我国黄曲霉遗传多样性与产毒特性

Genetic diversity and toxin-producing characters of Aspergillus flavus from China

黄曲霉(Aspergillus flavus)是一种广泛分布的腐生真菌,是黄曲霉毒素B(aflatoxin B,AFB)和圆弧偶氮酸(cyclopiazonic acid,CPA)的主要产生菌,也是动植物的条件致病菌。全球的玉米、花生和棉籽均不同程度地遭到黄曲霉及其毒素的污染。黄曲霉菌株间在形态学、遗传学和产毒特性上变异较大,且其居群遗传结构也尚不明确。为了揭示黄曲霉居群遗传结构及其产毒素特性的规律,本研究选取了从我国26省区(包括大小兴安岭)不同环境中分离的黄曲霉88株,结合模式菌株和国际权威菌株9株,基于钙调蛋白基因(Ca M)和β-微管蛋白基因(ben A)进行多基因序列分型(multi-locus sequence typing,MLST),使用MEGA 6.0和Structure 2.3.4软件进行系统发育学分析和居群结构推导,并结合菌株的产毒特性(AFB和CPA)进行比较分析。结果显示本研究的97株黄曲霉可分为3个居群,即黄曲霉居群I、黄曲霉居群II和米曲霉居群,该97株黄曲霉共有17个序列型(sequence type,ST),其中我国的88株菌分布于15个序列型。米曲霉居群均不产AFB,黄曲霉居群Ⅰ和Ⅱ的菌株绝大多数都产AFB和CPA,其产毒特性只具有菌株特异性,与居群和序列型无关。黄曲霉菌株产毒特性与地理分布或农作物类型间存在一定关系。我国东北玉米产区、西北干旱棉花产区和南方花生产区的黄曲霉居群Ⅰ和Ⅱ菌株均产AFB和CPA,我国青海可可西里和四川阿坝地区的黄曲霉仅产CPA而不产AFB,不产AFB的米曲霉居群大部分来自我国气候和地理环境多样的华北地区,该地区也是我国农村传统酿造黄豆酱的地区。

Aspergillus flavus is commonly regarded as a kind of saprophytic fungi with a wide distribution.It is the major aflatoxin B(AFB)and cyclopiazonic acid(CPA)producing species,as well as a pathogen to humans and animals.In the world,huge amounts of corns,peanuts and cotton seeds are vulnerable to be contaminated by A.flavus and aflatoxin each year.There is much variance in morphological,genetic and toxin-producing characters among isolates of A.flavus,resulting in its ambiguous population structure.In this paper,we analyzed 88 isolates of A.flavus from different environments of 26 provinces(including the Greater and Lesser Khinggan Mountains)in China,as well as nine ex-types and authentic strains based on CaM and benA sequences to infer their sequence types(STs)using multi-locus sequence typing(MLST),and their phylogenetic relationships and population structures employing MEGA 6.0 and Structure 2.3.4 softwares,together with their toxin-producing features(AFB and CPA).Our results showed that the 88 Chinese isolates and nine ex-type and authentic strains were distributed in three populations,i.e.A.flavus populationⅠ,A.flavus populationⅡand population A.oryzae.There were 17 STs among the 97 isolates,among which the 88 strains from China were distributed in 15 STs.All isolates of population A.oryzae did not produce AFB,but most isolates of the A.flavus populationsⅠandⅡproduced AFB and CPA.The toxin-producing features were strain-specific,but not correlated to sequence types or populations.Some correlations between toxin-producing characters and geographical environments or crop types were recognized.The isolates of A.flavus populationsⅠandⅡfrom the northeast areas planting corns,the arid northwest planting cottons and the south areas growing peanuts all produced AFB and CPA.The isolates from Hoh Xil of Qinghai and Aba of Sichuan did not produce AFB,though with the production of CPA.The isolates of A.oryzae population without AFB production were almost from North China with diverse climates and geographical environments,where the traditional Chinese soybean paste is made in the rural areas.