Comparison of the terrestrial cyanobacteriumLeptolyngbyasp. NIES-2104 and the freshwaterLeptolyngbya boryanaPCC 6306 genomes

Abstract

The cyanobacterial genus Leptolyngbya is widely distributed throughout terrestrial environments and freshwater. Because environmental factors, such as oxygen level, available water content, and light intensity, vary between soil surface and water bodies, terrestrial Leptolyngbya should have genomic differences with freshwater species to adapt to a land habitat. To study the genomic features of Leptolyngbya species, we determined the complete genome sequence of the terrestrial strain Leptolyngbya sp. NIES-2104 and compared it with that of the near-complete sequence of the freshwater Leptolyngbya boryana PCC 6306. The greatest differences between these two strains were the presence or absence of a nitrogen fixation gene cluster for anaerobic nitrogen fixation and several genes for tetrapyrrole synthesis, which can operate under micro-oxic conditions. These differences might reflect differences in oxygen levels where these strains live. Both strains have the genes for trehalose biosynthesis, but only Leptolyngbya sp. NIES-2104 has genetic capacity to produce a mycosporine-like amino acid, mycosporine-glycine. Mycosporine-glycine has an antioxidant action, which may contribute to adaptation to terrestrial conditions. These features of the genomes yielded additional insights into the classification and physiological characteristics of these strains.

What distinguishes cyanobacteria able to revive after desiccation from those that cannot: the genome aspect

“…NIES 2104 (hereafter Leptolyngbya 2104) and Leptolyngbya sp. PCC 6303 (about 6.4 Mb and 7.3Mb, respectively (Shimura et al ., )) and somewhat smaller than Leptolyngbya sp. Heron Island [8.06 Mb, (Paul et al ., )].…”

“…Nevertheless, like several other heterocyst‐lacking cyanobacteria, some Leptolyngbya strains such as PCC 6306 (Shimura et al ., ) are able to fix atmospheric N 2 and possess at least some of the essential genes (Janson et al ., ; Li et al ., ; Tsujimoto et al ., ). Analysis of the genome sequence of two other desiccation‐tolerant filamentous cyanobacteria, Leptolyngbya 2104 (Shimura et al ., ) and Microcoleus vaginatus PCC 9802, did not identify the gene cluster essential for anaerobic N 2 fixation. In contrast, our analysis revealed the presence of a large cluster of nif genes identified in scaffold 1 of the L. ohadii sequence (Fig.…”

“…We also confirmed that Nostoc 7120 represents an intermediate case, since it can withstand mild desiccation (Katoh et al ., ; Higo et al ., ; Katoh, ; Singh et al ., ) but not the rapid and repeated hydration/desiccations experienced by specialized cyanobacteria in desert crusts (Raanan et al ., ). Two Leptolyngbya species were included, L. ohadii and Leptolyngbya 2104 that was used as a model of desiccation‐tolerant organism in an earlier study (Shimura et al ., ). Although clustered closely to L. ohadii in the phylogenetic tree (Supporting Information Fig.…”

“…Like other so‐called Leptolyngbya spp., L. ohadii does not form heterocysts even when exposed to N‐limiting conditions (Janson et al ., ; Mes and Stal, ; Taton et al ., ). Nevertheless, like several other heterocyst‐lacking cyanobacteria, some Leptolyngbya strains such as PCC 6306 (Shimura et al ., ) are able to fix atmospheric N 2 and possess at least some of the essential genes (Janson et al ., ; Li et al ., ; Tsujimoto et al ., ). Analysis of the genome sequence of two other desiccation‐tolerant filamentous cyanobacteria, Leptolyngbya 2104 (Shimura et al ., ) and Microcoleus vaginatus PCC 9802, did not identify the gene cluster essential for anaerobic N 2 fixation.…”

“…These strains are spread over different clades in the cyanobacterial phylum (Shih et al, 2013) and are quite divergent in their habitat, spanning fresh, salty and marine water bodies and BSCs in hot and cold deserts. Some Leptolyngbya strains are able to resurrect after desiccation while others are restricted to humid habitats and are unable to revive after frequent hydration/ dehydration cycles; some but not all are able to fix atmospheric N 2 (Shimura et al, 2015). Thus, the so-called Leptolyngbya group is certainly not a true genus, but rather includes species from different genera and of little or no systematic relation to each other.…”