Enumeration of petroleum-degrading marine and estuarine microorganisms by the most probable number method

Abstract

Several media designed for use in a most probable number (MPN) determination of petroleum-degrading microorganisms were compared. The best results, i.e., largest numbers, were obtained using a buffered (32 mM PO4≡) liquid medium containing 1% hydrocarbon substrate. Of 104 presumptive oil degraders tested, 20 grew on oil agar medium but did not utilize oil or a mixture of pure paraffinic hydrocarbons (C10 to C16n-alkanes) in liquid (MPN) medium. Visible turbidity in the liquid medium was correlated with hydrocarbon utilization. Counts of petroleum degraders obtained using liquid medium (MPN) were in most cases higher than those obtained on an oil-amended silica gel medium. Both procedures yield an estimation of oil degraders, and the oil-amended agar permits growth of organisms which do not degrade crude oil. All strains of oil-degrading microorganisms examined in this study were lipolytic, but the converse was not always true.

Diesel oil and PCB-degrading psychrotrophic bacteria isolated from Antarctic seawaters (Terra Nova Bay, Ross Sea)

“…This highlights the strong relationship between lipolytic activity and the biodegradation of diesel oil as previously shown by Mills et al (1978).…”

“…In this kind of qualitative screening, the assumption of hydrocarbon utilization cannot be based only on the appearance of turbidity; instead a chromatographic analysis of the culture is needed. On the other hand, Mills et al (1978) showed that in liquid media it is possible that micro-organisms only grow in the oily phase, producing neither visible growth in the oil-water interface nor visible turbidity in the water phase. Mills and co-workers suggested that in such cases the quantity of proteins in the culture should be determined because production of protein in quantities greater than 30 µg/l is correlated to easily visible turbidity.…”

“…Hydrocarbon degradation was screened on a mineral liquid medium (Mills et al 1978) supplemented with commercial diesel oil at a fi nal concentration of 1 % (vol/vol). Ten-millilitre portions of the medium were placed in pre-sterilized screw cap tubes and 100 µl of pre-sterilized commercial diesel oil was added to each portion.…”

Assessment of the ecological state of soil above an underground natural gas storage using bioassay

“…The number of hydrocarbon-oxidizing microorganisms (HOMs) was evaluated on modified mineral agar medium, g l -1 : Na2HPO4 -6.0; КН2РО4 -3.0; NaCl -0.5; NH4Cl -1.0 with vaseline oil (1%) as a sole carbon and energy source (Mills et al, 1978). Methylotrophic microorganisms (MMs) were enumerated on mineral Hirsch medium, g l -1 : КН2РО4 -1.36; Na2HPO4×7Н2О -2.13; (NH4)2SO4 -0.5; MgSO4×7H2O -0.2; CaCl2×2H2O -0.1; FeSO4×7H2O -0.005; МnSO4×5H2O -0.0025; Na2MoO4×2H2O -0.0025; рН 7.0 with methanol (0.4%) as the only source of carbon and energy (Hirsch and Conti, 1964).…”

Diesel oil utilizing bacteria associated with four Ghanaian soils

“…Ten (10) g of soil was sampled, tenfold serial dilution prepared; 1 mL of appropriate dilution was plated onto modified mineral salts agar medium of Mills et al (1978) and modified vapour phase transfer technique of Okpokwasili and Amanchkwu (1988). The modified mineral salts medium contained 10 g NaCl, 0.42 g MgSO 4 .7H 2 O, 0.29 g KCl, 0.53 g KH 2 PO 4 , 0.42 g NH 4 NO 4 , and 15 g agar in 1L distilled water (adjusted pH= 6.8).…”