Changing partners in an obligate symbiosis: a facultative endosymbiont can compensate for loss of the essential endosymbiont Buchnera in an aphid

Almost all aphids harbour an endosymbiotic bacterium, Buchnera aphidicola, in bacteriocytes. Buchnera synthesizes essential nutrients and supports growth and reproduction of the host. Over the long history of endosymbiosis, many essential genes have been lost from the Buchnera genome, resulting in drastic genome reduction and the inability to live outside the host cells. In turn, when deprived of Buchnera, the host aphid suffers retarded growth and sterility. Buchnera and the host aphid are often referred to as highly integrated almost inseparable mutualistic partners. However, we discovered that, even after complete elimination of Buchnera, infection with a facultative endosymbiotic gamma-proteobacterium called pea aphid secondary symbiont (PASS) enabled survival and reproduction of the pea aphid. In the Buchnera-free aphid, PASS infected the cytoplasms of bacteriocytes that normally harbour Buchnera, establishing a novel endosymbiotic system. These results indicate that PASS can compensate for the essential role of Buchnera by physiologically and cytologically taking over the symbiotic niche. By contrast, PASS negatively affected the growth and reproduction of normal host aphids by suppressing the essential symbiont Buchnera. These findings illuminate complex symbiont-symbiont and host-symbiont interactions in an endosymbiotic system, and suggest a possible evolutionary route to novel obligate endosymbiosis by way of facultative endosymbiotic associations.     

The striking case of tryptophan provision in the cedar aphid Cinara cedri

Buchnera aphidicola BCc has lost its symbiotic role as the tryptophan supplier to the aphid Cinara cedri. We report the presence of a plasmid in this endosymbiont that contains the trpEG genes. The remaining genes for the pathway (trpDCBA) are located on the chromosome of the secondary endosymbiont “Candidatus Serratia symbiotica.” Thus, we propose that a symbiotic consortium is necessary to provide tryptophan.     

黑蚁对雪松长足大蚜集群时空变化的取食反应

我们研究了黑蚁 (Lasiusniger)如何开发距离其巢不同距离的多种食物资源 ,以及黑蚁的照看活动是否与雪松长足大蚜 (Cinaracedri)种群的增长有关 ,以及 /或者受空间分布的影响。笔者定期调查了Cinaracedri集群的空间分布 ,以及在雪松树枝上黑蚁取食的时间变化 ,发现只有 2 5 %的蚜虫集群在研究后数周内保持在同样的位置 ,这表明蚜虫集群的高度运动性迫使黑蚁改变活动路线以获取事物资源。实际上 ,黑蚁集群能选择最近的食物资源以及蚜虫数量最多的地点     

Coexistence of Wolbachia with Buchnera aphidicola and a secondary symbiont in the aphid Cinara cedri

Intracellular symbiosis is very common in the insect world. For the aphid Cinara cedri, we have identified by electron microscopy three symbiotic bacteria that can be characterized by their different sizes, morphologies, and electrodensities. PCR amplification and sequencing of the 16S ribosomal DNA (rDNA) genes showed that, in addition to harboring Buchnera aphidicola, the primary endosymbiont of aphids, C. cedri harbors a secondary symbiont (S symbiont) that was previously found to be associated with aphids (PASS, or R type) and an alpha-proteobacterium that belongs to the Wolbachia genus. Using in situ hybridization with specific bacterial probes designed for symbiont 16S rDNA sequences, we have shown that Wolbachia was represented by only a few minute bacteria surrounding the S symbionts. Moreover, the observed B. aphidicola and the S symbionts had similar sizes and were housed in separate specific bacterial cells, the bacteriocytes. Interestingly, in contrast to the case for all aphids examined thus far, the S symbionts were shown to occupy a similarly sized or even larger bacteriocyte space than B. aphidicola. These findings, along with the facts that C. cedri harbors the B. aphidicola strain with the smallest bacterial genome and that the S symbionts infect all Cinara spp. analyzed so far, suggest the possibility of bacterial replacement in these species.     

A synopsis of the obligate and facultative insect parasitic nematodes

A study of the pathogenicity of a cytoplasmic polyhedrosis virus of the gypsy moth, Porthetria dispar, was conducted. Third- and fourth-instar larvae were highly susceptible to the pathogen even when fed low dosages of polyhedra. Only 30–50% of the treated insects died of polyhedrosis, but the debilitating effects of the virus on larval and postlarval stages were remarkable. Pupal weights were consistently reduced. An inverse and, respectively, a direct, relationship was found between the size of diseased specimens and the developmental periods of larvae and pupae surviving to lethal infection. The highest infected male adults showed a lighter wing coloration. Structural abnormalities and melanotic abdominal inclusions, recorded in diseased adults, were more frequent in females than in males. The presence of melanotic inclusions in diseased females obtained from early larval infection experiments was associated with a greater pupal weight. Lower dosages were the most effective in producing larval mortality and reducing pupal weights and adult emergence. An interference phenomenon due to a mixed virus infection is suspected.     

Adenine methylation may contribute to endosymbiont selection in a clonal aphid population

Background

The pea aphid Acyrthosiphon pisum has two modes of reproduction: parthenogenetic during the spring and summer and sexual in autumn. This ability to alternate between reproductive modes and the emergence of clonal populations under favorable conditions make this organism an interesting model for genetic and epigenetic studies. The pea aphid hosts different types of endosymbiotic bacteria within bacteriocytes which help the aphids survive and adapt to new environmental conditions and habitats. The obligate endosymbiont Buchnera aphidicola has a drastically reduced and stable genome, whereas facultative endosymbionts such as Regiella insecticola have large and dynamic genomes due to phages, mobile elements and high levels of genetic recombination. In previous work, selection toward cold adaptation resulted in the appearance of parthenogenetic A. pisum individuals characterized by heavier weights and remarkable green pigmentation.

Results

Six adenine-methylated DNA fragments were isolated from genomic DNA (gDNA) extracted from the cold-induced green variant of A. pisum using deoxyadenosine methylase (Dam) by digesting the gDNA with the restriction enzymes DpnI and DpnII, which recognize the methylated and unmethylated GATC sites, respectively. The six resultant fragments did not match any sequence in the A. pisum or Buchnera genomes, implying that they came from facultative endosymbionts. The A1 fragment encoding a putative transposase and the A6 fragment encoding a putative helicase were selected for further comparison between the two A. pisum variants (green and orange) based on Dam analysis followed by PCR amplification. An association between adenine methylation and the two A. pisum variants was demonstrated by higher adenine methylation levels on both genes in the green variant as compared to the orange one.

Conclusion

Temperature selection may affect the secondary endosymbiont and the sensitive Dam involved in the survival and adaptation of aphids to cold temperatures. There is a high degree of adenine methylation at the GATC sites of the endosymbiont genes at 8°C, an effect that disappears at 22°C. We suggest that endosymbionts can be modified or selected to increase host fitness under unfavorable climatic conditions, and that the phenotype of the newly adapted aphids can be inherited.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-999) contains supplementary material, which is available to authorized users.     

Marine bioprocess engineering: the missing link to commercialization

Success of US biotechnology has been and continues to be dependent on new discoveries and their timely transformation into useful products through bioprocess engineering and a systems approach. Bioprocess engineering is an essential element of ‘generic applied’ or ‘precompetitive’ research. For marine biotechnology, like biopharmaceutical biotechnology, bioprocess engineering represents the key. The many hundreds of tantalizing bioactive compounds discovered and isolated from varied marine organisms over the past decades have led to only minimal commercialization due to the limited availability of the compounds in question. To address international competitiveness and the revitalization of key US industries, the National Science Foundation launched the Engineering Research Centers Program in the mid 1980s. The essential feature of this program is a partnership among academia, industry and the government to develop next-generation technology through cutting-edge research, relevant education and innovative technology transfer. MarBEC (Marine Bioproducts Engineering Center) is a recently established multi-disciplinary engineering-science cooperative effort of the University of Hawaii and the University of California at Berkeley. Additional partners include three federal laboratories—Argonne National Laboratory, the Edgewood Research, Development and Engineering Center and the Eastern Regional Research Center of the US Department of Agriculture—and the Bishop Museum. MarBEC's research program consists of four major thrusts: Production Systems; Marine Bioproducts and Bioresources; Separation and Conversion; and Bioproduct Formulation.     

Here come the SUNs: a nucleocytoskeletal missing link

The nuclear envelope has traditionally been thought of as a barrier that separates the nucleoplasm from the cytoplasm in eukaryotic cells. Increasing evidence shows that the nuclear envelope also links the inside of the nucleus to the cytoskeleton. Here we discuss recent papers showing that this link occurs through complexes of lamins on the inner aspect of the inner nuclear membrane, transmembrane proteins of the inner nuclear membrane called SUNs and large nesprin isoforms localized specifically to the outer nuclear membrane. These discoveries have implications for nuclear positioning, nuclear migration and pathogenesis of inherited diseases that are caused by mutations in nuclear envelope proteins.     

Drosophila gastrulation: identification of a missing link

Drosophila gastrulation serves as a model system to elucidate the genetic and molecular mechanisms involved in morphogenetic movements. The ligand of the FGF receptor Heartless, which is involved in mesoderm movement, has now been isolated and shown to be a link between a morphogen gradient and cell behavior.     

FTO and obesity: the missing link

The field of vascular molecular imaging is searching for the "holy grail" of an imaging technique that will quantitatively and reliably assess vulnerable coronary plaques. Fluorescence imaging with indocyanine green specifically identifies lipid-rich plaques in rabbits and in humans and represents a promising, though invasive, approach.     

Gut microbiota in antiviral strategy from bats to humans:a missing link in COVID-19

Bats are a potential natural reservoir for SARS-CoV-2 virus and other viruses detrimental to humans. Accumulated evidence has shown that, in their adaptation to a flight-based lifestyle, remodeling of the gut microbiota in bats may have contributed to immune tolerance to viruses. This evidence from bats provides profound insights into the potential influence of gut microbiota in COVID-19 disease in humans. Here, we highlight recent advances in our understanding of the mechanisms by which the gut microbiota helps bats tolerate deadly viruses, and summarize the current clinical evidence on the influence of gut microbiota on the susceptibility to SARS-CoV-2 infection and risk of COVID-19 leading to a fatal outcome. In addition, we discuss the implications of gut microbiota-targeted approaches for preventing infection and reducing disease severity in COVID-19 patients.     

Programmed cell death: a missing link is found

Two families of proteins have advanced our understanding of the molecular basis of programmed cell death (PCD) in animal cells - the caspases and Bcl-2-related proteins. While caspases lie at the heart of the death programme, Bcl-2-related proteins act as key intracellular regulators. Although there has been considerable progress in elucidating the biochemical functions of caspases, how Bcl-2-related proteins regulate caspase activation and thereby PCD, has remained a mystery. One key to resolving this mystery seems to lie with a new third family of proteins related to the Caenorhabditis elegans cell-death protein CED-4, which connects Bcl-2-related proteins to caspases. An important step in defining this new family has been made by the identification of a human CED-4 homologue.     

Chromosome segregation: a kinetochore missing link is found

During mitosis the kinetochore assembles on centromeric chromatin. The component that connects the chromatin-associated inner domain to the microtubule-binding outer domain has eluded researchers. Two new studies identify a conserved molecular linkage between the inner and outer kinetochore.