Contribution of Bacterial Cell Wall Components to DOM in Alkaline, Hypersaline Mono Lake, California

Abstract

Soda lakes are often characterized by high densities of prokaryotes and high concentrations of dissolved organic carbon. Since bacterial cell walls are less degradable than most other cell constituents, accumulation of cell wall material may occur in these lakes and contribute to the DOM pool, but composition of DOM in soda lakes has rarely been examined. Here we report concentrations of DOM components likely originating from bacterial cell walls, including D amino acids, glucosamine (GluA) and muramic acid (MurA), in depth profiles of stratified, alkaline, hypersaline Mono Lake, CA. Concentrations of cell wall components were related to total pools of dissolved free and combined amino acids (DFAA and DCAA), and bacterial density and production. In the free pool, total DFAA ranged from 50 to 3250 nM and typically increased with depth, while GluA (5 to 140 nM) and MurA (<0.5 nM and only detected in 2005) fluctuated with depth. In the combined pool, DCAA varied between 5000 and 15000 nM and did not show clear depth-related trends. GluA ranged from 1000 to 5000 nM and tended to increase in the hypolimnion, while MurA varied between 25 and 75 nM. Free D isomers in the DFAA pool either made up <13% (Asp and Ser) or varied from 10 to 57% (Glu and Ala). In the combined pool, D isomers of Asp, Glu, Ser and Ala made up 24-48% of these DCAA and typically showed minor changes with depth. In 2005, lysozyme activity had highest rates in the surface and correlated negatively with most D isomers among the combined amino acids. Our observations demonstrate that the pool of dissolved combined amino compounds in the lake was about 5-fold higher than in other eutrophic lakes and that a substantial portion of these amino compounds originated from bacterial cell walls.

Enhanced Resolution of Chiral Amino Acids with Capillary Electrophoresis for Biosignature Detection in Extraterrestrial Samples

“…Small nonprotein amino acids, including GABA, can be used by cells as osmolytes to prevent lysis in extreme salt environments . GABA has been found in Mono Lake in a previous study at all depths at abundances between 0.1 and 1.1% of all amino acids in the sample …”

Identifying sources of dissolved organic carbon in agriculturally dominated rivers using radiocarbon age dating: Sacramento–San Joaquin River Basin, California

“…In this case, the growth and decay cycles of the microbial mass could contribute to the DOC pool as well, adding saccharide and amino compounds from lyzed cells that have an apparently old age. Evidence for abundance of these compounds in colloidal hydrophilic fractions in terrestrial and marine water DOC is increasing (Guo and Santschi 1997;Leenheer et al 2004;Kawasaki and Benner 2006;Jorgensen et al 2008). This source of organic matter would be consistent with the hydrophilic fraction of DOC in the Sacramento and San Joaquin rivers, and its apparently old age a result of the intense cultivation and subsequent biodegradation of previously occluded but now exposed soil organic matter.…”

Hazenite, KNaMg2(PO4)2{middle dot}14H2O, a new biologically related phosphate mineral, from Mono Lake, California, U.S.A.

“…Another relatively rare mineral gaylussite, Na 2 Ca(CO 3 ) 2 ⋅5H 2 O, was also found in Mono Lake, which is believed to presently precipitate in a year-round process that probably only began after 1970 when the salinity of the lake exceeded 80‰ (Bischoff et al 1991), owing to the diversion of tributary streams by the Los Angeles Department of Water and Power. The salinity of Mono Lake has steadily increased since 1941 from 50‰ to the current ∼90‰ (Bischoff et al 1991;Budinoff and Hollibaugh 2007;Jørgensen et al 2008 …”