Cloning, sequencing, and characterization of lipase genes from a polyhydroxyalkanoate (PHA)-synthesizing Pseudomonas resinovorans

Lipase (lip) and lipase-specific foldase (lif) genes of a biodegradable polyhydroxyalkanoate (PHA)-synthesizing Pseudomonas resinovorans NRRL B-2649 were cloned using primers based on consensus sequences, followed by polymerase chain reaction-based genome walking. Sequence analyses showed a putative Lip gene product (314 amino acids, a.a.) with its catalytic active site (Ser(111), Asp(258), and His(280)) identified. The foldase lif gene that is located 55 bp downstream of lip codes for a putative Lif (345 a.a.). To verify the biological function of the cloned lip gene for lipase expression in P. resinovorans, we constructed a lip knock-out mutant (lip::Tn5<KAN-2>) by transposon insertion. Complementation of the lip knock-out P. resinovorans mutant with a lipase expression plasmid (pBS29-P2-lip) was performed, and its effect on lipase expression was investigated. The wild-type P. resinovorans and the lip::Tn5<KAN-2>[pBS29-P2-lip] recombinant (but not the lip::Tn5<KAN-2> mutant) showed fluorescence on rhodamine B plates indicative of lipase activity. The wild type exhibited extracellular lipase activity when grown on medium containing triacylglycerol substrates (tallow, olive oil, and tributyrin) as sole carbon sources, but the lip::Tn5<KAN-2> mutant did not show such activity. Lipase activity of various strains was also confirmed by TLC analysis of the composition of acylglycerols and free fatty acid in the extracts of the spent culture medium. We further found that tributyrin was more effective than olive oil in inducing lipase expression in P. resinovorans.

Methods for detection and characterization of lipases: A comprehensive review

Microbial lipases are very prominent biocatalysts because of their ability to catalyze a wide variety of reactions in aqueous and non-aqueous media. The chemo-, regio- and enantio-specific behaviour of these enzymes has caused tremendous interest among scientists and industrialists. Lipases from a large number of bacterial, fungal and a few plant and animal sources have been purified to homogeneity. This article presents a critical review of different strategies which have been employed for the detection, purification and characterization of microbial lipases.

The role and application of enterococci in food and health

The genus Enterococcus is the most controversial group of lactic acid bacteria. Studies on the microbiota of many traditional cheeses in the Mediterranean countries have indicated that enterococci play an important role in the ripening of these cheeses, probably through proteolysis, lipolysis, and citrate breakdown, hence contributing to their typical taste and flavour. Enterococci are also present in other fermented foods, such as sausages and olives. However, their role in these products has not been fully elucidated. Furthermore, the production of bacteriocins by enterococci is well documented. Moreover, enterococci are nowadays used as probiotics. At the same time, however, enterococci have been associated with a number of human infections. Several virulence factors have been described and the number of vancomycin-resistant enterococci is increasing. The controversial nature of enterococci has prompted an enormous increase in scientific papers and reviews in recent years, where researchers have been divided into two groups, namely pro and contra enterococci. To the authors' impression, the negative traits have been focused on very extensively. The aim of the present review is to give a balanced overview of both beneficial and virulence features of this divisive group of microorganisms, because it is only acquaintance with both sides that may allow their safe exploitation as starter cultures or co-cultures.

Physiological factors affecting production of extracellular lipase (LipA) in Acinetobacter calcoaceticus BD413: fatty acid repression of lipA expression and degradation of LipA

The extracellular lipase (LipA) produced by Acinetobacter calcoaceticus BD413 is required for growth of the organism on triolein, since mutant strains that lack an active lipase fail to grow with triolein as the sole carbon source. Surprisingly, extracellular lipase activity and expression of the structural lipase gene (lipA), the latter measured through lacZ as a transcriptional reporter, are extremely low in triolein cultures of LipA+ strains. The explanation for this interesting paradox lies in the effect of fatty acids on the expression of lipA. We found that long-chain fatty acids, especially, strongly repress the expression of lipA, thereby negatively influencing the production of lipase. We propose the involvement of a fatty acyl-responsive DNA-binding protein in regulation of expression of the A. calcoaceticus lipBA operon. The potential biological significance of the observed physiological competition between expression and repression of lipA in the triolein medium is discussed. Activity of the extracellular lipase is also negatively affected by proteolytic degradation, as shown in in vitro stability experiments and by Western blotting (immunoblotting) of concentrated supernatants of stationary-phase cultures. In fact, the relatively high levels of extracellular lipase produced in the early stationary phase in media which contain hexadecane are due only to enhanced stability of the extracellular enzyme under those conditions. The rapid extracellular degradation of LipA of A. calcoaceticus BD413 by an endogenous protease is remarkable and suggests that proteolytic degradation of the enzyme is another important factor in regulating the level of active extracellular lipase.

Use of continuous culture to screen for lipase-producing microorganisms and interesterification of butter fat by lipase isolates

The continuous cultivation technique was used to investigate the screening for lipase-producing microorganisms from four commercial starters suitable for the degradation of domestic wastes. Using this technique, three strains of lipase-producing bacteria were isolated and identified: Pantoea agglomerans (BB96CC1, BB168CC2) and Pseudomonas fluorescens (BW96CC1). In addition, butter fat induced more lipase production when present in the growth medium. Interesterification of butter fat triacylglycerols by enzymatic extracts of the isolated strains of microorganisms resulted in an appreciable interesterification yield, implying that hydrolysis was suppressed and interesterification of butter fat triacylglycerols was maximized in a microemulsion free-cosurfactant system.

Enterococci in milk and milk products

Enterococci are widely distributed in nature. They gain entry into milk and milk products through the water supply, equipment, and insanitary and unhygienic conditions of production and handling. They have been incriminated as direct or indirect agents of disease. The evidence concerning their involvement is only circumstantial. These reports are also disputed as the disease symptoms have not been experimentally induced in animal models. However, there is sufficient evidence to indicate that prolific growth of enterococci in foods may lead to formation of clinically significant levels of pressor amines. These amines are very thermostable and therefore remain active even after heat processing, which eliminates all viable streptococci. These pressor amines may be involved in the onset of migraine attacks and produce hypersensitive crises in psychiatric patients who are being treated with monoamine oxidase inhibitors for depression.