Persistent transport barrier on the West Florida Shelf.

Analysis of drifter trajectories in the Gulf of Mexico has revealed the existence of a region on the southern portion of the West Florida Shelf (WFS) that is not visited by drifters that are released outside of the region. This so-called "forbidden zone" (FZ) suggests the existence of a persistent cross-shelf transport barrier on the southern portion of the WFS. In this letter a year-long record of surface currents produced by a Hybrid-Coordinate Ocean Model simulation of the WFS is used to compute Lagrangian coherent structures (LCSs), which reveal the presence of a persistent cross-shelf transport barrier in approximately the same location as the boundary of the FZ. The location of the cross-shelf transport barrier undergoes a seasonal oscillation, being closer to the coast in the summer than in the winter. A month-long record of surface currents inferred from high-frequency (HF) radar measurements in a roughly 60 km × 80 km region on the WFS off Tampa Bay is also used to compute LCSs, and these also reveal the presence of transient transport barriers. While the HF-radar-derived transport barriers cannot be unambiguously linked to the boundary of the FZ, this analysis does demonstrate the feasibility of monitoring transport barriers on the WFS using a HF-radar-based measurement system. The implications of a persistent cross-shelf transport barrier on the WFS for the development of harmful algal blooms on the shoreward side of the barrier are considered.

Slow growing Bacillus subtilis: deoxyribonucleic acid replication in turbidostat cultures.

Comparisons of slowly growing Bacillus subtilis cultures grown in batch culture, a chemostat, and a turbidostat were made. Cultures in a turbidostat were found to grow optimally and to be in balanced growth. The duration of deoxyribonucleic acid (DNA) replication, or C period, was estimated by means of an autoradiographic analysis, a genetic analysis, and determinations of DNA per cell. These measurements were performed on cells growing at different slow rates. The results showed that the C period increased with increasing generation times, but the increase in duration of the C period was not proportional to the increase in generation time.

Biochemical studies on glucose initiated germination in Bacillus megaterium.

Bacillus megaterium QM B1551 spores contained the enzymes for the Embden-Meyerhof pathway and the initial reactions in the hexose monophosphate pathway but not the Entner-Doudoroff pathway. With [U-14C]glucose no metabolism was detected until after about 30% of the spores had lost heat resistance. Mutants that lacked either phosphofructokinase or 6-phosphogluconate dehydrogenase were able to initiate germination on glucose like wild type. Purified methyl alpha-D-glucopyranoside, 6-deoxyglucose and 6-deoxy-methyl alpha-D-glucopyranoside were not substrates for spore enzymes yet these compounds still initiated germination. Therefore, metabolism of exogenously added glucose is probably not the primary stimulatory effect in germination.

Production of large amounts of acetate during germination of Bacillus megaterium spores in the absence of exogenous carbon sources.

When Bacillus megaterium spores germinate in the absence of an exogenous carbon source, the first minutes of germination are accompanied by production of large amounts (approximately 70 nmol/mg of dry spores) of acetate and much smaller amounts of pyruvate and lactate. The majority of these compounds are excreted into the medium. Exogenous pyruvate and alanine are also converted to CO2 and acetate by germinating spores, presumably by using the pyruvate dehydrogenase that is present in dormant spores. These data suggest that the 3-phosphoglyceric acid stores in the dormant spore and alanine generated by proteolysis early in germination can be catabolized to acetate during germination with production of large amounts of reduced nicotinamide adenine dinucleotide, acetyl coenzyme A, and adenosine 5'-triphosphate.