Rhamnolipid
is the main group of biosurfactants predominantly produced
by Pseudomonas aeruginosa, a ubiquitous
and opportunistic pathogen, which limits its large-scale exploitation.
Thus, cost-effective rhamnolipid production from a newly isolated
nonpathogenic Enterobacter sp. UJS-RC was investigated.
The highest rhamnolipid production (4.4 ± 0.2 g/L) was achieved
in a medium constituting agroindustrial wastes (sugarcane molasses
and corn steep liquor) as substrates. Rhamnolipid exhibited reduced
surface tension to 72–28 mN/m with an emulsification index
of 75%. The structural analyses demonstrated the presence of methoxyl,
carboxyl, and hydroxyl groups in rhamnolipid. Mass spectra indicated
eight rhamnolipid congeners, where dirhamnolipid (m/z 650.01) was the dominant congener. Rhamnolipid
inhibited biofilm formation of Staphylococcus aureus in a dose-dependent manner, supported by scanning electron microscopy
disclosing the disruption of the microcolony/exopolysaccharide matrix.
Rhamnolipid’s ability to generate reactive oxygen species has
thrown light on the mechanism through which the killing of test bacteria
may occur.
The potential use of parboiled rice mill effluent as a cheap substrate for the production of homopolymer and copolymer of Polyhydroxyalkanoates (PHAs) by Acinetobacter junii BP 25 was investigated for the first time. Process optimization by one factor at a time led to homopolymer polyhydroxybutyrate (PHB) production of 2.64 ± 0.18 g/l with 94.28% PHB content using a two-stage batch cultivation mode. BP 25 furthermore produced polyhydroxybutyrate-co-hydroxyvalerate (P3 (HB-co-HV)), with the addition of valeric acid as an additive to the substrate, yielding (2.56 ± 0.12 g/l dry biomass, 2.20 ± 0.15 g/l PHA) a copolymer content of 85.93%. Thus, rice mill effluent can be an effective and relatively low-cost alternative for the production of PHA, replacing the pure substrates.
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