultivation was
determined by the method of image analysis. Results have
shown (Table III) that silicone is colonized more rapidly
and better that glass. Small colonies were visible on silicone
materials immediately after beginning of cultivation. Their
area increased in time.
Table III
Portion of carrier occupied area by biofilm
Image analysis
1h 24h
colonized area [%] 0.0 0.2
glass number of objects in the
measured area
0 46
colonized area [%] 12.5 47.9
silicone number of objects in
measured area
1,394 1,103
The biofilm experiments were carried out in glass
columns (Ø = 5 cm, volume 220 ml). The silicone and glass
tubes (external diameter 0.5 cm, 1.0 cm length) were chosen
as carriers. The biofilm growth was the first stage of
the process. The cells were cultivated in columns in mineral
medium (BSM) with phenol (concentration 0.3 g dm –3 ,
changed at regular intervals) for 3 weeks at 20 °C. After this
period the stabilized biofilm was used for phenol degradation.
The results are summarised in the Fig. 2. The biofilm
concentration on glass (silicone) tubes was 4.1 (8.7) g dm –3 ,
respectively. The concentration of suspended cells in medium
s704
was lower in column with silicon tubes than in column with
glass ones. The phenol was totally degraded in column with
glass/silicone after 65 h/90 h, respectively.
Fig. 2. Phenol biodegradation by biofilm of rhodococcus
erythopolis. The cultivation was carried out in glass columns
with two types of carrier (glass and silicone tubes, external diameter
0.5 cm, length 1 cm). The biomass was measured as total
protein concentration at 595 nm
The comparison of the biodegradation rates of the pollutants
are summarised in the Table IV. Results indicate that
catechol has a lower degradation rate than phenol. The highest
biodegradation rate is reached in biofilm system with
glass carriers.
Table IV
Comparison of biodegradation rate of the pollutants by suspended
and sessile cells
Biodegradation rate
Suspended
cells
Biofilm
Phenol Catechol
0.7 g dm –3 0.7 g dm –3
3.89 1.61
glass silicon not tested in
12.01 4.09 glass collums
Conclusions
It was found out that Rhodococcus erythroposlis cells
better colonize silicone carriers to glass ones. Although the
biomass concentration on glass carriers was two times lower
the biodegradation rate was three times higher than in system
with silicone. This indicates that only a part of biofilm is
metabolically active. Results confirmed the hypothesis of higher
biodegradation velocity of pollutants in biofilm system.