Biology

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A Historical Account of the Origin, Evolution, and Demise of NASA’s Oxymoronic “Astrobiology”/ The “Arsenic Monster” of Mono Lake/ and a Modest Proposal to Educate Dabblers in Microbiology Research
(2012-01-30) Gest, Howard
This essay presents a select Time Line for early speculations on “extraterrestrial life” and attempts to obtain experimental evidence for past or present life on the Moon and Mars. To date, there is no credible evidence for “life elsewhere,” even the simplest forms (microbes). Nevertheless, NASA continues to trumpet “astrobiology,” an oxymoron that suggests or implies that life has actually been found beyond Earth. NASA exploits the fallacious notion that the existence of terrestrial bacteria able to live under “extreme” chemical or physical conditions (“extremophiles”) provides evidence for “astrobiology.” In December 2010, NASA announced, in a massive publicity event, that their grantees isolated a bacterium from sediment mud of Mono Lake (CA) that defies basic biochemical principles of all known forms of life on Earth in that arsenic replaces phosphorus in its DNA and other P–containing essential metabolites. The so-called evidence for the “Arsenic Monster” [a presumed harbinger for “astrobiology”] has been strongly criticized and is being rigorously tested by independent investigators. These include Rosie Redfield and her collaborators who hope to submit their work to Science in early 2012.
A Panorama of the Emergence of Modern Microbiology: 1870’s—1950’s [which includes “A Time Line of Some Basic Discoveries in Microbiology/Biochemistry,1928-1955]
(2011-01-27) Gest, Howard
This SUPPLEMENT amplifies several aspects of the historic development of microbiological research from the 1870's to ca. 1955. During this period, great advances were made in understanding basic characteristics of a large number of physiologically diverse microorganisms that grow and persist under widely different natural conditions. Thousands of species were isolated in pure culture, and deposited in culture collections, making them available for detailed study of their genetic and biochemical processes, as well as their roles in the cyclic transformations of elements on the Earth. The complexity and basic features of microbial ecology were also discovered. Major research contributions of a number of leading microbiologists are reviewed.
A Rhizobiales-Specific Unipolar Polysaccharide Adhesin Contributes to Rhodopseudomonas palustris Biofilm Formation across Diverse Photoheterotrophic Conditions
(Applied and Environmental Microbiology, 2017-02) Fritts, Ryan K.; LaSarre, Breah; Stoner, Ari M.; Posto, Amanda L.; McKinlay, James B.
Bacteria predominantly exist as members of surfaced-attached communities known as biofilms. Many bacterial species initiate biofilms and adhere to each other using cell surface adhesins. This is the case for numerous ecologically diverse Alphaprotebacteria, which use polar exopolysaccharide adhesins for cell-cell adhesion and surface attachment. Here, we show that Rhodopseudomonas palustris, a metabolically versatile member of the alphaproteobacterial order Rhizobiales, contains a functional unipolar polysaccharide (UPP) biosynthesis gene cluster. Deletion of genes predicted to be critical for UPP biosynthesis and export abolished UPP production. We also found that R. palustris uses UPP to mediate biofilm formation across diverse photoheterotrophic growth conditions, wherein light and organic substrates are used to support growth. However, UPP was less important for biofilm formation during photoautotrophy, where light and CO2 support growth, and during aerobic respiration with organic compounds. Expanding our analysis beyond R. palustris, we examined the phylogenetic distribution and genomic organization of UPP gene clusters among Rhizobiales species that inhabit diverse niches. Our analysis suggests that UPP is a conserved ancestral trait of the Rhizobiales but that it has been independently lost multiple times during the evolution of this clade, twice coinciding with adaptation to intracellular lifestyles within animal hosts.
Adaptation, Exaptation, and Constraint: A Hormonal Perspective
(American Society of Naturalists, 1999-07) Ketterson, Ellen D.; Nolan, Val Jr
We approach conceptual issues in evolutionary biology from an endocrinological perspective, noting that single hormones typically act on several target tissues and thereby mediate suites of correlated phenotypic traits. When several components of such a suite are beneficial, an important evolutionary question is whether all are adaptations or some are exaptations. The answer may depend on whether the traits arose in response to selection on variation in systemic levels of the hormone on variation in responsiveness of target tissues to invariant levels of the hormone. If the former, selection probably acted directly on fewer than all traits; beneficial traits arising indirectly would be exaptations. In contrast, multiple beneficial traits that arose out of independent changes in target‐tissue sensitivity to invariant hormone levels could all be adaptations. Knowledge of specific hormonal mechanisms as well as of historical selective regimes will be necessary to draw such distinctions. Endocrine constraints on evolution can be studied experimentally by applying hormones systemically and measuring interdependent responses of beneficial and detrimental traits to selection (phenotypic engineering with hormones). Supposing that alteration of one trait in isolation would enhance fitness, cases in which the net effect of endocrine alteration of multiple traits is to depress fitness provide evidence for constraints. We briefly report results of recent studies employing hormonal manipulations, stressing our own work on the dark‐eyed junco (Junco hyemalis: Emberizidae).
An Escherichia coli nitrogen starvation response is important for mutualistic coexistence with Rhodopseudomonas palustris
(Applied and Environmental Microbiology, 2018-07) McCully, Alexandra L.; Behringer, Megan G.; Gliessman, Jennifer R.; Pilipenko, Evgeny V.; Mazny, Jeffrey L.; Lynch, Michael; Drummond, D. Allan; McKinlay, James B.
Microbial mutualistic cross-feeding interactions are ubiquitous and can drive important community functions. Engaging in cross-feeding undoubtedly affects the physiology and metabolism of individual species involved. However, the nature in which an individual species' physiology is influenced by cross-feeding and the importance of those physiological changes for the mutualism have received little attention. We previously developed a genetically tractable coculture to study bacterial mutualisms. The coculture consists of fermentative Escherichia coli and phototrophic Rhodopseudomonas palustris. In this coculture, E. coli anaerobically ferments sugars into excreted organic acids as a carbon source for R. palustris. In return, a genetically engineered R. palustris strain constitutively converts N$_2$ into NH$_4$+, providing E. coli with essential nitrogen. Using transcriptome sequencing (RNA-seq) and proteomics, we identified transcript and protein levels that differ in each partner when grown in coculture versus monoculture. When in coculture with R. palustris, E. coli gene expression changes resembled a nitrogen starvation response under the control of the transcriptional regulator NtrC. By genetically disrupting E. coli NtrC, we determined that a nitrogen starvation response is important for a stable coexistence, especially at low R. palustris NH$_4$+ excretion levels. Destabilization of the nitrogen starvation regulatory network resulted in variable growth trends and, in some cases, extinction. Our results highlight that alternative physiological states can be important for survival within cooperative cross-feeding relationships.
Analysis of model replication origins in Drosophila reveals new aspects of the chromatin landscape and its relationship to origin activity and the prereplicative complex
(The American Society for Cell Biology, 2012) Liu, J.; Mconnell, K.; Dixon, M.; Calvi, B.R.
Epigenetic regulation exerts a major influence on origins of DNA replication during development. The mechanisms for this regulation, however, are poorly defined. We showed previously that acetylation of nucleosomes regulates the origins that mediate developmental gene amplification during Drosophila oogenesis. Here we show that developmental activation of these origins is associated with acetylation of multiple histone lysines. Although these modifications are not unique to origin loci, we find that the level of acetylation is higher at the active origins and quantitatively correlated with the number of times these origins initiate replication. All of these acetylation marks were developmentally dynamic, rapidly increasing with origin activation and rapidly declining when the origins shut off and neighboring promoters turn on. Fine-scale analysis of the origins revealed that both hyperacetylation of nucleosomes and binding of the origin recognition complex (ORC) occur in a broad domain and that acetylation is highest on nucleosomes adjacent to one side of the major site of replication initiation. It was surprising to find that acetylation of some lysines depends on binding of ORC to the origin, suggesting that multiple histone acetyltransferases may be recruited during origin licensing. Our results reveal new insights into the origin epigenetic landscape and lead us to propose a chromatin switch model to explain the coordination of origin and promoter activity during development.
Calvin cycle mutants of photoheterotrophic purple non-sulfur bacteria fail to grow due to an electron imbalance rather than toxic metabolite accumulation
(Journal of Bacteriology, 2014-01) Gordon, Gina C.; McKinlay, James B.
Purple nonsulfur bacteria grow photoheterotrophically by using light for energy and organic compounds for carbon and electrons. Disrupting the activity of the CO$_2$-fixing Calvin cycle enzyme, ribulose 1,5-bisphosphate carboxylase (RubisCO), prevents photoheterotrophic growth unless an electron acceptor is provided or if cells can dispose of electrons as H$_2$. Such observations led to the long-standing model wherein the Calvin cycle is necessary during photoheterotrophic growth to maintain a pool of oxidized electron carriers. This model was recently challenged with an alternative model wherein disrupting RubisCO activity prevents photoheterotrophic growth due to the accumulation of toxic ribulose-1,5-bisphosphate (RuBP) (D. Wang, Y. Zhang, E. L. Pohlmann, J. Li, and G. P. Roberts, J. Bacteriol. 193:3293-3303, 2011, http://dx.doi.org/10.1128/JB.00265-11). Here, we confirm that RuBP accumulation can impede the growth of Rhodospirillum rubrum (Rs. rubrum) and Rhodopseudomonas palustris (Rp. palustris) RubisCO-deficient (ΔRubisCO) mutants under conditions where electron carrier oxidation is coupled to H$_2$ production. However, we also demonstrate that Rs. rubrum and Rp. palustris Calvin cycle phosphoribulokinase mutants that cannot produce RuBP cannot grow photoheterotrophically on succinate unless an electron acceptor is provided or H$_2$ production is permitted. Thus, the Calvin cycle is still needed to oxidize electron carriers even in the absence of toxic RuBP. Surprisingly, Calvin cycle mutants of Rs. rubrum, but not of Rp. palustris, grew photoheterotrophically on malate without electron acceptors or H$_2$ production. The mechanism by which Rs. rubrum grows under these conditions remains to be elucidated.
Conspecific plant-soil feedbacks of temperate tree species in the southern Appalachians, USA
(PLOS ONE, 2012) Reinhart, K.O.; Johnson, D.; Clay, K.
Many tree species have seedling recruitment patterns suggesting that they are affected by non-competitive distance-dependent sources of mortality. We conducted an experiment, with landscape-level replication, to identify cases of negative distance-dependent effects and whether variation in these effects corresponded with tree recruitment patterns in the southern Appalachian Mountains region. Specifically, soil was collected from 14 sites and used as inocula in a 62 day growth chamber experiment determining whether tree seedling growth was less when interacting with soil from conspecific (like) than heterospecific (other) tree species. Tests were performed on six tree species. Three of the tree species had been previously described as having greater recruitment around conspecifics (i.e. facilitator species group) compared to the other half (i.e. inhibitor species group). We were then able to determine whether variation in negative distance-dependent effects corresponded with recruitment patterns in the field. Across the six species, none were negatively affected by soil inocula from conspecific relative to heterospecific sources. Most species (four of six) were unaffected by soil source. Two species (Prunus serotina and Tsuga canadensis) had enhanced growth in pots inoculated with soil from conspecific trees vs. heterospecifics. Species varied in their susceptibility to soil pathogens, but trends across all species revealed that species classified as inhibitors were not more negatively affected by conspecific than heterospecific soil inocula or more susceptible to pathogenic effects than facilitators. Although plant-soil biota interactions may be important for individual species and sites, it may be difficult to scale these interactions over space or levels of ecological organization. Generalizing the importance of plant-soil feedbacks or other factors across regional scales may be especially problematic for hyperdiverse temperate forests where interactions may be spatially variable.
Cryptocephal, the Drosophila melanogaster ATF4, Is a Specific Coactivator for Ecdysone Receptor Isoform B2
(PLoS Genetics, 2012) Gauthier, S.A.; VanHaaften, E.; Cherbas, L.; Cherbas, P.; Hewes, R.S.
The ecdysone receptor is a heterodimer of two nuclear receptors, the Ecdysone receptor (EcR) and Ultraspiracle (USP). In $\textit{Drosophila melanogaster}$, three EcR isoforms share common DNA and ligand-binding domains, but these proteins differ in their most N-terminal regions and, consequently, in the activation domains (AF1s) contained therein. The transcriptional coactivators for these domains, which impart unique transcriptional regulatory properties to the EcR isoforms, are unknown. Activating transcription factor 4 (ATF4) is a basic-leucine zipper transcription factor that plays a central role in the stress response of mammals. Here we show that Cryptocephal (CRC), the $\textit{Drosophila}$ homolog of ATF4, is an ecdysone receptor coactivator that is specific for isoform B2. CRC interacts with EcR-B2 to promote ecdysone-dependent expression of ecdysis-triggering hormone (ETH), an essential regulator of insect molting behavior. We propose that this interaction explains some of the differences in transcriptional properties that are displayed by the EcR isoforms, and similar interactions may underlie the differential activities of other nuclear receptors with distinct AF1-coactivators.
De novo transcriptome sequencing in a songbird, the dark-eyed junco (Junco hyemalis): Genomic tools for an ecological model system
(BMC Genomics, 2012-07-09) Peterson, Mark P.; Whittaker, Danielle J.; Ambreth, Shruthi; Sureschandra, Suhas; Buechlein, Aaron; Podicheti, Ram; Choi, Jeong-Hyeon; Lai, Zhao; Mockatis, Keithanne; Colbourne, John; Tang, Haixu; Ketterson, Ellen D.
Though genomic-level data are becoming widely available, many of the metazoan species sequenced are laboratory systems whose natural history is not well documented. In contrast, the wide array of species with very well-characterized natural history have, until recently, lacked genomics tools. It is now possible to address significant evolutionary genomics questions by applying high-throughput sequencing to discover the majority of genes for ecologically tractable species, and by subsequently developing microarray platforms from which to investigate gene regulatory networks that function in natural systems. We used GS-FLX Titanium Sequencing (Roche/454-Sequencing) of two normalized libraries of pooled RNA samples to characterize a transcriptome of the dark-eyed junco (Junco hyemalis), a North American sparrow that is a classically studied species in the fields of photoperiodism, speciation, and hormone-mediated behavior.
Deciphering Information Encoded in Birdsong: Male Songbirds with Fertile Mates Respond Most Strongly to Complex, Low-Amplitude Songs Used in Courtship
(The American Naturalist, 2011-08-15) Reichard, Dustin G.; Rice, Rebecca J.; Vanderbilt, Carla C.; Ketterson, Ellen D.
Research on the function of acoustic signals has focused on high-amplitude long-range songs (LRS) and largely ignored low-amplitude songs produced by many species during close-proximity, conspecific interactions. Low-amplitude songs can be structurally identical to LRS (soft LRS), or they can be widely divergent, sharing few spectral and temporal attributes with LRS (short-range song [SRS]). SRS is often more complex than LRS and is frequently sung by males during courtship. To assess function, we performed two playback experiments on males of a socially monogamous songbird. We compared responses of males whose mates were fertile or nonfertile with differences in song structure (SRS vs. LRS and soft LRS), amplitude (SRS and soft LRS vs. LRS), and tempo (slow SRS vs. fast SRS). Males responded more strongly to SRS than to LRS or soft LRS, indicating that song structure had a greater effect on response than song amplitude. SRS tempo did not detectably affect male response. Importantly, males responded more strongly to SRS when their mates were fertile, presumably because hearing SRS can indicate that a male’s mate is being courted by an intruding male and a strong response can deter extrapair competitors. We conclude that low-amplitude songs can function in both inter- and intrasexual communication and should receive greater attention in future studies of mate choice and male-male competition.
Discovery and Exploration of the Microbial Universe: 1665 to "Modern Times"
(2010-04-21) Gest, Howard
Recent research has shown that the first observation and published depiction of a microorganism (Mucor) was made by Robert Hooke (1665), whose microscope expertise facilitated the later discovery of bacteria by Antoni v. Leeuwenhoek. In 1835, Agostino Bassi proved that an infectious disease of animals was caused by a microbe. Forty years later, Ferdinand Cohn's research ushered in the age of "modern microbiology," with major contributions from Robert Koch, Martinus Beijerinck, and Sergei Winogradsky. The present essay also highlights a number of subsequent investigators who discovered fundamental aspects of microbial (and virus) growth and biochemical mechanisms. Nowadays, scientists whose research provided the basis of microbial molecular biology are sometimes recognized by single-line entries in textbook tables.
Elevated CO2 increases root exudation from loblolly pine (Pinus taeda L.) seedlings as an N-mediated response
(Oxford University Press, 2009-10-08) Schlesinger, William; Bernhardt, Emily; Phillips, Richard P.
The degree to which forest ecosystems provide a long-term sink for increasing atmospheric CO2 depends upon the capacity of trees to increase the availability of growth-limiting resources. It has been widely speculated that trees exposed to CO2 enrichment may increase the release of root exudates to soil as a mechanism to stimulate microbes to enhance nutrient availability. As a first test to examine how the atmospheric CO2 and nitrogen availability affect the rates of root exudation, we performed two experiments in which the exudates were collected from loblolly pine (Pinus taeda L.) seedlings that were grown in controlled growth chambers under low and high CO2 and at low and high rates of N supply. Despite the differences in experimental design between the two studies, plants grown at high CO2 were larger, and thus whole plant exudation rates were higher under elevated CO2 (P = 0.019), but the magnitude of this response depended on the N level in both studies. Seedlings increased mass-specific exudation rates in response to elevated CO2 in both experiments, but only at low N supply. Moreover, N supply had a greater impact on the exudation rates than did CO2, with mass-specific exudation rates significantly greater (98% and 69% in Experiments 1 and 2, respectively) in the seedlings grown at low N supply relative to high N supply. These results provide preliminary evidence that loblolly pines alter exudation rates in response to both CO2 concentration and N supply, and support the hypothesis that increased C allocation to root exudates may be a mechanism by which trees could delay progressive N limitation in forested ecosystems.
Emerging Perspectives on the Mechanisms, Regulation, and Distribution of Light Color Acclimation in Cyanobacteria
(Molecular Plant, 2012-01) Gutu, Andrian; Kehoe, David
ABSTRACT Chromatic acclimation (CA) provides many cyanobacteria with the ability to tailor the properties of their lightharvesting antennae to the spectral distribution of ambient light. CA was originally discovered as a result of its dramatic cellular phenotype in red and green light. However, discoveries over the past decade have revealed that many pairs of light colors, ranging from blue to infrared, can trigger CA responses. The capacity to undergo CA is widespread geographically, occurs in most habitats around the world, and is found within all major cyanobacterial groups. In addition, many other cellular activities have been found to be under CA control, resulting in distinct physiological and morphological states for cells under different light-color conditions. Several types of CA appear to be the result of convergent evolution, where different strategies are used to achieve the final goal of optimizing light-harvesting antenna composition to maximize photon capture. The regulation of CA has been found to occur primarily at the level of RNA abundance. The CA-regulatory pathways uncovered thus far are two-component systems that use phytochrome-class photoreceptors with sensor-kinase domains to control response regulators that function as transcription factors. However, there is also at least one CAregulatory pathway that operates at the post-transcriptional level. It is becoming increasingly clear that large numbers of cyanobacterial species have the capacity to acclimate to a wide variety of light colors through the use of a range of different CA processes.
Facts and Myths about Authentic Bacteria/Lessons from Pioneers of Microbiology
(2009-01-07) Gest, Howard
A commentary on sundry aspects of bacteria in the natural world and in the laboratory, touching on: diversity, nutrition, the species concept, classification and taxonomy, “computer bacteroids,” the “unculturability” myth, “astrobiology.” extremophiles, and Gest’s Postulates
Functional Consequences of Subunit Diversity in RNA Polymerases II and V
(Elsevier (Cell Press), 2012) Tan, E.H.; Blevins, T.; Ream, T.S.; Pikaard, C.S.
Multisubunit RNA polymerases IV and V (Pol IV and Pol V) evolved as specialized forms of Pol II that mediate RNA-directed DNA methylation (RdDM) and transcriptional silencing of transposons, viruses, and endogenous repeats in plants. Among the subunits common to Arabidopsis thaliana Pols II, IV, and V are 93% identical alternative ninth subunits, NRP(B/D/E)9a and NRP(B/D/E)9b. The 9a and 9b subunit variants are incompletely redundant with respect to Pol II; whereas double mutants are embryo lethal, single mutants are viable, yet phenotypically distinct. Likewise, 9a or 9b can associate with Pols IV or V but RNA-directed DNA methylation is impaired only in 9b mutants. Based on genetic and molecular tests, we attribute the defect in RdDM to impaired Pol V function. Collectively, our results reveal a role for the ninth subunit in RNA silencing and demonstrate that subunit diversity generates functionally distinct subtypes of RNA polymerases II and V.
Generating enveloped virus-like particles with in vitro assembled cores
(Elsevier, 2011-02-19) Mukhopadhyay, Suchetana; Cheng, Fan
Alphaviruses are comprised of a nucleocapsid core surrounded by a lipid membrane containing glycoprotein spikes. Previous work demonstrated that in vitro assembled core-like particles are similar in structure to the nucleocapsid core in the native virus. Here we demonstrate that in vitro assembled core-like particles can be inserted into viral glycoprotein-expressing cells to generate enveloped virus-like particles. These virus-like particles bud from cells like native virus, are similar in size to the native virus, and can enter cells to release the contents of the core-like particle into the cytoplasm of the cell. Virus-like particles can be used to infect cells with biological and non-biological cargoes. The generation of enveloped virus-like particles containing an in vitro core and in vivo synthesized glycoproteins has applications for gene and drug delivery, medical imaging, and also basic mechanistic studies of virus assembly.
Global Patterns of Tissue-Specific Alternative Polyadenylation in Drosophila
(Cell Reports, 2012) Smibert, P.; Miura, P.; Westholm, J.O.; Shenker, S.; May, G.; Duff, M.O.; Zhang, D.; Eads, B.D.; Carlson, J.; Brown, J.B.; Eisman, R.C.; Andrews, J.; Kaufman, T.; Cherbas, P.; Celniker, S.E.; Graveley, B.R.; Lai, E.C.
We analyzed the usage and consequences of alternative cleavage and polyadenylation (APA) in $\textit{Drosophila melanogaster}$ by using >1 billion reads of stranded mRNA-seq across a variety of dissected tissues. Beyond demonstrating that a majority of fly transcripts are subject to APA, we observed broad trends for 3′ untranslated region (UTR) shortening in the testis and lengthening in the central nervous system (CNS); the latter included hundreds of unannotated extensions ranging up to 18 kb. Extensive northern analyses validated the accumulation of full-length neural extended transcripts, and in situ hybridization indicated their spatial restriction to the CNS. Genes encoding RNA binding proteins (RBPs) and transcription factors were preferentially subject to 3′ UTR extensions. Motif analysis indicated enrichment of miRNA and RBP sites in the neural extensions, and their termini were enriched in canonical cis elements that promote cleavage and polyadenylation. Altogether, we reveal broad tissue-specific patterns of APA in $\textit{Drosophila}$ and transcripts with unprecedented 3′ UTR length in the nervous system.
Growth‐independent cross‐feeding modifies boundaries for coexistence in a bacterial mutualism
(Environmental Microbiology, 2017-06) McCully, Alexandra L.; LaSarre, Breah; McKinlay, James B.
Nutrient cross‐feeding can stabilize microbial mutualisms, including those important for carbon cycling in nutrient‐limited anaerobic environments. It remains poorly understood how nutrient limitation within natural environments impacts mutualist growth, cross‐feeding levels and ultimately mutualism dynamics. We examined the effects of nutrient limitation within a mutualism using theoretical and experimental approaches with a synthetic anaerobic coculture pairing fermentative Escherichia coli and phototrophic Rhodopseudomonas palustris. In this coculture, E. coli and R. palustris resemble an anaerobic food web by cross‐feeding essential carbon (organic acids) and nitrogen (ammonium) respectively. Organic acid cross‐feeding stemming from E. coli fermentation can continue in a growth‐independent manner during nitrogen limitation, while ammonium cross‐feeding by R. palustris is growth‐dependent. When ammonium cross‐feeding was limited, coculture trends changed yet coexistence persisted under both homogenous and heterogenous conditions. Theoretical modelling indicated that growth‐independent fermentation was crucial to sustain cooperative growth under conditions of low nutrient exchange. In contrast to stabilization at most cell densities, growth‐independent fermentation inhibited mutualistic growth when the E. coli cell density was adequately high relative to that of R. palustris. Thus, growth‐independent fermentation can conditionally stabilize or destabilize a mutualism, indicating the potential importance of growth‐independent metabolism for nutrient‐limited mutualistic communities.
Historical Adventures in Scientific Discovery: Microbiology/Biochemistry
(2009-02-12) Gest, Howard
Recent textbooks are generally deficient in respect to the history of major discoveries in microbiology/biochemistry. These "Historical Adventures" focus on the backgrounds and contributions of a number of relatively unknown pioneering investigators, as well as some of the familiar "giants." This publication is part of "An Experiment in Scientific Biography". A companion part, "Associations with distinguished scientists ..." can be accessed at https://scholarworks.iu.edu/dspace/bitstream/2022/1083/1/Gestfinal.pdf.

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