Abstract
The potential utilization of cyanobacteria for the biological production of alkanes represents an exceptional system for the next generation of biofuels. Here, we analyzed a diverse group of freshwater and marine cyanobacterial isolates from Indian culture collections for their ability to produce both alkanes and alkenes. Among the 50 cyanobacterial isolates screened, 32 isolates; 14 freshwater and 18 marine isolates; produced predominantly alkanes. The GC-MS/MS profiles revealed a higher percentage of pentadecane and heptadecane production for marine and freshwater strains, respectively. Oscillatoria species were found to be the highest producers of alkanes. Among the freshwater isolates, Oscillatoria CCC305 produced the maximum alkane level with 0.43 μg/mg dry cell weight, while Oscillatoria formosa BDU30603 was the highest producer among the marine isolates with 0.13 μg/mg dry cell weight. Culturing these strains under different media compositions showed that the alkane chain length was not influenced by the growth medium but was rather an inherent property of the strains. Analysis of the cellular fatty acid content indicated the presence of predominantly C16 chain length fatty acids in marine strains, while the proportion of C18 chain length fatty acids increased in the majority of freshwater strains. These results correlated with alkane chain length specificity of marine and freshwater isolates indicating that alkane chain lengths may be primarily determined by the fatty acid synthesis pathway. Moreover, the phylogenetic analysis showed clustering of pentadecane-producing marine strains that was distinct from heptadecane-producing freshwater strains strongly suggesting a close association between alkane chain length and the cyanobacteria habitat.
Highlights
The increased carbon footprint and the rapidly depleting petroleum reserves have necessitated the development of responsible, environment-friendly alternatives with immediate impact (Timilsina, 2013)
S. elongatus PCC7942 was used as a positive control strain and S. elongatus PCC7002 was used as a negative control strain due to the presence and absence of the alkane-producing acyl carrier protein reductase (AAR)/aldehyde deformylating oxygenase (ADO) pathway, respectively (Schirmer et al, 2010)
FATTY ACID DISTRIBUTION IN CYANOBACTERIA Since environmental factor such as media composition did not contribute to differences in the hydrocarbon chain length in www.frontiersin.org freshwater and marine cyanobacteria, we looked at the possible involvement of fatty acid synthesis pathway in determining the hydrocarbon chain length characteristics
Summary
The increased carbon footprint and the rapidly depleting petroleum reserves have necessitated the development of responsible, environment-friendly alternatives with immediate impact (Timilsina, 2013). One pathway involves two terminal enzymes, acyl–acyl carrier protein reductase (AAR) and aldehyde deformylating oxygenase (ADO), which successively convert fatty acyl intermediates to alkanes (Schirmer et al, 2010; Li et al, 2011, 2012; Zhang et al, 2013). Through another pathway, medium chain alkenes ( known as α-olefins) are produced via large multi-domain protein homologous to type I polyketide synthases (PKS). Since different chain length alkanes were observed in different cyanobacteria, it is difficult to predict whether the difference in www.frontiersin.org
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