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- Volume 75, 2021
Annual Review of Microbiology - Volume 75, 2021
Volume 75, 2021
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Microbial Rhodopsins: The Last Two Decades
Vol. 75 (2021), pp. 427–447More LessMicrobial rhodopsins are diverse photoreceptive proteins containing a retinal chromophore and are found in all domains of cellular life and are even encoded in genomes of viruses. These rhodopsins make up two families: type 1 rhodopsins and the recently discovered heliorhodopsins. These families have seven transmembrane helices with similar structures but opposing membrane orientation. Microbial rhodopsins participate in a portfolio of light-driven energy and sensory transduction processes. In this review we present data collected over the last two decades about these rhodopsins and describe their diversity, functions, and biological and ecological roles.
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Quorum Sensing in Fungal Species
Xiuyun Tian, Hao Ding, Weixin Ke, and Linqi WangVol. 75 (2021), pp. 449–469More LessQuorum sensing (QS) is one of the most studied cell-cell communication mechanisms in fungi. Research in the last 20 years has explored various fungal QS systems that are involved in a wide range of biological processes, especially eukaryote- or fungus-specific behaviors, mirroring the significant contribution of QS regulation to fungal biology and evolution. Based on recent progress, we summarize in this review fungal QS regulation, with an emphasis on its functional role in behaviors unique to fungi or eukaryotes. We suggest that using fungi as genetically amenable eukaryotic model systems to address why and how QS regulation is integrated into eukaryotic reproductive strategies and molecular or cellular processes could be an important direction for QS research.
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The Type VII Secretion System of Staphylococcus
Lisa Bowman, and Tracy PalmerVol. 75 (2021), pp. 471–494More LessThe type VII protein secretion system (T7SS) of Staphylococcus aureus is encoded at the ess locus. T7 substrate recognition and protein transport are mediated by EssC, a membrane-bound multidomain ATPase. Four EssC sequence variants have been identified across S. aureus strains, each accompanied by a specific suite of substrate proteins. The ess genes are upregulated during persistent infection, and the secretion system contributes to virulence in disease models. It also plays a key role in intraspecies competition, secreting nuclease and membrane-depolarizing toxins that inhibit the growth of strains lacking neutralizing immunity proteins. A genomic survey indicates that the T7SS is widely conserved across staphylococci and is encoded in clusters that contain diverse arrays of toxin and immunity genes. The presence of genomic islands encoding multiple immunity proteins in species such as Staphylococcus warneri that lack the T7SS points to a major role for the secretion system in bacterial antagonism.
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Trypanosome Signaling—Quorum Sensing
Vol. 75 (2021), pp. 495–514More LessAfrican trypanosomes are responsible for important diseases of humans and animals in sub-Saharan Africa. The best-studied species is Trypanosoma brucei, which is characterized by development in the mammalian host between morphologically slender and stumpy forms. The latter are adapted for transmission by the parasite's vector, the tsetse fly. The development of stumpy forms is driven by density-dependent quorum sensing (QS), the molecular basis for which is now coming to light. In this review, I discuss the historical context and biological features of trypanosome QS and how it contributes to the parasite's infection dynamics within its mammalian host. Also, I discuss how QS can be lost in different trypanosome species, such as T. brucei evansi and T. brucei equiperdum, or modulated when parasites find themselves competing with others of different genotypes or of different trypanosome species in the same host. Finally, I consider the potential to exploit trypanosome QS therapeutically.
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Hostile Takeover: How Viruses Reprogram Prokaryotic Metabolism
Vol. 75 (2021), pp. 515–539More LessTo reproduce, prokaryotic viruses must hijack the cellular machinery of their hosts and redirect it toward the production of viral particles. While takeover of the host replication and protein synthesis apparatus has long been considered an essential feature of infection, recent studies indicate that extensive reprogramming of host primary metabolism is a widespread phenomenon among prokaryotic viruses that is required to fulfill the biosynthetic needs of virion production. In this review we provide an overview of the most significant recent findings regarding virus-induced reprogramming of prokaryotic metabolism and suggest how quantitative systems biology approaches may be used to provide a holistic understanding of metabolic remodeling during lytic viral infection.
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Multiscale Dynamic Structuring of Bacterial Chromosomes
Vol. 75 (2021), pp. 541–561More LessSince the nucleoid was isolated from bacteria in the 1970s, two fundamental questions emerged and are still in the spotlight: how bacteria organize their chromosomes to fit inside the cell and how nucleoid organization enables essential biological processes. During the last decades, knowledge of bacterial chromosome organization has advanced considerably, and today, such chromosomes are considered to be highly organized and dynamic structures that are shaped by multiple factors in a multiscale manner. Here we review not only the classical well-known factors involved in chromosome organization but also novel components that have recently been shown to dynamically shape the 3D structuring of the bacterial genome. We focus on the different functional elements that control short-range organization and describe how they collaborate in the establishment of the higher-order folding and disposition of the chromosome. Recent advances have opened new avenues for a deeper understanding of the principles and mechanisms of chromosome organization in bacteria.
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Molecular Basis of Lysis–Lysogeny Decisions in Gram-Positive Phages
Vol. 75 (2021), pp. 563–581More LessTemperate bacteriophages (phages) are viruses of bacteria. Upon infection of a susceptible host, a temperate phage can establish either a lytic cycle that kills the host or a lysogenic cycle as a stable prophage. The life cycle pursued by an infecting temperate phage can have a significant impact not only on the individual host bacterium at the cellular level but also on bacterial communities and evolution in the ecosystem. Thus, understanding the decision processes of temperate phages is crucial. This review delves into the molecular mechanisms behind lysis–lysogeny decision-making in Gram-positive phages. We discuss a variety of molecular mechanisms and the genetic organization of these well-understood systems. By elucidating the strategies used by phages to make lysis–lysogeny decisions, we can improve our understanding of phage–host interactions, which is crucial for a variety of studies including bacterial evolution, community and ecosystem diversification, and phage therapeutics.
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Deciphering the Chitin Code in Plant Symbiosis, Defense, and Microbial Networks
Vol. 75 (2021), pp. 583–607More LessChitin is a structural polymer in many eukaryotes. Many organisms can degrade chitin to defend against chitinous pathogens or use chitin oligomers as food. Beneficial microorganisms like nitrogen-fixing symbiotic rhizobia and mycorrhizal fungi produce chitin-based signal molecules called lipo-chitooligosaccharides (LCOs) and short chitin oligomers to initiate a symbiotic relationship with their compatible hosts and exchange nutrients. A recent study revealed that a broad range of fungi produce LCOs and chitooligosaccharides (COs), suggesting that these signaling molecules are not limited to beneficial microbes. The fungal LCOs also affect fungal growth and development, indicating that the roles of LCOs beyond symbiosis and LCO production may predate mycorrhizal symbiosis. This review describes the diverse structures of chitin; their perception by eukaryotes and prokaryotes; and their roles in symbiotic interactions, defense, and microbe-microbe interactions. We also discuss potential strategies of fungi to synthesize LCOs and their roles in fungi with different lifestyles.
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Bacterial Outer Membrane Vesicles: From Discovery to Applications
Vol. 75 (2021), pp. 609–630More LessSecretion of cellular components across the plasma membrane is an essential process that enables organisms to interact with their environments. Production of extracellular vesicles in bacteria is a well-documented but poorly understood process. Outer membrane vesicles (OMVs) are produced in gram-negative bacteria by blebbing of the outer membrane. In addition to their roles in pathogenesis, cell-to-cell communication, and stress responses, OMVs play important roles in immunomodulation and the establishment and balance of the gut microbiota. In this review, we discuss the multiple roles of OMVs and the current knowledge of OMV biogenesis. We also discuss the growing and promising biotechnological applications of OMV.
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Origin and Early Evolution of the Eukaryotic Cell
Vol. 75 (2021), pp. 631–647More LessThe origin of eukaryotes has been defined as the major evolutionary transition since the origin of life itself. Most hallmark traits of eukaryotes, such as their intricate intracellular organization, can be traced back to a putative common ancestor that predated the broad diversity of extant eukaryotes. However, little is known about the nature and relative order of events that occurred in the path from preexisting prokaryotes to this already sophisticated ancestor. The origin of mitochondria from the endosymbiosis of an alphaproteobacterium is one of the few robustly established events to which most hypotheses on the origin of eukaryotes are anchored, but the debate is still open regarding the time of this acquisition, the nature of the host, and the ecological and metabolic interactions between the symbiotic partners. After the acquisition of mitochondria, eukaryotes underwent a fast radiation into several major clades whose phylogenetic relationships have been largely elusive. Recent progress in the comparative analyses of a growing number of genomes is shedding light on the early events of eukaryotic evolution as well as on the root and branching patterns of the tree of eukaryotes. Here I discuss current knowledge and debates on the origin and early evolution of eukaryotes. I focus particularly on how phylogenomic analyses have challenged some of the early assumptions about eukaryotic evolution, including the widespread idea that mitochondrial symbiosis in an archaeal host was the earliest event in eukaryogenesis.
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Cellular Adaptations to Cytoplasmic Mg2+ Limitation
Vol. 75 (2021), pp. 649–672More LessMg2+ is the most abundant divalent cation in living cells. It is essential for charge neutralization, macromolecule stabilization, and the assembly and activity of ribosomes and as a cofactor for enzymatic reactions. When experiencing low cytoplasmic Mg2+, bacteria adopt two main strategies: They increase the abundance and activity of Mg2+ importers and decrease the abundance of Mg2+-chelating ATP and rRNA. These changes reduce regulated proteolysis by ATP-dependent proteases and protein synthesis in a systemic fashion. In many bacterial species, the transcriptional regulator PhoP controls expression of proteins mediating these changes. The 5′ leader region of some mRNAs responds to low cytoplasmic Mg2+ or to disruptions in translation of open reading frames in the leader regions by furthering expression of the associated coding regions, which specify proteins mediating survival when the cytoplasmic Mg2+ concentration is low. Microbial species often utilize similar adaptation strategies to cope with low cytoplasmic Mg2+ despite relying on different genes to do so.
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Virulence and Pathogenicity of Chytrid Fungi Causing Amphibian Extinctions
Vol. 75 (2021), pp. 673–693More LessAncient enzootic associations between wildlife and their infections allow evolution to innovate mechanisms of pathogenicity that are counterbalanced by host responses. However, erosion of barriers to pathogen dispersal by globalization leads to the infection of hosts that have not evolved effective resistance and the emergence of highly virulent infections. Global amphibian declines driven by the rise of chytrid fungi and chytridiomycosis are emblematic of emerging infections. Here, we review how modern biological methods have been used to understand the adaptations and counteradaptations that these fungi and their amphibian hosts have evolved. We explore the interplay of biotic and abiotic factors that modify the virulence of these infections and dissect the complexity of this disease system. We highlight progress that has led to insights into how we might in the future lessen the impact of these emerging infections.
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Life in the Dark: Phylogenetic and Physiological Diversity of Chemosynthetic Symbioses
Vol. 75 (2021), pp. 695–718More LessPossibly the last discovery of a previously unknown major ecosystem on Earth was made just over half a century ago, when researchers found teaming communities of animals flourishing two and a half kilometers below the ocean surface at hydrothermal vents. We now know that these highly productive ecosystems are based on nutritional symbioses between chemosynthetic bacteria and eukaryotes and that these chemosymbioses are ubiquitous in both deep-sea and shallow-water environments. The symbionts are primary producers that gain energy from the oxidation of reduced compounds, such as sulfide and methane, to fix carbon dioxide or methane into biomass to feed their hosts. This review outlines how the symbiotic partners have adapted to living together. We first focus on the phylogenetic and metabolic diversity of these symbioses and then highlight selected research directions that could advance our understanding of the processes that shaped the evolutionary and ecological success of these associations.
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The Bacterial Hsp90 Chaperone: Cellular Functions and Mechanism of Action
Vol. 75 (2021), pp. 719–739More LessHeat shock protein 90 (Hsp90) is a molecular chaperone that folds and remodels proteins, thereby regulating the activity of numerous substrate proteins. Hsp90 is widely conserved across species and is essential in all eukaryotes and in some bacteria under stress conditions. To facilitate protein remodeling, bacterial Hsp90 collaborates with the Hsp70 molecular chaperone and its cochaperones. In contrast, the mechanism of protein remodeling performed by eukaryotic Hsp90 is more complex, involving more than 20 Hsp90 cochaperones in addition to Hsp70 and its cochaperones. In this review, we focus on recent progress toward understanding the basic mechanisms of bacterial Hsp90-mediated protein remodeling and the collaboration between Hsp90 and Hsp70. We describe the universally conserved structure and conformational dynamics of these chaperones and their interactions with one another and with client proteins. The physiological roles of Hsp90 in Escherichia coli and other bacteria are also discussed. We anticipate that the information gained from exploring the mechanism of the bacterial chaperone system will provide a framework for understanding the more complex eukaryotic Hsp90 system.
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Previous Volumes
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Volume 78 (2024)
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Volume 77 (2023)
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Volume 76 (2022)
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Volume 75 (2021)
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Volume 74 (2020)
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Volume 73 (2019)
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Volume 72 (2018)
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Volume 71 (2017)
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Volume 70 (2016)
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Volume 69 (2015)
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Volume 68 (2014)
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Volume 67 (2013)
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Volume 66 (2012)
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Volume 65 (2011)
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Volume 64 (2010)
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Volume 63 (2009)
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Volume 62 (2008)
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Volume 61 (2007)
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Volume 60 (2006)
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Volume 59 (2005)
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Volume 58 (2004)
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Volume 57 (2003)
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Volume 56 (2002)
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Volume 55 (2001)
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Volume 54 (2000)
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Volume 53 (1999)
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Volume 52 (1998)
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Volume 51 (1997)
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Volume 50 (1996)
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Volume 49 (1995)
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Volume 48 (1994)
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Volume 47 (1993)
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Volume 46 (1992)
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Volume 45 (1991)
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Volume 44 (1990)
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Volume 43 (1989)
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Volume 42 (1988)
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Volume 41 (1987)
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Volume 40 (1986)
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Volume 39 (1985)
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Volume 38 (1984)
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Volume 37 (1983)
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Volume 36 (1982)
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Volume 35 (1981)
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Volume 34 (1980)
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Volume 33 (1979)
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Volume 32 (1978)
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Volume 31 (1977)
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Volume 30 (1976)
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Volume 29 (1975)
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Volume 28 (1974)
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Volume 27 (1973)
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Volume 26 (1972)
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Volume 25 (1971)
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Volume 24 (1970)
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Volume 23 (1969)
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Volume 22 (1968)
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Volume 21 (1967)
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Volume 20 (1966)
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Volume 19 (1965)
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Volume 18 (1964)
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Volume 17 (1963)
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Volume 16 (1962)
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Volume 15 (1961)
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Volume 14 (1960)
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Volume 13 (1959)
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Volume 12 (1958)
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Volume 11 (1957)
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Volume 10 (1956)
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Volume 9 (1955)
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Volume 8 (1954)
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Volume 7 (1953)
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Volume 6 (1952)
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Volume 5 (1951)
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Volume 4 (1950)
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Volume 3 (1949)
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Volume 2 (1948)
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Volume 1 (1947)
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Volume 0 (1932)