The polymer was discovered by (Shima and Sakai, 1977). The polymer has been found to be heat stable, and can even withstand autoclaving for 20 min. These properties led to the use of polylysine as a food preser­vative on a commercial scale in Japan (Yoshida and Nagasawa, 2003). Production of the compound is influ­enced substantially by the pH of the medium. Polylysine has not known to form any secondary or tertiary struc­ture, and its microbicidal activity is attributed to its pol­ycationic nature.

Production of e-Poly-L-Lysine

The strain Streptomyces albulus 346 spp. lysinopolyme — rus was the first organism to be isolated as a polylysine producer, following which many improvements were carried out on the same for industrial production of polylysine. Later more producers from the genus Streptomyces, Kitasatospora, and an ergot fungus epichole were found to produce polylysine. Polylysine is now industrially produced by aerobic fermentation, us­ing a mutant derived from S. albulus 346, isolated from soil. A maximum amount of polylysine, 0.5 g/l was reported under optimized conditions set at pH 6.0 (Shima and Sakai, 1981). A mutant strain resistant to S-(2-aminoethyl)-L-cysteine, an analogue for lysine and glycine were derived and gave higher productivity values of up to 20 mg/l of polylysine, after 120 h, with glucose as the carbon source and ammonium sulfate as the nitrogen source (Hiraki et al., 1998).

Streptomyces albulus 410, the strain that has been exploited for commercial production of polylysine displayed the two-stage polylysine production (pH 6.0 and pH 3.0—5.0). Accurate control of the process and pH led to a maximal production of about 48.3 g/l. It was found that the best pH for increasing the cellular mass was pH 6.0, while pH below 4.2 was favorable for high levels of polylysine production (Shi et al., 2007). Every poly(amino acid) produced is poly dispersed (has variable molecular weight), which in turn makes it difficult to obtain the product of the required specification. This problem was recently tackled to an extent, when new isolates belonging to the genus Streptomyces was obtained, which could pro­duce nearly monodispersed polylysine.

Degradation of Polylysine

There is not much report on the biodegradation of polylysine. The polylysine-resistant strain Chryseobacte — rium sp. OJ7 also was postulated to have a polylysine­degrading enzyme, with an exopeptidase activity (Obst and Steinbuchel, 2004). Polylysine was shown to be susceptible and was degraded by commercially avail­able enzymes proteases A, P and peptidase R from A. oryzae, Aspergillus melleus and Rhizopus oryzae (Kito et al., 2002).

Applications of Polylysine

The application of polylysine as a food preservative has been established. Other uses of polylysine include the production of an emulsifying agent through its conjugation with dextran. Polylysine can be used to coat biochips and surfaces of cell culture flasks, so as to provide a biocompatible adherent surface. One of the most industrially relevant applications of polylysine is its use as a drug delivery agent and an aid in cell trans­formation due to its polycationic nature.