Enhanced biosurfactant production by Corynebacterium alkanolyticum ATCC 21511 using self‐cycling fermentation

Abstract

Enhanced biosurfactant production by Corynebacterium alkanolyticum ATCC 21511 was accomplished in a self-cycling fermenter (SCF) on a hexadecane substrate. The phospholipid biosurfactant produced during each cycle could be monitored rapidly using fluorescence spectroscopy. By optimizing the cycling pattern of the SCF, significantly better yields of biosurfactant were obtained than previously reported for this microorganism. It was also possible to virtually eliminate the hydrocarbon residue in the product. Harvest concentrations of 1.9 g L −1 were obtained by using a two-stage fermentation. The first step was the growth of C. alkanolyticum in an SCF to yield a harvest of synchronous cells. These cells were transferred to a second vessel for the production stage. The concentration of biosurfactant could be further increased to 2.7 g L −1 by the addition of more hexadecane at the beginning of the second stage.The recent interest in industrial applications of biosurfactants has been driven by the biodegradability and broad applicability of these microbial surface-active compounds (1-5). The wide range of chemical structures and their effectiveness over a broad range of temperature and pH make biosurfactants appropriate for use in fields as diverse as oil-spill remediation, food processing, and cosmetics.A key factor hindering the widespread use of biosurfactants is that microorganisms generally produce these compounds in very small quantities. Although there are a few examples of large yields of sophorolipids (6,7), the concentrations of most biosurfactants are so low (8-13) that the recovery of these biosurfactants is both difficult and expensive (2,4,5,14,15).Previous work with Corynebacterium alkanolyticum showed that this organism produces a phospholipid biosurfactant in yields of 0.5 to 0.7 g L −1 (13). In this study, the same microorganism was grown in a self-cycling fermenter (SCF). The SCF has demonstrated enhanced yields for several biological products. The SCF technique has been described previously (16-19), but because it has several unusual features, it is useful to summarize the main features of its operation.Self-cycling fermentation is a computer-controlled series of batch growth cycles. A parameter related to growth, such as the concentration of dissolved oxygen (DO) in the growth medium, is monitored constantly. As growth proceeds, the DO gradually decreases in response to the demand from the cells. At some point, the limiting nutrient is completely consumed and there is a sharp decrease in growth rate. This results in an immediate increase in the DO as the cells are no longer removing oxygen as quickly as it is being added to the medium. The computer monitoring the DO recognizes the resulting minimum and starts a series of procedures with the result that half of the working volume in the fermenter is harvested and then this volume is replaced with an equal amount of fresh medium. With the replenished nutrients, growth immediately resumes, the DO starts to decrease, and the cycle is repeated. This t...

Biosurfactants Production from Low Cost Substrate and Degradation of Diesel Oil by a Rhodococcus Strain

“…Biodegradability and low environmental impact are some of the advantages shown by these compounds compared with surfactants chemically synthesized. However, the production costs of the separation and the concentration of biosurfactants are the limiting factor which prevents their large-scale production [7]. Thereby, the potential use of biosurfactants is in the oil industry with minimum purity specification [8], so that crude preparation could be used in clean-up of hydrocarbons contaminated sites and for Enhancing Oil Recovery (EOR).…”

Functional Characterization of Corynebacterium alkanolyticum β-Xylosidase and Xyloside ABC Transporter in Corynebacterium glutamicum

“…Homologues of ␤-xylosidase and xyloside transporter genes are extensively evident among completely sequenced actinobacterial genomes, but functional characterization of the encoded enzymes is not known except in Streptomycineae (5,22,28). In this study, the ␤-xylosidase and xyloside transporter genes of the glutamate-and biosurfactant-producing corynebacterium C. alkanolyticum (7,8) were shown to form a functional cluster exhibiting a 71.4% GϩC content that is markedly higher than the typical 51 to 65% of genomes of corynebacteria. The proteins encoded by xylD and xylE showed high homology to Cellulomonas flavigena glycoside hydrolase family 3 proteins and the extracellular solute-binding protein, respectively.…”

“…Bacterial xylooligosaccharide metabolism involves sugar uptake by xylooligosaccharide transporters prior to hydrolysis by intracellular ␤-xylosidases, but functional characterization of the genes involved in xylooligosaccharide metabolism in corynebacteria is not known. Nevertheless, knowing that Corynebacterium alkanolyticum ATCC 21511 (7,8) is able to grow in the presence of xylooligosaccharide as the sole carbon source facilitated the cloning of ␤-xylosidase and xylooligosaccharide transporter genes using degenerate primers, DPXF and DPXR (Table 2), designed from highly conserved regions of ␤-xylosidases of actinobacteria. Subsequent degenerate PCR using C. alkanolyticum chromosomal DNA as the template revealed a 360-bp core DNA fragment encoding a polypeptide homologous to bacterial ␤-glycosidase.…”

“…Though no reported molecular characterization of xylanolytic enzymes and related transporters in corynebacteria is known, glutamate-and biosurfactant-producing Corynebacterium alkanolyticum (7,8) grows on xylooligosaccharide as a sole carbon source. In this study, we clone ␤-xylosidase and xylooligosaccharide transporter genes from C. alkanolyticum and express them in the heterologous xylose-fermenting host Corynebacterium glutamicum (9).…”

Avaliação cinética da produção de biossurfactantes bacterianos

“…O biossurfactante do tipo fosfolipídio produzido foi capaz de reduzir a tensão superficial para valores abaixo de 32 mN m -1 . 22 Um estudo analisou a produção de biossurfactante por duas espécies de bactérias do gênero Bacillus. A bactéria Bacillus cereus foi capaz de reduzir a tensão superficial do meio para 28 mN m -1 e apresentar índice emulsificante em torno de 60%, tanto no meio na presença quanto na ausência das células do micro-organismo, o que indicou produção extracelular de biossurfactante.…”