FINITE H-DIMENSION DOES NOT IMPLY EXPRESSIVE COMPLETENESS

Accepted versio

Multiple-Peptidase Mutants of Lactococcus lactis Are Severely Impaired in Their Ability To Grow in Milk

To examine the contribution of peptidases to the growth of Lactococcus lactis in milk, 16 single- and multiple-deletion mutants were constructed. In successive rounds of chromosomal gene replacement mutagenesis, up to all five of the following peptidase genes were inactivated (fivefold mutant): pepX, pepO, pepT, pepC, and pepN. Multiple mutations led to slower growth rates in milk, the general trend being that growth rates decreased when more peptidases were inactivated. The fivefold mutant grew more than 10 times more slowly in milk than the wild-type strain. In one of the fourfold mutants and in the fivefold mutant, the intracellular pools of amino acids were lower than those of the wild type, whereas peptides had accumulated inside the cell. No significant differences in the activities of the cell envelope-associated proteinase and of the oligopeptide transport system were observed. Also, the expression of the peptidases still present in the various mutants was not detectably affected. Thus, the lower growth rates can directly be attributed to the inability of the mutants to degrade casein-derived peptides. These results supply the first direct evidence for the functioning of lactococcal peptidases in the degradation of milk proteins. Furthermore, the study provides critical information about the relative importance of the peptidases for growth in milk, the order of events in the proteolytic pathway, and the regulation of its individual components.

Integrated management of invasive cattails (Typha spp.) for wetland habitat and biofuel in the Northern Great Plains of the United States and Canada: A review

On many public lands in the Great Plains region of the USA and Canada, cattail (Typha spp.) growth has far exceeded the 50:50 distribution recommended for optimum wetland wildlife habitat. Excessive cattail growth is the primary concern of wetland managers and its integrated management is reviewed here. The coverage of this mostly hybrid cattail (T. latifolia × T. angustifolia) is often over 90 % and if partially removed for habitat enhancement represents a substantial biomass resource in sites such as conservation wetlands, water retention basins and roadside drainage ditches. Available biomass is estimated to be 3,000 kg/ha assuming a 50 % harvest rate. Cattail control using mowing, herbicides, and burning is expensive, therefore if harvest logistics can be improved along with developing biomass markets, harvest management would become much more viable. Energy values of cattails are comparable to wood pellets at 20 MJ/kg. Cattails can be simultaneously managed for wetland wildlife, harvested for biofuel, serve as a partial substitute for coal, generate carbon credits, and remove phosphorus from the watershed. Cattails extract nitrogen and phosphorous from runoff water that enters rivers and lakes that could be used for agricultural fertiliser while reducing eutrophication. Additionally, rural economies could be boosted by harvesting a renewable energy resource, especially in areas with little fossil fuels or unsustainable biomass practices