Humic substance and aquatic microbial ecology

Ahn, Tae-Seok

v DOC and POC

• Most allochthonous dissolved organic carbon (DOC) and particle organic carbon (POC) in aquatic ecosystem are coming from terrestrial ecosystemv DOC• From exudate (Rhizosphere)• Resultant of microbial degradation v POC• From debris of plant (lignin, cellulose from leaves, wooden particles)

Therefore, The characteristics of DOC and POC depend on land

use

More over Dissolved humic substances (HS) comprise 50-80 % of DOC in aquatic ecosystem (Farjalla et al, 2009)

IntroductionIntroduction

A. HS is biologically inert in aquatic ecosystem

B. Ecological function of HS is related to iron, phosphate bioavailability, pH condtion and light penetration (Steinberg et al 2008)

C. DOC and HS enter planktonic food web through Microbial Loop (Azam et al 1983), and are important source of energy and matter

IntroductionIntroduction

D. HS is consisted with acidic materials, so the streams and lakes with HS are acidic state

E. Acidic lake (pH about 4) in Japan zooplankton is abundant, but there is no phytoplankton.

IntroductionIntroduction

IntroductionIntroduction

Zooplankton are eating bacteria and phytoplankton

Red: phytoplanktonBlue: bacteria stained with DTAF

These microphotographys are evidence of the MICROBIAL LOOP

(Sim and Ahn, 1983)

G. HS is coming from forest, low nutrient concentration

IntroductionIntroduction

Brown colored HS in stream of forestJuly, 2009, Forest near Bayreuth

H. Another source of HS is coming from poultry waste, with high concentration of nutrient

IntroductionIntroduction

Over flow of black colored waste water form poultry June 2006, Pusan, Korea

HS + N, PEnergy and

Nutrientsupply

Bacteria

HS

Energy ?P source ?

Phytoplankton

Low pH

inhibits Exudatestimulates

Zooplankton

grazing

grazing

FISH

Natural source

Waste water

Over growth= Saprobic state

Stimulates=Eutrophication

HS vs Microbial loop

1. Bacterial community structure in HS conatinning stream and poultry waste water

MethodsMethods

Total bacterial number (Invitrogen, 1998)Community with DGGE & FISH method β-glucosidase & phsophatese activities (Chróst, 1989) -MUF method

Profiles of microbial community by DGGE

MethodsMethods

Samples

DNA extraction

TotalsampleDNA

PCR

PCRamplicon

DGGE

Community Fingerprinting

Sequence analysis

Phylogenetic &

functional diversity

Detection of Bacillus by fluorescent in situ hybridization (FISH)

MethodsMethods

Probe name probe sequence

S-G-Bacill-0597-a-A-22 5’-GGGTCATTGGAAACTGGGGAAC-3’

Hybridization : 45 , 4 hrs, ℃ Washing : 45 , 20 min℃

Bacillus sp. from Lake Baikal by FISH

2. Role of HS in aquatic ecosystem

MethodsMethods

After addition of HS containing water to natural lake water, and the change of bacterial community and activity will be analyzed

Grazing behavior of Zooplankton will be defined

Expected Expected resultsresults1. Microbial availability of HS

• HS is source for energy and matter…. So by the changes of enzymatic activities

hypothesis : if phosphatase activity is increasing=HS would be source for phosphate

if glucosidase activity is high=HS is for energy

2. Profile of microbial community

• HS would be acting as trigger for bacterial succession = how? What is the effects?

Expected Expected resultsresults3. Different effect of nutrient rich or poor

HS to aquatic ecosystem Do Zooplankton change their grazing behavior by

HS ? And nutrient is effecting for grazing behavior? If that what is the machanism?