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基于ARTP和适应性进化选育高抗逆性凝结芽孢杆菌及其发酵豆粕的研究.doc
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基于ARTP和适应性进化选育高抗逆性凝结芽孢杆菌及其发酵豆粕的研究.doc
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摘 要
凝结芽孢杆菌(Bacillus coagulans)是一种兼具乳酸菌和芽孢杆菌优势的益
生菌,相比于其他菌群,其芽孢体对热、酸、碱、盐等不敏感,可经受高温加工、
胃肠道酸碱环境,有效降低染杂菌风险,目前已成为饲料领域微生态制剂的优势
菌群之一。然而,并非所有天然存在的凝结芽孢杆菌都对酸、碱、盐等压力环境
具有优良的抵抗性能。因此,在前期已成功从健康猪肠道内容物分离纯化并鉴定
出一株凝结芽孢杆菌,命名为 WT-03 的基础上,本研究利用常压室温等离子体
诱变(Atmospheric and room temperature plasma, ARTP) 结合适应性进化 (Adaptive
laboratory evolution, ALE ) 策略对其进行抗逆性能改善,筛选具备耐酸、耐胆盐
等高抗逆性的目的菌株,并从胞内微环境、细胞结构以及细胞膜层面对其抗逆性
机制进行初步探究;最后,将其用于固态发酵豆粕,优化发酵条件,对发酵前后
的营养品质进行评价。
主要研究内容有:
(1)采用 ARTP 结合适应性进化选育了耐酸、耐胆盐的高抗逆性凝结芽孢
杆菌。ARTP 最优照射时间为 15s,致死率 93.84%。利用含 0.3%(w/v)胆盐的 MRS
筛选培养基对诱变 15s 的菌体进行初筛,得到 30 株生长态势良好、菌落较大的
突变株 artp-BC1、artp-BC2……artp-BC30。之后,利用盛有 pH4.0、pH3.5 和
pH3.0 的 24 孔板液体培养基对初筛菌进行复筛,最终得到 artp-BC5、artp-BC15、
artp-BC28 三株突变株,在 pH3.0 存活率显著高于野生株,分别为 18.2%、18.8%
和 19.3%。40d 的梯度酸驯化实验显示,artp-aleBC15 在 pH2.5 存活率最大,为
19.8%;而对照菌 WT-03 仅为 7.15%。体外模拟胃肠道实验表明,artp-aleBC15、
artp-BC15 和 WT-03 最 终 存 活 率 分 别 为 20.5% 、 15.2% 和 7.98% 。 因 此 ,
artp-aleBC15 为 理 想 菌 株 , 已 存 于 中 国 工 业 微 生 物 菌 种 保 藏 中 心 , 编 号
CGMCC1.17145。
(2)从胞内微环境变化、细胞结构和细胞膜水平对凝结芽孢杆菌突变株和
野生株的耐酸性机理进行了探究。外界酸胁迫导致胞内 pH(pHi)降低,pH6.2
时,artp-aleBC15、artp-BC15 和对照组 WT-03 的 pHi 均在 7.10 左右;而 pH2.5
时,突变株 artp-aleBC15、artp-BC15 和对照株 WT-03 的 pHi 分别为 4.90、4.45
和 4.23。扫描电镜结果表明,artp-aleBC15 在 pH2.5 环境能更好的保持结构完整
性。细胞膜水平的分析显示,artp-aleBC15 能够形成更高强度的生物膜,且疏水
性增强,通透性较低;同时,酸胁迫导致细胞膜饱和脂肪酸 (Saturated fatty acid,
FA)增多、不饱和脂肪酸 (Unsaturated fatty acid, UFA) 减少、不饱和度增大。荧
光定量 PCR(qRT-PCR)分析发现,突变株 artp-aleBC15 中编码脂肪酸合成的基
因 plsX、acpP 及 fabD 表达量显著上调,分别是野生株的 6.998 倍、15.995 倍和
9.474 倍。
(3)以酸溶性蛋白含量为测定指标,优化了 B. coagulans artp-aleBC15 固态
发酵豆粕的条件,分析了豆粕发酵前后的营养品质变化。单因素及正交设计结果
表明,最优条件为:接种量 12%,料水比 1.0:1.2,发酵温度 37℃,发酵时间
72h。发酵后,豆粕中酸溶性蛋白含量由 3.285±0.690%提高到 20.438±0.550%、
粗蛋白含量由 46.774±0.242%提高到 49.125±0.486%,总酸度由 2.281±0.150 提高
到 8.457±0.260,氨基酸总量由 53.0%提高到 55.8%。SDS-PAGE 电泳图谱显示,
发酵后豆粕蛋白被充分降解,分子量<20KDa。
关键词:凝结芽孢杆菌,常压室温等离子体诱变,适应性进化,抗逆性机理,发
酵豆粕,工艺优化
Abstract
Bacillus coagulans is a probiotic with the advantages of both Lactic acid bacteria
and Bacillus. Compared with other bacteria, its spores are not sensitive to heat, acids,
alkalis, salts, etc., and can withstand high temperature processing, gastrointestinal
acid and alkali environment,which can significantly reduce the risk of contaminating
bacteria. At present, it has become one of the dominant flora in the feed field for the
preparations of microecological, However, not all B.coagulans existing in the nature
have excellent resistance to stress environments such as acids, alkali and bile salts.
Hence, the present study attempted to apply atmospheric and room temperature
plasma (ARTP) coupled with adaptive laboratory evolution (ALE) strategy for
improving the stress resistant of a B. coagulans strain WT-03 isolated and purified
from freshly slaughtered pigs, and screen for target strains with high resistance to
acids and bile salts. Moreover, The mechanism of stress resistance was preliminary
explored from the aspects of intracellular microenvironment, cell structure and cell
membrane. Finally, it was applied to solid fermented soybean meal, optimizing
fermentation conditions and evaluating the nutritional qualities before and after
fermentation.
The main research contents include:
(1) Highly resistant B. coagulans mutant having significant tolerance to acid and
bile salt were selected using ARTP and ALE. The optimal exposure time of ARTP
was 15 s, when the lethal rate reached 93.84%. Thirty of mutants with good growth
and large colonies were obtained through the MRS screening medium containing
0.3% (w/v) bile salt, which named artp-BC1, artp-BC2 ... artp-BC30. After that, the
primary screening mutant isolates were re-screened using a 24-well plate liquid
medium whose pH were 4.0, 3.5 and 3.0. Three mutants of artp-BC5, artp-BC15, and
artp-BC28 were obtained and had significantly higher survival rate than that of
wild-type strain when cultured at pH of 3.0, which were 18.2%, 18.8% and 19.3%,
respectively. A 40-day gradient acid acclimation experiment showed that
artp-aleBC15 had the highest survival rate of 19.8 % at pH 2.5,whereas B. coagulans
WT-03 only had a final survival rate of 7.15 %. In vitro simulated gastrointestinal
tract experiments demonstrated that the final survival rates of artp-aleBC15,
artp-BC15, and WT-03 were 20.5%, 15.2%, and 7.98%, respectively. Therefore,
artp-aleBC15 was chosen as the ideal strain and deposited in China General
Microbiological Culture Collection (CGMCC) with the Accession number
CGMCC1.17145.
(2) The mechanisms of acid resistance between B. coagulans mutants and the
parent strain were explored from the changes of intracellular micro-environment, cell
structure and cell membrane level.The external pH stress caused the intracellular pH
(pHi) to decrease. At pH 6.2, the pHi of artp-aleBC15, artp-BC15 and WT-03 were all
approximately 7.10; and at pH 2.5, the pHi of artp-aleBC15, artp-BC15 and
WT-03 were 4.90, 4.45 and 4.23, respectively. Scanning electron microscopy results
showed that artp-aleBC15 could maintain a better intact cell structure at pH 2.5.The
analysis of cell membrane level demonstrated that artp-aleBC15 could form a
higher-strength biofilm with enhanced hydrophobicity and lower permeability. At the
same time, acid stress resulted in reduced saturated fatty acids (FA), increased
unsaturated fatty acids (UFA), and increased unsaturation in cell membrane.
Quantitative real-time PCR (qRT-PCR) analysis revealed that the expression of plsX,
acpP and fabD, which encode fatty acid synthesis genes in the mutant strain
artp-aleBC15, was significantly up-regulated, which were 6.998 times, 15.995 times,
and 9.474 times, respectively.
(3) With the acid-soluble protein content as the measurement index, the process
conditions of B. coagulans artp-aleBC15 solid fermented soybean meal were
optimized, and changes of the nutritional quality before and after fermented were
analyzed. The results of single factor and orthogonal design showed that the optimal
conditions were: inoculation amount 12%, feed-water ratio 1.0: 1.2, fermentation
temperature 37 ° C, and fermentation time 72h. After fermentation, the acid soluble
protein in soybean meal increased from 3.285 ± 0.690% to 20.438 ± 0.550%, the
crude protein content increased from 46.774 ± 0.242% to 49.125 ± 0.486%, and the
total acidity increased from 2.281 ± 0.150 to 8.457 ± 0.260, total amino acids
increased from 53.0% to 55.8%. Moreover, SDS-PAGE electrophoresis indicated that
the protein in soybean meal was effectively degraded after fermentation, and its
molecular weight was less than 20KDa.
Key Words: Bacillus coagulans, Atmospheric and room temperature plasma,
Adaptive laboratory evolution, resistance mechanism, Fermented soybean meal,
Process Optimization.
V
缩略词表
PBS
Phosphate Buffered Solution
磷酸盐缓冲溶液
ARTP
Atmospheric And Room Temperature Plasma
常压室温等离子体诱变
ALE
Adaptive Laboratory Evolution
适应性进化
GC-MS
Gas Chromatography Mass Spectrometer
气相质谱联用
BCECF
AM
5-carboxyfluorescein, diacetoxymethyl ester
5-羧基荧光素,二乙酰甲酯
HEPES
N-2-hydroxyethylpiperazine-N-ethane-sulphonicacid
羟乙基哌秦乙硫磺酸
SEM
Scanning Electron Microscope
扫描电子显微镜
PCR
Polymerase Chain Reaction
聚合酶链式反应
ONPG
o-nitro phenyl-b-D-galactopyranoside
2-硝基苯基-β-D-吡喃半乳糖苷
qRT-PCR
Quantitative Real-time PCR
实时荧光定量聚合酶链式反应
TCA
Trichloroacetic acid
三氯乙酸
SDS-PAGE
dodecyl sulfate,sodium salt (SDS)-Polyacrylamide
gel electrophoresis
十二烷基磺酸钠-聚丙烯酰胺
凝胶电泳
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