Bacteria involved in sulfur amendment oxidation and acidification processes of alkaline 'alperujo' compost.

Eight strains of sulfur oxidizing bacteria were isolated from alkaline 'alperujo' compost, seven being identified as Paracoccus thiocyanatus and one as Halothiobacillus neapolitanus. This was the first time that P. thiocyanatus was isolated from mature compost. Acidification capability of isolated strains was compared with type strains H. neapolitanus CIP104769, Thiobacillus denitrificans CIP104767 and Thiomonas intermedia CIP104401. Indigenous P. thiocyanatus strains were as much as or more efficient for acidifying compost than type strains. Sulfur oxidizing population naturally occurring in compost showed maximum acidification efficiency and no extra effect was found with the help of type strains. pH reduction caused by S○ was paralleled by a decrease in CaCO3 and an increase in CaSO4 and salinity levels. A remarkable increase in cultivable sulfur oxidizing bacteria population along with the acidification process was also recorded. Amended compost showed a range of chemical and biological characteristics suitable for use as container media constituent.

Biological oxidation of elemental sulphur added to three composts from different feedstocks to reduce their pH for horticultural purposes.

The biological oxidation of elemental sulphur (S(o)) added to three alkaline composts prepared with a range of organic wastes (CC, melon crop residues; MC, mixed manures; and BC, pine bark) to reduce their pH was studied. The titration curves showed that to achieve an equivalent pH drop, compost CC needed a larger dose of S(o) than did composts MC and BC. The acidification efficiency was high in the three composts (53%), but the pH reduction obtained from the titration curves in MC and BC composts was lower than expected. S(o) oxidation in amended composts was found to be related to pH and CaCO(3) content decreases, and to the rise in CaSO(4) and electrical conductivity levels. A remarkable increase in the autotrophic bacteria population and a slight increase in heterotrophic bacteria along with S(o) oxidation were recorded. Actinomycetes, fungi and yeasts were not affected by the addition of S(o) to composts.