Microbial Mats and Microbialites: Ingredients of Lithification

Pieter T. Visscher, Joan Bernhard, Brendan Burns, Olivier Braissant, Lindsay Collins, Alan Decho, David Des Marais, Christophe Dupraz, Ginny Edgcomb, Jamie Foster, Kim Gallagher, Kristen Myshrall, Brett Neilan, Kim Gallagher, Ricardo Jahnert, Therese Morris, Noah Planavsky, Pamela Reid, Roger Summons, Malcolm Walter

Center for Integrative Geosciences Department of Marine Sciences University of Connecticut – Storrs, USA

Symposium on Research and Conservation: South West Australian WA’s Microbialites, Kensington, Oct 2012

Outline of this talk:

- Microbial Mats 101

- Microbial Mats vs. Microbialites

- Three Ingredients of Lithification

- Words of Warning

PRE - MAT

DEPTH

IPRENITIAL - MAT MAT

DEPTH

N2-Fixing Cyano’s

INITIALPRECYANO’S - MAT MATAND A EROBIC HETEROROPHS

DEPTH

N2-Fixing Cyano’s Cyanobacteria

Aerobic Heterotrophs

AINITIALPRENAEROBIC - MAT MAT H ETEROTROPHS APPEAR

DEPTH

N2-Fixing Cyano’s Cyanobacteria Aerobic Heterotrophs Anaerobic Heterotrophs

MATUREINITIALPRE M - ATMAT :MAT M ETABOLLICALLY DIVERSE

DEPTH

N2-Fixing Cyano’s Cyanobacteria

Aerobic Heterotrophs Anaerobic Heterotrophs

Anoxygenic Phototrophs Sulfide Oxidizers

Characteristics of Microbial Mats

Organo-sedimentary biofilms, some almost completely inorganic, typically containing copious amounts of EPS

Bind and trap sediment; precipitate/dissolve minerals

Lamination due to stratification of phototrophs (light regime), with strong resemblance to fossil record

Inventors of oxygenic photosynthesis

High productivity (up to 5.5 g C m-2 d-1)

Semi-closed; highly efficient in element cycling (tight coupling of P and R)

Limited number of functional groups of microbes 5 cm or, limited “heap of genes to make them tick”

Stromatolitic reefs Thrombolitic reefs

Foster, Dupraz, Reid, Visscher

crusty

(% sequence similarity)

soft Ingredients of Lithification 1. The Alkalinity Engine Microbial Metabolism: Photosynthesis

removal of CO2 from a bicarbonate buffered environment results in an increase in alkalinity:

CO2 + H2O [CH2O] + O2

- - HCO3 CO2 + OH 2+ - + Ca + HCO3 CaCO3 + H + - H + OH H2O

- 2+ sum: 2HCO3 + Ca [CH2O] + CaCO3+ O2

+1 CaCO3 per CO2 fixed Metabolic pathways in (lithifying) microbial mats

Dupraz et al. 2009 Metabolic pathways in (lithifying) microbial mats

Dupraz et al. 2009 SI = log (IAP/kSP) = log (Q/k)

2+ 2- IAP = ion activity product = {Ca } x {CO3 }

kSP = solubility product constant

2+ 2- Ca + CO3 CaCO3

2+ 2- -8.42 -8.22 Ca x CO3 /CaCO3 = 10 (calcite);10 (aragonite)

IAP > kSP then supersaturated and precipitation likely

photosynthesis (cyanobacteria) - 2+ 2HCO3 + Ca [CH2O] + CaCO3 + O2

- [CH2O] + CaCO3 + O2 HS + 2O2 + CaCO3 - 2+ - 2+ 2- 2HCO3 + Ca HCO3 + Ca + SO4

2- 2+ - - 2[CH2O] + SO4 + Ca + OH CaCO3 + CO2 + 2H2O + HS

SRB metabolism using ΔDIC ΔTA ΔH+ /mole eq/mole donor donor ethanol: 2- - - - 2C2H6O + 3SO4 + OH 4HCO3 + 3HS + 3H2O 2 3 +½ lactate: - 2- - - - 2C3H5O3 + 3SO4 + OH 6HCO3 + 3HS + H2O 3 3 +½ formate: - 2- - - - 4CHO2 + SO4 + H2O 4HCO3 + HS + OH 1 ½ -¼ acetate: - 2- - - C2H3O2 + SO4 2HCO3 + HS 2 1 0

Ingredients of Lithification 2. Extracellular Organic Matrix EPS Matrix

CaCO3 Precipitate

Ooid

Ooid

Key Role in:

1.Precipitation (CaCO3) 2.Chemical Communication (Quorum Sensing) 3. Sediment Stabilization (Gel Formation), etc

Surface biofilm in Bahamian stromatolite Initial EPS Production and Ca2+ Binding Calcium binding capacity

0.15 g Ca2+/g EPS (0.29 g/g) Acid-Base Titration

“S” group Amino group

Carboxyl group FT-IR Spectrometry

After: Braissant, 2005

Potential Consumption of EPS

Substrate AR SR 2- (dO2/dt) (dS /dt)*2 µmol/.ml slurry.h

Endogenous 6.4±0.8 0.5±0.2 Acetate 32.1±3.3 12.8±3.8 Lactate 26.9±1.9 13.0±5.9 Glucose 37.2 ±2.5 8.0±2.2 Xylose 35.1±2.1 8.4 ±3.6 Mannose 33.5±2.1 8.2 ± 2.6 Xanthan 9.4 ±2.0 1.3 ±0.8 Site EPS 18.2±2.0 5.6±2.6 D. auto EPS 11.1±2.4 1.6±0.6 Desulfovibrio EPS 18.3±2.5 3.8±1.2 Schizothrix EPS 11.5±2.9 4.1±2.0

„Fossilized EPS‟

Example from the Silurian from Morocco Barbieri et al. 2004 Ingredients of lithification: 3. Chemical Communication? AHL O AIP O Phe Asp ile O R NH ile Cys Met S Asn O AI-2 HO OH -butyrolactones - B OH CH O O O 3

HO CH3 O CH3 O O HO

O O O PQS OH C-HSL O

NH

N CH3 H HO

Decho, Visscher and Norman 2010 Chemical Communication or Quorum Sensing

Acylated Homoserine Lactone (C6) Acylated Homoserine Lactones from Cultures, Mats

Sample Designation Major AHL detected Desulfovibrio ATCC 33405D C4, C8 vulgaris D. sp. strain H0407- GenBank C4, C6, C7, C8 12.1Lac DQ822785 t½ = 4.2h (pH 8.2); 0.5h (pH 9.6) D. sp. GenBank C4, C6, C7, C10, Strain H0407- DQ822786 C12

2.3jLac t½ = 22h (pH 8.2); 1.1h (pH 9.6) Natural mat - C4, C6, C7, C8, samples C10, C12, C14

t½ = 36h (pH 8.2); 11.4h (pH 9.6)

Decho, Visscher et al. 2009

Words of warning: - Open (marine) systems vs. closed (lacustrine) ones (different models!) - Mats vs. microbialites - Rates matter (not species or genes) - Not only cyanobacteria – the entire community matters - Need to know plasticity of the community - Stressors? Light! Temperature, salinity, nutrients, “water quality”………. ORGANOMINERALIZATION