Cave microbial community composition in oceanic islands: disentangling the effect of different colored mats in diversity patterns of Azorean lava caves

Abstract

Processes determining diversity and composition of bacterial communities in island volcanic caves are still poorly understood. Here, we characterized colored microbial mats in 14 volcanic caves from two oceanic islands of the Azores using 16S rRNA gene sequences. Factors determining community diversity (α) and composition (β) were explored, namely colored mats, caves and islands, as well as environmental and chemical characteristics of caves. Additive partitioning of diversity using OTU occurrence showed a greater influence of β-diversity between islands and caves that may relate to differences in rare OTUs (singletons and doubletons) across scales. In contrast, Shannon diversity partitioning revealed the importance of the lowest hierarchical level (α diversity, colored mat), suggesting a dominance of cosmopolitan OTUs (>1%) in most samples. Cosmopolitan OTUs included members involved in nitrogen cycling, supporting the importance of this process in Azorean caves. Environmental and chemical conditions in caves did not show any significant relationship to OTU diversity and composition. The absence of clear differences between mat colors and across scales may be explained by (1) the geological youth of the cave system (cave communities have not had enough time to diverge) or/and (2) community convergence, as the result of selection pressure in extreme environments.

Microbial Diversity in Moonmilk of Baeg-nyong Cave, Korean CZO

“…Purple sulfur bacteria Chromatiales were the most abundant in dry moonmilk, but were rarely detected in the other samples. A representative sequence of the OTU of Chromatiales was found to be identical to that of bacteria in a limestone cave in Spain and Portugal (Riquelme et al, 2015). Previous studies also reported the phylotype of Chromatiales to be one of the core microbiomes in limestone caves (Porca et al, 2012;Engel, 2015).…”

“…Many spheroidal grains were found in dry moonmilk and some materials stuck around these structures (Figures 6C,D). Recent studies of microbial mats in limestone caves showed that roundshaped microstructures were present in various microbial mats (Riquelme et al, 2015;Cao et al, 2016). These structures were similar to bacteria in size, suggesting that bacterial activity has the potential to affect the formation of these round-shaped structures.…”

Yellow coloured mats from lava tubes of La Palma (Canary Islands, Spain) are dominated by metabolically active Actinobacteria

“…Different researches based on the study of bacterial communities demonstrated the prevalence of several phylogenetic groups at higher taxonomic levels (e.g. phylum and class) in lava tubes around the world 5 , 13 , 14 . The authors reported Actinobacteria , Proteobacteria , Acidobacteria , Nitrospirae , Firmicutes , Bacteroidetes and Chloroflexi as the main bacterial phyla present in lava tubes.…”

“…The appearance of coloured microbial mats on rock art caves producing biodeterioration awakened interest for studying these communities 2 , 17 , 18 . In recent years, study efforts have been focused on trying to explain the origin of coloured biogenic formations as well as the direct relationship between pigmentation and its production by specific phylogenetic groups 4 , 13 , 19 . In fact, several studies have been focused on determining bacterial phylotypes as the cause of pigmentation 4 , 13 , 14 , 19 .…”

Microbial megacities fueled by methane oxidation in a mineral spring cave

“…In subsurface and groundwater systems, biofilms are largely considered oligotrophic ( Griebler and Lueders, 2009 ; Ortiz et al , 2014 ). Nonetheless, a number of caves and karstic systems have been reported to host biofilms rich in microbial diversity and with elevated, mostly lithotrophic biogeochemical activities ( Holmes et al , 2001 ; Engel et al , 2010 ; Jones et al , 2010 ; Rusznyák et al , 2012 ; Barton et al , 2014 ; Riquelme et al , 2015 ).…”