Biology subjects

Zacchetti, B.

Publications and source records attributed to Zacchetti, B..

3 recordsLinked to original sources

bioRxiv2018

Dynamics of pellet fragmentation in liquid-grown cultures of Streptomyces lividans

Streptomycetes are extensively used for the production of valuable products, including various antibiotics and industrial enzymes. The preferred way to grow these bacteria in industrial settings is in large-scale fermenters. Growth of streptomycetes under these conditions is characterized by the formation of complex mycelial particles, called pellets. While the process of pellet formation is well characterized, little is known about their disintegration. Here, we use a qualitative and quantitative approach to show that pellet fragmentation in Streptomyces lividans is initiated when cultures enter the stationary phase, which coincides with a remarkable change in pellet architecture. Unlike young pellets, aging pellets have a less dense appearance and are characterized by the appearance of filaments protruding from their outer edges. These morphological changes are accompanied by a dramatic increase in the number of mycelial fragments in the culture broth. In the presence of fresh nutrients, these fragments are able to aggregate with other small fragments, but not with disintegrating pellets, to form new mycelial particles. Altogether, our work indicates that fragmentation might represent an escape mechanism from the environmental stress caused by nutrient scarcity, with striking similarities to the disassembly of bacterial biofilms.

microbiology↗

bioRxiv2017

Micro-encapsulation extends mycelial viability of Streptomyces lividans 66 and increases enzyme production

BackgroundFilamentous bacteria of the genus Streptomyces produce a large arsenal of industrially relevant antibiotics and enzymes. The industrial production of these molecules occurs in large fermenters, where many streptomycetes form dense mycelial networks called pellets. Pellets are characterized by slow growth and inefficient nutrient transfer and therefore regarded as undesirable from the perspective of productivity. Although non-pelleting strains have increased growth rates, their morphology also leads to a dramatic increase in the viscosity of the culture broth, which negatively impacts the process dynamics.\n\nResultsHere, we applied immobilization of Streptomyces lividans 66 using alginate as semi-solid matrix. This alginate-mediated micro-encapsulation increased the production of the extracellular enzyme tyrosinase more than three-fold. The increased production was accompanied by extended viability of the mycelium and a dramatic reduction in the release of intracellular proteins into the culture broth.\n\nConclusionsOur data demonstrate the utility of microencapsulation as a powerful technique to achieve higher yields and lower downstream-processing costs of streptomycetes.

microbiology↗

bioRxiv2016

Hyphal aggregation and surface attachment of Streptomyces is governed by extracellular poly-β-1,6-N-acetylglucosamine

Streptomycetes are multicellular filamentous microorganisms, which are major producers of antibiotics, anticancer drugs and industrial enzymes. When grown in submerged cultures, the preferred enzyme producer, Streptomyces lividans, forms dense mycelial aggregates or pellets, which requires the activity of the proteins encoded by the matAB and cslA-glxA. Here we show that matAB encodes the biosynthetic genes for the extracellular polymeric substance (EPS) poly-{beta}-1,6-N-acetylglucosamine or PNAG. Heterologous expression of matAB in actinomycetes that naturally lack these genes was sufficient for PNAG production and induction of mycelial aggregation. Also, overexpression of matAB in a non-pelleting cslA mutant restored pellet formation, which could effectively be antagonized by the PNAG-specific hydrolase, dispersin B. Extracellular accumulation of PNAG allowed Streptomyces to attach to hydrophilic surfaces, unlike attachment to hydrophobic surfaces, which involves a cellulase-degradable EPS produced by CslA. Altogether, our data support a model in which pellet formation depends on hydrophilic interactions mediated by PNAG and hydrophobic interactions involving the EPS produced by CslA. These new insights may be harnessed to improve growth and industrial exploitation of these highly versatile natural product and enzyme producers.

microbiology↗