Biology ETDs

Publication Date

Fall 11-13-2017


Lechuguilla and Spider caves, Carlsbad Caverns National Park, contain a rich microbial diversity. Despite oligotrophic conditions, the microorganisms in these caves have developed strategies to acquire essential nutrients. I hypothesized that cave bacteria use siderophores, a ferric iron chelating compound, to acquire iron for essential life processes. To understand the backdrop against which the cave bacteria would produce siderophores, I examined the bacterial physiological characteristics, determined whether cave bacteria have an ability to produce siderophores, and investigated a possible correlation between iron and manganese concentrations in cave deposits and siderophore production by bacteria cultured from the same site. I carried out microbial physiological assays, siderophore assays, small subunit ribosomal RNA (SSU rRNA) sequence-based analyses, and geochemical analyses. Microbial physiological studies showed a dominant presence of Gram-positive bacteria isolated from parent cultures that were inoculated from cave deposits. In addition, physiological assays revealed a higher presence of non-catalase and non-oxidase usage and three growth curve patterns among cave bacterial isolates that were subcultured from a decade-long parent culture incubation. Siderophore assays revealed that most bacterial isolates from caves have the capability to produce siderophores with a preference for hydroxamate siderophores. For the small subunit ribosomal RNA (SSU rRNA) study, DNA was extracted from all bacterial isolates that produce siderophores, and 16S rRNA genes were amplified by PCR, cloned, and sequenced. I found that our siderophore producing isolates classified into Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes phyla (from most abundant to least). Geochemical analyses of different cave deposits indicated higher concentrations of iron and manganese in ferromanganese deposits (FMDs) when compared to other secondary mineral deposits and moonmilk. A relationship was revealed of higher iron and manganese concentrations in these deposits linked to a decrease in fast siderophore production by bacterial isolates collected from the same sites. My studies provide evidence that cave bacteria have the capability to produce siderophores, which may be an essential suite of compounds for survival in oligotrophic cave environments.

Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Committee Member (Chair)

Margaret Werner-Washburne

Second Committee Member

Diana E. Northup

Third Committee Member

Cristina Takacs-Vesbach

Fourth Committee Member

Clifford N. Dahm

Fifth Committee Member

Penelope J. Boston

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Biology Commons