Anaerobic 3-methylhopanoid production by an acidophilic photosynthetic purple bacterium

Bacterial lipids are well-preserved in ancient rocks and certain ones have been used as indicators of specific bacterial metabolisms or environmental conditions existing at the time of rock deposition. Here we show that an anaerobic bacterium produces 3-methylhopanoids, pentacyclic lipids previously detected only in aerobic bacteria and widely used as biomarkers for methane-oxidizing bacteria. Both Rhodopila globiformis, a phototrophic purple nonsulfur bacterium isolated from an acidic warm spring in Yellowstone, and a newly isolated Rhodopila species from a geochemically similar spring in Lassen Volcanic National Park (USA), synthesized 3-methylhopanoids and a suite of related hopanoids and contained the genes encoding the necessary biosynthetic enzymes. Our results show that 3-methylhopanoids can be produced under anoxic conditions and challenges the use of 3-methylhopanoids as biomarkers of oxic conditions in ancient rocks and as prima facie evidence that methanotrophic bacteria were active when the rocks were deposited.

A Novel Membrane Protein in the Rhodobacter sphaeroides LH1-RC Photocomplex

We present a cryo-EM structure of the monomeric light-harvesting-reaction center (LH1-RC) core complex from photosynthetic purple bacterium Rhodobacter (Rba.) sphaeroides at 2.9 Å resolution. The LH1 complex forms a C-shaped structure composed of 14 αβ-polypeptides around the RC with a large ring opening. From the cryo-EM density map, a previously unrecognized integral membrane protein, referred to as protein-U, was identified. Protein-U has a U-shaped conformation near the LH1-ring opening and was annotated as a hypothetical protein in the Rba. sphaeroides genome. Deletion of protein-U resulted in a mutant strain that expressed a much-reduced amount of the dimeric LH1-RC, indicating an important role for protein-U in dimerization of the LH1-RC complex. PufX was located opposite protein-U on the LH1-ring opening, and both its position and conformation differed from that of previous reports of dimeric LH1-RC structures obtained at low-resolution. Twenty-six molecules of the carotenoid spheroidene arranged in two distinct configurations were resolved in the Rba. sphaeroides LH1 and were positioned within the complex to block its pores. Our findings offer a new view of the core photocomplex of Rba. sphaeroides and the connections between structure and function in bacterial photocomplexes in general.

Anaerobic 3-Methylhopanoid Production By An Acidophilic Phototrophic Purple Bacterium

Bacterial lipids are well preserved in ancient rocks and certain ones have been used as indicators of specific bacterial metabolisms or environmental conditions existing at the time of rock deposition. Here we show that an anaerobic bacterium produces 3-methylbacteriohopanepolyols (3-MeBHPs), pentacyclic lipids previously detected only in aerobic bacteria and widely used as biomarkers for methane-oxidizing bacteria. Both Rhodopila globiformis, a phototrophic purple nonsulfur bacterium isolated from an acidic warm spring in Yellowstone, and a newly isolated Rhodopila species from a geochemically similar spring in Lassen Volcanic National Park (USA), synthesized 3-MeBHPs and a suite of related BHPs and contained the genes encoding the necessary biosynthetic enzymes. Our results show that 3-MeBHPs can be produced under anoxic conditions and challenges the use of 3-MeBHPs as biomarkers of oxic conditions in ancient rocks and as prima facie evidence that methanotrophic bacteria were active when the rocks were deposited.

Construction of engineered RuBisCO Kluyveromyces marxianus for a dual microbial bioethanol production system

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) genes play important roles in CO2 fixation and redox balancing in photosynthetic bacteria. In the present study, the kefir yeast Kluyveromyces marxianus 4G5 was used as host for the transformation of form I and form II RubisCO genes derived from the nonsulfur purple bacterium Rhodopseudomonas palustris using the Promoter-based Gene Assembly and Simultaneous Overexpression (PGASO) method. Hungateiclostridium thermocellum ATCC 27405, a well-known bacterium for its efficient solubilization of recalcitrant lignocellulosic biomass, was used to degrade Napier grass and rice straw to generate soluble fermentable sugars. The resultant Napier grass and rice straw broths were used as growth media for the engineered K. marxianus. In the dual microbial system, H. thermocellum degraded the biomass feedstock to produce both C5 and C6 sugars. As the bacterium only used hexose sugars, the remaining pentose sugars could be metabolized by K. marxianus to produce ethanol. The transformant RubisCO K. marxianus strains grew well in hydrolyzed Napier grass and rice straw broths and produced bioethanol more efficiently than the wild type. Therefore, these engineered K. marxianus strains could be used with H. thermocellum in a bacterium-yeast coculture system for ethanol production directly from biomass feedstocks.

Electrode assisted production of platform chemicals in Rhodobacter sphaeroides.

<p>The aim of this study was to establish cathodic biofilms of the photosynthetic non sulfur purple bacterium <em>Rhodobacter sphaeroides</em> as biocatalyst for the production of platform chemicals from carbon dioxide as carbon source and an electrical current as energy and electron source.  Therefore, <em>R. sphaeroides</em> was cultivated in a bioelectrical system (BES) in which light, CO<sub>2</sub> and a stable current were provided. Chronopotentiometric measurements revealed the cathode potential necessary to maintain the applied current of I = 22,2 µA/cm². Interestingly, exposure of <em>R. sphaeroides</em> to the antibiotic kanamycin lead to increased biofilm production on the cathode although the organism expressed the necessary resistance marker. This enhanced biofilm production raised the potential by 170 mV to E = -1 V compared to the wildtype (E = -1,17 V) and hence increased the efficiency of the process. To date, the molecular basis of this effect remains unclear and is under investigation using a proteomic approach. To elucidate, if the productivity of <em>R. sphaeroides</em> as a production strain is also enhanced, the production of acetoin was established as proof of principle. After the confirmation of the acetoin production under autotrophic conditions, various approaches to increase the space-time yields of the process were conducted and their effect will be presented.  </p>

Draft Genome Assembly of Rhodobacter sphaeroides 2.4.1 Substrain H2 from Nanopore Data

ABSTRACT Rhodobacter sphaeroides is a purple bacterium with complex genomic architecture. Here, a draft genome is reported for R. sphaeroides strain 2.4.1 substrain H2, which was generated exclusively from Nanopore sequencing data.

A marine photosynthetic microbial cell factory as a platform for spider silk production

Photosynthetic microorganisms such as cyanobacteria, purple bacteria and microalgae have attracted great interest as promising platforms for economical and sustainable production of bioenergy, biochemicals, and biopolymers. Here, we demonstrate heterotrophic production of spider dragline silk proteins, major ampullate spidroins (MaSp), in a marine photosynthetic purple bacterium, Rhodovulum sulfidophilum, under both photoheterotrophic and photoautotrophic growth conditions. Spider silk is a biodegradable and biocompatible material with remarkable mechanical properties. R. sulfidophilum grow by utilizing abundant and renewable nonfood bioresources such as seawater, sunlight, and gaseous CO2 and N2, thus making this photosynthetic microbial cell factory a promising green and sustainable production platform for proteins and biopolymers, including spider silks.