Biology subjects

LaSarre, B.

Publications and source records attributed to LaSarre, B..

4 recordsLinked to original sources

bioRxiv2018

Diverse spatial organization of photosynthetic membranes among purple nonsulfur bacteria

In diverse bacteria, proper cellular physiology requires the utilization of protein- or membrane-bound compartments that afford specific metabolic capabilities. One such compartment is the light-harvesting intracytoplasmic membrane (ICM) of purple nonsulfur bacteria (PNSB). Here we reveal that ICMs are subject to differential spatial organization among PNSB. We visualized ICMs in live cells of fourteen PNSB species by exploiting the natural autofluorescence of the photosynthetic machinery. We then quantitatively characterized ICM localization using automated computational analysis of autofluorescence patterns within single cells across the population. Our studies revealed that ICMs are localized in distinct subcellular patterns that differ between species; some PNSB elaborate ICMs throughout the cell, while others spatially restrict ICM to varying degrees. The most highly-restricted ICMs were localized in a specific pattern corresponding to progression of cell growth and division. An identical pattern of ICM restriction was conserved across at least two genera. Phylogenetic and phenotypic comparisons established that ICM localization and ICM architecture are not strictly interdependent and that neither trait fully correlates with the evolutionary relatedness of the species. This discovery of new diversity in bacterial cell organization has implications for understanding both the mechanisms underpinning spatial arrangement of bacterial compartments and the potential benefits of adopting different spatiotemporal patterns.

microbiology↗

bioRxiv2017

Recipient-Biased Competition For A Cross-Fed Nutrient Is Required For Coexistence Of Microbial Mutualists

Many mutualistic microbial relationships are based on nutrient cross-feeding. Traditionally, cross-feeding is viewed as being unidirectional from the producer to the recipient. This is likely true when a producers metabolic waste, such as fermentation products, provides carbon for a recipient. However, in some cases the cross-fed nutrient holds value for both the producer and the recipient. In such cases, there is potential for nutrient reacquisition by producer cells in a population, leading to competition against recipients. Here we investigate the consequences of inter-partner competition for cross-fed nutrients on mutualism dynamics using an anaerobic coculture pairing fermentative Escherichia coli and phototrophic Rhodopseudomonas palustris. In this coculture, E. coli excretes waste organic acids that provide carbon for R. palustris. In return, R. palustris cross-feeds E. coli ammonium (NH4+), a valuable nitrogen compound that both species prefer. To explore the potential for inter-partner competition, we first used a kinetic model to simulate cocultures with varied affinities for NH4+ in each species. The model predicted that inter-partner competition for cross-fed NH4+ could profoundly impact population dynamics. We then experimentally tested the predictions by culturing mutants lacking NH4+ transporters in both NH4+ competition assays and cooperative cocultures. Both theoretical and experimental results indicated that the recipient must have a competitive advantage in acquiring valuable cross-fed NH4+ to avoid collapse of the mutualism. Thus, the very metabolites that form the basis for cooperative cross-feeding can also be subject to competition between mutualistic partners.\n\nSignificanceMutualistic relationships, particularly those based on nutrient cross-feeding, promote stability of diverse ecosystems and drive global biogeochemical cycles. Cross-fed nutrients within these systems can be either waste products valued only by one partner or nutrients that both partners value. Here, we explore how inter-partner competition for a communally-valuable cross-fed nutrient impacts mutualism dynamics. We discovered that mutualism stability necessitates that the recipient have a competitive advantage against the producer in obtaining the cross-fed nutrient. We propose that the requirement for recipient-biased competition is a general rule for mutualistic coexistence based on the transfer of communally valuable resources, microbial or otherwise.

microbiology↗

bioRxiv2016

A Rhizobiales-specific unipolar polysaccharide adhesin contributes to Rhodopseudomonas palustris biofilm formation across diverse photoheterotrophic conditions

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 -proteobacteria, which use polar exopolysaccharide adhesins for cell-cell adhesion and surface attachment. Here, we show that Rhodopseudomonas palustris, a metabolically versatile member of the -proteobacterial order Rhizobiales, encodes 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.\n\nIMPORTANCEBacteria are ubiquitously found as surface-attached communities and cellular aggregates in nature. Here, we address how bacterial adhesion is coordinated in response to diverse environments using two complementary approaches. First, we examined how Rhodopseudomonas palustris, one of the most metabolically versatile organisms ever described, varies its adhesion to surfaces in response to different environmental conditions. We identified 2 critical genes for the production of a unipolar polysaccharide (UPP) and showed that UPP is important for adhesion when light and organic substrates are used for growth. Looking beyond R. palustris, we performed the most comprehensive survey to date on the conservation of UPP biosynthesis genes among a group of closely related bacteria that occupy diverse niches. Our findings suggest that UPP is important for free-living and plant-associated lifestyles but dispensable for animal pathogens. Additionally, we propose guidelines for classifying the adhesins produced by various -proteobacteria, facilitating future functional and comparative studies.

microbiology↗

bioRxiv2016

Growth-independent cross-feeding modifies boundaries for coexistence in a bacterial mutualism

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 nutrient 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 modeling indicated that growth-independent fermentation was crucial to sustain cooperative growth under conditions of low nutrient exchange. We also show that growth-independent fermentation sets the upper E. coli cell density at which this mutualism is supported. Thus, growth-independent fermentation can conditionally stabilize or destabilize a mutualism, indicating the potential importance of growth-independent metabolism for nutrient-limited mutualistic communities.\n\nConflict of interestThe authors declare no conflict of interest.

microbiology↗