SAO PAULO (Bloomberg) — Cosan SA Industria & Comercio, the world's biggest sugar-cane processor, plunged as much as 15 percent after a credit-rating cut by Moody's Investors Service, which cited expansion costs and declining profit margins.

Cosan sank 2.21 reais, or 14 percent, to 13.29 reais at 2:53 p.m. in Sao Paulo, leading the benchmark Bovespa index lower. Cosan shares have dropped 55 percent in the past two months, reaching 12.55 reais last week, the lowest since they began trading in November, 2005. Moody's lowered Cosan's global rating to Ba3.

The sugar and ethanol producer will use cash to fund expansion and will consider using shares to buy "large" rivals as rising costs and credit-market turmoil place competitors in a "precarious" situation, chief financial officer Paulo Diniz said on Monday on a conference call. Moody's cited prospective effects on cash flow at Cosan in cutting its debt rating.

Billionaire Rubens Ometto, chief executive officer and controlling shareholder of Piracicaba, Brazil-based Cosan, has expanded the company by acquiring 14 mills over the past decade, more than quadrupling the number of units to 18.

In January, Cosan sold 1.74 billion reais of shares to investors, doubling its capital. Bermuda-based Cosan Ltd., controlled by Ometto, bought 1.19 billion reais of shares, or 68 percent of the amount sold.