The kinetics of changes in the fatty acid composition of Neurospora crassa lipids after a temperature increase

Investigation of Raman Spectroscopic Signatures with Multivariate Statistics: An Approach for Cataloguing Microbial Biosignatures

Spectroscopic instruments are increasingly being implemented in the search for extraterrestrial life. However, microstructural spectral analyses of alien environments could prove difficult without knowledge on the molecular identification of individual spectral signatures. To bridge this gap, we introduce unsupervised K-means clustering as a statistical approach to discern spectral patterns of biosignatures without prior knowledge of spectral regions of biomolecules. Spectral profiles of bacterial isolates from analogous polar ice sheets were measured with Raman spectroscopy. Raman analysis identified carotenoid and violacein pigments, and key cellular features including saturated and unsaturated fats, triacylglycerols, and proteins. Principal component analysis and targeted spectra integration biplot analysis revealed that the clustering of bacterial isolates was attributed to spectral biosignatures influenced by carotenoid pigments and ratio of unsaturated/saturated fat peaks. Unsupervised K-means clustering highlighted the prevalence of the corresponding spectral peaks, while subsequent supervised permutational multivariate analysis of variance provided statistical validation for spectral differences associated with the identified cellular features. Establishing a validated catalog of spectral signatures of analogous biotic and abiotic materials, in combination with targeted supervised tools, could prove effective at identifying extant biosignatures.

Changes in fatty acid composition of Neurospora crassa accompany sexual development and ascospore germination

Fatty acid composition was determined during several stages of sexual development in Neurospora crassa. Triacylglycerol was the predominant acyl lipid in cultures undergoing sexual development. The absolute amounts of triacylglycerol in fertilized cultures varied over time, in contrast to control (unfertilized or mock-fertilized) cultures, in which the amount of triacylglycerol decreased linearly with age. In cultures competent to undergo sexual development, alpha-linoleate was the predominant fatty acid, ranging from 53 to 65% of the total fatty acid mass. alpha-Linolenate was 3% or less of the total fatty acid, in marked contrast to the much higher levels (10-35%) typically reported for vegetative cultures. In fertilized cultures, a slightly higher mass ratio of oleate was also observed. This difference was due to the developing asci: in developing asci and mature ascospores, oleate replaced alpha-linoleate as the predominant fatty acid (45 to 50% of the total). In germinating ascospores, the fatty acid composition approached that of vegetative cultures 6 h after inducing germination by heat activation. These results show that the fatty acid composition of sexual tissues of Neurospora differs substantially from the composition of asexual tissues, and that extensive changes in fatty acid composition correlate with several events in the sexual stage of development.

Microbial fatty acids and thermal adaptation

The existing literature on the role of fatty acids in microbial temperature adaptation is reviewed. Several modes of change of cellular fatty acids at varying environmental temperatures are shown to exist in yeasts and fungi, Gram-negative bacteria, and bacteria containing iso- and anteiso-branched fatty acids, as well as in a few Gram-positive bacteria. Consequently, the degree of fatty acid unsaturation and cyclization, fatty acid chain length, branching, and cellular fatty acid content increase, decrease, or remain unaltered on lowering the temperature. Moreover, microorganisms seem to be able to change from one mode or alter the cellular fatty acid profile temperature dependently to another on lowering the temperature, as well as even within the same growth temperature range, depending on growth conditions. Therefore, the effect of the temperature on cellular fatty acids appears to be more complicated than known earlier. However, similarities found in the modes of change of cellular fatty acids at varying environmental temperatures in several microorganisms within the above mentioned groups support the existence of a limited amount of common regulatory mechanisms. The models presented enable the prediction of temperature-induced changes occurring in the fatty acids of microorganisms, and enzymatic steps of the fatty acid biosynthesis that possibly are under temperature control.

De novo fatty acid synthesis mediated by acyl-carrier protein in Neurospora crassa mitochondria

The acyl-carrier protein (ACP) in Neurospora crassa mitochondria [Brody, S. & Mikolajczyk, S. (1988) Eur. J. Biochem. 173, 353-359] mediated a cerulenin-sensitive, de novo fatty acid synthesis independent of the fatty acid synthetase complex present in the cytoplasm. Incubation of mitochondria with [2-14C]malonate labeled only the ACP as indicated by autoradiography after SDS/PAGE. Under these in vitro conditions ATP was required for the initial acyl-ACP formation, but further elongation required either magnesium or the direct addition of NADPH. Labeled hexanoic (6:0) and caprylic (8:0) acids were detected as intermediates in the pathway, as well as hydroxymyristic acid. All of the intermediates, and the eventual product of the reaction, myristic acid (14:0), were released from the ACP by alkaline treatment. Pulse-chase experiments demonstrated the incorporation on to, and release of label from, the ACP. In vivo labeling of ACP with [2-14C]malonate was also detected and the label was in the form of hydroxymyristic acid. This newly discovered pathway is discussed from the standpoint of its possible role in providing acyl chains for mitochondrial lipids.

Circadian rhythms in Neurospora crassa: membrane composition of a mutant defective in temperature compensation

The cel mutant of Neurospora, partially blocked in fatty acid synthesis and lacking temperature compensation of its circadian rhythm below 22 degrees C, had a phospholipid fatty acid composition in liquid shaker culture distinctly different from that of a cel+ control strain. During growth, cel+ exhibited a reproducible increase in its linoleic acid level from about 32 to a plateau at 63 mol%, and a corresponding decrease in its linolenic acid level from about 40 to a plateau at 10 mol%. The level of palmitic acid was constant at 19 mol%. In the cel strain, the linoleic acid level was constant at 54 mol% while the palmitic acid level increased from about 12 to about 23 mol%. Supplementation with palmitic or linoleic acids altered the patterns of fatty acid composition of cel, but did not affect the pattern of cel+. Altered fatty acid composition cosegregated with the cel marker. The mitochondrial phospholipids of cel in liquid culture also had abnormal fatty acid composition, as did the whole mycelial phospholipids on solid medium. These results are consistent with the involvement of membrane homeostasis in the temperature compensation of circadian rhythms.