Gene functionalities and genome structure in Bathycoccus prasinos reflect cellular specializations at the base of the green lineage

Background: Bathycoccus prasinos is an extremely small cosmopolitan marine green alga whose cells are covered with intricate spider's web patterned scales that develop within the Golgi cisternae before their transport to the cell surface. The objective of this work is to sequence and analyze its genome, and to present a comparative analysis with other known genomes of the green lineage. Research: Its small genome of 15 Mb consists of 19 chromosomes and lacks transposons. Although 70% of all B. prasinos genes share similarities with other Viridiplantae genes, up to 428 genes were probably acquired by horizontal gene transfer, mainly from other eukaryotes. Two chromosomes, one big and one small, are atypical, an unusual synapomorphic feature within the Mamiellales. Genes on these atypical outlier chromosomes show lower GC content and a significant fraction of putative horizontal gene transfer genes. Whereas the small outlier chromosome lacks colinearity with other Mamiellales and contains many unknown genes without homologs in other species, the big outlier shows a higher intron content, increased expression levels and a unique clustering pattern of housekeeping functionalities. Four gene families are highly expanded in B. prasinos, including sialyltransferases, sialidases, ankyrin repeats and zinc ion-binding genes, and we hypothesize that these genes are associated with the process of scale biogenesis. Conclusion: The minimal genomes of the Mamiellophyceae provide a baseline for evolutionary and functional analyses of metabolic processes in green plants

Cyanobacterial Siderophores—Physiology, Structure, Biosynthesis, and Applications

Siderophores are low-molecular-weight metal chelators that function in microbial iron uptake. As iron limits primary productivity in many environments, siderophores are of great ecological importance. Additionally, their metal binding properties have attracted interest for uses in medicine and bioremediation. Here, we review the current state of knowledge concerning the siderophores produced by cyanobacteria. We give an overview of all cyanobacterial species with known siderophore production, finding siderophores produced in all but the most basal clades, and in a wide variety of environments. We explore what is known about the structure, biosynthesis, and cycling of the cyanobacterial siderophores that have been characterized: Synechobactin, schizokinen and anachelin. We also highlight alternative siderophore functionality and technological potential, finding allelopathic effects on competing phytoplankton and likely roles in limiting heavy-metal toxicity. Methodological improvements in siderophore characterization and detection are briefly described. Since most known cyanobacterial siderophores have not been structurally characterized, the application of mass spectrometry techniques will likely reveal a breadth of variation within these important molecules

Manganese acquisition is facilitated by PilA in the cyanobacterium Synechocystis sp. PCC 6803.

Manganese is an essential element required by cyanobacteria, as it is an essential part of the oxygen-evolving center of photosystem II. In the presence of atmospheric oxygen, manganese is present as manganese oxides, which have low solubility and consequently provide low bioavailability. It is unknown if cyanobacteria are able to utilize these manganese sources, and what mechanisms may be employed to do so. Recent evidence suggests that type IV pili in non-photosynthetic bacteria facilitate electron donation to extracellular electron acceptors, thereby enabling metal acquisition. Our present study investigates whether PilA1 (major pilin protein of type IV pili) enables the cyanobacterium Synechocystis PCC 6808 to access to Mn from manganese oxides. We present physiological and spectroscopic data, which indicate that the presence of PilA1 enhances the ability of cyanobacteria to grow on manganese oxides. These observations suggest a role of PilA1-containing pili in cyanobacterial manganese acquisition

Exponential growth doubling times and maximal growth densities of <i>Synechocystis</i> sp. PCC 6803 in various growth conditions.

<p>Exponential growth doubling times and maximal growth densities of <i>Synechocystis</i> sp. PCC 6803 in various growth conditions.</p

Absorption spectra of a photoautotrophically grown <i>Synechocystis</i>. sp. PCC 6803 agar plate cultures.

<p>Wild type and Δ<i>sll1694</i> strains were grown on agar plates containing BG11 with Mn(II) chloride (A), Mn(III) (B), pyrolusite (C), and Mn(II, III) (D) as the exclusive manganese sources (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184685#pone.0184685.t002" target="_blank">Table 2</a>). Samples were standardized to an OD750 of 0.3, then traces normalized to 700 nm. Trend shown is indicative of nine separate measurements (three strains with three replicates each). The standard error of these replicates was calculated. Wild type standard error: ±3.9×10⁻² (A), ±4.1×10⁻² (B), ±2.8×10⁻² (C), ±4.5×10⁻² (D). Δ<i>sll1694</i> standard error: ±3.2×10⁻² (A), ±5.1×10⁻² (B), ±4.2×10⁻² (C), ±5.2×10⁻² (D).</p

<i>Synechocystis</i> sp. PCC 6803 growth phenotype observed on agar plate.

<p>Images of wild type and Δ<i>sll1694</i> strains on petri dishes containing agar-solidified BG11 medium with Mn(II) chloride (A), Mn(III) (B), pyrolusite (C), and Mn(II, III) (D) as the exclusive manganese sources. The extracellular protein harvested from the strains and normalized to chlorophyll content before analyzed by gel electrophoresis. The PilA protein (encoded by <i>sll1694</i>) is present in wild type strain where <i>sll1694</i> is intact, but not in the Δ<i>sll1694</i> strain where <i>sll1694</i> has been interrupted.</p

Gibson assembly primers for Δ<i>sll1694</i> strain generation.

<p>Gibson assembly primers for Δ<i>sll1694</i> strain generation.</p

Growth of various BG11 media.

<p>Photoautotrophic growth characteristics of wild type and the Δ<i>sll1694</i> strain grown on agar plates containing BG11 with Mn(II) chloride (A), Mn(III) (B), pyrolusite (C), and Mn(II, III) (D) as the exclusive manganese sources (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184685#pone.0184685.t002" target="_blank">Table 2</a>). The exponential doubling time of these growth conditions for both wild type and the Δ<i>sll1694</i> strain are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184685#pone.0184685.t003" target="_blank">Table 3</a>. Trend shown is indicative of nine separate measurements (three strains with three replicates each). Error bars showing the standard error of the biological replicates.</p

<i>Synechocystis</i> sp. PCC 6803 operon containing <i>pilA1</i> deletion schematic.

<p>The genomic organization of the <i>pilA1</i>-containing operon housed between <i>sll1693</i> and <i>slr1816</i> in the native wild type. The relative positions of primers used for strain construction are shown, with the number corresponding to the specific primer in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184685#pone.0184685.t001" target="_blank">Table 1</a>.</p