Presence of methyl sterol and bacteriohopanepolyol in an outer-membrane preparation from Methylococcus capsulatus (Bath)
L L Jahnke1, H Stan-Lotter, K Kato
1NASA-Ames Research Center, Moffett Field, California 94035, USA.
Abstract:
Cytoplasmic/intracytoplasmic and outer membrane preparations of Methylococcus capsulatus (Bath) were isolated by sucrose density gradient centrifugation of a total membrane fraction prepared by disruption using a French pressure cell. The cytoplasmic and/or intracytoplasmic membrane fraction consisted of two distinct bands, Ia and Ib (buoyant densities 1.16 and 1.8 g ml-1, respectively) that together contained 57% of the protein, 68% of the phospholipid, 73% of the ubiquinone and 89% of the CN-sensitive NADH oxidase activity. The only apparent difference between these two cytoplasmic bands was a much higher phospholipid content for Ia. The outer membrane fraction (buoyant density 1.23 - 1.24 g ml-1) contained 60% of the lipopolysaccharide-associated, beta-hydroxypalmitic acid, 74% of the methylsterol, and 66% of the bacteriohopanepolyol (BHP); phospholipid to methyl sterol or BHP ratios were 6:1. Methanol dehydrogenase activity and a c-type cytochrome were also present in this outer membrane fraction. Phospholipase A activity was present in both the cytoplasmic membrane and outer membrane fractions. The unique distribution of cyclic triterpenes may reflect a specific role in conferring outer membrane stability in this methanotrophic bacterium.
Insights
Researchers isolated and characterized membrane fractions from Methylococcus capsulatus (Bath). The outer membrane contains unique cyclic triterpenes, potentially crucial for stability in this methanotrophic bacterium.
Area of Science:
- Microbiology
- Biochemistry
Background:
- Methylococcus capsulatus (Bath) is a methanotrophic bacterium.
- Understanding bacterial membrane composition is key to comprehending cellular processes.
Purpose of the Study:
- To isolate and characterize the cytoplasmic/intracytoplasmic and outer membrane fractions of Methylococcus capsulatus (Bath).
- To identify the biochemical components and enzymatic activities present in each membrane fraction.
- To investigate the potential role of specific lipids in outer membrane stability.
Main Methods:
- Bacterial cell disruption using a French pressure cell.
- Separation of membrane fractions via sucrose density gradient centrifugation.
- Analysis of protein, phospholipid, ubiquinone, lipopolysaccharide, methyl sterol, and bacteriohopanepolyol content.
- Assay of NADH oxidase, methanol dehydrogenase, and phospholipase A activities.
Main Results:
- Two distinct cytoplasmic/intracytoplasmic membrane fractions (Ia and Ib) were identified with differing phospholipid content.
- The outer membrane fraction was enriched in lipopolysaccharide-associated fatty acids, methyl sterols, and bacteriohopanepolyols (BHPs).
- Methanol dehydrogenase and c-type cytochrome activities were found in the outer membrane, alongside phospholipase A activity in both fractions.
Conclusions:
- The distinct lipid composition of the outer membrane, particularly the presence of cyclic triterpenes like BHPs, may confer structural stability.
- Phospholipase A activity in both membrane types suggests a role in membrane remodeling or repair.
- This study provides a detailed biochemical characterization of Methylococcus capsulatus (Bath) membranes, highlighting unique features of the outer membrane.
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