Colored Microbial Coatings in Show Caves from the Galapagos Islands (Ecuador): First Microbiological Approach

Ana Z Miller,Fernando Gázquez,Ana T Caldeira,Paolo Forti,Jesús Martínez-Frías,Cesareo Saiz-Jimenez,Mathilda L Coutinho,José M Calaforra,Theofilos Toulkeridis,Manuel F Costa Pereira,Angela M García-Sánchez

doi:10.3390/coatings10111134

Abstract

The Galapagos Islands (Ecuador) have a unique ecosystem on Earth due to their outstanding biodiversity and geological features. This also extends to their subterranean heritage, such as volcanic caves, with plenty of secondary mineral deposits, including coralloid-type speleothems and moonmilk deposits. In this study, the bacterial communities associated with speleothems from two lava tubes of Santa Cruz Island were investigated. Field emission scanning electron microscopy (FESEM) was carried out for the morphological characterization and detection of microbial features associated with moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves. Microbial cells, especially filamentous bacteria in close association with extracellular polymeric substances (EPS), were abundant in both types of speleothems. Furthermore, reticulated filaments and Actinobacteria-like cells were observed by FESEM. The analysis of 16S rDNA revealed the presence of different bacterial phylotypes, many of them associated with the carbon, nitrogen, iron and sulfur cycles, and some others with pollutants. This study gives insights into subsurface microbial diversity of the Galapagos Islands and further shows the interest of the conservation of these subterranean geoheritage sites used as show caves.

Highlights

The Galapagos Islands were declared Natural Heritage of Humanity by the UNESCO in 1978 due to their outstanding biodiversity and unique geological features [1]
Abundant actinobacterial-like cells were observed on the surface of the coralloids, representing the most common fraction of the microbial components on the coralloid deposits found in the Royal Palm lava tube (Figure 3D)
To fully understand the microbial diversity of moonmilk and coralloid speleothems from lava tubes of the Galapagos Islands, we conducted for the first time a comprehensive microscopy and molecular biology investigation

Summary

Introduction

The Galapagos Islands were declared Natural Heritage of Humanity by the UNESCO in 1978 due to their outstanding biodiversity and unique geological features [1]. Several studies have shown that complex microbial communities are found in lava tubes, forming microbial mats (or biofilms) coating cave walls and secondary mineral deposits [12,13,14,15,16]. These biofilms are frequently found on the walls and ceilings of lava tubes, ranging from extensive coatings to small colonies. Riquelme et al [13] performed one of the largest sampling efforts in volcanic caves from Spain, Portugal, USA and Canada

Methods

Results

Conclusion