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1. Wolbachia modifies thermal preference in Drosophila melanogaster

   https://doi.org/10.1111/1462-2920.14347  

   Truitt, Amy M. ; Kapun, Martin ; Kaur, Rupinder ; Miller, Wolfgang J. ( October 2018 , Environmental Microbiology)

   Environmental variation can have profound and direct effects on fitness, fecundity, and host–symbiont interactions. Replication rates of microbes within arthropod hosts, for example, are correlated with incubation temperature but less is known about the influence of host–symbiont dynamics on environmental preference. Hence, we conducted thermal preference (T_p) assays and tested if infection status and genetic variation in endosymbiont bacteriumWolbachiaaffected temperature choice ofDrosophila melanogaster. We demonstrate that isogenic flies infected withWolbachiapreferred lower temperatures compared with uninfectedDrosophila. Moreover,T_pvaried with respect to three investigatedWolbachiavariants (wMel,wMelCS, andwMelPop). While uninfected individuals preferred 24.4°C, we found significant shifts of −1.2°C inwMel‐ and −4°C in flies infected either withwMelCS orwMelPop. We, therefore, postulate thatWolbachia‐associatedT_pvariation within a host species might represent a behavioural accommodation to host–symbiont interactions and trigger behavioural self‐medication and bacterial titre regulation by the host.

    

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2. Passage of Wolbachia pipientis through Mutant Drosophila melanogaster Induces Phenotypic and Genomic Changes

   https://doi.org/10.1128/AEM.02987-14  

   Newton, Irene L. ; Sheehan, Kathy B. ( January 2015 , Applied and Environmental Microbiology)

   Goodrich-Blair, H. (Ed.)

   ABSTRACT Wolbachia pipientis is a nearly ubiquitous, maternally transmitted bacterium that infects the germ line of insect hosts. Estimates are that Wolbachia infects 40 to 60% of insect species on the planet, making it one of the most prevalent infections on Earth. However, we know surprisingly little about the molecular mechanisms used by Wolbachia to infect its hosts. We passaged Wolbachia through normally restrictive Drosophila melanogaster hosts, bottlenecking Wolbachia through stochastic segregation while simultaneously selecting for mutants that could recolonize these previously restrictive hosts. Here, we show that Wolbachia alters its behavior when passaged through heterozygous mutant flies. After only three generations, Wolbachia was able to colonize the previously restrictive hosts at control titers. Additionally, the Wolbachia organisms passaged through heterozygous mutant D. melanogaster alter their pattern of tissue-specific Wsp protein production, suggesting a behavioral response to the host genotype. Using whole-genome resequencing, we identified the mutations accumulated by these lineages of Wolbachia and confirmed the existence and persistence of the mutations through clone library Sanger sequencing. Our results suggest that Wolbachia can quickly adapt to new host contexts, with genomic mutants arising after only two generations. 

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3. Mitochondria and Wolbachia titers are positively correlated during maternal transmission

   https://doi.org/10.1111/mec.14700  

   Henry, Lucas P. ; Newton, Irene L. G. ( May 2018 , Molecular Ecology)

   Mothers provide their offspring with symbionts. Maternally transmitted, intracellular symbionts must disperse from mother to offspring with other cytoplasmic elements, like mitochondria. Here, we investigated how the intracellular symbiontWolbachiainteracts with mitochondria during maternal transmission. Mitochondria andWolbachiamay interact antagonistically and compete as each population tries to ensure its own evolutionary success. Alternatively, mitochondria andWolbachiamay cooperate as both benefit from ensuring the fitness of the mother. We characterized the relationship between mitochondria andWolbachiatiters in ovaries ofDrosophila melanogaster. We found that mitochondria andWolbachiatiters are positively correlated in common laboratory genotypes ofD. melanogaster. We attempted to perturb this covariation through the introduction ofWolbachiavariants that colonize at different titers. We also attempted to perturb the covariation through manipulating the female reproductive tract to disrupt maternal transmission. Finally, we also attempted to disrupt the covariation by knocking down gene expression for two loci involved in mitochondrial metabolism:NADHdehydrogenase and a mitochondrial transporter. Overall, we find that mitochondria andWolbachiatiters are commonly positively correlated, but this positive covariation is disrupted at high titers ofWolbachia. Our results suggest that mitochondria andWolbachiahave likely evolved mechanisms to stably coexist, but the competitive dynamics change at highWolbachiatiters. We provide future directions to better understand how their interaction influences the maintenance of the symbiosis.

    

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4. The ClpX and ClpP2 Orthologs of Chlamydia trachomatis Perform Discrete and Essential Functions in Organism Growth and Development

   https://doi.org/10.1128/mBio.02016-20  

   Wood, Nicholas A. ; Blocker, Amanda M. ; Seleem, Mohamed A. ; Conda-Sheridan, Martin ; Fisher, Derek J. ; Ouellette, Scot P. ( October 2020 , mBio)

   Msadek, Tarek (Ed.)

   ABSTRACT Chlamydia trachomatis is an obligate intracellular bacterium that undergoes a complex developmental cycle in which the bacterium differentiates between two functionally and morphologically distinct forms, the elementary body (EB) and reticulate body (RB), each of which expresses its own specialized repertoire of proteins. Both primary (EB to RB) and secondary (RB to EB) differentiations require protein turnover, and we hypothesize that proteases are critical for mediating differentiation. The Clp protease system is well conserved in bacteria and important for protein turnover. Minimally, the system relies on a serine protease subunit, ClpP, and an AAA+ ATPase, such as ClpX, that recognizes and unfolds substrates for ClpP degradation. In Chlamydia , ClpX is encoded within an operon 3′ to clpP2 . We present evidence that the chlamydial ClpX and ClpP2 orthologs are essential to organism viability and development. We demonstrate here that chlamydial ClpX is a functional ATPase and forms the expected homohexamer in vitro . Overexpression of a ClpX mutant lacking ATPase activity had a limited impact on DNA replication or secondary differentiation but, nonetheless, reduced EB viability with observable defects in EB morphology noted. Conversely, overexpression of a catalytically inactive ClpP2 mutant significantly impacted developmental cycle progression by reducing the overall number of organisms. Blocking clpP2X transcription using CRISPR interference led to a decrease in bacterial growth, and this effect was complemented in trans by a plasmid copy of clpP2 . Taken together, our data indicate that ClpX and the associated ClpP2 serve distinct functions in chlamydial developmental cycle progression and differentiation. IMPORTANCE Chlamydia trachomatis is the leading cause of infectious blindness globally and the most reported bacterial sexually transmitted infection both domestically and internationally. Given the economic burden, the lack of an approved vaccine, and the use of broad-spectrum antibiotics for treatment of infections, an understanding of chlamydial growth and development is critical for the advancement of novel targeted antibiotics. The Clp proteins comprise an important and conserved protease system in bacteria. Our work highlights the importance of the chlamydial Clp proteins to this clinically important bacterium. Additionally, our study implicates the Clp system playing an integral role in chlamydial developmental cycle progression, which may help establish models of how Chlamydia spp. and other bacteria progress through their respective developmental cycles. Our work also contributes to a growing body of Clp-specific research that underscores the importance and versatility of this system throughout bacterial evolution and further validates Clp proteins as drug targets. 

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5. Plasmid-Mediated Stabilization of Prophages

   https://doi.org/10.1128/msphere.00930-21  

   Tuttle, Matthew J. ; May, Frank S. ; Basso, Jonelle T. ; Gann, Eric R. ; Xu, Julie ; Buchan, Alison ( April 2022 , mSphere)

   McMahon, Katherine (Ed.)

   ABSTRACT Mobile genetic elements (MGEs) drive bacterial evolution, alter gene availability within microbial communities, and facilitate adaptation to ecological niches. In natural systems, bacteria simultaneously possess or encounter multiple MGEs, yet their combined influences on microbial communities are poorly understood. Here, we investigate interactions among MGEs in the marine bacterium Sulfitobacter pontiacus . Two related strains, CB-D and CB-A, each harbor a single prophage. These prophages share high sequence identity with one another and an integration site within the host genome, yet these strains exhibit differences in “spontaneous” prophage induction (SPI) and consequent fitness. To better understand mechanisms underlying variation in SPI between these lysogens, we closed their genomes, which revealed that in addition to harboring different prophage genotypes, CB-A lacks two of the four large, low-copy-number plasmids possessed by CB-D. To assess the relative roles of plasmid content versus prophage genotype on host physiology, a panel of derivative strains varying in MGE content were generated. Characterization of these derivatives revealed a robust link between plasmid content and SPI, regardless of prophage genotype. Strains possessing all four plasmids had undetectable phage in cell-free lysates, while strains lacking either one plasmid (pSpoCB-1) or a combination of two plasmids (pSpoCB-2 and pSpoCB-4) produced high (>10 5 PFU/mL) phage titers. Homologous plasmid sequences were identified in related bacteria, and plasmid and phage genes were found to be widespread in Tara Oceans metagenomic data sets. This suggests that plasmid-dependent stabilization of prophages may be commonplace throughout the oceans. IMPORTANCE The consequences of prophage induction on the physiology of microbial populations are varied and include enhanced biofilm formation, conferral of virulence, and increased opportunity for horizontal gene transfer. These traits lead to competitive advantages for lysogenized bacteria and influence bacterial lifestyles in a variety of niches. However, biological controls of “spontaneous” prophage induction, the initiation of phage replication and phage-mediated cell lysis without an overt stressor, are not well understood. In this study, we observed a novel interaction between plasmids and prophages in the marine bacterium Sulfitobacter pontiacus . We found that loss of one or more distinct plasmids—which we show carry genes ubiquitous in the world’s oceans—resulted in a marked increase in prophage induction within lysogenized strains. These results demonstrate cross talk between different mobile genetic elements and have implications for our understanding of the lysogenic-lytic switches of prophages found not only in marine environments, but throughout all ecosystems. 

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