Metarhizium anisopliae lipolytic activity plays a pivotal role in Rhipicephalus (Boophilus) microplus infection

Lipases secreted by Metarhizium anisopliae, an important biological control agent, could potentially be involved in the host infection process. Here, we present the activity profile during the host infection process and the effect of lipase activity inhibitor ebelactone B on infection. The previous treatment of spores with lipase activity inhibitor, ebelactone B, completely inhibited lipolytic activity and prevented the infection of the Rhipicephalus (Boophilus) microplus host. The results herein presented prove, for the first time, the importance of lipase activity in M. anisopliae host infection process. The filamentous fungus Metarhizium anisopliae is one of the most important and studied biological agents for the control of several arthropod pests, including the cattle tick Rhipicephalus (Boophilus) microplus. Lipases secreted by M. anisopliae could potentially be involved in the host infection process. This work presents the activity profile during the host infection process and the effect of lipase activity inhibitor ebelactone B on infection. During the course of tick exposure to spores (6-120 h) lipase activity increased from 0.03 ± 0.00 U to 0.312 ± 0.068 U using rho NP palmitate as substrate. In zymograms, bands of lipase activity were detected in ticks treated with spores without inhibitor. The previous treatment of spores with lipase activity inhibitor, ebelactone B, completely inhibited lipolytic activity, at all times specified, and prevented the infection of the R. microplus host. Spores treated with the inhibitor did not germinate on the tick, although this effect was not observed in the culture medium. The results herein presented prove, for the first time, the importance of lipase activity in M. anisopliae host infection process.     

Bystander CD4 T-cell death is inhibited by broadly neutralizing anti-HIV antibodies only at levels blocking cell-to-cell viral transmission

The progressive loss of CD4+ T cells during HIV infection of lymphoid tissues involves both the apoptotic death of activated and productively infected CD4 T cells and the pyroptotic death of large numbers of resting and abortively infected bystander CD4 T cells. HIV spreads both through cellular release of virions and cell-to-cell transmission involving the formation of virological synapses. Cell-to-cell transmission results in high-level transfer of large quantities of virions to the target cell exceeding that achieved with cell-free virions. Broadly neutralizing anti-HIV antibodies (bNAbs) binding to HIV envelope protein capably block cell-free virus spread, and when added at higher concentrations can also interdict cell-to-cell transmission. Exploiting these distinct dose–response differences, we now show that four different bNAbs block the pyroptotic death of bystander cells, but only when added at concentrations sufficient to block cell-to-cell transmission. These findings further support the conclusion that HIV killing of abortively infected bystander CD4 T cells requires cell-to-cell transfer of virions. As bNAbs attract more interest as potential therapeutics, it will be important to consider the higher concentrations of these antibodies required to block the inflammatory death of bystander CD4 T cells.     

Structure analysis of the extracellular domain reveals disulfide bond forming-protein properties of Mycobacterium tuberculosis Rv2969c

Disulfide bond-forming (Dsb) protein is a bacterial periplasmic protein that is essential for the correct folding and disulfide bond formation of secreted or cell wallassociated proteins. DsbA introduces disulfide bonds into folding proteins, and is re-oxidized through interaction with its redox partner DsbB. Mycobacterium tuberculosis, a Gram-positive bacterium, expresses a DsbA-like protein ( Rv2969c), an extracellular protein that has its Nterminus anchored in the cell membrane. Since Rv2969c is an essential gene, crucial for disulfide bond formation, research of DsbA may provide a target of a new class of anti-bacterial drugs for treatment of M.tuberculosis infection. In the present work, the crystal structures of theextracellular region of Rv2969c (Mtb DsbA) were determined in both its reduced and oxidized states. The overall structure of Mtb DsbA can be divided into two domains: a classical thioredoxin-like domain with a typical CXXC active site, and an α-helical domain. It largely resembles its Escherichiacoli homologue EcDsbA, however, it possesses a truncated binding groove; in addition, its active site is surrounded by an acidic, rather than hydrophobic surface. In our oxidoreductase activity assay, Mtb DsbA exhibited a different substrate specificity when compared to EcDsbA. Moreover, structural analysis revealed a second disulfide bond in Mtb DsbA, which is rare in the previously reported DsbA structures, and is assumed to contribute to the overall stability of Mtb DsbA. To investigate the disulphide formation pathway in M.tuberculosis, we modeled Mtb Vitamin K epoxide reductase (Mtb VKOR), a binding partner of Mtb DsbA, to Mtb DsbA.     

Black box of phage–bacterium interactions: exploring alternative phage infection strategies

The canonical lytic–lysogenic binary has been challenged in recent years, as more evidence has emerged on alternative bacteriophage infection strategies. These infection modes are little studied, and yet they appear to be more abundant and ubiquitous in nature than previously recognized, and can play a significant role in the ecology and evolution of their bacterial hosts. In this review, we discuss the extent, causes and consequences of alternative phage lifestyles, and clarify conceptual and terminological confusion to facilitate research progress. We propose distinct definitions for the terms ‘pseudolysogeny’ and ‘productive or non-productive chronic infection’, and distinguish them from the carrier state life cycle, which describes a population-level phenomenon. Our review also finds that phages may change their infection modes in response to environmental conditions or the physiological state of the host cell. We outline known molecular mechanisms underlying the alternative phage–host interactions, including specific genetic pathways and their considerable biotechnological potential. Moreover, we discuss potential implications of the alternative phage lifestyles for microbial biology and ecosystem functioning, as well as applied topics such as phage therapy.     

白背飞虱中的Wolbachia和Cardinium双重感染特性

为了明确自然种群白背飞虱Sogatella furcifera中Wolbachia和Cardinium的感染情况以及Wolbachia与其特有的WO噬菌体之间的关系, 以采自中国7个省区9个地点的白背飞虱为研究材料, 运用PCR检测的方法调查了Wolbachia, Cardinium以及WO噬菌体在各飞虱种群中的感染率和组织分布特点。结果表明： 白背飞虱广泛双重感染Wolbachia和Cardinium, 并且都表现出很高的感染率。白背飞虱各种群Cardinium的感染率几乎均为100%; Wolbachia的感染率也较高, 但雌雄虫感染率差异较大, 雌虫的感染率几乎均为100％, 而雄虫的感染率从22.2%~95.0%不等。另外, 通过不同DNA聚合酶、 不同提取方法的对比, 揭示了DNA粗提样品在基于PCR技术的胞内共生菌检测中的不足之处。对白背飞虱头部、 胸部、 腹部、 足和翅5个不同部位组织的检测结果表明, 不仅在含有生殖组织的腹部有这两类共生菌的感染, 在其他非生殖组织中同样也感染了这两类共生菌; 虽然Wolbachia和Cardinium在寄主的各个组织中均有分布, 但是两者在白背飞虱成虫（尤其是雄虫）阶段的动态变化有明显的差异。进一步对Wolbachia宿主特异性WO噬菌体的检测结果表明, 自然种群雄虫中Wolbachia的感染率与不感染个体中WO噬菌体的比率呈明显的负相关。因此推测, 雄虫中Wolbachia感染率相对较低的原因可能是由于Wolbachia基因组中溶原性的WO噬菌体受到某种因素的诱导已转化为裂解性噬菌体。研究结果为进一步揭示Wolbachia和Cardinium双重感染条件下对寄主的生殖调控作用及其机制、 垂直传播规律、 两者之间的相互关系以及进一步的应用研究等方面提供了重要的理论基础。     

福建红树林植物丛枝菌根侵染研究

2010年5月和12月,对福建沿海3个红树林生长区(洛阳江、九龙江口、漳江口)的红树林植物丛枝菌根（AM）侵染状况进行研究。结果表明：（1）红树林生长区中6种植物根内均发现AMF侵染结构,其中桐花树、秋茄、鱼藤和芦苇的丛枝为Arum（疆南星）型;（2）6种植物的丛枝菌根侵染率差异较大,老鼠簕的侵染率最高,鱼藤最低;（3）桐花树和秋茄的丛枝菌根侵染率呈显著差异,而其在不同生长区之间无差异;（4）桐花树和秋茄的丛枝菌根侵染率在不同时间呈显著差异,而钝草的丛枝菌根侵染率在不同时间的差异不显著。     

Neopterin and oxidative stress markers in the diagnosis of extrapulmonary tuberculosis

Background: Extrapulmonary tuberculosis (EPTB) often presents with nonspecific signs and symptoms. Further the paucibacillary nature of extrapulmonary specimens and irregular distribution of bacilli lower the sensitivity of conventional diagnostic methods making EPTB, a diagnostic dilemma.

Objective: To study neopterin, protein carbonyl and malondialdehyde (MDA) in EPTB.

Methods: Sixty nine clinically confirmed cases with an equal number of age and sex matched healthy controls were enrolled. Ziehl–Neelsen staining for acid fast bacilli and culture on Lowenstein–Jensen medium were performed on all the extrapulmonary specimens. Serum neopterin and protein carbonyl levels were estimated using commercial ELISA kits. Malondialdehyde was determined by measuring thiobarbituric acid reactive substances.

Results: Serum neopterin, protein carbonyl and MDA levels were significantly discriminative for cases of EPTB from healthy controls (p?<?0.05). Levels of all the three biomarkers under study significantly differed between culture as well as smear positive and negative cases. A positive correlation between neopterin and protein carbonyl was seen among the cases.

Conclusions: So far few studies have integrated combination of validated host biomarkers for active disease in EPTB. Our study suggests the potential diagnostic role of neopterin, protein carbonyl and MDA in EPTB.