Mycoplasma penetransunder nutritional stress: influence on lipid and lipoprotein profiles and on the binding to and invasion of HeLa cells

Development of a Serum-Free Medium To Aid Large-Scale Production of Mycoplasma-Based Therapies

To assist in the advancement of the large-scale production of safe Mycoplasma vaccines and other Mycoplasma-based therapies, we developed a culture medium free of animal serum and other animal components for Mycoplasma pneumoniae growth. By establishing a workflow method to systematically test different compounds and concentrations, we provide optimized formulations capable of supporting serial passaging and robust growth reaching 60 to 70% of the biomass obtained in rich medium. Global transcriptomic and proteomic analysis showed minor physiological changes upon cell culture in the animal component-free medium, supporting its suitability for the production of M. pneumoniae-based therapies. The major contributors to growth performance were found to be glucose as a carbon source, glycerol, cholesterol, and phospholipids as a source of fatty acids. Bovine serum albumin or cyclodextrin (in the animal component-free medium) were required as lipid carriers to prevent lipid toxicity. Connaught Medical Research Laboratories medium (CMRL) used to simplify medium preparation as a source of amino acids, nucleotide precursors, vitamins, and other cofactors could be substituted by cysteine. In fact, the presence of protein hydrolysates such as yeastolate or peptones was found to be essential and preferred over free amino acids, except for the cysteine. Supplementation of nucleotide precursors and vitamins is not strictly necessary in the presence of yeastolate, suggesting that this animal origin-free hydrolysate serves as an efficient source for these compounds. Finally, we adapted the serum-free medium formulation to support growth of Mycoplasma hyopneumoniae, a swine pathogen for which inactivated whole-cell vaccines are available. IMPORTANCE Mycoplasma infections have a significant negative impact on both livestock production and human health. Vaccination is often the first option to control disease and alleviate the economic impact that some Mycoplasma infections cause on milk production, weight gain, and animal health. The fastidious nutrient requirements of these bacteria, however, challenges the industrial production of attenuated or inactivated whole-cell vaccines, which depends on the use of animal serum and other animal raw materials. Apart from their clinical relevance, some Mycoplasma species have become cellular models for systems and synthetic biology, owing to the small size of their genomes and the absence of a cell wall, which offers unique opportunities for the secretion and delivery of biotherapeutics. This study proposes medium formulations free of serum and animal components with the potential of supporting large-scale production upon industrial optimization, thus contributing to the development of safe vaccines and other Mycoplasma-based therapies.

Model-driven design allows growth of Mycoplasma pneumoniae on serum-free media

Mycoplasma pneumoniae is a slow-growing, human pathogen that causes atypical pneumonia. Because it lacks a cell wall, many antibiotics are ineffective. Due to its reduced genome and dearth of many biosynthetic pathways, this fastidious bacterium depends on rich, undefined medium for growth, which makes large-scale cultivation challenging and expensive. To understand factors limiting growth, we developed a genome-scale, constraint-based model of M. pneumoniae called iEG158_mpn to describe the metabolic potential of this bacterium. We have put special emphasis on cell membrane formation to identify key lipid components to maximize bacterial growth. We have used this knowledge to predict essential components validated with in vitro serum-free media able to sustain growth. Our findings also show that glycolysis and lipid metabolism are much less efficient under hypoxia; these findings suggest that factors other than metabolism and membrane formation alone affect the growth of M. pneumoniae. Altogether, our modelling approach allowed us to optimize medium composition, enabled growth in defined media and streamlined operational requirements, thereby providing the basis for stable, reproducible and less expensive production.

The Variable Internal Structure of the Mycoplasma penetrans Attachment Organelle Revealed by Biochemical and Microscopic Analyses: Implications for Attachment Organelle Mechanism and Evolution

Although mycoplasmas have small genomes, many of them, including the HIV-associated opportunist Mycoplasma penetrans, construct a polar attachment organelle (AO) that is used for both adherence to host cells and gliding motility. However, the irregular phylogenetic distribution of similar structures within the mycoplasmas, as well as compositional and ultrastructural differences among these AOs, suggests that AOs have arisen several times through convergent evolution. We investigated the ultrastructure and protein composition of the cytoskeleton-like material of the M. penetrans AO with several forms of microscopy and biochemical analysis, to determine whether the M. penetrans AO was constructed at the molecular level on principles similar to those of other mycoplasmas, such as Mycoplasma pneumoniae and Mycoplasma mobile We found that the M. penetrans AO interior was generally dissimilar from that of other mycoplasmas, in that it exhibited considerable heterogeneity in size and shape, suggesting a gel-like nature. In contrast, several of the 12 potential protein components identified by mass spectrometry of M. penetrans detergent-insoluble proteins shared certain distinctive biochemical characteristics with M. pneumoniae AO proteins, although not with M. mobile proteins. We conclude that convergence between M. penetrans and M. pneumoniae AOs extends to the molecular level, leading to the possibility that the less organized material in both M. pneumoniae and M. penetrans is the substance principally responsible for the organization and function of the AO.IMPORTANCEMycoplasma penetrans is a bacterium that infects HIV-positive patients and may contribute to the progression of AIDS. It attaches to host cells through a structure called an AO, but it is not clear how it builds this structure. Our research is significant not only because it identifies the novel protein components that make up the material within the AO that give it its structure but also because we find that the M. penetrans AO is organized unlike AOs from other mycoplasmas, suggesting that similar structures have evolved multiple times. From this work, we derive some basic principles by which mycoplasmas, and potentially all organisms, build structures at the subcellular level.

Exploitation of host lipids by bacteria

Bacteria that interact with eukaryotic cells have developed a variety of strategies to divert host lipids, or cellular processes driven by lipids, to their benefit. Host lipids serve as building blocks for bacterial membrane formation and as energy source. They promote the formation of specific microdomains, facilitating interactions with the host. Host lipids are also critical players in the entry of bacteria or toxins into cells, and, for bacteria growing inside parasitophorous vacuoles, in building a secure shelter. Bacterial dissemination is often dependent on enzymatic activities targeting host lipids. Finally, on a larger scale, long lasting parasitic association can disturb host lipid metabolism so deeply as to 'reprogram' it, as proposed in the case of Mycobacterium infection.

Calpastatin upregulation in Mycoplasma hyorhinis-infected cells is promoted by the mycoplasma lipoproteins via the NF-κB pathway

Mycoplasma hyorhinis frequently contaminates cultured cells, with effects on synthetic and metabolic pathways. We demonstrated for the first time that contamination of cells by a strain of M. hyorhinis (NDMh) results in increased levels of calpastatin (the endogenous inhibitor of the ubiquitous Ca(2+) -dependent protease calpain). We now show that the calpastatin upregulation by NDMh in neuroblastoma SH-SY5Y cells resides in the NDMh lipoprotein fraction (LPP), via the NF-κB transcription pathway. NF-κB activation requires dissociation of the cytoplasmic NF-κB/IκB complex followed by NF-κB translocation to the nucleus. NDMh-LPP induced translocation of the NF-κB RelA subunit to the nucleus and upregulated calpastatin. RelA translocation and calpastatin elevation were prevented when dissociation of the NF-κB/IκB complex was inhibited either by transfection with the non-phosphorylatable IκB mutant ΔNIκBα, or by using PS1145, an inhibitor of the IκB kinase (IKK complex). Increased calpastatin levels attenuate calpain-related amyloid-β-peptide and Ca(2+) -toxicity (these are central to the pathogenesis of Alzheimer's Disease). LPP-induced elevation of calpastatin provides an example of effects on non-inflammatory intracellular proteins, the outcome being significant alterations in host cell functions. Since calpastatin level is important in the control of calpain activity, mycoplasmal LPP may be of interest in treating some pathological processes involving excessive calpain activation.

Invasion of melanoma cells by Mycoplasma hyorhinis: enhancement by protease treatment

Mycoplasma hyorhinis (strain MCLD) was recently isolated from a melanoma cell culture. Growth of MCLD was considerably improved by 24 serial passages in a modified Hayflick's mycoplasma medium. Transmission electron microscopy showed that MCLD exhibits a polymorphic appearance, with ovoid or elongated cells frequently harboring an electron-dense core at one of the poles. Adherence of M. hyorhinis to melanoma cells followed saturation kinetics. Furthermore, although M. hyorhinis has been considered to remain attached to the surface of the host cells, we show for the first time, qualitatively by confocal laser scanning microscopy and quantitatively by a gentamicin resistance assay, that MCLD is able to invade melanoma cells. The ingested mycoplasmas were randomly distributed in the cytoplasm, tending to concentrate near the plasma membrane. Both adherence to and invasion of melanoma cells by M. hyorhinis strain MCLD were dramatically enhanced by mild proteolytic digestion with proteinase K (2.5 microg/mg cell protein for 2.5 min at 37 degrees C) that affected the surface-exposed proteins of this organism, mainly the major 47-kDa lipoprotein. We suggest that the intracellular location of M. hyorhinis strain MCLD is a privileged niche, which may explain the survival of M. hyorhinis in tissue cultures. The enhanced binding to and invasion of melanoma cells by protease treatment may be due to either the activation or the enhanced exposure of an adhesin(s) on the mycoplasmal cell surface.