Anchialine sinkholes provide insight into coastal aquifer systems and coastal mixing processes. Aquifer microbial community function is usually inferred from hydrochemical information, but there are few direct studies of microbial communities in the Floridan Aquifer. Hospital Hole is a 43 m-deep stratified sinkhole under the Weeki Wachee River, FL, with three distinct brackish layers: a hypoxic layer, a chemocline and a sulfidic anoxic layer. Illumina sequencing and bioinformatic tools were used to reconstruct metabolic functions and interactions of microbial communities in each layer. Each layer appears to originate from different parts of the coastal mixing zone and has a distinct microbial community with unique functions, which are influenced by the respective hydrochemistry. Sulfide oxidation and nitrate reduction are the most abundant functions. Syntrophy between methane oxidizers, methanogens and sulfate reducers is present. Similarities between the hydrochemistry and potential connectivity of Hospital Hole and the Floridan Aquifer coastal mixing zone suggest that microbial communities of Hospital Hole could be a surrogate for the coastal mixing zone of the aquifer in the absence of direct studies. Understanding how groundwater microbial communities react to saltwater intrusion and nutrient flux will be useful in predicting how coastal aquifer regions might react to anthropogenic change.
Caves formed by sulfuric acid dissolution have been identified worldwide. These caves can host diverse microbial communities that are responsible for speleogenesis and speleothem formation. It is not well understood how microbial communities change in response to surface water entering caves. Illumina 16S rRNA sequencing and bioinformatic tools were used to determine the impact of surface water on the microbial community diversity and function within a spring pool found deep in the Monte Conca Cave system in Sicily, Italy. Sulfur oxidizers comprised more than 90% of the microbial community during the dry season and were replaced by potential anthropogenic contaminants such as Escherichia and Lysinibacillus species after heavy rains. One sampling date appeared to show a transition between the wet and dry seasons when potential anthropogenic contaminants (67.3%), sulfur-oxidizing bacteria (13.6%), and nitrogen-fixing bacteria (6.5%) were all present within the spring pool.
Two sulphur-oxidizing, chemolithoautotrophic aerobes were isolated from the chemocline of an anchialine sinkhole located within the Weeki Wachee River of Florida. Gram-stain-negative cells of both strains were motile, chemotactic rods. Phylogenetic analysis of the 16S rRNA gene and predicted amino acid sequences of ribosomal proteins, average nucleotide identities, and alignment fractions suggest the strains HH1T and HH3T represent novel species belonging to the genus
Thiomicrorhabdus
. The genome G+C fraction of HH1T is 47.8 mol% with a genome length of 2.61 Mb, whereas HH3T has a G+C fraction of 52.4 mol% and 2.49 Mb genome length. Major fatty acids of the two strains included C16 : 1, C18 : 1 and C16 : 0, with the addition of C10:0 3-OH in HH1T and C12 : 0 in HH3T. Chemolithoautotrophic growth of both strains was supported by elemental sulphur, sulphide, tetrathionate, and thiosulphate, and HH1T was also able to use molecular hydrogen. Neither strain was capable of heterotrophic growth or use of nitrate as a terminal electron acceptor. Strain HH1T grew from pH 6.5 to 8.5, with an optimum of pH 7.4, whereas strain HH3T grew from pH 6 to 8 with an optimum of pH 7.5. Growth was observed between 15–35 °C with optima of 32.8 °C for HH1T and 32 °C for HH3T. HH1T grew in media with [NaCl] 80–689 mM, with an optimum of 400 mM, while HH3T grew at 80–517 mM, with an optimum of 80 mM. The name Thiomicrorhabdus heinhorstiae sp. nov. is proposed, and the type strain is HH1T (=DSM 111584T=ATCC TSD-240T). The name Thiomicrorhabdus cannonii sp. nov is proposed, and the type strain is HH3T (=DSM 111593T=ATCC TSD-241T).
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