Indole 3-acetic acid (IAA) is the principal hormone which regulates various developmental and physiological processes in plants. IAA production is considered as a key trait for supporting plant growth. Hence, in this study, production of indole-3-acetic acid (IAA) by a basidiomycetous red yeast Rhodosporidium paludigenum DMKU-RP301 (AB920314) was investigated and improved by the optimization of the culture medium and culture conditions using one factor at a time (OFAT) and response surface methodology (RSM). The study considered the effects of incubation time, carbon and nitrogen sources, growth factor, tryptophan, temperature, shaking speed, NaCl and pH, on the production of IAA. The results showed that all the factors studied, except NaCl, affected IAA production by R.paludigenum DMKU-RP301. Maximum IAA production of 1,623.9 mg/l was obtained as a result of the studies using RSM. The optimal medium and growth conditions observed in this study resulted in an increase of IAA production by a factor of up to 5.0 compared to the unoptimized condition, i.e. when yeast extract peptone dextrose (YPD) broth supplemented with 0.1% l-tryptophan was used as the production medium. The production of IAA was then scaled up in a 2-l stirred tank fermenter, and the maximum IAA of 1,627.1 mg/l was obtained. This experiment indicated that the obtained optimal medium and condition (pH and temperature) from shaking flask production can be used for the production of IAA in a larger size production. In addition, the present research is the first to report on the optimization of IAA production by the yeast Rhodosporidium.
A phytase-producing bacterium, Burkholderia sp. a13 (JCM 30421), was isolated from Lake Kasumigaura by enrichment cultivation using minimum medium containing phytic acid as the sole phosphorus source. The phytase production by strain a13 was induced by the presence of phytic acid and repressed by the addition of glucose. The purified enzyme had a molecular weight of 44 kDa and a phytase activity of 174 μmol min–1 mg–1. The enzyme showed broad substrate specificity, but the highest activity was observed with phytic acid. The enzyme activity was strongly inhibited by Cu2+, Zn2+, Hg2+, and iodoacetic acid, indicating the requirement of a thiol group for the activity. Genetic cloning reveals that the mature portion of this enzyme consists of 428 amino acids with a calculated molecular weight of 46 kDa. The amino acid sequence showed the highest similarity to the phytase produced by Hafnia alvei with 48% identity; it also contained histidine acid phosphatase (HAP) motifs (RHGXRXP and HD), indicating the classification of this enzyme in the HAP phytase family. We have successfully expressed the cloned gene in Escherichia coli from its putative initiation codon, showing that the gene actually encodes the phytase.