POLISH JOURNAL OF ECOLOGY
(Pol. J. Ecol.)
54
1
3–14
2006
Regular research paper
Zbigniew Jan MUDRYK*, Piotr SKÓRCZEWSKI
Department of Experimental Biology, Pomeranian Pedagogical University,
Arciszewskiego 22 B, 76-200 Słupsk, Poland
*e-mail: [email protected] (corresponding author)
ENZYMATIC ACTIVITY AND DEGRADATION OF ORGANIC
MACROMOLECULES BY NEUSTONIC AND PLANKTONIC
BACTERIA IN AN ESTUARINE LAKE
ABSTRACT: Neustonic (film layer ~ 90 µm,
surface layer ~ 240 µm) and planktonic bacteria
(subsurface layer ~ 10–15 cm) participating in
the processes of decomposition of organic macromolecular compounds, and their potential capability to synthesise extracellular enzymes were
studied in a shallow estuarine lake (Lake Gardno
– Baltic coast). The studied bacteria were capable
of decomposing a wide spectrum of organic macromolecular compounds. Most bacteria inhabiting surface and subsurface water layers hydrolysed lipids, proteins and DNA. The microflora
hydrolysing cellulose was represented by the least
abundant group of organisms. Of the studied enzymes, alkaline and acid phosphatases, leucine
arylaminase, esterase, and esterase lipase were
synthesised most actively while β-glucouronidase
(βGl) and α-fucosidase (αFu) were synthesized
least actively. It can be clearly seen that enzymatic
activity was stratified, and there were differences
between studied water layers. Bacterial strains
isolated from surface and subsurface layers were
more active in synthesizing extracellular enzymes
than bacteria inhabiting the film layer. Bacteria isolated from various parts of Lake Gardno
synthesized the tested hydrolytic enzymes with
a similar intensity.
KEY WORDS: estuarine lake, bacterioneuston, bakterioplankton, organic matter decomposition, enzymatic activity
1. INTRODUCTION
Heterotrophic bacteria play a key role in
regulating accumulation, export, re-mineralization and transformation of the largest
part of organic matter in aquatic ecosystems (Shi a h et al. 2001). These processes
include microbiological biotransformation
of dissolved (DOM) and particulate (POM)
organic matter of auto- and allochtonous
origin (Mü nster and C hróst 1990). In
water bodies, heterotrophic bacteria are able
to decompose a wide spectrum of organic
compounds whose molecules differ in size
from monomeres to polymeres (Q ueme ne u r and Mar t y 1992). For heterotrophic
bacteria, those compounds constitute a very
important source of carbon, nitrogen, and
energy, and are used for biosynthesis or respiration processes (Brow n and G ou lder
1996, Patel et al. 2000).
Because most of DOM and POM in
aquatic ecosystems is polymeric in structure,
it cannot be assimilated directly by bacteria because of the insufficient permeability
of their membranes (Ar nost i et al. 1998,
Hopp e et al. 2002). Therefore, many heterotrophic bacteria are characterized by the
ability to synthesize various extracellular hy-
4
Zbigniew Jan Mudryk, Piotr Skórczewski
drolytic enzymes. Those biocatalysts carry
out the processes of depolymerisation of
macromolecular compounds to mono- or
oligomers that can be actively assimilated
by heterotrophic bacteria (Mar t ine z et al.
1996, Unanue et al. 1999). For this reason,
according to B o et ius (1995), Jacks on et
al. (1995), Ma l let nad D ebro as (1999),
enzyme assays can provide powerful tools
for studying organic matter degradation in
aquatic ecosystems. Relationships between
enzyme activities and the polymeric composition of the sources of organic matter suggest that patterns of enzyme activities can
be used to infer the composition of organic
matter sources in aquatic ecosystems (B osch ler and C app enb erg 1998).
This paper presents the results of a study
of the potential capability of estuarine neustonic and planktonic bacteria to decompose
macromolecular organic compounds and to
synthesise extracellular enzymes.
2. MATERIAL AND METHODS
2.1. Study area
The study was carried out in an estuarine
Lake Gardno situated in the World Biosphere
Reserve – Słowiński National Park (Poland)
in Baltic coast (54o 39`N, 17o 07`E). The lake
is very shallow (1.3 m average depth) but
covers a large area (2.500 ha). Lake Gardno
is characterized by conditions intermediate
between marine and inland environment, as
it is supplied by the fresh waters of the river
(River Łupawa) while being connected to
the Baltic Sea by a 1.3 km channel (Fig. 1).
Because large amount of sea water can penetrate into the lake, its waters – or a part of
them – acquire seawater properties, with the
salinity of 2–5‰. Consistently with the Venetian system, Lake Gardno can be classified
as belonging to the mixo-oligohaline type
(0.5–5.0‰) (D e t hier 1992).
Fig. 1. Estuarine Lake Gardno (Baltic coast) with location of sampling sites (1–3).
Enzymatic activity of neustonic and planktonic bacteria
The studied estuary is a polymictic water
body with no thermal or oxygen stratification, and with a considerable eutrophication. This high trophic level together with
a high concentration of nutrients (Mud r y k
et al. 2003) and the penetration of light to
the bottom of the lake create perfect conditions for the development of phytoplankton,
whose bloom lasts practically from spring
to autumn. The phototrophic community is
dominated by aggregate-forming cyanobacterium Anabena flos-aquae, Aphanizomennon flos-aquae and Microcystis aeruginosa
(St rz ele ck i and Półtora k 1971).
This shallow and productive estuarine
lake is characterized by an extensive growth
of macrophytes. The emergent macroflora
covers 4% of the lake surface forming a 20–
100 m wide offshore belt, a home for many
bird species. The main macrophytes are: Typha angustifolia, Phragmites australis, Scirpus
lacustris and Schoenoplectus lacustris.
2.2. Sampling
Water samples were taken quaterly (in
spring, summer, and autumn) in 1999 at
three sites: site 1, near the River Łupawa inflow (freshwater zone); site 2, in the mid-lake
(mixed water zone); site 3, close to the inflow
of the sea-water (seawater zone) (Fig. 1). At
each site, three layers of water were sampled.
Samples from the film layer (FL, thickness of
90 ±17 µm) were taken with a 30 × 30 glass
plate (Harvey and Burzell 1972), and samples
from the surface layer (SL, thickness of 242
±40 µm) were collected with a 40 × 50 cm
Garrett net (24 mesh net of 2.54 cm length)
(G ar rett 1965). Prior to sampling, the glass
plate and polyethylene net were rinsed with
ethyl alcohol and distilled sterile water. Samples from the subsurface layer (SUB) were
taken at the depth of about 10–15 cm. All
water samples were placed in sterile glass
bottles and stored in an ice-box at a temperature not exceeding 7oC. The time between
sample collection and their analysis usually
did not exceed 6–8 h.
2.3. Isolation of bacterial strains
Plate techniques were used in order to
isolate neustonic (FL and SL) and planktonic
5
bacteria (SUB). Water samples were vortex
mixed, and then serial tenfold dilutions were
prepared with sterile buffered water (phosphate buffer, pH = 7.2) (D aubner 1967) to
reach final concentrations ranging from 10–1
to 10–4. Diluted samples were inoculated by
the spread method in three parallel replicates
on iron-peptone agar medium (IPA) prepared according to Fer rer et al. (1963). Incubation was carried out at 20oC for 10 days.
Subsequently, from the whole surface of the
plates or from selected sectors, 30 bacterial
colonies from each site and each water layer
were picked out and transferred to a semiliquid (5.0 g agar per dm–3) IPA medium. The
cultures maintained on this medium after
purity control were kept at 4oC and used for
further analyses.
2.4. Bacterial decomposition of organic
macromolecular compounds
In order to determine the ability of studied bacteria to decompose organic macromolecular compounds, 30 bacterial strains
isolated from each season, site and water
layer were inoculated on several test media
containing various organic compounds such
as: cellulose (C), DNA (D), chitin (Ch), lecithin (Lc), lipids (L), pectin (Pc), proteins (P)
and starch (S). Detailed description of those
tests is given by Mud r y k and D ondersk i
(1997). The capacity index (CI) of macromolecule decomposition by bacterial strains
was calculated according to the formula:
CI =
1)
proposed by D ä h lb äck et al. (1982).
2.5. Measurement of the activity of
bacterial extracellular enzymes
The activity of extracellular bacterial
enzymes was determined with the use of
the semi-quantitative API Zym (API bioMerieux Ltd.) micro-method (Z d anowsk i
and F i guer i as 1999). Nineteen tests for the
presence of the following enzymes were carried out: alkaline phosphatase (Bph), esterase
(Est), esterase lipase (Esl), lipase (Lip), leu-
6
Zbigniew Jan Mudryk, Piotr Skórczewski
cine arylamidase (Leu), valine arylamidase
(Val), cysteine arylamidase (Cys), trypsin
(Try), chymotrypsin (Chy), acid phosphatase (Aph), naphtol-AS-Bi-phosphopydrase
(Nap), α-galactosidase (αGa), β-galactosidase
(βGa), β-glucuronidase (βGl), α-glucosidase
(αGs), β-glucosidase (βGs), N-acetyl-β-glucosaminidase (Nac), α-mannosidase (αMa),
and α-fucosidase (αFu).
Bacteria isolated in spring from each
site and each water layer were multiplied
on agar slants (IPA) for 72 h at 20oC. Afterwards, they were rinsed from the slants with
5 cm3 of liquid IPA medium, and adjusted to
the turbidity of 4 MacFarland standard corresponding to 109 bacterial cells per 1 cm3.
According to the manufacturer’s instruction,
65 µl of this suspension was inoculated on
a plastic strip to cupules containing different
substrates. All strips were incubated at 20oC
for 24 h; afterwards API reagents ZYM 1 and
ZYM 2 were applied. The obtained results
were compared with the colour chart provided by the kit manufacturer; enzyme activities
were expressed in nanomoles of hydrolysed
substrates.
The significance of differences between
sites and layers water in activity of extracellular bacterial enzymes were assessed by
a two-way ANOVA.
80
Percentage of strains
60
3. RESULTS
The majority of the strains of heterotrophic bacteria isolated from the waters of
Lake Gardno were capable of decomposing
a wide spectrum of macromolecular organic compounds (Fig. 2). Bacteria capable
of hydrolysing lipids constituted the highest
percentage of total number of 810 strains of
the studied microflora, those capable of hydrolysing proteins and DNA were also rather
numerous, while bacteria able to decompose
starch and lecithin were present at lower frequencies. Bacteria capable of hydrolysing
cellulose were the least numerous.
The horizontal distribution of the studied physiological groups was relatively homogenous. In all parts of the lake, the abundance of bacteria showing the specific ability
to decompose organic macromolecular compounds was similar (Fig. 2).
There are the distinct vertical changes
in the occurrence of bacteria capable of depolymerizing macromolecular compounds
(Fig. 3). It can be clearly seen that the distribution of various physiological groups is
stratified, and there are differences between
surface and subsurface water layers. Among
neustonic bacteria (FL, SL), the strains capable of hydrolyzing proteins, lipids, lecicellulose
chitin
DNA
lecithin
lipid
pectin
protein
starch
40
20
0
site 1
site 2
site 3
Fig. 2. Decomposition of selected macromolecules by heterotrophic bacteria isolated from water of lake
Gardno (percentages derived from the pooled data of seasons and water layers). Sites 1–3 – see Fig. 1.
Fig. 2
Enzymatic activity of neustonic and planktonic bacteria
cellulose
0
2
4
0
6 % strains
chitin
10 15
5
7
20 % strains
FL
FL
SL
SL
SUB
SUB
lecithin
DNA
10 20 30 40 50 % strains
30 40 50 60 70 80 % strains
FL
FL
SL
SL
SUB
SUB
lipid
60
70
pectin
80
0
90 % strains
FL
FL
SL
SL
SUB
SUB
55
65
10
15 % strains
starch
protein
45
5
75 % strains
20
FL
FL
SL
SL
SUB
SUB
30
40
50 % strains
Fig. 3. Vertical distribution
of bacteria able to decompose different macromolecules in three studied
Fig. 3
water layer (percentages derived from the pooled data of all sites and seasons) FL (~ 90 µm) – film layer,
SL (~240 µm) – surface layer, SUB (~15 cm) – subsurface water. Horizontal bars represented standard
error of the mean, n = 270.
thin, starch, DNA, and cellulose were more
numerous, while among planktonic bacteria
(SUB) more numerous were bacteria capable
of hydrolyzing pectin and chitin.
The occurrence of bacteria hydrolyzing
macromolecular compounds was fairly constant throughout the growing season, as indicated by only slight oscillations (33–37) of
the CI index (Table 1).
Bacteria isolated from the waters of Lake
Gardno varied in their ability to synthesize
hydrolytic extracellular enzymes (Fig. 4). Alkaline phosphatase (Bph), acid phosphatase
(Aph) leucine arylamidase (Leu), esterase
lipase (Esl) and esterase (Est) were synthesized most actively, while β-glucouronidase
(βGl) and α-fucosidase (αFu) were synthesized least actively (Fig. 4).
8
Zbigniew Jan Mudryk, Piotr Skórczewski
Data presented in Figure 4 show that
bacteria isolated from various parts of Lake
Gardno synthesized the tested hydrolytic
enzymes with a similar intensity, with the
exception of bacteria inhabiting the region of
the River Łupawa inflow (site 1) which synthesized β-galactosidase (βGa), α-glucosidase
(αGs), N-acetyl-β-glucosaminidase (Nac),
and α-mannosidase (αMa) more actively.
Figure 5 shows vertical changes in the
potential activity of bacterial extracellular
enzymes in film layer (FL), surface layer (SL)
and subsurface water (SUB). It can be seen
that enzymatic activity was stratified between studied water layers. Bacterial strains
isolated from SL and SUB synthesized 15 (esterase (Est), esterase lipase (Esl), lipase (Lip),
leucine arylamidase (Leu), valine arylamidase (Val), cysteine arylamidase (Cys), trypsin (Try), chymotrypsin (Chy), naphtol-ASBi-phosphopydrase (Nap), α-galactosidase
(αGa), β-galactosidase (βGa), α-glucosidase
Table 1. Percent distribution of bacteria strains able to decompose tested macromolecules in water of
Lake Gardno (percentages derived from the pooled data of all water layers).
% of bacteria decomposing tested substrates
chitin
Ch
lecithin
Lc
lipid
L
pectin
Pc
protein
P
starch
S
CI
61
6
43
73
5
71
43
38
3
54
13
33
69
5
61
54
37
90
mean
3
2
47
54
2
7
36
37
81
74
4
4
68
67
55
51
37
37
1
90
3
57
8
44
69
10
49
33
34
2
90
3
56
8
38
81
0
39
31
32
3
90
mean
4
4
57
57
3
6
35
39
76
75
9
6
49
45
37
34
34
33
1
90
3
37
11
41
71
9
58
27
32
2
90
3
65
8
37
72
2
78
24
36
3
90
0.7
68
7
32
70
3
77
35
37
2
57
8
37
71
5
71
29
35
Season Site*
n
Spring
1
90
0.7
2
90
3
Summer
Autumn
cellulose DNA
C
D
mean
Substrate hydrolysed by enzyme (nM · 24 h-1)
* see Fig. 1; n – number of strains studied; CI – capacity index calculated from equation (1) (see text)
40
30
site 1
site 2
site 3
20
10
0
Bph Est Esl Lip Leu Val Cys Try Chy Aph Nap �Ga��Ga �Gl �Gs �Gs Nac �Ma �Fu
Fig. 4. Spatial variation of potential enzymatic activity in different parts of Lake Gardno. Activities are
expressed as nanomoles of substrate hydrolysed by a bacterial inoculum of standard turibidity (109 cells
65µl) and presented asFig.4
an average of activities for the enzyme. Sites 1–3 – see Fig. 1.
9
FL
50
40
30
20
10
0
Bph Est Esl Lip Leu Val Cys Try Chy Aph Nap��Ga �Ga �Gl �Gs �Gs Nac �Ma �Fu
SL
50
40
30
20
10
Substrate hydrolysed by enzyme (nM · 24 h -1)
Substrate hydrolysed by enzyme (nM · 24 h -1)
-1
Substrate hydrolysed by enzyme (nM · 24 h )
Enzymatic activity of neustonic and planktonic bacteria
0
Bph Est Esl Lip Leu Val Cys Try Chy Aph Nap���Ga �Ga �Gl �Gs �Gs Nac �Ma �Fu
SUB
50
40
30
20
10
0
Bph Est Esl Lip Leu Val Cys Try ChyAph Nap��Ga �Ga �Gl �Gs �Gs Nac �Ma �Fu
Fig. 5. Vertical distribution of enzymatic activity in film layer (FL ~ 90 µm) surface layer (SL ~240 µm)
and subsurface water (SUB
cm). Vertical bars represented standard deviation of the mean, n = 90.
Fig. ~15
5
Table 2. Two-way-ANOVA in the activity of extracellular bacterial enzymes, due to site and layer. Significant differences at P <0.05.
SS
df
MS
MS error
F
P
Site
40.07
2
20.03
149.32
0.134
0.875
Layer
124.43
2
62.21
140.42
0.443
0.644
0.49
5
0.49
141.17
0.004
0.953
Source of variation
Site × Layer
10
Zbigniew Jan Mudryk, Piotr Skórczewski
(αGs), β-glucosidase (βGs), N-acetyl-β-glucosaminidase (Nac), α-fucosidase (αFu)) out
of 19 tested exoenzymes more actively than
bacteria isolated from FL.
By grouping the results by water layers
and sites, a factorial ANOVA test was carried
out for the activity of extracellular bacterial
enzymes in a estuarine Lake Gardno. The
statistical analyses showed no significant differences for the activity of extracellular bacterial enzymes among grouped data using
two-way ANOVA (Table 2).
4. DISCUSSION
In previously studied estuaries, lipolytic
bacteria constituted a dominant physiological group of microflora (Aust in et al.1977,
Siebur t h 1978, Mudr y k and D ondersk i
1997). Also in the estuarine Lake Gardno,
bacteria capable of hydrolysing lipids were
very abundant and amounted to more than
70% of the total number of culturable neustonic and planktonic bacteria. According to
C hróst and G aj e wsk i (1995) and Mart ine z et al. (1996), lipolytic bacteria have
been shown to play a key role in the processes of modification and transformation
of lipid compounds in water bodies. Lipids
are actively assimilated by bacteria and used
in respiratory processes or in biosynthesis
of cellular structures (Me yer-R ei l 1987,
MacC ar t hy et al. 1998). In aquatic ecosystems concentration of lipids in dissolved and
particulate organic matter ranges from 10 to
500 µg dm–3 (G aj e wsk i et al. 1997). Live as
well as dead phytoplankton, zooplankton,
meiobentos, macrobentos and detritus are
the main sources of lipids in the water bodies
(A lb ers et al. 1996).
Apart from lipolytic bacteria, bacteria
capable of hydrolyzing proteins were also
abundant in the water of Lake Gardno. Previous bacteriological studies of this estuary
(Mudr y k and D ondersk i 1997) confirm
this regularity. In other water bodies, bacteria hydrolyzing proteins were also a predominant group (Sug it a et al. 1987, Krstu lov ić
and S olić 1988). According to Patel et
al. (2000), high concentration of proteins,
polypeptides and peptides in water bodies
is the major factor causing intensive growth
of proteolytic bacteria. The main sources of
those compounds are the excretions of phytoplankton, zooplankton, and benthos, as
well as their remains (Bi l len and Font i g ny
1987). This is most probably the reason why
in the autumn, when large amounts of phytoand zooplankton were dying, the fraction of
proteolytic bacteria in the bacteriocoenosis
of Lake Gardno was the highest.
DNA is the basic biopolymer occurring
in the cells of all living organisms, and released after their death to the environment.
Heterotrophic bacteria can utilize DNA in
their metabolic processes as a source of carbon, nitrogen, and phosphorus (Jørgens en
et al. 1993, D el l Anno et al. 1999). Therefore, many aquatic bacteria are capable of
synthesizing extracellular deoxyribonuclease catalyzing the process of DNA decomposition (Pau l et al.1988). De F l au n et al.
(1987) determined that a high concentration
of nucleic acids, especially DNA, was noted
in estuaries. In the estuarine Lake Gardno,
DNA was hydrolyzed by more than 50% of
isolated bacterial strains. Abundance of this
physiological group of bacteria in other water bodies has also been reported by Pau l et
al. (1988) and Ste w ar t et al. (1991).
Bacteria capable of hydrolyzing cellulose
constituted the least abundant bacterial group
in Lake Gardno. In other water bodies those
bacteria also amounted to only a small percentage of the total bacteriocoenosis, or were
absent altogether (Su g it a et al. 1987, Pe t r ycka et al. 1990, Mud r y k and D ondersk i 1997). According to L ack l and et al.
(1982), one of the reasons for their low numbers in water bodies is the fact that cellulose is
relatively resistant to the processes of bacterial degradation, and its transformation into
glucose requires a considerable amount of
energy. For a microbiological depolymerization of cellulose, a synergistic activity of many
hydrolytic enzymes, synthesized by bacteria,
actinomycetales, fungi and protozoa, is needed (Münster and C hróst 1990).
The intensity of decomposition of organic macromolecules in water bodies is
usually determined not only by the number
of bacteria capable of carrying out those processes, but also by the level of activity of their
enzymes. Numerous studies (Jack s on et al.
1995, Patel et al. 2000, Hopp e et al. 2002,
Mud r y k and Skórc z e wsk i 2004) indi-
Enzymatic activity of neustonic and planktonic bacteria
cate that enzymatic activity of heterotrophic
bacteria is significantly higher in estuarine
basins than in freshwater or marine ones.
The strains isolated from the estuarine Lake
Gardno were also capable of synthesizing
a wide spectrum of hydrolytic enzymes.
In Lake Gardno of all the extracellular
enzymes assayed, phosphatases showed the
highest potential level of activity. According
to Hopp e and Urlich (1999) and Hopp e
(2003), phosphatase activity is widespread in
aquatic bacteria and is closely related to both
the P and the C cycles. Extracellular phosphatases can play an important role in supplying
phosphorus to heterotrophic microorganisms and to autotrophic algae (Mar xen and
S chmidt 1993).
Phosphatases occur in two forms, as
alkaline and acid; both forms are able to
hydrolyse all phosphoric esters (C hróst
and O ver b e ck 1987). Z d anowsk i and
D onachie (1993) and Mudr y k (2004)
note that in aquatic ecosystems the activity of alkaline phosphatase is usually higher
than the activity of acid phosphatase. Higher
activity of alkaline phosphatase was also determined in the present study.
Apart from phosphatases, leucine arylaminase was also synthesized very intensively
by bacteria inhabiting Lake Gardno. Similar
results were obtained by Middelb o e et al.
(1995) in Danish lakes, and by Z d anowsk i
and D onachie (1993) in arctic waters. According to Jones and L o ck (1989), the level
of leucine arylaminase is a good measure
of the proteolitic activity of bacteria as it is
a peptide bond hydrolyzing enzyme. A high
level of its synthesis in Lake Gardno corresponds to the high level of proteolytic activity of bacterial strains isolated from this estuary. Thomps on and Sins ab aug h (2000)
reported that peptidase activity increased
with the degree of eutrophication of the lake.
This is probably the reason why a high potential activity of leucine arylaminase was
also noted in the heavily eutrophicated Lake
Gardno.
B o et ius (1995), B os ch ker and C ap p enb erg (1998) and Mudr y k and Skórcz e wsk i (2004) draw attention to the high
level of activity of esterases and lipases in
aquatic environments. Those hydrolases are
capable of attacking emulsified mono-, di-
11
and triglycerides, and of splitting them with
the yield of glycerol and fatty acid residues
(G aj e wsk i et al. 1997). In Lake Gardno,
esterases and lipases, apart from phosphateses and proteases, belong to the group of
the most active extracelluar enzymes. This
high activity of lipid-hydrolyzing enzymes
might be due to the fact that in the study area
bacteria synthesizing lipases amounted to as
much 70% of all bacterial strains. In the studied lake, lipolytic activity against long-chain
fatty acids, was lower than against lipids with
short-chain fatty acids. The same results
were obtained by Z d anowsk i and F i gue r i as (1999) who studied enzymatic activity
of heterotrophic bacteria isolated from the
centre of the Ria de Vigo, Spain (northwestern corner of Iberian peninsula).
The least actively synthesized enzymes
included β-glucoronidase i α-fucosidase. The
same results were obtained by Po d górska
and Mud r y k (2003) who studied enzymatic
activity of bacteria isolated from the coastal
zone of the Baltic Sea.
Many authors (Hopp e and Url ich
1999, Mü nster et al.1998, Hopp e et al.
2002, Mud r y k and Skórc z e wsk i 2004)
draw attention to the considerable variability
in the activity of extracellular enzymes in the
vertical profiles of water basins. The results
of the present study also indicate that there
were differences in the potential activity of
the enzymes among studied water layers.
Bacteria inhabiting surface and subsurface
layers synthesized hydrolytic enzymes much
more actively than bacteria isolated from the
film layer. Lower activity of enzymes synthesised by bacteria inhabiting film layer could
have been caused by stressful effect of many
environmental factors, mainly by solar radiation and considerable fluctuations of the
temperature and salinity of the water. A relatively high content of heavy metals, polychlorinated biophenyls and pesticides in the film
layer can also have an inhibiting effect on the
synthesis and activity of bacterial enzymes
(Ma k i 1993).
In an earlier study Mud r y k and Skórc z e wsk i (2004) have shown significant differences in the level of potential enzyme activity in the horizontal profile of Lake Gardno.
According to B o e t ius (1995) and Mar t i ne z et al. (1996) such horizontal variation in
12
Zbigniew Jan Mudryk, Piotr Skórczewski
enzyme activity may reflect variations in the
composition, availability and degradability
of organic compounds, as well as differences
in the composition of microbial populations.
Results of the present study do not indicate
clear differences in the level of potential activity of bacterial enzymes among different
parts of the studied lake.
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(Received after revising October 2005)