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Due to the importance of Brevibacterium linens in the industrial production of enzymes,
amino acids and vitamins, the vast majority of research carried out has focused on
expression of extra cellular proteins and amino acid biosynthesis. Most research to date
on B. linens has demonstrated that the physiological and metabolic activities of the
bacterium are significantly strain dependent. The heterogeneity among different stains of
B. linens has also been confirmed by studies of DNA-DNA homology and partial 16S
rDNA sequence analysis. A large number of questions remain to be answered in many
areas of the physiology, metabolism, genetics, and taxonomy of Brevibacterium linens
DSM 20158. As far as we are aware, there has not yet been a report on the global analysis
of cellular proteins associated with B. linens DSM 20158. It may be because of the
unsequenced genome of this strain. However in the present study due to the establishment
of the Brevibacterium linens BL2 shotgun genome sequence, we have focused on three
aspects of this bacterium in order to understand the physiology and biochemistry of the
organism as a whole (i) by optimizing production, purification and characterization of
industrially important extra cellular enzymes such as alpha-amylase, protease, lipase and
an important amino acid L-Lysine which this strain produces naturally, (ii) by isolation,
purification and characterization of respiratory chain complexes (iii) by charting the
cellular and extra cellular proteome analysis of Brevibacterium linens DSM 20158 which
lacks a sequenced genome by mass spectrometry-driven sequence similarity searches.
One factor optimization is time consuming, laborious and does not give information
about interactions between various fermentation variables. Therefore, we used a
statistical approach to optimize factors that influence the production of extra cellular
enzymes and amino acids. We used solid state fermentation due to its preference over
submerged fermentation. Various cultivation parameters were optimized using a
statistical approach to improve the alpha amylase, protease, lipase and L-lysine yield by
Brevibacterium linens DSM 20158. The Plackett-Burman design was used to screen the
fermentation variables followed by the optimization of significant parameters by response
surface CCD in each case. Using the optimal factors, alpha amylase and protease yield
was found to be twofold higher than that obtained in the unoptimized reference medium
whereas lipase and L-lysine production was also found to be improved by using statistical
IAbstract
approach. The closeness of optimized values to experimental values proved the validity
of the statistical model.
B.linens was found to have a branched electron transport chain (Respiratory chain), in
which electrons can enter the respiratory chain either at NADH (complex I) or at complex
II level. In the present study, we were able to isolate and purify the complex-II (succinate
dehydrogenase), complex III (menaquinole cytochrome c reductase cytochrome c
subunit, complex IV (cytochrome c oxidase) and complex V (ATP synthase) of the
plasma membrane of Brevibacterium linens strain DSM 20158. Oxidized, reduced and
pyridine ferrohemochrome spectra of membrane-bound complex-II, III and IV of this
bacterium showed the presence of cytochrome b, cytochrome c and cytochrome aa3
respectively which were further confirmed by the heme staining. The complex II isolated
from Brevibacterium linens strain DSM 20158 seems to contain three subunits of 64.8-,
30- and 12- kDa. The enzymatic activity of succinate dehydrogenase showed that it is
highly active in this microorganism. The complex III, also known as Menaquinol-
cytochrome c reductase cytochrome c subunit, was identified with a single band of about
26 kDa. The complex IV (cytochrome c oxidase) was seen to be composed of two
subunits at 62.8-, 32- kDa and was further confirmed by its enzymatic activity. The
Complex V (F 1 F o -ATP synthase), essential for ATP generation by oxidative
phosphorylation, is isolated, purified and appears to be biphasic in nature during its
kinetic studies.
Brevibacterium linens DSM 20158 is an industrially important actinobacterium, but the
lack of a genome sequence limits the applicability of conventional protein identification
methods to the proteome of this bacterium. Although a shotgun genome sequence for the
BL2 strain of this microbe, it does not cover the entire scope of its proteome. This study
has established the first comprehensive proteomic reference map of B. linens DSM
20158. The present study is carried out first by identification of proteins by homology
database MASCOT followed by the advanced approach of de novo genome sequence
assembly and MS BLAST to drive the expanding B. linens scope of proteomics. This
study will help to enhance the usability of this strain of B. linens in different areas of
research in future rather in food industries only. |
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