Lysine acetylation is a common protein post-translational modification in bacteria and eukaryotes. Unlike phosphorylation, whose functional role in signaling has been established, it is unclear what regulatory mechanism acetylation plays and whether it is conserved across evolution. By performing a proteomic analysis of 48 phylogenetically distant bacteria, we discovered conserved acetylation sites on catalytically essential lysine residues that are invariant throughout evolution. Lysine acetylation removes the residue’s charge and changes the shape of the pocket required for substrate or cofactor binding. Two-thirds of glycolytic and tricarboxylic acid (TCA) cycle enzymes are acetylated at these critical sites. Our data suggest that acetylation may play a direct role in metabolic regulation by switching off enzyme activity. We propose that protein acetylation is an ancient and widespread mechanism of protein activity regulation.

DOC Dissolved organic carbon DOE U.S. Department of Energy DPMAS Direct-polarization magic-angle spinning DWS Drinking water standard EXAFS Extended X-ray absorption fine structure spectra Eh Oxidation/reduction potential Stored in single-shell and double-shell tanks Discharged to liquid disposal sites (e.g., cribs and trenches) Released to the atmosphere during fuel reprocessing operations Captured by off-gas absorbent devices (silver reactors) at chemical separations facilities (PUREX, B-Plant, T-Plant, and REDOX)

The metal-reducing gammaproteobacterium Shewanella oneidensis reduces iodate (IO 3 Ϫ ) as an anaerobic terminal electron acceptor. Microbial IO 3 Ϫ electron transport pathways are postulated to terminate with nitrate (NO 3 Ϫ ) reductase, which reduces IO 3 Ϫ as an alternative electron acceptor. Recent studies with S. oneidensis, however, have demonstrated that NO 3Ϫ reductase is not involved in IO 3 Ϫ reduction. The main objective of the present study was to determine the metal reduction and protein secretion genes required for IO 3 Ϫ reduction by Shewanella oneidensis with lactate, formate, or H 2 as the electron donor. With all electron donors, the type I and type V protein secretion mutants retained wild-type IO 3Ϫ reduction activity, while the type II protein secretion mutant lacking the outer membrane secretin GspD was impaired in IO 3 Ϫ reduction. Deletion mutants lacking the cyclic AMP receptor protein (CRP), cytochrome maturation permease CcmB, and inner membrane-tethered c-type cytochrome CymA were impaired in IO 3Ϫ reduction with all electron donors, while deletion mutants lacking c-type cytochrome MtrA and outer membrane ␤-barrel protein MtrB of the outer membrane MtrAB module were impaired in IO 3Ϫ reduction with only lactate as an electron donor. With all electron donors, mutants lacking the c-type cytochromes OmcA and MtrC of the metalreducing extracellular electron conduit MtrCAB retained wild-type IO 3 Ϫ reduction activity. These findings indicate that IO 3 Ϫ reduction by S. oneidensis involves electron donor-dependent metal reduction and protein secretion pathway components, including the outer membrane MtrAB module and type II protein secretion of an unidentified IO 3 Ϫ reductase to the S. oneidensis outer membrane.IMPORTANCE Microbial iodate (IO 3 Ϫ ) reduction is a major component in the biogeochemical cycling of iodine and the bioremediation of iodine-contaminated environments; however, the molecular mechanism of microbial IO 3 Ϫ reduction is poorly understood. Results of the present study indicate that outer membrane (type II) protein secretion and metal reduction genes encoding the outer membrane MtrAB module of the extracellular electron conduit MtrCAB are required for IO 3 Ϫ reduction by S. oneidensis. On the other hand, the metal-reducing c-type cytochrome MtrC of the extracellular electron conduit is not required for IO 3 Ϫ reduction by S. oneidensis. These findings indicate that the IO 3 Ϫ electron transport pathway terminates with an as yet unidentified IO 3Ϫ reductase that associates with the outer membrane MtrAB module to deliver electrons extracellularly to IO 3 Ϫ .

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Species of cyanobacteria in the genera Synechococcus and Synechocystis are known to be the catalysts of a phenomenon called "whitings", which is the formation and precipitation of fine-grained CaCO3 particles. Whitings occur when the cyanobacteria fix atmospheric CO2 through the formation of CaCO3 on their cell surfaces, which leads to precipitation to the ocean floor and subsequent entombment in mud. Whitings represent one potential mechanism for CO2 sequestration. Research was performed to determine the ability of various strains of Synechocystis and Synechococcus to calcify when grown in microcosms amended with 2.5 mM HCO(3-) and 3.4 mM Ca2+. Results indicated that although all strains tested have the ability to calcify, only two Synechococcus species, strains PCC 8806 and PCC 8807, were able to calcify to the extent that a CaCO3 precipitate was formed. Enumeration of the cyanobacterial cultures during testing indicated that cell density did not appear to have a direct effect on calcification. Factors that had the greatest effect on calcification were CO2 removal and subsequent generation of alkaline pH. Whereas cell density was similar for all strains tested, differences in maximum pH were demonstrated. As CO2 was removed, growth medium pH increased and soluble Ca2+ was removed from solution. The largest increases in growth medium pH occurred when CO2 levels dropped below 400 ppmv. Research presented demonstrates that, under the conditions tested, many species of cyanobacteria in the genera Synechocystis and Synechococcus are able to calcify but only two species of Synechococcus were able to calcify to an extent that led to the precipitation of calcium carbonate.