Biology subjects

Havlena, Z. E.

Publications and source records attributed to Havlena, Z. E..

3 recordsLinked to original sources

bioRxiv2025

Microbial ecology of acidic, biogenic gypsum: Community structure and distribution of extremophiles on freshly formed and relict sulfate deposits in a hydrogen sulfide-rich cave

Sulfate minerals are abundant on the Martian surface, and many of these evaporite deposits are thought to have precipitated from acidic fluids. On Earth, gypsum (CaSO4*2H2O) and other sulfates sometimes form under acidic conditions, so exploring the extremophilic life that occurs in these mineral environments can help us evaluate the astrobiological potential of acid sulfate depositional settings. Here, we characterized the microbial communities associated with acidic gypsum deposits in a sulfuric acid cave, where sulfate precipitation is driven by sulfide-oxidizing bacteria and archaea. We used 16S rRNA gene sequencing and cell counts to characterize gypsum-associated microorganisms in freshly formed and relict deposits throughout the cave, in order to test hypotheses about how microbial community composition and abundance would vary with distance from the sulfidic water table and with the concentration of H2S(g) and other gases in the cave atmosphere. We found that actively-forming gypsum in the lower cave levels was colonized by low diversity communities of sulfide-oxidizing chemolithotrophs and other acidophiles that have few cells compared to other environments in the cave. The most abundant taxa were Acidithiobacillus, Metallibacterium, Mycobacteria, and three different Thermoplasmatales-group archaea, which occupied distinct niches based on proximity to sulfidic streams and the concentration of gases in the cave air. In contrast, deposits in older cave levels had more diverse communities that are dominated by chemoorganotrophic and methanotrophic taxa. These findings show that acidic sulfate deposits serve as habitats for extremophilic microorganisms, and broaden our knowledge of the life associated with terrestrial sulfates. ImportanceGypsum and other sulfate salts are common on Mars, and many of these deposits are thought to have formed from acidic fluids early in the planets history. Understanding the life that survives and thrives in similar environments on Earth is therefore crucial for evaluating whether these Martian sulfates are or ever were habitable. One such environment where acidic gypsum occurs is in sulfuric acid caves, where extremophilic microorganisms drive the precipitation of sulfate minerals by oxidizing hydrogen sulfide gas from the cave atmosphere. Here, we characterized the communities of microorganisms on freshly formed and ancient gypsum in the Frasassi Caves, and found that the gypsum deposits hosted microbial communities that changed based on chemical energy availability and the age of the gypsum. Our findings underscore the importance of chemical and microbiological interactions in shaping habitable niches, and provide context for searching for past or present life in acidic Martian sulfates.

microbiology↗

bioRxiv2024

Metagenomic insights into an enigmatic gammaproteobacterium that is important for carbon cycling in cave ecosystems worldwide

Caves are windows into the subsurface through which we can directly evaluate the microbiological processes responsible for rock weathering and biogeochemical cycling in more expansive areas of Earths subsurface. However, many cave microbial communities are dominated by microorganisms from uncultivated groups with unknown genomic capabilities that cannot be resolved from marker gene surveys alone. An example of this is a genus of Gammaproteobacteria known as "wb1-P19", which are ubiquitous and abundant in rRNA gene surveys from limestone and volcanic caves around the world. We recovered a nearly complete metagenome-assembled genome (MAG) representing a population of wb1-P19 from Lehman Caves in Great Basin National Park, Nevada, USA, and used it to identify additional MAGs representing this group from the Frasassi Caves in Italy and in publicly available databases. Although members of the wb1-P19 group have often been thought to be autotrophs that oxidize inorganic nitrogen compounds, we show that wb1-P19 are actually obligate or facultative methanotrophs capable of aerobic and anaerobic growth. Based on genomic classification, wb1-P19 are members of upland soil cluster {gamma} (USC{gamma}; part of the newly proposed order "Candidatus Methyloligotrophales"), and are likely important for methane consumption and carbon cycling in caves and other subterranean ecosystems globally.

microbiology↗

bioRxiv2023

Origin and modern microbial ecology of secondary mineral deposits in Lehman Caves, Great Basin National Park, NV, USA

Lehman Caves is an extensively decorated, high desert cave that represents one of the main tourist attractions in Great Basin National Park, Nevada. Although traditionally considered a water table cave, recent studies identified abundant speleogenetic features consistent with a hypogenic and, potentially, sulfuric acid origin. Here, we characterized white mineral deposits in the Gypsum Annex (GA) passage to determine whether these secondary deposits represent biogenic minerals formed during sulfuric acid corrosion, and explored microbial communities associated with these and other mineral deposits throughout the cave. Powder X-ray diffraction (pXRD), scanning electron microscopy with electron dispersive spectroscopy (SEM-EDS), and electron microprobe analyses (EPMA) showed that, while most white mineral deposits from the GA contain gypsum, they also contain abundant calcite, silica, and other phases. Gypsum and carbonate-associated sulfate isotopic values of these deposits are variable, with {delta}34SV-CDT between +9.7{per thousand} and +26.1{per thousand}, and do not reflect depleted values typically associated with replacement gypsum formed during sulfuric acid speleogenesis. Petrographic observations show that the sulfates likely co-precipitated with carbonate and SiO2 phases. Taken together, these data suggest that the deposits resulted from later stage meteoric events and not during an initial episode of sulfuric acid speleogenesis. Most sedimentary and mineral deposits in Lehman Caves have very low microbial biomass, with the exception of select areas along the main tour route that have been impacted by tourist traffic. High-throughput 16S rRNA gene amplicon sequencing showed that microbial communities in GA sediments are distinct from those in other parts of the cave. The microbial communities that inhabit these oligotrophic secondary mineral deposits include OTUs related to known ammonia-oxidizing Nitrosococcales and Thaumarchaeota, as well as common soil taxa such as Acidobacteriota and Proteobacteria. This study reveals microbial and mineralogical diversity in a previously understudied cave and expands our understanding of the geomicrobiology of arid, hypogene cave systems.

microbiology↗