Cloning, purification and comparative characterization of two digestive lysozymes from Musca domestica larvae.

cDNA coding for two digestive lysozymes (MdL1 and MdL2) of the Musca domestica housefly was cloned and sequenced. MdL2 is a novel minor lysozyme, whereas MdL1 is the major lysozyme thus far purified from M. domestica midgut. MdL1 and MdL2 were expressed as recombinant proteins in Pichia pastoris, purified and characterized. The lytic activities of MdL1 and MdL2 upon Micrococcus lysodeikticus have an acidic pH optimum (4.8) at low ionic strength (mu = 0.02), which shifts towards an even more acidic value, pH 3.8, at a high ionic strength (mu = 0.2). However, the pH optimum of their activities upon 4-methylumbelliferyl N-acetylchitotriozide (4.9) is not affected by ionic strength. These results suggest that the acidic pH optimum is an intrinsic property of MdL1 and MdL2, whereas pH optimum shifts are an effect of the ionic strength on the negatively charged bacterial wall. MdL2 affinity for bacterial cell wall is lower than that of MdL1. Differences in isoelectric point (pI) indicate that MdL2 (pI = 6.7) is less positively charged than MdL1 (pI = 7.7) at their pH optima, which suggests that electrostatic interactions might be involved in substrate binding. In agreement with that finding, MdL1 and MdL2 affinities for bacterial cell wall decrease as ionic strength increases.

Cloning, purification and comparative characterization of two digestive lysozymes from Musca domestica larvae

cDNA coding for two digestive lysozymes (MdL1 and MdL2) of the Musca domestica housefly was cloned and sequenced. MdL2 is a novel minor lysozyme, whereas MdL1 is the major lysozyme thus far purified from M. domestica midgut. MdL1 and MdL2 were expressed as recombinant proteins in Pichia pastoris, purified and characterized. The lytic activities of MdL1 and MdL2 upon Micrococcus lysodeikticus have an acidic pH optimum (4.8) at low ionic strength (ì = 0.02), which shifts towards an even more acidic value, pH 3.8, at a high ionic strength (ì = 0.2). However, the pH optimum of their activities upon 4-methylumbelliferyl N-acetylchitotrioside (4.9) is not affected by ionic strength. These results suggest that the acidic pH optimum is an intrinsic property of MdL1 and MdL2, whereas pH optimum shifts are an effect of the ionic strength on the negatively charged bacterial wall. MdL2 affinity for bacterial cell wall is lower than that of MdL1. Differences in isoelectric point (pI) indicate that MdL2 (pI = 6.7) is less positively charged than MdL1 (pI = 7.7) at their pH optima, which suggests that electrostatic interactions might be involved in substrate binding. In agreement with that finding, MdL1 and MdL2 affinities for bacterial cell wall decrease as ionic strength increases.

Expression of functional Anopheles merus alpha-amylase in the baculovirus/Spodoptera frugiperda system.

The Anopheles merus (Diptera, Nematocera, Culicoidea) alpha-amylase gene (AmerAmy, GenBank Accession Number U01210) was amplified with its own or with the Zabrotes subfasciatusalpha-amylase signal peptide (ZsAmerAmy, GenBank Accession Number AY270183) by PCR, using designed primers. The AmerAmy gene was sequenced from its promotor to the TGA codon. As a positive control, the Z. subfasciatusalpha-amylase gene with its own signal peptide (ZsAmy, GenBank Accession Number AF255722) was also amplified by PCR. These three sequences were inserted into the baculovirus genome using the Bac-to-Bac trade mark system. Recombinant baculovirus preparations were used to infect Sf9 Spodoptera frugiperda insect cells. The A. merusalpha-amylase was successfully expressed as an active enzyme detected mainly in cell culture supernatants.

A simple and rapid method for screening amylolytic bacteria.

A laboratory class was designed for the study of the ecology of amylolytic bacteria in soil, although other sources may be equally suitable for this purpose. Groups of three students carried out the following: (a) preparation and sterilization of medium and plates, (b) collection and preparation of soil samples, spreading the samples on the plates, (c) incubation of the plates at 37 degrees C overnight, a further 1 h incubation at 60 degrees C to observe amylolytic activity due to thermophilic bacteria, and (d) interpretation and discussion of the results. These tasks are accomplished in two periods of 4h on consecutive days. No sophisticated instruments are required for these experiments, which can be carried out in three classes of 4h each. On the first day the students prepare culture media, buffers and reagents, as well as collect and grow soil samples. The second day is spent for both taxonomic identification of colonies and the HAI determination.