Selection of Saccharomyces cerevisiae Strains Tolerant to Lead and Cadmium Toxicity

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1 Seletion of Shromyes erevisie Strins Tolernt to Led nd Cdmium Toxiity Ndi R. A. Nssr, Yehi A. Heikl, Mhmoud A. M. Aou Doni, Mohmed Fdel, Gom N. Adel-Rhmn Astrt The im of this study ws to selet the est strins of Shromyes erevisie le to resist led nd dmium. Ten strins were sreened on the sis of their resistne t different onentrtions of 0, 2, 4, 8, 12, 16, 20 nd 24 ppm for P nd 0, 0.5, 1, 2, 4, 6, 8 nd 10 ppm for Cd. The properties of ker's yest qulity were deresed y the inrese of P or Cd in growth medium. The slope vlues of yield, totl vile ells nd gssing power of produed ker's yest were investigted s n inditor of metl resistnt. In ddition, onentrtions of P nd Cd in produed ker's yest were determined. The strin of S. erevisie FH-620 hd the highest resistne ginst P nd Cd nd hd the minimum levels of oth two investigted metls in produed ker's yest. Keywords Cdmium, led, S. erevisie, tolernt. I. INTRODUCTION AKER S yest (Shromyes erevisie) is one of the B oldest produts of industril fermenttion tht ws used trditionlly. It is still one of the most importnt ingredients in industries sed on its use for red-mking, stle food for lrge setion of world s popultion [1]. Also, ker's yest is good soure for proteins, essentil mino ids, vitmins nd lso mny minerls, i.e., lium, phosphorous, mgnesium nd iron [2]. Cne or eet molsses is the primry rw mteril for kery yest prodution. It supplies ll the sugr tht yest needs for growth nd energy long with prt of the needed nitrogen [3]. Moreover, [4] reported tht molsses is used s rw mteril for the prodution of ker's nd feed yest. In ddition, [5] studied the metls ontent of Egyptin ne molsses. He onfirmed the presene of opper, led, dmium nd nikel in ne molsses. The metls onentrtions rnged from 7.35 to (men vlue ppm) for opper, from 1.55 to 9.46 (men vlue 5.12 ppm) for led, from 0.14 to 0.82 (men vlue 0.40 ppm) for dmium nd from 1.07 to 1.85 (men vlue 1.31 ppm) for nikel. Also, [5] reported tht the metls onentrtions in ker's yest rnged from 2.38 to 6.49 (men vlue 3.82 ppm) for opper, from 0.71 to 2.28 (men vlue 1.21 ppm) for led, from 0.04 G. N. Adel-Rhmn is with the Dept. of Food Toxiology nd Contminnts, Ntionl Res. Center, Dokki, Giz, Egypt (orresponding uthor to provide phone: ; fx: ; e-mil: Gomm1985@yhoo.om). N. R. A. Nssr nd Y. A. Heikl re with the Food Siene Dept., Fulty of Agri., Ain Shms University, Ciro, Egypt. M. A. M. Aou Doni is with the Dept. of Food Toxiology nd Contminnts, Ntionl Res. Center, Dokki, Giz, Egypt. Mohmed Fdel is hed of Miroil Chemistry Dept., Ntionl Res. Center, Dokki, Giz, Egypt. to 0.14 (men vlue 0.08 ppm) for dmium nd from 0.38 to 0.45 (men vlue 0.41 ppm) for nikel. The hevy metls, suh s led, dmium nd merury, re non-essentil for iologil funtions, nd some hevy metls, suh s dmium nd merury, re strong inhiitors of miroil metolism, even t low onentrtions [6]. The metl toxi effets inlude the loking of funtionl groups, displement nd sustitution of essentil metl ions from imoleulr, onformtionl modifitions, denturtion nd intivtion of enzymes s well s disruption of ellulr nd orgnellr memrne integrity [7]. The effet of led on S. erevisie ws studied y [8]. They reported tht ddition of 200 µm led to yest ell suspension resulted in derese of out 15% of the viility in the first 20 min. Bker s yest is sensitive to high onentrtions of led with n extension of lg phse nd durtion of the fermenttion nd n overll derese in finl ell iomss prodution. Inresing led onentrtion resulted in negtive effet on growth rte nd mximum dry ell onentrtion in the eroi fermenttion of molsses [9]. Also, [10] studied the effet of opper onentrtions on two wine strins of Shromyes erevisie. The sensitive strin SN9 ws strongly ffeted y opper onentrtion (32 ppm), wheres the resistnt strin SN41 exhiited good growth tivity in presene of 32 ppm of opper. In ddition, [11] studied the effet of P nd Cd on tolerne of Shromyes erevisie. The reltive growth rte (% of ontrol) ws used to nlyze the effet of P nd Cd t different onentrtions on the growth of the yest ells. They dislosed tht the reltive growth rte ws deresed y inresing P or Cd onentrtions. The trget of this study is one of the importnt prolems of ker's yest prodution in El-Hwmdi for Chemils Ftory, whih produes out 45% of the yest needed for lol mrket. This ftory reeives different thes of molsses from different lotions whih differ in their hevy metls ontent throughout the yer. In ddition, the gssing power of produed ker's yest in some thes of molsses ws deresed ompring with other thes. Therefore, the present study imed to evlute the yield, gssing power nd totl vile ells of produed ker's yest of different Shromyes erevisie strins s ffeted y different onentrtions of P nd Cd to hieve seletion of Shromyes erevisie strins tht re le to resist the negtive effet of these metls. 93

2 II. MATERIALS AND METHODS A. Shromyes erevisie Strins Yest strins s desrie in Tle І were otined from Miroil Chemistry Dep. olletion, Ntionl Reserh Center, Dokki, Giz, Egypt. The yest strins were mintined in YMP gr slnts (0.3% yest extrt, 0.3% mlte extrt 0.5% peptone nd 2% gr) t 4 C. Pre-ulturing of S. erevisie strins ws done y tivting ells twie s desried y [8]. The yest ells were first trnsferred to fresh YMP gr slnt nd inuted t 30 C for 24 h. Therefter, loopful of the ultures were trnsferred to 250 ml Erlenmeyer flsks ontining 50 ml YMPS roth medium (0.3% yest extrt, 0.3 % mlte extrt 0.5% peptone nd 5% surose) nd inuted for 24 h. t 30 C under shking ondition (150 rpm). TABLE І DIFFERENT STRAINS OF SACCHAROMYCES CEREVISIAE No. Yest strins No. Yest strins S 1 S. erevisie F-707 S 6 S. erevisie FK-727 S 2 S. erevisie FA-91 S 7 S. erevisie FC-620 S 3 S. erevisie FF-725 S 8 S. erevisie FH-620 S 4 S. erevisie F-235 S 9 S. erevisie FAT-12 S 5 S. erevisie F-25 S 10 S. erevisie F-514 B. Cultivtion Stok solutions of the studied hevy metl ions were prepred y dissolving dmium (CdCl 2 ), nd led s P (No 3 ) 2 in de-ionized wter. Four hundred ml of YMPS ultivtion medium were pled in 1l Erlenmeyer flsks, P nd Cd were dded seprtely to ultivte medium to get finl onentrtions of 0, 2, 4, 8, 12, 16, 20 nd 24 ppm for P nd 0, 0.5, 1, 2, 4, 6, 8 nd 10 ppm for Cd. The flsks were utolved for 30 min t 121 C, 16 ml of previously prepred inoulum were used to inoulte eh flsk. Growth ws eroilly rried out t 30 C under shking ondition (150 rpm) for 24 h. At the end of inution period, yest yield ws reovered y entrifugtion t 4500 rpm for 5 min [8]. C. Estimtion of Yest Yield After entrifugtion, yest ells were wshed twie with distilled wter nd the preipitted lyer ws weighed [12]. D. Determintion of Totl Vile Yest Cells Count Yest suspension (1:10) ws prepred using sline solution. Smples were then serilly diluted nd plted on idi dextrose gr medium (0.3% eef extrt, 1% peptone 1% dextrose, 0.5% sodium hloride nd 1.5% gr) using pour plte tehnique ording to [12]. The inoulted pltes were inuted t 30 o C for 2 dys. The developing olonies were ounted nd the totl vile yest ounts were expressed s olony forming unit (CFU) per grm of yest. E. Evlution of Gssing Power Gssing power of ker's yest ws determined using n SJA-Fermentogrph NASSJO-Sweden. The nlysis ws onduted to determine the totl ron dioxide evolved during yest fermenttion in norml dough per one hour. The omposition of the prepred dough ws 160 ml wter, 4g NC1, 10g (wet weight) of ker's yest nd 280g whet flour (72%). Mixing of the dough t 35 o C for 5min ws rried out using Diosn D-4500 mixer. After mixing, the dough ws trnsferred to plte nd pled in the hmer of the Fermentogrph (35 o C). The hmer ws losed nd the reorder ws llowed to tre the urve of CO 2 formtion for 1 h. The fermenttion power ws reorded s CO 2 volume fter 1 h. [12], [13]. F. Determintion of Hevy Metls in Bker's Yest A well known weight smple of the otined yest (out 2 g) ws dried in n oven (105 C). The dried mteril ws shed in muffle furne t C until the smple ws ompletely omusted (sh turned white / gry or slightly olored). The otined sh ws dissolved using 1 ml onentrted HCl t ruile wlls. Dissolved smples were trnsferred to 50 ml volumetri flsk nd de-ionized wter ws dded to omplete volume. The solution ws filtered through shless filter pper Whtmn No. 42 nd stored in refrigertor until determintion y Atomi Asorption Spetrophotometer (PG-990) [5]. G. Sttistil Anlysis Results were sujeted to one-wy nlysis of vrine (ANOVA) of the generl liner model (GLM) using SAS sttistil pkge [14]. The results were the verge of three experiments (p 0.05). III. RESULTS AND DISCUSSION The yield, gssing power nd totl vile ells of different Shromyes erevisie strins fter growth t different onentrtions of led (P) nd dmium (Cd) re given in Figs. 1-3, respetively for P nd Figs. 4-6, respetively for Cd. Generlly, inresing P or Cd onentrtions in the growth medi deresed the yield, totl vile ells nd gssing power of ll S. erevisie strins. A. Effet of Led The growth medium ws djusted to P onentrtions in the rnge from 0 to 24 ppm. Signifint grdul dereses in yield s well s totl vile ells nd gssing power were oserved y inresing the onentrtion of P in the growth medium (Figs. 1-3). The derese of ll prmeters under investigtion my e due to the high toxiity of P, whih onsidered non essentil element for ker's yest growth. The redution of yest prmeters ws vrile depending on P onentrtions nd yest strins. 94

3 Gssing power (m 3 CO2/1 st h) Gssing power (m 3 CO2/1 st h) Gssing power (m 3 CO2/1 st h) Fig. 1 () Effet of led on yield of S. erevisie F-707, S. erevisie FA-91 nd S. erevisie FF-725 strins; () Effet of led on yield of S. erevisie F-235, S. erevisie F-25, S. erevisie FK-727, S. erevisie FK-727 nd S. erevisie FC-620 strins; () Effet of led on yield of S. erevisie FH-620, S. erevisie FAT-12 nd S. erevisie F-514 strins Fig. 2 () Effet of led on gssing power of S. erevisie F-707, S. erevisie FA-91 nd S. erevisie FF-725 strins; () Effet of led on gssing power of S. erevisie F-235, S. erevisie F-25, S. erevisie FK-727, S. erevisie FK-727 nd S. erevisie FC-620 strins; () Effet of led on gssing power of S. erevisie FH-620, S. erevisie FAT-12 nd S. erevisie F-514 strins 95

4 Totl vile ells (CFU/g 10 9 ) Totl vile ells (CFU/g 10 9 ) Totl vile ells (CFU/g 10 9 ) Fig. 3 () Effet of led on totl vile ells of S. erevisie F-707, S. erevisie FA-91 nd S. erevisie FF-725 strins; () Effet of led on totl vile ells of S. erevisie F-235, S. erevisie F-25, S. erevisie FK-727, S. erevisie FK-727 nd S. erevisie FC-620 strins; () Effet of led on totl vile ells of S. erevisie FH-620, S. erevisie FAT-12 nd S. erevisie F-514 strins TABLE ІІ EFFECT OF LEAD ON BAKER'S YEAST PROPERTIES OF S. CEREVISIAE STRAINS Rte of redution (Slope) No. Yest strins Gssing Yield power Totl vile ells S 1 S. erevisie F S 2 S. erevisie FA S 3 S. erevisie FF S 4 S. erevisie F S 5 S. erevisie F S 6 S. erevisie FK S 7 S. erevisie FC S 8 S. erevisie FH S 9 S. erevisie FAT S 10 S. erevisie F Conerning the effet of P on yield of different S. erevisie strins, the results presented in Figs. 1 ()-() nd Tle ІІ showed tht the S. erevisie FH-620 strin (S 8 ) hd minimum vlue of slope (-0.154) s n inditor of the high resistnt, followed y S. erevisie F-707 strin (S 1 ) with slope vlue of , then S. erevisie FC-620 strin (S 7 ) with slope vlue of Menwhile S. erevisie FA-91 strin (S 2 ) reorded the highest vlue of slope (-0.863) followed y S. erevisie FK-727 strin (S 6 ) eing s n inditor of the low resistnt. Regrding the effet of P on gssing power, results in Figs. 2 ()-() nd Tle ІІ indite tht the S. erevisie FH-620 strin (S 8 ) hd the lowest vlue of slope (-26.61) followed y S. erevisie F-707 strin (S 1 ) nd S. erevisie FAT-12 strin (S 9 ) eing nd , respetively. On the other hnd, S. erevisie FA-91 strin (S 2 ) nd S. erevisie FK-727 strin (S 6 ) reorded the highest vlue of slope eing nd , respetively. Similr trend ws found for totl vile ells (Figs. 3 ()-() nd Tle ІІ), where the lowest vlues of slope in this respet ws reorded for S. erevisie FH-620 strin (S 8 ), S. erevisie F-707 strin (S 1 ) nd S. erevisie FAT-12 strin (S 9 ) eing , nd , respetively. Menwhile S. erevisie FA-91 strin (S 2 ) reorded the highest vlue of slope (-0.551) followed y S. erevisie FK-727 strin (S 6 ) eing These results oinide with those of [8] who reveled tht ddition of 200µM P to yest ell suspension resulted in derese of out 15% of the viility in the first 20min. Bker s yest is sensitive to ny onentrtions of P with n extension of lg phse nd durtion of the fermenttion nd n overll derese in finl ell iomss prodution. Similr findings were notied y [11] who indited tht ker's yest growth ws ffeted y dding P ( mmol/l), resulted in negtive effet on growth rte when ompred to the ontrol. B. Effet of Cdmium Different Cd onentrtions rnged etween 0 to 10 ppm were tested in order to determine their effet on ker's yest properties of different S. erevisie strins (yield, gssing power nd totl vile ells). Dt presented in Figs. 4-6 show signifint grdul derese in ll tested prmeters y 96

5 inresing Cd onentrtion in the growth medium. Inhiition ws vrile depending on Cd onentrtions nd yest strins. Gssing power (m 3 CO2/1 st h) Gssing power (m 3 CO2/1 st h) Gssing power (m 3 CO2/1 st h) Fig. 4 () Effet of dmium on yield of S. erevisie F-707, S. erevisie FA-91 nd S. erevisie FF-725 strins; () Effet of dmium on yield of S. erevisie F-235, S. erevisie F-25, S. erevisie FK-727, S. erevisie FK-727 nd S. erevisie FC-620 strins; () Effet of dmium on yield of S. erevisie FH-620, S. erevisie FAT-12 nd S. erevisie F-514 strins Fig. 5 () Effet of dmium on gssing power of S. erevisie F-707, S. erevisie FA-91 nd S. erevisie FF-725 strins; () Effet of dmium on gssing power of S. erevisie F-235, S. erevisie F-25, S. erevisie FK-727, S. erevisie FK-727 nd S. erevisie FC-620 strins; () Effet of dmium on gssing power of S. erevisie FH- 620, S. erevisie FAT-12 nd S. erevisie F-514 strins 97

6 Totl vile ells (CFU/g 10 9 ) TABLE ІІІ EFFECT OF CADMIUM ON BAKER'S YEAST PROPERTIES OF S. CEREVISIAE STRAINS RATE OF REDUCTION (SLOPE) No. Yest strins Gssing Yield power Totl vile ells S 1 S. erevisie F S 2 S. erevisie FA S 3 S. erevisie FF S 4 S. erevisie F S 5 S. erevisie F S 6 S. erevisie FK S 7 S. erevisie FC S 8 S. erevisie FH S 9 S. erevisie FAT S 10 S. erevisie F Totl vile ells (CFU/g 10 9 ) Totl vile ells (CFU/g 10 9 ) Fig. 6 () Effet of dmium on totl vile ells of S. erevisie F- 707, S. erevisie FA-91 nd S. erevisie FF-725 strins; () Effet of dmium on totl vile ells of S. erevisie F-235, S. erevisie F-25, S. erevisie FK-727, S. erevisie FK-727 nd S. erevisie FC-620 strins; () Effet of dmium on totl vile ells of S. erevisie FH-620, S. erevisie FAT-12 nd S. erevisie F-514 strins With regrd to the effet of Cd on yield of different S. erevisie strins, the results presented in Figs. 4 ()-() nd Tle ІІІ showed tht S. erevisie FH-620 strin (S 8 ) ws more resistnt to Cd followed y S. erevisie F-707 (S 1 ) nd S. erevisie FAT-12 (S 9 ) strins. Where S. erevisie FH-620 strin (S 8 ) hd lowest vlue of slope (-1.671), menwhile, the yield slope of S. erevisie F-707 (S 1 ) nd S. erevisie FAT- 12 (S 9 ) strins were nd , respetively. On other hnd, S. erevisie FA-91 (S 2 ) nd S. erevisie FK-727 strins (S 6 ) were more sensitivity to Cd, where the yield slopes were nd , respetively. Conerning the effet of Cd on gssing power of different S. erevisie strins, the results presented in Figs. 5 ()-() nd Tle ІІІ pper tht the S. erevisie F-707 strin (S 1 ) hd minimum vlue of slope (-81.09), followed y S. erevisie FH-620 strin (S 8 ) eing , then S. erevisie FAT-12 strin (S 9 ) with slope vlue of Menwhile, S. erevisie FK-727 strin (S 6 ) reorded the highest vlue of slope (-97.60) followed y S. erevisie FA-91 strin (S 2 ), eing Results in Figs. 6 ()-() nd Tle ІІІ indite tht vrile inhiition effet of Cd on totl vile ells depended on the yest strins nd Cd onentrtions in the growth medium. Generlly, higher onentrtions of metl used higher inhiition. Throughout the rnge of pplied Cd onentrtions (0-10 ppm), the S. erevisie FH-620 strin (S 8 ) nd S. erevisie F-707 strin (S 1 ) hd the lowest vlue of slope for totl vile ells eing followed y S. erevisie FAT-12 strin (S 9 ), eing then S. erevisie F-235 (S 4 ) with slope vlue of Menwhile S. erevisie FK-727 strin (S 6 ) reorded the highest vlue of slope (-1.434) followed y S. erevisie F-514 strin (S 10 ), eing These results were in greement with those reported y [11] who found vrile inhiition effet of Cd on Shromyes erevisie depending on the Cd onentrtions in the medium. Generlly, higher onentrtions of metl used higher inhiition. In this respet, [15] stted tht Cd is nonessentil for iologil funtions nd strong inhiitors of yest metolism even t low onentrtions. Moreover, [16] 98

7 reported tht Cd strongly inds to funtionl groups on yest ell wlls. Hene, this result in formtion of Cd-omplex with high formtion onstnt filittes the displement of other metls. Cd toxiity depends on its ility to form omplexes with some iologil nti-oxidnt defense. In support of this hypothesis, mjor effet of Cd is to use oxidtive stress, prtiulrly lipid peroxidtion [17]. Toxiity of Cd my e lso used y depletion of glutthione (GSH), onsidered s mjor ntioxidnt in yest ells [18]. From the results (Figs. 1-6), it ould e onluded tht S. erevise strins gve the highest resistne to led ompred with dmium. Similr findings were notied y [11] who indited tht, S. erevisie ws sensitive to dmium ut tolernt to opper, zin, led, nd iron. C. Determintion of Led nd Cdmium in Produed Bker's Yest Bker's yest of different S. erevisie strins produed on growth medium ontined different P onentrtions were nlyzed for its ontent of P nd the otined results re shown in Tle ІV. The dt indite tht the P onentrtions were grdully inresed y inresing P onentrtion in the growth medium from 2 to 24 ppm. A similr trend ws reported y [9] who oserved tht P uptke Yest strins y yest ws inresed from 0.6 to 20.4 mg/g y inresing P onentrtion in the growth medium from 3 to 150 ppm. Cdmium onentrtions of produed ker's yest for different S. erevisie strins grown on medium ontined different Cd onentrtions rnged from 0.5 to 10 ppm ws investigted nd the results re shown in Tle V. Dt revel lso tht the Cd onentrtions in yest iomss were inresed y inresing Cd onentrtions from 0.5 to 10 ppm. These results re in ordne with those otined y [19], [20] who reported tht the proess of Cd uptke y S. erevisie would e rried out more suffiiently t higher Cd onentrtions, the tive sites of S. erevisie would e surrounded y more metl ions. Therefore, the vlue of Cd uptke inresed with inresing of initil Cd ions onentrtion. Dt in Tles ІV, V show lso tht the highest onentrtions of P nd Cd were hieved for S. erevise FA-91 strin, followed y S. erevise FK-727. On other hnd, the S. erevisie FH-620 strin hd the lowest vlues of P nd Cd followed y S. erevisie F-707 strin, then S. erevisie FAT-12 strin. The vrition in P nd Cd onentrtions of produed ker's yest my e due to the differenes in the iohemistry of the ell wll, thus motivting differenes in the iosorption pity of the onsidered strins [21]. TABLE ІV CONCENTRATION OF LEAD IN BAKER'S YEAST OF SACCHAROMYCES CEREVISAE STRAINS Led onentrtion (ppm) S. erevisie F g ± e ± g ± f ± g ± e ± f ±0.02 S. erevisie FA ± ± ± ± ± ± ±0.08 S. erevisie FF d ± ± d ± d ± d ± ± d ±0.05 S. erevisie F e ± ± e ± d ± e ± ± ±0.01 S. erevisie F ± ± ± ± ± ± ±0.10 S. erevisie FK ± ± ± ± ± ± ±0.04 S. erevisie FC e ± d ± f ± e ± f ± d ± e ±0.06 S. erevisie FH g ± e ± h ± f ± h ± f ± g ±0.06 S. erevisie FAT f ± d ± f ± e ± f ± d ± e ±0.08 S. erevisie F ± ± d ± ± ± ± ±0.01 LSD Mens followed y different susripts within olumn re signifintly different t the 5% level. Yest strins TABLE V CONCENTRATION OF CADMIUM IN BAKER'S YEAST OF SACCHAROMYCES CEREVISAE STRAINS Cdmium onentrtion (ppm) S. erevisie F e ± ± d ± d ± e ± f ± d ±0.08 S. erevisie FA ± ± ± ± ± ± ±0.07 S. erevisie FF d ± ± ± ± ± ± ±0.07 S. erevisie F d ± ± ± ± ± ± ±0.06 S. erevisie F ± ± ± ± ± ± ±0.07 S. erevisie FK ± ± ± ± ± ± ±0.07 S. erevisie FC ± ± ± ± d ± d ± ±0.05 S. erevisie FH e ± ± d ± d ± e ± f ± d ±0.05 S. erevisie FAT e ± ± ± ± e ± e ± ±0.05 S. erevisie F ± ± ± ± ± ± ±0.04 LSD Mens followed y different susripts within olumn re signifintly different t the 5% level. 99

8 Also, it n e notied tht S. erevise strins hd the lowest vlues of P nd Cd, they themselves strins hd the highest resistne to P nd Cd. They demonstrte tht, the resistnt of S. erevise strins to metls my e return to relevnt role of ell wll in ell protetion ginst entry of metls. Mny studies reported tht hevy metl toxiity ws usully relted to the intrellulr hevy metl onentrtion, nd the hevy metl tolerne ws improved or redued y wekening or enhning hevy metl ioumultion [22]- [24]. In ddition, [25] reported tht the highest onentrtions of hevy metls y yest (Yrrowi lipolyti) were found in the ell wll nd memrne deris while the lowest onentrtions were deteted in the ytoplsm. IV. CONCLUSION From the previous presenttion of the results, it n e found tht presene of P or Cd metls in the growth medi of S. erevisie strins t onentrtions rnged etween 0 to 24 ppm for P nd 0 to 10 ppm for Cd hd negtive effet on the yield, totl vile ells nd gssing power t ll pplied onentrtions. This is euse P nd Cd re non essentil metls for iologil funtion of the yest nd they re strong inhiitors of its metolism. In ddition, the growth medi must e free from P nd Cd s they inhiited the tivity nd the growth of ker's yest t ny onentrtions. Generlly, higher onentrtions of metls used higher inhiition nd the effet of metl ions on yest growth depended on speies nd onentrtion of metl s well s yest strin. Results revel lso ontrry reltionship etween resistnt of S. erevisie strins nd metl onentrtion in produed ker's yest. The S. erevisie FH-620 strin followed y S. erevisie F-707 strin, then S. erevisie FAT-12 strin hd the highest resistne to P nd Cd, t the sme time, hd the lowest vlues of P nd Cd onentrtions in produed ker's yest. ACKNOWLEDGMENT This work ws finnilly supported y the Ntionl Reserh Center, Dokki, Ciro, Egypt. The uthors would like to thnk Dr. Mohmed Bedir, Esm Adel-Ftth nd Mohmed Rmdn for their kind help nd support. REFERENCES [1] W. Dmtew. 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