Fusion-mediated transfer of plasmids into Spiroplasma floricola cells

Transformation of the Drosophila Sex-Manipulative Endosymbiont Spiroplasma poulsonii and Persisting Hurdles for Functional Genetic Studies

Insects are frequently infected by bacterial symbionts that greatly affect their physiology and ecology. Most of these endosymbionts are, however, barely tractable outside their native host, rendering functional genetics studies difficult or impossible. Spiroplasma poulsonii is a facultative bacterial endosymbiont of Drosophila melanogaster that manipulates the reproduction of its host by killing its male progeny at the embryonic stage. S. poulsonii, although a very fastidious bacterium, is closely related to pathogenic Spiroplasma species that are cultivable and genetically modifiable. In this work, we present the transformation of S. poulsonii with a plasmid bearing a fluorescence cassette, leveraging techniques adapted from those used to modify the pathogenic species Spiroplasma citri We demonstrate the feasibility of S. poulsonii transformation and discuss approaches for mutant selection and fly colonization, which are persisting hurdles that must be overcome to allow functional bacterial genetics studies of this endosymbiont in vivo IMPORTANCE Dozens of bacterial endosymbiont species have been described and estimated to infect about half of all insect species. However, only a few them are tractable in vitro, which hampers our understanding of the bacterial determinants of the host-symbiont interaction. Developing a transformation method for S. poulsonii is a major step toward genomic engineering of this symbiont, which will foster basic research on endosymbiosis. This could also open the way to practical uses of endosymbiont engineering through paratransgenesis of vector or pest insects.

Mechanism of the augmentative effect of high polyethylene glycol (PEG) concentrations on the thyroid stimulating activity in TSAb-IgG using a porcine thyroid cell assay

We previously demonstrated that high polyethylene glycol (PEG) concentrations (5% PEG) significantly augmented cAMP production in response to TSAb-IgG using the porcine thyroid cell (PTC) assay. The mechanism of the stimulatory effect of 5% PEG on cAMP production was examined by a two-step incubation with PTC. TSAb-IgG was preincubated with or without addition of 5% PEG in the PTC assay for 2.5 hr (1st incubation) and separated PTC was re-incubated with fresh Hank's buffer for 5 hr (2nd incubation). cAMP production in the 1st incubation medium by co-incubation of TSAb-IgG and 5% PEG for 2.5 hr was significantly increased (3.3-fold) compared to that without 5% PEG. When the cAMP content in PTC and the incubation medium were compared in the same volume of incubation medium after co-incubation of TSAb-IgG and 5% PEG for 2.5 hr, cAMP contents in PTC were about 7-fold higher than that in the incubation medium, and this ratio did not change in the incubation medium of TSAb-IgG without 5% PEG. Similar increases in cAMP contents in PTC (6.6-fold) compared to the incubation medium were also observed with bTSH, although there was no augmentative effect of 5% PEG on cAMP production by bTSH in either the incubation medium or PTC. When PTC, which had been preincubated with normal-IgG and 5% PEG in the 1st incubation, was re-incubated with TSAb-IgG in the 2nd incubation medium, cAMP production by TSAb-IgG was not stimulated by 5% PEG. The augmentative effect of 5% PEG on cAMP production by TSAb-IgG was observed whenever 5% PEG and TSAb-IgG were co-incubated in either the 1st or 2nd incubation. However, no stimulatory effect of 5% PEG on bTSH was observed. These results suggested the stimulatory effect of 5% PEG on TSAb-IgG-stimulated cAMP production may be due to the increase of binding or incorporation of TSAb-IgG into the membranes of PTC compared to TSH.

Molecular biology and pathogenicity of mycoplasmas

The recent sequencing of the entire genomes of Mycoplasma genitalium and M. pneumoniae has attracted considerable attention to the molecular biology of mycoplasmas, the smallest self-replicating organisms. It appears that we are now much closer to the goal of defining, in molecular terms, the entire machinery of a self-replicating cell. Comparative genomics based on comparison of the genomic makeup of mycoplasmal genomes with those of other bacteria, has opened new ways of looking at the evolutionary history of the mycoplasmas. There is now solid genetic support for the hypothesis that mycoplasmas have evolved as a branch of gram-positive bacteria by a process of reductive evolution. During this process, the mycoplasmas lost considerable portions of their ancestors' chromosomes but retained the genes essential for life. Thus, the mycoplasmal genomes carry a high percentage of conserved genes, greatly facilitating gene annotation. The significant genome compaction that occurred in mycoplasmas was made possible by adopting a parasitic mode of life. The supply of nutrients from their hosts apparently enabled mycoplasmas to lose, during evolution, the genes for many assimilative processes. During their evolution and adaptation to a parasitic mode of life, the mycoplasmas have developed various genetic systems providing a highly plastic set of variable surface proteins to evade the host immune system. The uniqueness of the mycoplasmal systems is manifested by the presence of highly mutable modules combined with an ability to expand the antigenic repertoire by generating structural alternatives, all compressed into limited genomic sequences. In the absence of a cell wall and a periplasmic space, the majority of surface variable antigens in mycoplasmas are lipoproteins. Apart from providing specific antimycoplasmal defense, the host immune system is also involved in the development of pathogenic lesions and exacerbation of mycoplasma induced diseases. Mycoplasmas are able to stimulate as well as suppress lymphocytes in a nonspecific, polyclonal manner, both in vitro and in vivo. As well as to affecting various subsets of lymphocytes, mycoplasmas and mycoplasma-derived cell components modulate the activities of monocytes/macrophages and NK cells and trigger the production of a wide variety of up-regulating and down-regulating cytokines and chemokines. Mycoplasma-mediated secretion of proinflammatory cytokines, such as tumor necrosis factor alpha, interleukin-1 (IL-1), and IL-6, by macrophages and of up-regulating cytokines by mitogenically stimulated lymphocytes plays a major role in mycoplasma-induced immune system modulation and inflammatory responses.

Fusion of Spiroplasma floricola cells with small unilamellar vesicles is dependent on the age of the culture

Small unilamellar vesicles were labeled with the fluorescent probe octadecylrhodamine B chloride and mixed with intact Spiroplasma floricola cells. The increase in fluorescence observed was interpreted as a result of the dilution of the probe in the unlabeled S. floricola membranes because of lipid mixing upon fusion. The progression of S. floricola cultures to the stationary phase of growth was accompanied by a sharp decrease in the ability of the cells to fuse with small unilamellar vesicles. Low fusogenic activity was also detected in cells from cultures that were aged in a growth medium maintained at pH 7.5 throughout the growth cycle. Chemical analysis of the cell membrane preparations isolated from cells harvested at the various phases of growth revealed that the phospholipid content and composition and the cholesterol/phospholipid molar ratio were changed very little upon aging of the cultures. Likewise, no changes in the fatty acid composition of membrane lipids were detected, with palmitic and oleic acids predominating throughout the cycle. Nonetheless, upon aging of S. floricola cultures, a pronounced increase in the levels of both cholesteryl esters, incorporated from the growth medium, and organic peroxides was observed. A decrease in both fluorescence anisotropy of diphenylhexatriene and merocyanine 540 binding to membranes of aged cells was also detected. The possible influence of these changes on the fusogenic activity of the cells is discussed.