Abstract
Eichhornia crassipes (Mart) Solms is an invasive weed known to out-compete native plants and negatively affect microbes
including phytoplankton. The spread and population density of E. crassipes will be favored by global warming. The aim here
was to identify compounds that underlie the effects on microbes. The entire plant of E. crassipes was collected from El
Zomor canal, River Nile (Egypt), washed clean, then air dried. Plant tissue was extracted three times with methanol and
fractionated by thin layer chromatography (TLC). The crude methanolic extract and five fractions from TLC (A–E) were tested
for antimicrobial (bacteria and fungal) and anti-algal activities (green microalgae and cyanobacteria) using paper disc
diffusion bioassay. The crude extract as well as all five TLC fractions exhibited antibacterial activities against both the Gram
positive bacteria; Bacillus subtilis and Streptococcus faecalis; and the Gram negative bacteria; Escherichia coli and
Staphylococcus aureus. Growth of Aspergillus flavus and Aspergillus niger were not inhibited by either E. crassipes crude
extract nor its five fractions. In contrast, Candida albicans (yeast) was inhibited by all. Some antialgal activity of the crude
extract and its fractions was manifest against the green microalgae; Chlorella vulgaris and Dictyochloropsis splendida as well
as the cyanobacteria; Spirulina platensis and Nostoc piscinale. High antialgal activity was only recorded against Chlorella
vulgaris. Identifications of the active antimicrobial and antialgal compounds of the crude extract as well as the five TLC
fractions were carried out using gas chromatography combined with mass spectroscopy. The analyses showed the presence
of an alkaloid (fraction A) and four phthalate derivatives (Fractions B–E) that exhibited the antimicrobial and antialgal
activities.