Influence of temperature, pH and dissolved oxygen on growth of Brevibacterium linens in a fermentor

Multifactorial experimental design for optimizing transformation: Electroporation of Streptococcus thermophilus

A multifactorial process was used to optimize transformation of Streptococcus thermophilus by electroporation. Simple experimental designs were applied to study three, four, or five factors in eight experiments. Four qualitative factors, growth and recovering media, and plasmid and bacterial strains, were studied empirically. Eight quantitative factors, including electrical, physiological, and chemical parameters, were studied by fractional factorial designs. Effects of individual parameters as well as interactions between them were investigated and optimized. Optimization was performed for one S. thermophilus strain, ST11, and proved to work for all other tested strains of the same species. Transformation efficiencies of 9 x 10(2) to 6 x 10(5) transformants per microgram DNA were achieved, depending on the strains and vectors used. (c) 1994 John Wiley & Sons, Inc.

Growth characteristics of Brevibacterium, Corynebacterium, Microbacterium, and Staphylococcus spp. isolated from surface-ripened cheese

The growth characteristics of five bacteria, Brevibacterium aurantiacum 1-16-58, Corynebacterium casei DPC 5298(T), Corynebacterium variabile DPC 5310, Microbacterium gubbeenense DPC 5286(T), and Staphylococcus saprophyticus 4E61, all of which were isolated from the surface of smear cheese, were studied in complex and chemically defined media. All of the coryneforms, except M. gubbeenense, grew in 12% salt, while B. aurantiacum and S. saprophyticus grew in 15% salt. All five bacteria assimilated lactate in a semisynthetic medium, and none of the coryneform bacteria assimilated lactose. Glucose assimilation was poor, except by S. saprophyticus and C. casei. Five to seven amino acids were assimilated by the coryneforms and 12 by S. saprophyticus. Glutamate, phenylalanine, and proline were utilized by all five bacteria, whereas utilization of serine, threonine, aspartate, histidine, alanine, arginine, leucine, isoleucine, and glycine depended on the organism. Growth of C. casei restarted after addition of glutamate, proline, serine, and lactate at the end of the exponential phase, indicating that these amino acids and lactate can be used as energy sources. Pantothenic acid was essential for the growth of C. casei and M. gubbeenense. Omission of biotin reduced the growth of B. aurantiacum, C. casei, and M. gubbeenense. All of the bacteria contained lactate dehydrogenase activity (with both pyruvate and lactate as substrates) and glutamate pyruvate transaminase activity but not urease activity.

Industrial importance of the genus Brevibacterium

The genus Brevibacterium has long been difficult for taxonomists to classify due to its close morphological similarity to other genera. Since it was proposed in 1953, the genus has often been redefined. The genus is best known for its important role in the ripening of certain cheeses (B. linens) and for its supposed over-production of L: -amino acids. Other interesting industrial applications, including the production of ectoine, have recently been proposed. The general characteristics, the occurrence and the recent taxonomy of Brevibacterium are reviewed here. Furthermore, known and potential industrial applications for Brevibacterium species are briefly discussed.

Behavior of Brevibacterium linens and Debaryomyces hansenii as ripening flora in controlled production of smear soft cheese from reconstituted milk: growth and substrate consumption dairy foods

Experimental cheeses inoculated with Debaryomyces hansenii and Brevibacterium linens were ripened for 76 d under aseptic conditions. Triplicate cheese-making trials were similar as a result of efficient control of the atmosphere. In all trials, D. hansenii grew rapidly during the first 2 d and then slowed, but growth remained exponential until d 10 (generation time around 70 h). Total cell counts were higher than the number of viable cells, and after 10 d they remained around 3 x 10(9) yeast/g of DM. This difference resulted from the nonviability of a fraction of D. hansenii. After d 15, the pH of the rind was close to 7, and B. linens grew exponentially until d 25 (generation time around 70 h). The growth rate subsequently decreased but remained exponential (generation time around 21 d). Cell counts of D. hansenii and B. linens were correlated with the environmental technical conditions. Total D. hansenii counts were also correlated with total B. linens counts. Viable B. linens counts were related to rind lactate, and total counts depended on rind pH, internal lactate, and D. hansenii viable counts. The internal pH of the cheese depended on lactate concentrations, whereas surface pH was related to internal lactose, temperature, and relative humidity. These results suggest a determining role of the diffusion of the carbon sources in the ripening of smear soft cheese.

Behavior of Brevibacterium linens and Debaryomyces hansenii as ripening flora in controlled production of soft smear cheese from reconstituted milk: protein degradation

Model smear soft cheeses, prepared with Debaryomyces hansenii and Brevibacterium linens as ripening starters, were ripened under aseptic conditions. Results of the cheese-making trials, in triplicate, were similar and showed similar patterns of protein degradation. In all of the trials, the acid-soluble nitrogen and nonprotein nitrogen (NPN) indexes and NH3 concentrations of the rind were low until d 10. The acid-soluble nitrogen and NPN of the rind then increased to 100 and 18% of total nitrogen, respectively, at d 76. The NH3 concentrations remained low until d 24 and increased until d 70, reaching about 1.8 g of NH3/kg of DM, and then remained constant. The acid-soluble nitrogen and NPN indexes and NH3 concentrations in the inner cheese mass were lower than in the rind. They showed the same evolution, reaching about 18% for acid-soluble nitrogen, 10% for NPN, and 1.5 g of NH3/kg of DM. It was shown that the inner cheese pH and populations of D. hansenii and B. linens have an effect on proteolysis. Viable cell counts of D. hansenii and B. linens were correlated with the environmental conditions and with proteolytic products. The determining role of carbon source and NH3 diffusions on the cheese ripening process were confirmed.

Aspects of enzymology and biochemical properties of Brevibacterium linens relevant to cheese ripening: a review

Brevibacterium linens is a major surface microorganism that is present in the smear of surface-ripened cheeses. The enzymology and biochemical characteristics of B. linens influence the ripening and final characteristics of smear surface-ripened cheeses. Proteolytic, peptidolytic, esterolytic, and lipolytic activities, which are of particular importance in the ripening process, are discussed in detail. This review also describes the production of volatile compounds, especially sulfur-containing ones, by B. linens, which are thought to be important in respect to the flavor of smear surface-ripened cheeses. The unique orange-colored carotenoids and the factors effecting their production by B. linens are also presented. The catabolism of aromatic amino acids, bacteriocin production, plasmids, and miscellaneous biochemical and physiological properties (peptidoglycan type, antibiotic resistance, insecticide degradation, and biotechnological applications) of B. linens are discussed. The problem associated with the current taxonomical classification of B. linens strains caused by strain variation is evaluated. Finally, the application of B. linens cell extracts or its proteolytic enzymes as cheese ripening accelerants for semi-hard or hard cheese varieties is considered.