All ETDs from UAB

Advisory Committee Chair

Asim K Bej

Advisory Committee Members

Robert Thacker

Thane Wibbels

Jason Linville

Chris Murdock

Document Type

Dissertation

Date of Award

2013

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

Antarctic freshwater ecosystems offer a unique opportunity to study the microbial biodiversity, adaptation, function, and interaction in extreme environments. In general, there is a dearth of higher trophic organisms in Antarctic freshwater lakes thus microbes are essential for the sustainability of biological life. This study describes the similarities and differences in microbial diversity among seasonal and perennially ice-covered lacustrine ecosystems from East and West Antarctica. In particular, we investigated the microbial diversity in three different freshwater lakes, (1) seasonal lakes of the Schirmacher Oasis, East Antarctica, (2) perennially ice-covered Lake Untersee, East Antarctica, and (3) perennially ice-covered Lake Joyce, West Antarctica. We utilized both culture-dependent and culture-independent methodologies (clone library construction and next-generation high throughput sequencing - bTEFAP `bacterial Tag Encoded FLX Amplicon Pyrosequencing' and Illumina HiSeq) to compare the microbial community structure and functions in these lakes. Overall, OTU-based analyses revealed each lake possesses its own microbial signature. However, there are common OTUs between the Antarctic lakes but they are less abundant than those microbes specialized to survive and function in each lake. Furthermore, we found some of these specialized microbes, for example OTUs that were identified as Flavobacterium, play key roles in the nitrogen biogeochemical cycling in Lake Joyce. Hence, this study provides a working model to investigate and compare the microbial diversity and function among freshwater ecosystems. Besides taxonomic identification of the microbial consortium in these freshwater lakes, we isolated a purple violet pigment (PVP) from Janthinobacterium sp. Ant5-2 that has important adaptive characteristics to survive the Antarctic extreme conditions. This pigment has been previously shown to have protective function against constant UV radiation during the austral summer months and alleopathic competition for space and nutrients. We applied this pigment on human pathogens such as multiple drug resistant (MDR) and methicillin-resistant Staphylococcus aureus (MRSA). We determined the minimum inhibitory concentration (MIC90) of PVP against MDR and MRSA ranged between 1.57 µg/mL and 3.13 µg/mL. Thus the investigation of the microbial diversity in Antarctic freshwater lakes is not only important to understand microbial processes in extreme environments but to bioprospect the next antimicrobial compound against increasingly drug-resistant human pathogens.

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