Diversity assessment of photosynthesizers: comparative analysis of pre-cultivated and natural microbiome of sediments from Cerrado biome in Maranhão, Brazil.

Photosynthetic microorganisms are important components of most ecosystems and have important roles regarding biogeochemical cycles and the basis of the trophic chain. However, they sometimes are present in low abundance compared to other heterotrophic organisms. The Chapada das Mesas National Park (PNCM) is a Conservation Unit in Brazilian Cerrado biome, which is considered a hotspot for biodiversity conservation and possesses important rivers, waterfalls, and springs with economical and touristic importance. The aim of this study was to perform a comparative analysis of enriched and total microbiome of sediments to understand the impact of pre-cultivation in discovery of underrepresented groups like photosynthesizers. All sediment samples were cultivated in BG-11 medium under illumination to enrich for photosynthetic microorganisms and both the raw samples and the enriched ones were submitted to DNA extraction and sequencing of the V3-V4 hypervariable region of the 16S rRNA gene on the Ion Torrent platform. The reads were analyzed using QIIME2 software and the Phyloseq package. The enrichment allowed detection and identification of many genera of cyanobacteria in the Chapada das Mesas National Park (PNCM), which would probably not be possible without the combination of approaches. A total of 58 groups of photosynthetic microorganisms were classified in the samples from the enrichments and their relative abundance based on amplified 16S rRNA sequences were estimated, highlighting the genus Synechocystis which represented 10.10% of the abundance of the phylum Cyanobacteria and the genus Dunaliella, which represented 45.66% of the abundance of algae as the most abundant groups at the PNCM. In the enrichments, microorganisms from the phyla Proteobacteria (45.2%), Bacteroidetes (18%), and Planctomycetes (3.3%) were also identified, since there are ecological associations between the photosynthetic community and other groups of heterotrophic microorganisms. As for the functional analysis, metabolic functions associated with methanotrophy and methylotrophy, hydrocarbon degradation, phototrophy, and nitrogen fixation were predicted. The results highlight a great diversity of photosynthetic microorganisms in Cerrado and the importance of using a combination of approaches when analyzing target groups which are usually underrepresented such as cyanobacteria and microalgae.

High-quality draft genome sequence of pantanalinema sp. GBBB05, a cyanobacterium from cerrado biome

Cyanobacteria comprise one of the oldest and most diverse phyla in the Bacteria domain and are recognized for their importance in the biosphere evolution. Members of this phylum can be found in a wide variety of environments reflecting their photosynthetic ability, adaptability to various environmental conditions, and diversified metabolism. Such characteristics make cyanobacteria one of the preferred targets for research on bioactive compounds and new enzymes (Schirrmeister et al., 2011; Dittmann et al., 2015). Pantanalinema was described as a new genus of the Leptolyngbyaceae cyanobacterial family by a polyphasic approach, which included morphological characteristics, 16S rRNA gene phylogeny, 16S-23S ITS rRNA secondary structures, and physiological characteristics such as adaptability to pH variations (Vaz et al., 2015). This genus has been described only in Brazilian biomes such as the Pantanal and the Amazon, the first isolates being found in a lake. These Pantanalinema isolates were characterized by their ability to grow over a wide pH range (pH 4 to 11) as well as to modify the culture medium pH around neutrality (pH 6 to 7.4). Due to these characteristics, it is thought that this genus can occupy a variety of ecological niches, such as alkaline or slightly acidic water bodies (Vaz et al., 2015; Genuário et al., 2017). Taxonomic classification of Pantanalinema isolates requires the use of molecular markers as this genus is morphologically very similar to the recently described genus Amazoninema, which, in turn, has comparable morphology to other genera of the Leptolyngbyaceae family (Genuário et al., 2018). In this work, we report the genome sequence of a new Pantanalinema strain, named GBBB05, which was isolated from the Brazilian Cerrado biome. This is the first genome assembly for the Pantanalinema genus, which, along with the analyses provided here, is expected to enhance our understanding of this genus’s metabolic potential