浙江大学学报(农业与生命科学版)  2016, Vol. 42 Issue (4): 485-494
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利用味精废液发酵枯草芽孢杆菌的培养基配方优化[PDF全文]
刘丽1,2, 曾真1, 方萍1,3    
1. 浙江大学环境与资源学院,污染环境修复与生态健康教育部重点实验室,杭州 310058;
2. 贵州大学农学院农业资源与环境系,贵阳 550025;
3. 浙江大学环境与资源学院,浙江省亚热带土壤与植物营养重点研究实验室,杭州 310058
摘要: 以营养肉汤(nutrient broth,NB)培养基为对照,通过对比试验、正交试验和单因素试验,对以味精废液为主要营养源的摇瓶培养的枯草芽孢杆菌F-2培养基配方及培养条件进行优化,以提高F-2发酵液的活菌密度并实现味精废液的资源化利用。对比试验表明,用12.5 g/L浓缩味精废液(concentrated monosodium glutamate wastewater,CMGW)培养的F-2菌悬液的 D (600 nm)值及活菌密度显著高于NB培养基,其培养F-2后的氨基酸含量显著降低。通过L16(43×26)正交试验筛选出F-2的优化配方为CMGW 12.5 g/L,牛肉膏1.0 g/L,蛋白胨4.0 g/L,MnSO4 · 2H2O 0.5 g/L,H3BO3 0.02 g/L,FeSO4 · 7H2O 0.1 g/L,MgSO4 · 7H2O 0.5 g/L。按此优化配方接种培养F-2菌株,其菌液的活菌密度分别是未经优化的CMGW培养基和NB培养基的2.9倍和6.3倍。 通过单因素试验,筛选出基于该优化配方的F-2菌株适宜的初始pH范围为6.5~7.5,适宜的培养温度为30~35 ℃。 以上结果显示,培养基CMGW对菌株F-2的发酵效果优于NB培养基,其优化配方的效果更佳
关键词: 浓缩味精废液    枯草芽孢杆菌    正交试验设计    培养基优化    氨基酸    
Optimization of a culture medium for Bacillus subtilis based on monosodium glutamate wastewater
LIU Li1,2, ZENG Zhen1, FANG Ping1,3    
1. Key Laboratory of Environment Remediation and Ecological Health of the Ministry of Education, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China;
2. Department of Agricultural Resource and Environment, College of Agriculture, Guizhou University, Guiyang 550025, China;
3. Zhejiang Provincial Key Laboratory of Subtropical Soil and Plant Nutrition, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China
Summary: Concentrated monosodium glutamate wastewater (CMGW) generated from the production of monosodium glutamate is an organic wastewater with high concentration of ammonia, chemical oxygen demand, biochemical oxygen demand and SO2-4 and low pH. Discharge of CMGW has raised serious environmental problems, and potential secondary pollution existed even treated with traditional physical and chemical processes. It has already been reported that the richness of nitrogen and carbon makes the recycling of this wastewater possible in the way of microbial fermentation as medium. However, the differences of strain and fermentation purpose require that the medium contains different nutritional compositions with a certain dosage. Bacillus subtilis F-2, isolated from a commercial organic fertilizer, can inhibit the growth of 18 plant pathogenic fungi with varying degrees, especially in F.oxysoporum f.sp niweum with inhibition rate of 93%, which reveal the potential to prepare bio-organic fertilizer under biocontrol. In addition, F-2 also plays an important role in decomposition of organic waste. The study on degradation of food waste has pointed to its dominance in microbial community. Therefore, F-2 as a prospective functional bacteria in agriculture and environment, it is necessary to improve F-2 viable cell production as much as possible. Massive studies were focused on medium optimization of B. subtilis to enhance its cell density in fermentation liquor. However, the main ingredients of medium used in most of these studies were peptone, yeast extracts, beef extracts, soy or corn flour, associated with great cost and excessive consumption of resources. The purpose of this study was to investigate a cost-effective resource utilization of CMGW by increasing the density of B. subtilis F-2 viable cells in cultures. The CMGW medium which was 80-fold diluent of the wastewater, i.e. , 12.5 g/L CMGW, was served as the main carbon and nitrogen sources of strain F-2. Contrast experiments of shaking cultures, orthogonal and single factor experiments were applied to find the optimal CMGW medium formula and its culturing condition. The contrast experiments showed that the D (600 nm) value of F-2 suspension and viable cell density of the CMGW medium was significantly higher than that of nutrient broth (NB) medium, and the amino acid content in the CMGW medium decreased significantly after culturing. The optimal formula identifying F-2 by the orthogonal experiment of L16 (43×26) was as follows: 12.5 g/L CMGW, 1.0 g/L beef extracts, 4.0 g/L peptone, 0.5 g/L MnSO4 · 2H2O, 0.02 g/L H3BO3, 0.1 g/L FeSO4 · 7H2O and 0.5 g/L MgSO4 · 7H2O. The viable cell density in the optimized CMGW medium was 2.9 and 6.3 times of the CMGW medium and NB medium, respectively. Furthermore, according to the results of single factor experiment, the proper initial pH and culturing temperature of the optimized CMGW medium were screened as pH 6.5-7.5 and 30-35 ℃. In conclusion, the CMGW medium is an ideal substitute for NB medium in the fermentation of B. subtilis F-2, providing a practicable and promising approach to reuse and recover CMGW. Moreover, the CMGW medium is superior to NB medium, and the fermentation effect is even better after the medium and culturing condition are optimized.
Key words: concentrated monosodium glutamate wastewater (CMGW)    Bacillus subtilis    orthogonal experiment design    medium optimization    amino acid    

味精废液是在味精生产中通过离子交换法提取谷氨酸后剩余的离交尾液,属于高氨氮、高化学需氧量、高生化需氧量、高SO2-4、低pH的有机发酵废水[1-2]。我国是味精生产和消费大国,从2006年开始年产量均超过170万t,占世界总产量的50%以上[2]。而每生产1 t味精会排放浓缩味精废液15~20 t以上[3]。该类废水直接排放将严重污染环境,而采取常用的物理化学方法(如絮凝沉淀、膜分离法等)[4]处置则能耗大,费用高,还可能造成二次污染,因此,处置难度大。然而,味精废液含有大量碳、氮及多种氨基酸,已有不少研究者将其作为微生物发酵的营养源实现了该废水的资源化利用,开辟了一条解决味精废液处理难题的理想途径,如:GU等[5]以味精废液为培养基的氮源发酵多粘类芽孢杆菌( Paenibacillus polymyxa)EBL-06;BAI等[6]在果胶酶生产中利用味精废液作为固体发酵培养基的氮源和水源发酵黑曲霉(Aspergillus niger);XUE等[7]和LIU等[8]分别以味精废液为培养基发酵黏红酵母菌(Rhodotorula glutinis)和斯达油脂酵母菌(Lipomyces starkeyi)获取生物柴油前体生物油脂。一般认为,味精废液氮含量较高,在研究应用中常常添加适量的碳源,如马铃薯淀粉废液[5]、甜菜渣[6]、葡萄糖[7-8]等,以满足微生物的生长需求。此外,微生物菌株不同、发酵目的不同对培养基的营养组成要求也不尽相同,因此,以味精废液为主要营养源的培养基配方有必要针对不同菌株和目的等进行优化。

枯草芽孢杆菌(Bacillus subtilis)是一种嗜温、好氧、产芽孢的革兰氏阳性杆状细菌,具有促进作物生长[9-11]、抑制植物病原菌[12-14]、加快畜禽粪便及日常生活废弃物堆肥的腐熟进程等功能[15-17],是用于制备有机废弃物堆肥发酵菌剂[16]或生物有机肥的重要功能菌[17]。关于通过优化枯草芽孢杆菌培养基以提高发酵的活菌密度的研究报道较多[18-20],但大多以蛋白胨、酵母膏、牛肉膏或大豆粉、玉米粉等为主料,生产成本较高且需要消耗大量资源[21]。鉴于此,本研究以营养肉汤(nutrient broth,NB)培养基为对照,通过一系列摇瓶培养试验,对以浓缩味精废液为主要营养源的枯草芽孢杆菌F-2液体发酵培养基配方进行优化研究,以达到提高F-2菌株发酵的活菌密度、降低微生物菌剂的生产成本并实现废弃物资源化利用的目的。

1 材料与方法 1.1 供试材料

供试菌株为枯草芽孢杆菌F-2,由本研究室自某商品有机肥中分离、筛选获得,经中国普通微生物菌种保藏管理中心鉴定并保藏,保藏号为CGMCC No.3882。该菌株能产生抗真菌物质丰原素(fengycin)[22],对18种植物病原真菌具有不同程度的拮抗作用,对西瓜枯萎病菌 (Fusarium oxysporum f. sp. niveum)的抑制率高达93%。

浓缩味精废液(concentrated monosodium glutamate wastewater,CMGW)为味精废液的蒸发浓缩液(由安徽环宇肥料有限公司提供),pH 3.1,电导率33.2mS/cm;营养元素含量分别为全碳25.5%,全氮5.13%,全钾2.07%,全磷0.16%,钠5.51%,硫15.1%,铁0.26 g/kg,钙0.62 g/kg,镁0.93 g/kg,钼9.17 g/kg,锌2.16 mg/kg,铜2.54 mg/kg,镍2.29 mg/kg;其他重金属含量见表 1,均低于城镇垃圾农用控制标准[23]

表1 浓缩味精废液中重金属含量及控制标准 Table 1 Heavy metal contents in concentrated monosodium glutamate wastewater (CMGW) and its control standard
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1.2 培养基

NB培养基:牛肉膏 3.0g,蛋白胨10.0 g,NaCl 5.0 g,加水至1 000 mL,pH 7.0;1×105 Pa灭菌30 min。

NB固体培养基:在NB培养基的基础上加入琼脂20.0g;1×105 Pa灭菌30 min。

CMGW培养基:CMGW12.5g,加水稀释至1 000 mL,pH 7.0;1×105 Pa灭菌30 min。

1.3 F-2种子菌液制备

取1环F-2斜面菌苔于NB固体培养基平板上划线,在30 ℃恒温培养箱中培养24 h后挑取单菌落接种于NB培养基中,于30 ℃、150 r/min下 振荡培养18 h(经前期F-2生长曲线测定试验确定),获得F-2种子菌液。

1.4 试验设计 1.4.1 CMGW和NB培养基对F-2培养对比试验

按1%接种量分别接种F-2种子菌液于CMGW培养基和NB培养基中,每种培养基处理各重复5次,于30 ℃、150 r/min下振荡培养18 h,观察2种培养基培养F-2后菌悬液浓度及活菌密度。

1.4.2 基于CMGW的F-2菌株培养基配方优化试验

采用L16(43×26)正交设计对CMGW培养基配方进行优化,试验方案详见表 2,并以NB培养基为对照,共17个处理。各处理培养液的pH均调至7.0,分别取100 mL分装于规格为250 mL的盐水瓶中,1×105 Pa灭菌30 min;冷却后,接种1% F-2 种子液,每处理重复3次,于30 ℃、150 r/min下振荡培养18 h。根据正交试验结果获得各试验因子的优选水平。

表2 L16(43×26)正交设计试验方案 Table 2 Design of L16(43×26) orthogonal array experiments
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1.4.3 基于优化配方的F-2培养条件优选试验

以1.4.2节所筛选的优化配方对菌株F-2进行不同培养基初始pH(6.0、6.5、7.0、7.5、8.0)和不同培养温度(25、30、35、40 ℃)的振荡培养试验。各处理的F-2种子液接种量均为1%,并在150 r/min下振荡培养18 h。其中,不同初始pH试验的培养温度为30 ℃,不同培养温度试验的培养基初始pH为优选确定的初始pH。各处理重复3次。

1.5 测定项目与方法 1.5.1 菌悬液细胞浓度测定

在一定浓度范围内,菌悬液的细胞浓度与其浊度即光密度成正比[24]80-84。以各培养基的原液为空白,采用紫外可见分光光度计(PerkinElmer Lambda 35,美国)测定在600 nm处相应处理培养终止时的菌悬液光密度值,记作 D (600 nm),用以表示该菌悬液的细胞浓度。

1.5.2 培养液活菌密度测定

采用平板菌落计数法统计相关处理培养液的活菌数[24]327-333

1.5.3 总碳和总氮测定

采用碳氮分析仪(Analytik Jean multi N/C 3100,德国)测定培养液的总碳和总氮,并计算碳氮比(C/N)。

1.5.4 氨基酸测定

取1.000g培养液样品于25 mL刻度试管中,加6 mol/L盐酸10 mL,抽真空密封后,于110 ℃水解24 h,定容到25 mL。取上清液0.5 mL,于70 ℃以下旋转蒸发仪上浓缩干燥后加2 mL 0.022 mol/L稀盐酸,完全溶解后过0.225 μm水相滤膜。滤液采用全自动氨基酸分析仪(HITCHI L-8900,日本)测定氨基酸含量。

1.6 数据分析

试验数据采用Excel 2010整理并作图,利用DPS 14.5软件[25]进行单因素试验和正交试验结果的方差分析。

2 结果与分析 2.1 枯草芽孢杆菌F-2在CMGW与NB培养基中的生长量比较

图 1所示,振荡培养18 h后,CMGW培养基中F-2菌液的 D (600 nm)值显著高于NB培养基(P =0.0003)。通过平板计数测得活菌密度,前者为1.55×108 CFU/mL,后者为7.10×107 CFU/mL,两者相差1倍以上。可见,以供试浓缩味精废液的80倍水稀释液(CMGW 12.5 g/L)培养F-2菌株的效果优于常规NB培养基。

短栅上的不同大写字母表示在 P <0.01水平差异有统计学意义 Different capital letters above bars represent statistically significant differences at the 0.01 probability level. 图1 CMGW与NB培养基中F-2菌悬液的 D (600 nm)值比较 Fig. 1 Comparison of D (600 nm) values of F-2 suspension in CMGW and NB media
2.2 CMGW培养基与NB培养基的碳、氮源比较

作为微生物细胞的基本构成物质,碳源和氮源在微生物生长繁殖过程中有着至关重要的作用[24]80-84。CMGW与NB培养基的总碳和总氮含量如图 2所示,氨基酸组分含量如图 3所示。尽管CMGW的总碳、总氮及总氨基酸含量均显著低于NB,分别为后者的55.9%、36.9%和48.9%,且除 γ -氨基丁酸(G-ABA)外,各氨基酸组分含量也均低于NB培养基,但CMGW的碳氮比(C/N)(4.97)显著高于NB(3.28)(P =0.008),且F-2菌株在CMGW中的生长优于NB。这说明供试的CMGW的80倍水稀释液所提供的总碳源、总氮源及氨基酸能够满足F-2生长之需。

短栅上的不同小写字母表示在P <0.05水平差异有统计学意义。 Different lowercase letters above bars represent statistically significant differences between CMGW and NB media treatments at the 0.05 probability level. 图2 CMGW与NB培养基的总碳和总氮含量比较 Fig. 2 Comparisons of total carbon (TC) and total nitrogen (TN) contents in CMGW and NB media

图3 CMGW与NB培养基的氨基酸组分含量比较 Fig. 3 Comparisons of amino acid contents in CMGW and NB media

进一步分析CMGW培养基在培养F-2前后的氨基酸组分及总量变化,结果表明:培养F-2后氨基酸总量较培养前显著降低(P =0.000 4)(图 4),降低率达12%;除半胱氨酸(Cys)有所上升外,其余氨基酸组分均不同程度地降低,其中谷氨酸(Glu)降低了129.6 mg/L,天冬氨酸(Asp)、甘氨酸(Gly)和丙氨酸(Ala)也都至少降低了51.5 mg/L(图 5)。可见,在味精废液中丰富的 氨基酸可作为氮源或生长因子为F-2所利用,同时在F-2的代谢过程中可能还产生了半胱氨酸(Cys)。

短栅上的不同大写字母表示在P <0.01水平差异有统计学意义。 Different capital letters above bars represent statistically significant differences at the 0.01 probability level. 图4 培养 F-2前后CMGW培养基的氨基酸总量比较 Fig. 4 Comparison of total amino acid contents in CMGW medium before and after culturing F-2

图5 CMGW培养基的氨基酸组分在培养F-2后的减少量 Fig. 5 Reduction amount of amino acids in CMGW medium after culturing F-2

上述结果表明,CMGW培养基的碳源和氮源总量、C/N及氨基酸组分及含量可满足F-2生长繁殖的需求,但均与NB培养基有一定差别,若对其组分作适当改进可望进一步提高F-2菌液的菌体密度。

2.3 基于CMGW的F-2培养基配方优化

方差分析结果表明,F-2菌悬液 D (600 nm)值在L16(43×26)正交试验的16个处理组合(1~16)及NB(17)处理间差异显著(图 6),除处理4、8、9、10和13外,其余处理的 D (600 nm)值均显著高于NB,其中处理11最高,其平板计数的活菌密度为3.55×108 CFU/mL,比前述未经优化的CMGW培养基的活菌密度提高了1.3倍,比NB培养基提高了4.0倍。

处理(1~16)的配方方案详见表 2;处理17为NB培养基。短栅上的不同小写字母表示在P <0.05水平差异有统计学意义。 Please see Table 2 for the details of the culture medium formula of the first 16 treatments,and the treatment 17 is NB medium. Different lowercase letters above bars represent statistically significant differences at the 0.05 probability level. 图6 L16(43×26)正交试验不同处理及NB处理的F-2菌悬液 D (600 nm)值比较 Fig. 6 Comparisons of F-2 suspension D (600 nm) values among the treatments of the orthogonal array experiments and NB medium

图 7可见,F-2菌悬液 D (600 nm)值除了在因子E(Mo)的水平间未见统计学上的显著差异外,在其余8个供试因子的水平间差异均有统计学意义(P <0.05)。其中:效应最大的因子为C,表现为 D (600 nm)值随CMGW稀释倍数的增加而降低,其优选稀释倍数为80倍(12.5g/L);其次为因子B,其 D (600 nm)值随蛋白胨用量提高呈先升后降趋势,其优选用量为4.0 g/L;因子F(Co)对 D (600 nm)值表现为负效应,其余因子均有正效应。各因子的优选水平列于表 3。按此组合配制培养基接种培养F-2,其菌液的活菌密度为4.45×108 CFU/mL,分别是正交试验中处理11、未经优化的CMGW培养基和NB培养基的1.3倍、2.9倍和6.3倍。

(A~I)表示的含义详见表 2。图中不同小写字母表示同一因子水平间在P <0.05水平差异有统计学意义 Please see Table 2 for the details of factors A to I. Different lowercase letters represent statistically significant differences among levels of the same factor at the 0.05 probability level. 图7 F-2菌悬液 D (600 nm)值在正交试验各因子水平间的比较 Fig. 7 Comparisons of D (600 nm) values of F-2 suspensions among different levels of each factor in orthogonal array experiment

表3 各正交试验因子的极差、效应显著性 P 值与优选量 Table 3 Range,P value and optimal dosage of each orthogonal array factor
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2.4 基于CMGW优化配方的F-2培养条件优选

表 3所列的各因子优选水平组合配制不同初始pH培养基对F-2进行培养,测得各pH处理下的F-2菌悬液 D (600 nm)值如图 8所示。方差分析表明,培养基初始pH对 D (600 nm)值有显著影响(P =0.045),其中在初始pH 6.5~7.5范围内 D (600 nm)值均高于1.35,显著高于pH 8的D (600 nm)值,而pH 6.0与8.0之间的差异未达统计学上的显著水平( P >0.05)。说明基于该优化配方的适宜F-2生长的初始pH范围为6.5~7.5。

短栅上的不同小写字母表示在P <0.05水平差异有统计学意义。 Different lowercase letters above bars represent statistically significant differences at the 0.05 probability level. 图8 基于CMGW优化配方的培养基初始pH对F-2生长的影响 Fig. 8 Effects of initial pH on F-2 growth cultured in optimal CMGW medium

图 9表明,在培养基优化配方及优选初始pH条件下,培养温度对F-2菌悬液的 D (600 nm)值也具有统计学上的显著影响(P =0.0006)。在供试温度范围内,D (600 nm)值呈现出先升后降的趋势,以30~35 ℃范围内 D (600 nm)值最高(均大于1.35),在25 ℃和40 ℃时 D (600 nm)值显著降低。说明基于该优化配方的F-2适宜生长的培养温度为30~35 ℃。

短栅上的不同小写字母表示在P <0.05水平差异有统计学意义。 Different lowercase letters above bars represent statistically significant differences at the 0.05 probability level. 图9 基于CMGW优化配方及优选pH的培养温度对F-2生长的影响 Fig. 9 Effects of temperatures on F-2 growth cultured in optimal CMGW medium at preferred initial pH
3 讨论

味精废液是一类难处理的食品工业有机废水,因含有多种营养物质,仍具有极高的资源化利用价值。GU等[5]研究指出,以味精废液为主要氮源,以马铃薯淀粉废液为主要碳源,可提高菌株EBL-06的发酵产量。BAI等[6]指出,以味精废液为主要氮源,以甜菜渣为主要碳源,能提高黑曲霉发酵中果胶酶和果胶裂解酶的产量。本研究表明,供试的浓缩味精废液不仅含有大量氮元素,也含有丰富的碳元素,可以为微生物提供充足的氮源和碳源;同时,该浓缩味精废液用水稀释80倍并调节pH至7.0后作为培养基对枯草芽孢杆菌F-2进行摇瓶振荡培养,培养后F-2菌悬液的 D (600 nm)值及活菌密度均显著高于对照NB培养基。说明可采用CMGW培养基代替NB培养基发酵F-2。测定CMGW与NB培养基的碳、氮源与氨基酸总量及组分含量后发现,CMGW培养基的总碳、总氮、总氨基酸含量均显著低于NB培养基,极大部分氨基酸组分含量也低于NB;然而,CMGW的C/N却显著高于NB。赵瑞[26]研究表明,高C/N更有利于枯草芽孢杆菌TU100的生长代谢。由此推测,相对于NB培养基,CMGW培养基中F-2菌悬液具有更高的 D (600 nm)值及活菌密度可能与其较高的C/N有关。进一步检测培养F-2后CMGW培养基的氨基酸组分变化发现,氨基酸总量降低12%,除半胱氨酸(Cys)外,其余氨基酸组分含量均明显降低。表明CMGW培养基的氨基酸或许为F-2的氮源和生长因子,并且通过发酵菌株F-2能有效达到资源化回收该工业废水之目的。此外,由于微生物生长受多种因素限制,尽管CMGW培养基的氨基酸大部分未被F-2利用,其氮源以外的碳源及其他营养物质、氨基酸以外的其他生长因子、矿质养分和能源等的匮乏和均衡情况以及培养条件等都会影响到发酵的活菌密度;因此,为进一步提高F-2的活菌密度,有必要对CMGW培养基的营养物质和培养条件进行优化。

考虑到CMGW培养基的营养成分低于NB培养基,适当提高碳、氮及氨基酸等含量也可能有利于提高F-2的活菌密度。但在前期研究中发现,CMGW稀释倍数越低,Na含量越高,电导率越大,F-2生长受到抑制;因此,不宜通过降低CMGW的稀释倍数来提高CMGW培养基的营养物质含量。而若提高其稀释倍数又必然会导致培养基营养成分尤其是碳、氮源的降低;因此,在提高其稀释倍数的同时有必要添加适量的碳、氮营养。牛肉膏和蛋白胨作为天然有机营养物质可同时满足在CMGW培养基优化中对碳、氮源和多种营养物质的需求。同时,为了考察在CMGW培养基的基础上添加矿质养分是否有益,本研究通过L16(43×26)正交试验,对包括CMGW稀释倍数、牛肉膏和蛋白胨添加量和6个矿质养分在内的9个正交因子的水平进行了优化。结果表明:CMGW稀释倍数对F-2菌悬液的 D (600 nm)值影响效应最大,从80倍(12.5g/L)到约300倍(3.3 g/L)范围内 D (600 nm)值随稀释倍数加大而降低,而适量添加牛肉膏和蛋白胨均有助于 D (600 nm)值的升高;在6个矿质养分因子中,Mo的营养效应不显著,Co有显著负效应,其余4个营养因子Mn、B、Fe和Mg都具有正效应。可见,在12.5 g/L CMGW培养基(即CMGW的80倍水稀释液)的基础上增大其稀释倍数不能满足F-2的生长所需,而向培养基中添加适量的牛肉膏、蛋白胨以及矿质养分如Mn、B、Fe和Mg有助于提高F-2的活菌密度。综合各因子的影响效应及用料成本,优选出基于味精废液的F-2培养基配方为CMGW 12.5 g/L,牛肉膏1.0 g/L,蛋白胨4.0 g/L,MnSO4 · 2H2O 0.5 g/L,H3BO3 0.02 g/L,FeSO4 · 7H2O 0.1 g/L,MgSO4 · 7H2O 0.5 g/L,pH 7.0。 采用该优化配方培养F-2所获得的菌悬液活菌密度达4.45×108 CFU/mL,比NB培养基提高了5.3倍。

培养基的初始pH和培养温度是影响微生物生长代谢的重要环境因子[26]。本研究结果表明,利用CMGW优化配方培养F-2,其适宜的培养基初始pH范围为 6.5~7.5,适宜的培养温度为30~35 ℃。

综上所述,供试浓缩味精废液的80倍水稀释液(CMGW 12.5 g/L)可作为枯草芽孢杆菌F-2的培养基,其培养效果优于肉汤培养基;对该培养基作进一步优化可明显提高发酵液的F-2活菌密度。因此,以味精废液作为枯草芽孢杆菌F-2的培养基可实现废弃物的资源化利用和降低菌剂生产成本的双重目的。

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