Alternative dimethylsulfoniopropionate biosynthesis enzymes in diverse and abundant microorganisms.

Dimethylsulfoniopropionate (DMSP) is an abundant marine organosulfur compound with roles in stress protection, chemotaxis, nutrient and sulfur cycling and climate regulation. Here we report the discovery of a bifunctional DMSP biosynthesis enzyme, DsyGD, in the transamination pathway of the rhizobacterium Gynuella sunshinyii and some filamentous cyanobacteria not previously known to produce DMSP. DsyGD produces DMSP through its N-terminal DsyG methylthiohydroxybutyrate S-methyltransferase and C-terminal DsyD dimethylsulfoniohydroxybutyrate decarboxylase domains. Phylogenetically distinct DsyG-like proteins, termed DSYE, with methylthiohydroxybutyrate S-methyltransferase activity were found in diverse and environmentally abundant algae, comprising a mix of low, high and previously unknown DMSP producers. Algae containing DSYE, particularly bloom-forming Pelagophyceae species, were globally more abundant DMSP producers than those with previously described DMSP synthesis genes. This work greatly increases the number and diversity of predicted DMSP-producing organisms and highlights the importance of Pelagophyceae and other DSYE-containing algae in global DMSP production and sulfur cycling.

The Triceptide Maturase OscB Catalyzes Uniform Cyclophane Topology and Accepts Diverse Gly-Rich Precursor Peptides.

Triceptides are a class of ribosomally synthesized and post-translationally modified peptides defined by an aromatic C(sp2) to Cß(sp3) bond. The Gly-rich repeat family of triceptide maturases (TIGR04261) are paired with precursor peptides (TIGR04260) containing a Gly-rich core peptide. These maturases are prevalent in cyanobacteria and catalyze cyclophane formation on multiple Ω1-X2-X3 motifs (Ω1 = Trp and Phe) of the Gly-rich precursor peptide. The topology of the individual rings has not been completely elucidated, and the promiscuity of these enzymes is not known. In this study, we characterized all the cyclophane rings formed by the triceptide maturase OscB and show the ring topology is uniform with respect to the substitution at Trp-C7 and the atropisomerism (planar chirality). Additionally, the enzyme OscB demonstrated substrate promiscuity on Gly-rich precursors and can accommodate a diverse array of engineered sequences. These findings highlight the versatility and implications for using OscB as a biocatalyst for producing polycyclophane-containing peptides for biotechnological applications.

Cyanobacterial α-carboxysome carbonic anhydrase is allosterically regulated by the Rubisco substrate RuBP.

Cyanobacterial CO2 concentrating mechanisms (CCMs) sequester a globally consequential proportion of carbon into the biosphere. Proteinaceous microcompartments, called carboxysomes, play a critical role in CCM function, housing two enzymes to enhance CO2 fixation: carbonic anhydrase (CA) and Rubisco. Despite its importance, our current understanding of the carboxysomal CAs found in α-cyanobacteria, CsoSCA, remains limited, particularly regarding the regulation of its activity. Here, we present a structural and biochemical study of CsoSCA from the cyanobacterium Cyanobium sp. PCC7001. Our results show that the Cyanobium CsoSCA is allosterically activated by the Rubisco substrate ribulose-1,5-bisphosphate and forms a hexameric trimer of dimers. Comprehensive phylogenetic and mutational analyses are consistent with this regulation appearing exclusively in cyanobacterial α-carboxysome CAs. These findings clarify the biologically relevant oligomeric state of α-carboxysomal CAs and advance our understanding of the regulation of photosynthesis in this globally dominant lineage.

A systematic exploration of bacterial form I rubisco maximal carboxylation rates.

Autotrophy is the basis for complex life on Earth. Central to this process is rubisco-the enzyme that catalyzes almost all carbon fixation on the planet. Yet, with only a small fraction of rubisco diversity kinetically characterized so far, the underlying biological factors driving the evolution of fast rubiscos in nature remain unclear. We conducted a high-throughput kinetic characterization of over 100 bacterial form I rubiscos, the most ubiquitous group of rubisco sequences in nature, to uncover the determinants of rubisco's carboxylation velocity. We show that the presence of a carboxysome CO2 concentrating mechanism correlates with faster rubiscos with a median fivefold higher rate. In contrast to prior studies, we find that rubiscos originating from α-cyanobacteria exhibit the highest carboxylation rates among form I enzymes (≈10 s-1 median versus <7 s-1 in other groups). Our study systematically reveals biological and environmental properties associated with kinetic variation across rubiscos from nature.

DesC1 and DesC2, Δ9 Fatty Acid Desaturases of Filamentous Cyanobacteria: Essentiality and Complementarity.

DesC1 and DesC2, which are fatty acid desaturases found in cyanobacteria, are responsible for introducing a double bond at the Δ9 position of fatty-acyl chains, which are subsequently esterified to the sn-1 and sn-2 positions of the glycerol moiety, respectively. However, since the discovery of these two desaturases in the Antarctic cyanobacterium Nostoc sp. SO-36, no further research has been reported. This study presents a comprehensive characterization of DesC1 and DesC2 through targeted mutagenesis and transformation using two cyanobacteria strains: Anabaena sp. PCC 7120, comprising both desaturases, and Synechocystis sp. PCC 6803, containing a single Δ9 desaturase (hereafter referred to as DesCs) sharing similarity with DesC1 in amino acid sequence. The results suggested that both DesC1 and DesC2 were essential in Anabaena sp. PCC 7120 and that DesC1, but not DesC2, complemented DesCs in Synechocystis sp. PCC 6803. In addition, DesC2 from Anabaena sp. PCC 7120 desaturated fatty acids esterified to the sn-2 position of the glycerol moiety in Synechocystis sp. PCC 6803.

Scavenging of nickel and chromium toxicity in Aulosira fertilissima by immobilization: effect on nitrogen assimilating enzymes

The ubiquity of heavy metals in the biosphere results in the introduction of high amounts of toxic metals into the food chain from various sources. In the present study, one of the strongest nitrogen fixing cyanobacterium of the rice fields, Aulosira fertilissima, was subjected to nickel and chromium stress and the ameliorating effect of immobilization was investigated. Cell immobilization could protect the organism's growth against the toxicity of both heavy metals at LC50 as compared to lethal concentrations. The nitrate reductase activity in free cells treated with the metals was substantially inhibited but immobilized cells treated with 0.1 ppm nickel was not affected by the metal treatment. Cell immobilization also resulted in a significant protection against sub-lethal concentration of chromium but to a lesser degree than it did with sub- lethal levels of nickel. Control immobilized cells also had higher Nitrogenase activity than control free cells. Nickel and chromium addition markedly decreased the enzyme activity in free cells but immobilized cells exposed to sublethal concentrations of both metals could overcome this decrease. Glutamine synthetase showed similar response under immobilized conditions compared to free cells with both metals. The addition of algal filtrate in 3:1 ratio further increased the nitrogenase activity compared with immobilized cells treated with sublethal doses of both metals. Immobilization facilitated higher uptake of nickel as compared to chromium. The observations of the present study clearly demonstrate the protective effect of immobilization on Aulosira fertilissima against Nickel and chromium toxicity. Rice field ecosystem thus possess a bidirectional natural metal ameliorating system where Aulosira mats act as a naturally immobilized system and the decay of Aulosira along with other cyanobacteria act as natural chelators protecting the rice plants from deleterious effects of the heavy metals. Most importantly is...

Biologically active peptides in cyanobacteria

Las cianobacterias se encuentran en el medio natural tanto en aguas dulces como saladas. Ellas pueden desarrollarse en grandes masas formando "blooms" (florecimientos) en aguas dulces y saladas en diferentes partes del mundo, incluyendo América del Sur. Tales florecimientos, así como crecimientos axénicos de cianobacterias, pueden ser una rica fuente de péptidos lineales o cíclicos únicos, muchos de los cuales presentan actividad biológica. En el pasado la mayor atención ha sido puesta en las toxinas microcistina y nodulatoria. Estos péptidos ciclicos son hepatotoxinas que inhíben la proteína fosfatasa 1 y 2A, después de ingresar específicamente al hepatocito mediante la captación de las sales biliares. Sin embargo, en cianobacterias se están encontrando péptidos con otras actividades biológicas. No obstante, auque no se consideren tóxicos, estos péptidos tienen actividades biológicas tales como: una fuerte y específica inhibición de las proteasas (tripsina, quimo-tripsina, elastasa, trombina, plasmina y la enzima procesadora angiotensina), anticianobacterias, antialgas, antihongos, inmunosupresores y promotores de diferenciación celular. Ejemplos de péptidos cianobacteriales inhibidores de proteasas son las cianopeptolina. Las interacciones de microcistina/proteína fosfatasa y de cianopeptolina/proteasa, han sido bien estudiadas por difracción de rayos x en cocristales y la determinación de microcistina y de otros péptidos puede ser realizada por métodos químicos y biológicos. Ambas, microcistina y cianopeptolina han sido recientemente determinadas en blooms producidos en cuerpos de agua en Chile, utilizando cromatografía líquida de alta resolución (HPLC), espectrometría de masas (MALDI-TOF) (PSD), además de bioensayos de inhibición enzimática