Proposed sum-and-difference method for optical-frequency measurement in the near infrared

Comparative genomics of transport proteins in developmental bacteria: Myxococcus xanthus and Streptomyces coelicolor

Background

Two of the largest fully sequenced prokaryotic genomes are those of the actinobacterium, Streptomyces coelicolor (Sco), and the δ-proteobacterium, Myxococcus xanthus (Mxa), both differentiating, sporulating, antibiotic producing, soil microbes. Although the genomes of Sco and Mxa are the same size (~9 Mbp), Sco has 10% more genes that are on average 10% smaller than those in Mxa.

Results

Surprisingly, Sco has 93% more identifiable transport proteins than Mxa. This is because Sco has amplified several specific types of its transport protein genes, while Mxa has done so to a much lesser extent. Amplification is substrate- and family-specific. For example, Sco but not Mxa has amplified its voltage-gated ion channels but not its aquaporins and mechano-sensitive channels. Sco but not Mxa has also amplified drug efflux pumps of the DHA2 Family of the Major Facilitator Superfamily (MFS) (49 versus 6), amino acid transporters of the APC Family (17 versus 2), ABC-type sugar transport proteins (85 versus 6), and organic anion transporters of several families. Sco has not amplified most other types of transporters. Mxa has selectively amplified one family of macrolid exporters relative to Sco (16 versus 1), consistent with the observation that Mxa makes more macrolids than does Sco.

Conclusions

Except for electron transport carriers, there is a poor correlation between the types of transporters found in these two organisms, suggesting that their solutions to differentiative and metabolic needs evolved independently. A number of unexpected and surprising observations are presented, and predictions are made regarding the physiological functions of recognizable transporters as well as the existence of yet to be discovered transport systems in these two important model organisms and their relatives. The results provide insight into the evolutionary processes by which two dissimilar prokaryotes evolved complexity, particularly through selective chromosomal gene amplification.

Frequency metrology by use of quantum interference

Quantum interference in the rate of two-photon excitation of the 6S((1/2)) ?6P(3/2) ? 6D(5/2) transition in atomic cesium is exploited to demonstrate phase-sensitive frequency demodulation for an optical interval of +/- 12.5 THz. By thus using atoms as ultrafast nonlinear mixing elements, we suggest and analyze a new avenue for absolute comparisons of a dense set of frequencies over the range of 200-2000 nm.

30-THz upconversion of an AlGaAs diode laser with AgGaS(2): bridging the several-terahertz frequency gap in the near infrared

We report as much as 6-micro W upconverted cw radiation at lambda = 778 nm from the sum-frequency mixing of a 50-mW diode laser at lambda = 842 nm and a 200-mW CO(2) laser at lambda = 10.2 microm by use of a 15-mm-long silver thiogallate crystal. This nonlinear material provides a convenient connection between IR and visible/near-IR optical standards. We describe simple frequency chains based on this upconversion process that permit the absolute frequency measurement of many visible or near-IR possible standards at the 10(-12) accuracy level. Transposition of terahertz-scale frequency-difference measurements from the near IR to the 10-microm domain is also proposed.