Novel Moderate Halophiles: Application of Halomonas boliviensis in Biopolyester Production
Abstract: The south-west Andean region of Bolivia has vast landscapes comprising salt deserts and dry lands interspersed with a number of saline lakes. Much of this region lies above 4000 m above sea level that allows the survival of limited and unique flora and fauna. This thesis involves studies on novel, moderately halophilic microorganisms isolated from this region. Strains LC1T and LC2 were isolated from a soil sample around the lake Laguna Colorada. Based on 16S rDNA analysis, the isolates were identified as members of the genus Halomonas. Due to the low DNA-DNA relatedness between the new isolates and related Halomonas spp. and also several taxonomic differences, strains LC1T and LC2 were classified as new bacterial species called Halomonas boliviensis. Strain LV4T was isolated from saline soil around the lake Laguna Verde. It showed close phylogenetic relationship with Chromohalobacter spp., but differed sufficiently to become a novel species, which was named Chromohalobacter sarecensis.Halomonas boliviensis is able to accumulate a biogegradable polymer, poly(b-hydroxybutyrate) (PHB), when grown under conditions of nutrient limitation and excess carbon source. Cultivation with butyric acid and sodium acetate as carbon sources and 4.5 % (w/v) sodium chloride under controlled conditions in a fermentor led to a maximum PHB yield of 88 wt% with respect to cell dry weight, but a low cell concentration of 2 g/L. The use of glucose and sucrose, respectively, as carbon source resulted in the production of PHB at an average level of 55 wt%. Starch hydrolysate, generated by the action of a recombinant maltooligosaccharide forming amylase from Bacillus halodurans LBK34, was also used as the carbon source for the production of PHB by H. boliviensis LC1. Optimization of the culture conditions containing sucrose led to an improvement in the cell concentration to 14 g/L with a PHB content of 54% in batch fermentations.
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