Ghosh Saptarshi, Bouvaine Sophie, Maruthi M N
Natural Resources Institute, University of Greenwich, Chatham, ME4 4 TB, Kent, UK.
BMC Microbiol. 2015 May 2;15:93. doi: 10.1186/s12866-015-0425-5.
Cassava provides over half of the dietary requirement for more than 200 million poor in Africa. In recent years, cassava has been affected by an epidemic of a virus disease called cassava brown streak disease (CBSD) that is spreading in much of eastern and central Africa, affecting food security and the economic development of the poor. The viruses that cause CBSD are transmitted by the insect vector whitefly (Bemisia tabaci), which have increased to very high numbers in some African countries. Strains of endosymbiotic bacteria infecting whiteflies have been reported to interact specifically with different whitefly populations with varied effects on its host biology and efficiency of virus transmission. The main aim of this study was therefore to investigate the prevalence and diversity of the secondary endosymbiotic bacteria infecting cassava whiteflies with a view to better understand their role on insect population dynamics and virus disease epidemics.
The genetic diversity of field-collected whitefly from Tanzania, Malawi, Uganda and Nigeria was determined by mitochondrial DNA based phylogeny and restriction fragment length polymorphism. Cassava in these countries was infected with five whitefly populations, and each one was infected with different endosymbiotic bacteria. Incidences of Arsenophonus, Rickettsia, Wolbachia and Cardinium varied amongst the populations. Wolbachia was the most predominant symbiont with infection levels varying from 21 to 97%. Infection levels of Arsenophonus varied from 17 to 64% and that of Rickettsia was 0 to 53%. Hamiltonella and Fritschea were absent in all the samples. Multiple locus sequence typing identified four different strains of Wolbachia infecting cassava whiteflies. A common strain of Wolbachia infected the whitefly population Sub-Saharan Africa 1-subgroup 1 (SSA1-SG1) and SSA1-SG2, while others were infected with different strains. Phylogeny based on 16S rDNA of Rickettsia and 23S rDNA of Arsenophonus also identified distinct strains.
Genetically diverse bacteria infect cassava whiteflies in Africa with varied prevalence across different host populations, which may affect their whitefly biology. Further studies are required to investigate the role of endosymbionts to better understand the whitefly population dynamics.
木薯为非洲2亿多贫困人口提供了一半以上的膳食需求。近年来，木薯受到一种名为木薯褐色条纹病（CBSD）的病毒病流行的影响，该病正在非洲东部和中部的大部分地区蔓延，影响粮食安全和贫困人口的经济发展。引发CBSD的病毒通过昆虫媒介烟粉虱（Bemisia tabaci）传播，在一些非洲国家，烟粉虱数量已增至极高水平。据报道，感染烟粉虱的内共生菌菌株与不同的烟粉虱种群存在特异性相互作用，对其宿主生物学特性和病毒传播效率有不同影响。因此，本研究的主要目的是调查感染木薯烟粉虱的次生内共生菌的流行情况和多样性，以便更好地了解它们在昆虫种群动态和病毒病流行中的作用。
通过基于线粒体DNA的系统发育和限制性片段长度多态性，确定了从坦桑尼亚、马拉维、乌干达和尼日利亚田间采集的烟粉虱的遗传多样性。这些国家的木薯受到五个烟粉虱种群的感染，每个种群都感染了不同的内共生菌。不同种群中，嗜菌共生体属（Arsenophonus）、立克次氏体属（Rickettsia）、沃尔巴克氏体属（Wolbachia）和卡丁氏体属（Cardinium）的感染率各不相同。沃尔巴克氏体是最主要的共生菌，感染水平在21%至97%之间变化。嗜菌共生体属的感染水平在17%至64%之间，立克次氏体的感染率为0至53%。所有样本中均未检测到汉密尔顿菌属（Hamiltonella）和弗里茨菌属（Fritschea）。多位点序列分型鉴定出感染木薯烟粉虱的四种不同的沃尔巴克氏体菌株。一种常见的沃尔巴克氏体菌株感染了撒哈拉以南非洲1亚组1（SSA1-SG1）和SSA1-SG2烟粉虱种群，而其他种群感染的是不同菌株。基于立克次氏体16S rDNA和嗜菌共生体属23S rDNA的系统发育分析也鉴定出了不同的菌株。
基因多样化的细菌感染非洲的木薯烟粉虱，不同宿主种群中的流行率各不相同，这可能会影响烟粉虱的生物学特性。需要进一步研究内共生菌的作用，以更好地了解烟粉虱的种群动态。
