Actinobacteria and Cyanobacteria Diversity in Terrestrial Antarctic Microenvironments Evaluated by Culture-Dependent and Independent Methods.

Adriana Rego,Pedro N Leão,Charles K Lee,António G G Sousa,Mafalda S Baptista,Teresa P Martins,S Craig Cary,Vitor Ramos,Francisco Raio,Maria F Carvalho,Catarina Magalhães,Hugo Ribeiro,Joana Séneca

doi:10.3389/fmicb.2019.01018

Adriana Rego, Pedro N Leão + Show 11 more

Open Access

https://doi.org/10.3389/fmicb.2019.01018

Copy DOI

Abstract

Bacterial diversity from McMurdo Dry Valleys in Antarctica, the coldest desert on earth, has become more easily assessed with the development of High Throughput Sequencing (HTS) techniques. However, some of the diversity remains inaccessible by the power of sequencing. In this study, we combine cultivation and HTS techniques to survey actinobacteria and cyanobacteria diversity along different soil and endolithic micro-environments of Victoria Valley in McMurdo Dry Valleys. Our results demonstrate that the Dry Valleys actinobacteria and cyanobacteria distribution is driven by environmental forces, in particular the effect of water availability and endolithic environments clearly conditioned the distribution of those communities. Data derived from HTS show that the percentage of cyanobacteria decreases from about 20% in the sample closest to the water source to negligible values on the last three samples of the transect with less water availability. Inversely, actinobacteria relative abundance increases from about 20% in wet soils to over 50% in the driest samples. Over 30% of the total HTS data set was composed of actinobacterial strains, mainly distributed by 5 families: Sporichthyaceae, Euzebyaceae, Patulibacteraceae, Nocardioidaceae, and Rubrobacteraceae. However, the 11 actinobacterial strains isolated in this study, belonged to Micrococcaceae and Dermacoccaceae families that were underrepresented in the HTS data set. A total of 10 cyanobacterial strains from the order Synechococcales were also isolated, distributed by 4 different genera (Nodosilinea, Leptolyngbya, Pectolyngbya, and Acaryochloris-like). In agreement with the cultivation results, Leptolyngbya was identified as dominant genus in the HTS data set. Acaryochloris-like cyanobacteria were found exclusively in the endolithic sample and represented 44% of the total 16S rRNA sequences, although despite our efforts we were not able to properly isolate any strain from this Acaryochloris-related group. The importance of combining cultivation and sequencing techniques is highlighted, as we have shown that culture-dependent methods employed in this study were able to retrieve actinobacteria and cyanobacteria taxa that were not detected in HTS data set, suggesting that the combination of both strategies can be usefull to recover both abundant and rare members of the communities.

Highlights

The continent of Antarctica comprises about 0.34% ice-free areas (Convey, 2011) characterized by extreme cold and dry conditions (Wierzchos et al, 2004)
The bacterial community composition across the transect was assessed through 454 pyrosequencing of the 16S rRNA gene
Leptolyngbya is usually associated with lake and maritime Antarctic communities (Taton et al, 2006; Zakhia et al, 2008), while Phormidium is commonly found in Antarctic water-saturated soils and river beds (Vincent et al, 1993) but both were found in polar deserts (Michaud et al, 2012). These findings suggest, as already shown for Antarctic (Pointing et al, 2007; Wood et al, 2008; Van Goethem et al, 2016) and other hyper-arid deserts (Kastovská et al, 2005), that water availability and distance to aquatic ecosystems shapes the taxonomic composition of the cyanobacterial communities

Summary

Introduction

The continent of Antarctica comprises about 0.34% ice-free areas (Convey, 2011) characterized by extreme cold and dry conditions (Wierzchos et al, 2004). In the McMurdo Dry Valleys ( Dry Valleys), the largest ice-free region of the Antarctic continent (Pointing et al, 2009) and the coldest and driest desert on earth (Wood et al, 2008), the environmental stresses range from high variations in temperature (Doran et al, 2002), low nutrient availability and soil moisture (Buelow et al, 2016) to high ultraviolet solar radiation incidence (Perera et al, 2018) Under such constraints, embracing the limits of physiological adaptability, microorganisms developed specialized strategies to survive, such as the colonization of edaphic and endolithic microenvironments (Walker and Pace, 2007), the entry into dormancy states (Goordial et al, 2017) and the biosynthesis of secondary metabolites (Wilson and Brimble, 2009; Tian et al, 2017). The formation of spores allows the survival in desert-like habitats (Mohammadipanah and Wink, 2016) and cyst-like resting forms have been described for non-sporulating actinobacteria species (Soina et al, 2004)

Methods

Results

Conclusion