Temperature drives the continental-scale distribution of key microbes in topsoil communities.

Global warming will likely force terrestrial plant and animal species to migrate toward cooler areas or sustain range losses; whether this is also true for microorganisms remains unknown. Through continental-scale compositional surveys of soil crust microbial communities across arid North America, we observed a latitudinal replacement in dominance between two key topsoil cyanobacteria that was driven largely by temperature. The responses to temperature of enrichment cultures and cultivated strains support this contention, with one cyanobacterium (Microcoleus vaginatus) being more psychrotolerant and less thermotolerant than the other (M. steenstrupii). In view of our data and regional climate predictions, the latter cyanobacterium may replace the former in much of the studied area within the next few decades, with unknown ecological consequences for soil fertility and erodibility.

A comparative genomics approach to understanding the biosynthesis of the sunscreen scytonemin in cyanobacteria.

BACKGROUND: The extracellular sunscreen scytonemin is the most common and widespread indole-alkaloid among cyanobacteria. Previous research using the cyanobacterium Nostoc punctiforme ATCC 29133 revealed a unique 18-gene cluster (NpR1276 to NpR1259 in the N. punctiforme genome) involved in the biosynthesis of scytonemin. We provide further genomic characterization of these genes in N. punctiforme and extend it to homologous regions in other cyanobacteria. RESULTS: Six putative genes in the scytonemin gene cluster (NpR1276 to NpR1271 in the N. punctiforme genome), with no previously known protein function and annotated in this study as scyA to scyF, are likely involved in the assembly of scytonemin from central metabolites, based on genetic, biochemical, and sequence similarity evidence. Also in this cluster are redundant copies of genes encoding for aromatic amino acid biosynthetic enzymes. These can theoretically lead to tryptophan and the tyrosine precursor, p-hydroxyphenylpyruvate, (expected biosynthetic precursors of scytonemin) from end products of the shikimic acid pathway. Redundant copies of the genes coding for the key regulatory and rate-limiting enzymes of the shikimic acid pathway are found there as well. We identified four other cyanobacterial strains containing orthologues of all of these genes, three of them by database searches (Lyngbya PCC 8106, Anabaena PCC 7120, and Nodularia CCY 9414) and one by targeted sequencing (Chlorogloeopsis sp. strain Cgs-089; CCMEE 5094). Genomic comparisons revealed that most scytonemin-related genes were highly conserved among strains and that two additional conserved clusters, NpF5232 to NpF5236 and a putative two-component regulatory system (NpF1278 and NpF1277), are likely involved in scytonemin biosynthesis and regulation, respectively, on the basis of conservation and location. Since many of the protein product sequences for the newly described genes, including ScyD, ScyE, and ScyF, have export signal domains, while others have putative transmembrane domains, it can be inferred that scytonemin biosynthesis is compartmentalized within the cell. Basic structural monomer synthesis and initial condensation are most likely cytoplasmic, while later reactions are predicted to be periplasmic. CONCLUSION: We show that scytonemin biosynthetic genes are highly conserved among evolutionarily diverse strains, likely include more genes than previously determined, and are predicted to involve compartmentalization of the biosynthetic pathway in the cell, an unusual trait for prokaryotes.

Modestobacter versicolor sp. nov., an actinobacterium from biological soil crusts that produces melanins under oligotrophy, with emended descriptions of the genus Modestobacter and Modestobacter multiseptatus Mevs et al. 2000.

A novel isolate, CP153-2(T), was obtained from topsoil biological crusts in the Colorado Plateau (USA). Colonies were black in colour due to melanin-like pigments when grown on oligotrophic medium, but not when grown on copiotrophic medium. Induction of melanogenesis was independent of growth phase or illumination conditions, including exposure to UVB and UVA radiation, but exposure to UVB could enhance total pigment production and growth under low nitrogen prevented its synthesis. This mode of regulation was previously unknown among melanin-producing bacteria. Polyphasic characterization of the strain revealed that cells were short, straight to curved or irregular rods that developed into pairs and formed multiseptate short filaments, with rare bud-like cells. Short rods were typically motile by means of flagella; multicellular structures tended to be sessile. Cells stained Gram-positive, grew at 4-30 degrees C and had a narrow range of pH tolerance (pH 5-9). The major fatty acids were iso-C(15:0) iso-C(16 : 0), anteiso-C(15 : 0) and C(18 : 1); MK-9(H(4)) was the major respiratory quinone. Its peptidoglycan contained meso-diaminopimelic acid. Based on 16S rRNA gene sequence similarity data, its closest relative (98.1 % similarity) was Modestobacter multiseptatus DSM 44406(T), which is similar morphologically. Based on the above characteristics, strain CP153-2(T) was also assigned to the genus Modestobacter. However, CP153-2(T) had a relatedness of only 49.9 % in whole-genome reassociation comparisons with the type strain of M. multiseptatus and thus formally represents a novel species, for which the name Modestobacter versicolor sp. nov. is proposed. Additional evidence in support of a novel species comes from phenotypic and chemotaxonomic characteristics. Strain CP153-2(T) (=ATCC BAA-1040(T) =DSM 16678(T)) is the type strain of M. versicolor.