DAYTONIGHT ACTIVITY OF BACTERIA IN THE SURFACE

7/29/2019 DAY TO NIGHT ACTIVITY OF BACTERIA IN THE SURFACE

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Maciej WALCZAK

Department of Environmental Microbiology and BiotechnologyInstitute of Ecology and Environment Protection, Nicolaus Copernicus University

Gagarina 9, 87-100 Toru, Poland,e-mail: [email protected]

DAYTONIGHT ACTIVITY OF BACTERIA IN THE SURFACE

MICROLAYER OF EUTROPHIC LAKE

ABSTRACT: This study examined changes

of bacteria numbers in the surface microlayer(SM) and subsurface water (SW) of a lake duringa day- and night-time. The research also address-es the synthesis of DNA and cell protein as well as

the activity of cellular dehydrogenases dependingon time of the day. Results demonstrated that inspring and summer the numbers of bacteria (percm3) in the SM was significantly greater duringnight-time than day-time (average: May, day-time 30.058 106, night-time 71.343 106;July, day-time 10.801 106, night-time 40.353 106). In October, numbers of bacteria in day-and night-time were not statistically different (re-spectively: 5.841 106 and 3.664 106).

Results indicated also that the rate of DNAsynthesis by SM bacteria was much higher in thenight-time (average: May 2.049 106 pg h1

cell1; July 1.363 106 pg h1 cell1), than in the

day-time (average: May 0.7263 106

pg h1

cell1; July 0.3404 106 pg h1 cell1). In con-trast, in October the values of DNA synthesis bySM bacteria were higher in night-time.

These changes are significantly smaller in SWat a depth of several dozen centimetres. However,no significant impact was observed of a time ofthe day on the activity of protein synthesis andactivity of cellular dehydrogenases by bacteria in-habiting SM and SW.

KEY WORDS: surface microlayer, hetero-trophic bacteria, day-night impact on bacteria

1. INTRODUCTION

The surface microlayer (SM) covers of the earths surface and at the same timeincludes an infinitely small volume of the

earths total water mass. This layer consti-tutes a specific chemical and physical envi-ronment, which differs substantially fromthe subsurface water (SW).

As a result of such phenomena as ad-sorption, diffusion, flotation or rainfall, allkinds of organic matter, mostly lipids, pro-teins, polysaccharides and their derivativesaccumulate in this layer, creating a super-ficial film or biofilm (Join and Moris1982, Korzeniewski 1990, Plasquellecet al. 1991, Kostrzewska-Szlakowska2003). The film separates the hydrous habi-tat from the air. The presence of diversechemical compounds in SM, generally oc-curring in higher concentrations than in SW(Falkowska 2001, Hillbricht-Ilkowskaand Kostrzewska-Szlakowska 2004)enhances the accumulation of both autotro-phic (Kostrzewska-Szlakowska 2000)and heterotrophic organisms (Hoppe 1986)

The surface microlayer generally con-tains an elevated number of bacteria, calledbacterioneuston. Bacterioneuston both con-

POLISH JOURNAL OF ECOLOGY

(Pol. J. Ecol.)

56 3 379389 2008

Regular research paper

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Maciej Walczak

sumes and produces organic substances con-tributing in this way to the development ofthe surface microlayer. The physical stabilityof this layer is maintained by surface tensionof the water surface. On the other hand, thisenvironment is highly unstable in compari-son to the subsurface water. This instabilityis caused by extreme temperature or solarenergy variations.

Due to the fact that bacterioneuston in-habits the surface microlayer, its membersare exposed to stressful ecological conditionsto a greater degree than organisms inhabitingthe water column. Potential harmful factors,such as intense solar radiation, temperature,or the presence of toxic substances, play an

important role in the struggle for survivaland growth. All of these factors are selec-tive and affect the composition of the micro-biological assemblages (Sh i lo 1979, Ves taland Hob bi e 1988).

Among the physical and chemical fac-tors determining the bioactivity of the sur-face water, the most important one seems tobe the solar radiation. Light reaching the wa-ter surface may penetrate the water columndown as far as several dozen meters. How-ever, the highest light intensity occurs withinthe upper dozen centimeters. The amount of

absorbed and diffused solar radiation variesand depends on the concentration and typeof organic matter present in the water col-umn. At high concentrations of dissolved or-ganic matter, which contains a considerableamount of humic substances, harmful UVBradiation penetrates only the upper severalcentimeters of the water (He ssen et al. 1997).According to Zaitsev (1971), the upper10 cm of the water column absorbs ca. 75% ofthe UV radiation at = 254 nm. Consideringthe entire range of solar radiation reachingthe air-water interphase, medium wave UVradiation, i.e. UVB 290320 nm and UVA320400 nm, is of the highest biological im-portance due to its harmful effects. Radiationwithin this range causes DNA damage (lethaleffect) or limits the growth of organisms byinhibiting enzyme synthesis, reducing activetransport, or by inducing mutations.

The 24-hour cycle of the solar radiationentails an entire sequence of changes takingplace in the surface water. As a result of thenatural changes of the intensity of the solar

radiation within twenty-four hours, the con-centrations of many organic and inorganiccompounds of the SM water as well as thenumbers and the activity of both the phyto-and the zooplankton (Falkowska 2001)

vary adequately. This is why the solar insola-tion is also one of the main factors workingindirectly and directly on the numbers andthe activity of bakterioneuston.

Despite numerous studies reportingpotentially unfavorable impacts of light onbacterioneuston, many empirical studiesexist which fail to demonstrate differencesin neuston activity with and without solarexposure (Hermansson and Dahlbck1983) and also report an insignificant impact

of UV and visible light on total bacterio-neuston activity (Gara be ti an 1991, Wi l-l iams et al. 1986). On the other hand, thereare numerous studies that demonstrate thatsolar radiation, especially UVB radiation, isdetrimental to the production of bacterialbiomass and exoenzyme activity (Herndl etal. 1993, Boa vi da an d Wetz el 1998). It isalso noteworthy that photooxidation of dis-solved organic matter (DOM) and particu-late organic matter (POM), which results inthe release of considerable quantities of easilyassimilable organic matter and may increase

the activity of bacterioplankton (Herndl etal. 1997), occurs under the influence of UV.

This study examined the dynamics ofnumbers of bacteria in SM and SW as well astheir metabolic activity in twenty-four hourcycle, depending on light conditions.

2. MATERIAL AND METHODS

The studies were carried out in the eu-trophic, small lake, (local name JeziorakMay), area 26 ha, maximal depth 6.4 m(Table 1). The lake has no inlets or outlets,but in its northern section is connected toanother lake by a narrow and shallow (1.5 m)strait. The lake waters are considered asstrongly eutrophic with hypertrophic symp-toms due to water blooming and oxygen rela-tions (Z be k 2005)

Water samples used for analyses werecollected in month: May, July and Octoberof 2005 from two stands localized in pelagiczone. Water of the surface microlayer was col-lected using plexiglas plate, which collects a

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Day-to-night activity of bacteria in the surface microlayer of eutrophic lake

150 m water layer, and a Garrett mesh (Gar-rett 1965) with a hole diameter of 200 m,which collects a 200 m water layer. The SMwater samples, collected in this way were ex-amined separately, but the results were aver-aged and subjected to analysis as an averagemeasurements for SM.

The subsurface water (SW) was collectedfrom a depth of 20 cm using a sterile, glasspipette and an automatic pump Pippet-boy(De Ville). Water was collected every 3 hoursover a 24-hour period.

Samples were poured into sterile, glasscontainers, from which 10 ml subsampleswere obtained for analysis.

The samples were analyzed for totalnumbers of bacteria (TNB), numbers ofmetabolically active bacteria TNAB (withan active electron transport system), activityof cellular dehydrogenases, and rates of pro-tein and DNA synthesis. In all of the aboveanalyses, the sample incubation was carriedout for 2 hours in lake water with appropri-ate reagents (in situ). The intensity of visiblelight and UVB were measured simultane-ously (Photometer PMA 2200, Solar LightCo) with collection of the samples used formicrobiological analyses (Table 2).

Total numbers of bacteria (TNB)was de-termined by a direct enumeration methodon membrane filters (Millipore) with a porediameter of 0.22 m. Samples were dyed withacridine orange (Zi mmer man n 1977), and

visualized under an epifluorescent micro-scope (Carl Zeiss Jena).

Numbers of metabolically active bacte-ria (TNAB) was determined following themethod of Zi mm er ma nn et al. (1978).

Activity of cellular dehydrogenases(ACdH)was examined with the INT (2-p-io-dophenyl-3-p-nitrophenyl-5-phenyl tetrazo-lium chloride) method, in which the amountof triphenyl formazan (TF) produced fromthe colorless substrate INT as a result of theactivity of cellular dehydrogenases was mea-sured. The color intensity is proportional tothe activity of cellular dehydrogenases. Anal-

ysis of TF concentration was carried out on aspectrophotometer (Marcel Pro) in relationto a standard curve.

Rate of cell protein synthesis (CPS) wasanalyzed by measuring the rate of incorpo-ration of tritium labelled leucine, followingKir chm an, K Nes s and Hudso n (1985).The amount of generated protein was deter-mined using a conversion factor based on anassumption that leucine constitutes on aver-age 0.073% of bacterial protein mass (Ki rch-man et al. 1989).

Rate of DNA synthesiswas determinedby measuring the rate of incorporation oftritium labelled thymidyne (Chrst et al.1998]).

Statistical analyses were done using pro-gram STATISTICA 6.0. Analysis of Variance(ANOVA) was the primary statistical methodused in calculations. This method facilitatedcomparison of the following independentfactors: TNB, TNAB, activity of cellular de-hydrogenases, rate of protein and DNA syn-thesis in day and night periods.

Table 1. Morphometric and trophic characteristics of eutrophic lake (lake Jeziorak May) under study.

Characteristic Value

Area (ha) 26

Maximal depth (m) 6.4Mean depth (m) 3.4

pH(1) 7.39.0

Total phosphorus (mg dm3) (2) 0.31

Total nitrogen (mg dm3) (2) 2.70

Electrolytic conductivity (S cm1) (1) 134380

(1) data supplied by Department of Environmental Microbiology and Biotechnology, Nicolaus Copernicus University (mean for

surface water, spring, summer and autumn 2005)(2) data supplied by Department of Hydrobiology, Nicolaus Copernicus University (mean for surface water, spring, summer and

autumn 2005)

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Table2.Dailychangesoftheintensityofsolarlight,UVBradiationand

temperatureinsurfacemicrolayer(S

M)andsubsurfacewater(SW)forthreeperiods.

Day-time:MayandJuly6.0018

.00;October9.0015.00;Night-time

:MayandJuly21.003.00;October18.006.00.

Sam-

pling

time

May

July

October

Light

(klx)

UV

B

(Wcm2)

Temp.

(C)

Light

(klx)

UVB

(Wcm2)

Temp.

(C)

Light

(klx)

UVB

(Wcm2)

Temp.

(C)

SM

SW

SM

SW

SM

SW

SM

SW

SM

SW

SM

SW

SM

SW

SM

SW

SM

SW

3.00

0.32

0.01

0.05

0.00

18.90

18.90

0.00

0.0

0

0.00

0.00

22.40

22.70

0.00

0.00

0.00

0.00

13.7

0

14.00

6.00

40.00

9.00

5.88

0.29

18.80

19.20

14.00

6.0

0

1.50

0.33

22.60

22.60

4.00

1.00

0.34

0.07

14.0

0

13.70

9.00

82.00

46.00

11.92

1.48

18.60

18.50

30.00

22.00

3.37

1.22

22.60

22.50

14.00

5.00

1.19

0.38

14.3

0

13.80

12.00

125.00

60.00

18.11

1.93

18.60

18.70

40.00

28.00

6.00

1.55

23.00

22.70

20.00

8.00

1.71

0.61

14.2

0

13.90

15.00

76.00

6.00

11.00

0.19

19.70

19.70

38.00

26.00

4.56

1.32

23.50

22.90

22.00

10.00

1.88

0.76

14.3

0

14.10

18.00

10.00

8.00

1.42

0.25

19.80

20.20

15.00

8.0

0

1.68

0.44

23.20

23.20

0.10

0.00

0.00

0.00

14.2

0

14.30

21.00

0.04

0.00

0.00

0.00

19.40

20.00

0.80

0.1

0

0.09

0.00

23.10

23.10

0.00

0.00

0.00

0.00

14.0

0

14.30

24.00

0.00

0.00

0.00

0.00

19.00

19.20

0.00

0.0

0

0.00

0.00

22.80

23.00

0.00

0.00

0.00

0.00

13.7

0

14.20

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3. RESULTS

Comparison of TNB values estimated inSM during the day-time and night-time dem-onstrates that in May and July, TNB is signif-icantly greater in night (results of statisticalanalyses are presented in Table 3). In May, inthe day-time, the average total numbers ofbacteria (TNB) equaled 30.058 106, whileat night-time, this number was much higherand equaled 71.343 106 cells cm3 (Fig. 1).An analogous relationship was observed inJuly; the average TNB in day-time equaled

10.801 106, while this number increased to40.353 106 cells cm3 at nigh-time. In con-trast, in October the mean values of the to-tal numbers of bacteria at night-time and indaytime were not statistically different (5.841 106 and 3.664 106 cells cm3, respectively).However, this daily cycle was not observed inSW samples collected at the same time as SMsamples (Fig. 1).

The changes observed in TNAB in twen-ty-four hour cycle are largely analogous tochanges in TNB (Fig. 2). In the SM waterin May the average value of TNAB in day-

Fig. 1. Total numbers of bacteria (TNB) in surface microlayers 150200 m (SM) and in subsurfacewater 20 cm (SW) in day and night periods. Vertical bars represent standard deviation.

Table 3. Statistical differences (P-values) in investigated parameters in surface microlayer (SM) and sub-

surface water (SW) between day and night periods. See Fig. 15 for the values. Significant differencesare given in bold.

Month

Total numbers ofbacteria

Total numbers ofactive bacteria

Dehydrogenasesactivity

Cell protein syn-thesis

DNA synthesis

SM SW SM SW SM SW SM SW SM SW

May 0.019 0.078 0.037 0.359 0.186 0.490 0.543 0.688 0.004 0.017

July 0.036 0.394 0.048 0.743 0.681 0.808 0.383 0.991 0.004 0.218

October 0.052 0.001 0.699 0.949 0.422 0.071 0.347 0.818 0.018 0.013

cells106cm-3

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Fig. 2. Total numbers of metabolically active bacteria (TNAB) in surface microlayer 150200 m (SM) andin subsurface water 20 cm (SW) in day and night periods. Vertical bars represent standard deviation.

Fig. 3. Activity of cellular dehydrogenases (ACdH) in surface microlayers 150200 m (SM) and insubsurface water 20 cm (SW) in day and night periods. Vertical bars represent standard deviation.

time equaled 8.35 106 cells cm3, while atnight-time this value increased to 17.14 106 cells cm3. Similarly, elevated numbersof metabolically active bacteria in the night-time were also observed in July. During that

month, in the day-time, the average TNABvalue equaled 7.17 106 cells cm3, while theaverage value at night-time was much higherand equaled 21.96 106 cells cm3. In con-trast, such changes in the number of meta-

cells106cm-3

molTFh-1cell-1

Day Night

Day Night

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bolically active bacteria related to twenty-four hour cycle were not observed during

October. The mean TNAB values in the SMin October were similar and equaled 1.38 106 cells cm3 during day-time and 1.07 106cells cm3 at night-time. In subsurface water,the number of metabolically active bacteriawas not correlated with the time of the day(Fig. 2).

The activity of cellular dehydrogenases(ACdH) in both SM and SW samples did not

vary significantly in twenty-four hour cycle(Fig. 3). In May and October, the ACdH inthe SM layer was higher at night-time thanin day-time; however, these differences werenot statistically significant. In contrast, dur-ing July the activity of the SM bacteria washigher in day-time than during night. In theSW, the activity of bacterial dehydrogenases(ACdH) did not vary in twenty-four hourcycle, and only in October the value in SMwas significantly higher in day-time.

In May and July, protein synthesis (CPS)for the SM bacteria was higher at night-time (in May: day-time 0.8002, night-time 1.3224; in July: day-time 0.0758, night-

time 0.1944 106 ng protein h1 cell1).However, the differences were not consid-

erable and this relationship was not statisti-cally significant. In contrast, in October theCPS by bacteria from the surface microlayerwas higher in the day-time, but the observeddifferences were small and statistically non-significant (day-time 1.1762; night-time 0.7194 106 ng protein h1 cell1). Whenanalyzing the CPS in the subsurface water(Fig. 4) in subsequent seasons, no correla-tion was observed in twenty-four hour cycle.Average values obtained in a given month, indaytime and at nigh-time, were very similar.

The rate of DNA synthesis by SM bac-teria was much higher at night-time duringMay and July. In May, the average quantityof synthesized DNA per active bacterial cellin the SM in day-time and at night-timeequaled 0.7263 and 2.049 106 pg h1 cell1,respectively. In July, this dependence alsowas clear and statistically significant. Duringthis month the average amount of synthe-sized DNA per metabolically active bacte-rial cell equaled 0.3404 106 pg h1 cell1 inday-time. At night-time, the average value of

Fig. 4. The rate of protein synthesis (CPS) by bacteria inhabiting surface microlayer 150200 m (SM)and subsurface water 20 cm (SW) in day and night periods. Vertical bars represent standard deviation.

ng106h-1cell-1

Day Night

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Maciej Walczak

DNA produced increased to 1.363 106 pgh1 cell1.

In contrast, in October, the rate of DNAsynthesis by SM bacteria was opposite, i.e.higher activity of DNA synthesis was ob-served in day-time. In the SW, where thequantity of incoming radiation is less, par-ticularly in the case of UV, a reduced rateof DNA synthesis was noted only in May inday-time (day 0.6492; night 4.068 106pg h1 cell1). In October, DNA synthesis bythe SW bacteria was greater in day-time. InJuly, differences in the rate of DNA synthe-sis by SW bacteria in twenty-four hour cyclewere so minimal that they were not statisti-cally significant.

4. DISCUSSION

The research demonstrated that day/nightcycle affects both the total numbers of bacte-ria (TNB) and the numbers of bacteria withan active electron transport system (TNAB)in the SM water. The abundances of thesebacteria decreased in the day-time. Chrstand Faust (1999) obtained similar results.

Despite the fact that these changes were clearand significant, their explanation is still un-

satisfactory. The question could be raised asto whether reduced numbers of bacteria in theSM water during day-time is an effect of themigration of bacteria into deeper water layersor of lower reproductive activity or perhaps ofmore complex relationships connected withinfluence of light on primary production andbacterivores activity. Information providedin the literature is also inconsistent. Some re-searchers suggest that solar radiation has nosignificant impact on the numbers of bacte-ria in the SM, or that such impact is very lim-ited (Dalbck 1983, Denward et al. 1999,Sk rcz ew sk i and Mud ry k 2003).

The activity of DNA synthesis by bacteriacells was examined in this study in twenty-four hour cycle. Obtained results were sup-posed to make up a basis for interpretation ofTNB and TNAB changes undergoing withintwenty-four hours. If bacteria migrations orbacterivores activity caused observed fluc-tuation, the degree of DNA synthesis by SMbacteria should be roughly the same duringthe day.

Fig. 5. The rate of DNA synthesis by bacteria inhabiting surface microlayer 150200 m (SM) and sub-surface water 20 cm (SW) in day and night periods. Vertical bars represent standard deviation.

pg106h-1cell-1

Day Night

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However, results presented in this studyregarding the rate of DNA synthesis dem-onstrate clearly that this synthesis is limitedin the SM water in day-time. Numerous re-searchers (Davidson 1998, Herndl et al.1997, Kaiser and Herndl 1997, Chrstand Faust 1999) have obtained similar re-sults, reporting that DNA synthesis in bac-terial cells was inhibited during day-time.According to Ch rs t and Faus t (1999) andDavidson (1999), solar radiation with UVhindered incorporation of 3H thymidynefrom 15 to 50% in comparison to the control(night-time). In the present study, the reduc-tion of DNA synthesis was observed to equal65% in May and 75% in July in relation to the

value obtained in SM at night-time. Com-parison of DNA synthesis by bacteria in SMand SW in the day-time (July) reveals loweractivity of DNA synthesis in SM of as muchas 94%. Above differences of DNA synthesismight partly be explained by the fact that theSM bacteria numbers changes between day-and night-time. Perhaps observed decreaseof DNA synthesis by SM bacteria is not onlya result of UV unfavourable impact, but thisradiation is either the most important or oneof the most crucial factors that hamper DNAsynthesis.

The greater reduction of DNA synthesis,in comparison to investigations of Kaiserand Hernd l (1997) as well as of Ch r st andFau st (1999), observed here results from thefact that the thickness of the sampled SM wa-ter equaled 100300 m. Whereas, the citedstudies sampled surface water over a thick-ness of several dozen centimeters. The dif-ference in sampling depth is of fundamentalimportance, due to the quantity of radiation,and in particular the UV radiation, penetrat-ing the water. It is notable that in subsurfacewater samples, collected from a depth ofca.20 cm, a significant impact of solar radia-tion on the rate of DNA synthesis was notobserved. This is a result of the fact that theanalyzed water originated from a eutrophiclake characterized by high concentrationsof dissolved and particulate organic matter(DOM and POM), which absorbs UV radia-tion intensively (Cockell 2000). Therefore,the quantity of UV radiation reaching theSW was significantly reduced in comparisonto SM (Table 1). The studies cited above were

conducted in marine ecosystems where theconcentration of organic matter was muchlower and the penetration depth of UV ra-diation greater.

A significant impact of the day-time ornight-time on the rate of bacterial cell pro-tein synthesis (CPS) was not observed in thepresent study. However, it should be notedthat the rate of CPS by the SM bacteria wasgreater at night-time, though these differenc-es were not large and were not statisticallysignificant. Results presented by Herndl etal. (1997), Kaiser and Herdl (1997) as wellas Chrst and Faust (1999), demonstratethat absorption of3H leucine by bacteria wasalso inhibited during day-time. However, it

should be noted that the investigations ofother authors were carried out at differentlatitudes. It pertains in particular to Chrstand Faust (1999) who conducted their re-search in the subequatorial zone where thesolar radiation intensity is much greater thanin temperate zone. Furthermore, the resultspresented by Ka is er and Hernd l (1997) aswell as Chrst and Faust (1999) indicatedthat the effect of solar radiation on CPS is lesssignificant than on DNA synthesis. Based onthese results, it can be inferred that the syn-thesis of DNA containing thymine, which

easily creates dimmers under the influenceof UV, is more sensitive to radiation than thesynthesis of protein. Protein synthesis occurson the RNA matrix, where uracil is presentinstead of thymine, and this feature poten-tially reduces the negative effect of UV onprotein synthesis.

This study also includes the results onchanges in the activity of cellular dehydro-genases (ACdH) in twenty-four hour cycle.The present analysis demonstrated that thetime of the day has no significant impact onactivity of cellular dehydrogenases of bac-teria from either the SM or SW. Unfortu-nately, no prior results of studies examiningthe changes of activity of these enzymes intwenty-four hour periods have been foundin the available literature. However, accord-ing to research conducted by Boavida andWetzel (1998), extracellular phosphataseactivity was highly inhibited under the in-fluence of solar radiation, during day-time.The activity of -glucosidase and ureasealso was inhibited by several dozen percent

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in the presence of strong solar radiation(Jorgensen et al. 1998). However phos-phatase and glucosidase are categorized asexoenzymes, and are secreted to the externalenvironment, where there is no protectionagainst the harmful effect of UV. In con-trast, dehydrogenases are intracellular en-zymes, and are protected by cellular shieldsor caroteinoids inside the cell. Furthermore,it is difficult to unambiguously confirm thatUV did not limit the activity of these en-zymes. Measured ACdH can result from twotypes of UV effects. As in the case of extra-cellular enzymes or DNA, UV may inhibitdehydrogenase activity. On the other hand,photooxidation of organic matter in water

occurs under the influence of UV radiation(Hder et al. 1998). This effect consider-ably increases the quantity of organic mattereasily accessible to bacteria, and this mustcause an increase in the activity of dehydro-genases participating in oxidation of organiccompounds. Thus, it seems that the ob-served lack of differences in enzyme activ-ity in day/night cycle constitutes a result ofmany physical and chemical factors, includ-ing UV radiation. The results testifying theindirect effect of insolation on the SM bac-teria were presented by Falko wsk a (2001).

In this work, a sequence of results was given,testifying the changes of concentrations ofseveral kinds of nutrient compounds in theSM water and the changes concerning phy-toplankton within twenty-four hours.

The conducted research confirmed andexpanded earlier reports regarding the im-portant impact of day-time on overall ac-tivities of bacteria in aquatic environments.However, it should be noted that the effectof solar radiation, including UV, is not lim-ited to simple and direct impacts on bacterialcells. Radiation also influences the environ-ment through a wide range of indirect ef-fects, e.g. organic matter photooxidation orthe impact on phyto- and zooplankton andbacteriophages, which in turn affect the ac-tivity of aquatic bacteria.

ACKNOWLEDGEMENTS: This workwas supported by the Ministry of Science and In-formation Society Technologies under grant no.0541/P04/2005/28

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DAYTONIGHT ACTIVITY OF BACTERIA IN THE SURFACE