As a matter of style, most journals advise authors not to start any sentence with an abbreviation or a number. However, acronyms are generally acceptable in that position, either because they are words in their own right (such as laser and radar) or represent names of organizations (such as NASA and CERN).
In the “Results” section of a typical research paper, you may find it convenient to begin sentences with numbers, as in “15% of the plants survived” or “48% of the patients recovered.” In such cases, either spell out the numbers, as in “Fifteen per cent of the plants . . .” or “Forty-eight per cent of the patients . . .” or rephrase the sentences, as in “Of the treated plants, 15% survived” or “Nearly half (48%) the patients recovered.” Incidentally, “per cent” (two words) is the more common form in the UK whereas most US publishers prefer “percent.”
The same advice applies to abbreviations at the beginning of sentences: either spell out the abbreviation in full or rephrase. With scientific names, it is common to abbreviate the genus to its first letter after the first mention so long as only one genus is being represented (Aspergillus niger at first mention and A. niger thereafter, for example). However, it is better to spell out the genus in full at the beginning of a sentence.